Wahab MMA, Hilmy I, Ashcroft IA, Crocombe AD (2011) Damage Parameters of Adhesive Joints with General Triaxiality, Part 2: Scarf Joint Analysis, JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 25 (9) pp. 925-947 BRILL ACADEMIC PUBLISHERS
Almost all structural applications of adhesive joints will experience cyclic loading and in most cases this is irregular in nature, a form of loading commonly known as variable amplitude fatigue (VAF). This paper is concerned with the VAF of adhesively bonded joints and has two main parts. In the first part, results from the experimental testing of adhesively bonded single lap joints subjected to constant and variable amplitude fatigue are presented. It is seen that strength wearout of bonded joints under fatigue is non-linear and that the addition of a small number of overloads to a fatigue spectrum can greatly reduce the fatigue life. The second part of the paper looks at methods of predicting VAF. It was found that methods of predicting VAF in bonded joints based on linear damage accumulation, such as the Palmgren-Miner rule, are not appropriate and tend to over-predict fatigue life. Improved predictions of fatigue life can be made by the application of non-linear strength wearout methods with cycle mix parameters to account for load interaction effects. © 2009 Elsevier Ltd. All rights reserved.
Advanced structural adhesives are now an important joining technique in automobile and aerospace applications. The perceived uncertainty in the long-term structural performance of bonded members when subjected to static/fatigue loads in aggressive environments is probably restricting an even more widespread use of this joining technology. In this article, the effect of moisture on the static and fatigue resistances of adhesively bonded laminate joints was investigated. Experimental tests were performed on both aged and unaged adhesively bonded laminate joints for static and fatigue responses. Further, using a cohesive zone approach for the adhesive bondlines, a combined diffusion?stress analysis was developed to predict the progressive damage observed in the joints tested experimentally. The numerical predictions were found to be in good agreement with the experimental test results.
Capell TF, Palaniappan J, Ogin SL, Crocombe AD, Reed GT, Thorne AM, Mohanty L, Tjin SC (2007) The use of an embedded chirped fibre Bragg grating sensor to monitor disbond initiation and growth in adhesively bonded composite/metal single lap joints, JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS 9 (6) pp. S40-S44 IOP PUBLISHING LTD
Crocombe AD, Ashcroft IA, Shenoy V, Critchlow GW, Abdel Wahab MM (2007) The Initiation and Propagation of Damage in Adhesively Bonded Joints Subjected to Constant and Variable Amplitude Fatigue,
Hilmy I, Wahab MMA, Crocombe AD, Ashcroft IA, Solana AG (2007) Effect of triaxiality on damage parameters in adhesive, Advances in Fracture and Damage Mechanics VI 348-349 pp. 37-40 TRANS TECH PUBLICATIONS LTD
A bonded anchorage was investigated where a CFRP tendon was potted in a steel tube using an epoxy adhesive. Experimental creep tests on single lap joints and fatigue tests on anchorages, both with different adhesive thickness, were undertaken with failure occurring in the bond, close to the CFRP interface in cases. The creep and fatigue response of the adhesively bonded CFRP tendon anchors were separately predicted using Finite Element analysis. A visco-plastic material model was used to predict the time to failure of the anchors in creep. The effect of creep damage was modelled by degrading the yield stress of the adhesive. Moreover, a bi-linear traction-separation cohesive zone model was incorporated at the adhesive-tendon interface when simulating the fatigue loading of the anchorages. A fatigue damage model based on the degradation of the cohesive elements was implemented to take into account the fatigue damage evolution. The predicted results were found to be in good agreement with the experimentally recorded data. © 2014 Elsevier Ltd.
Gauntlett FE, Rihawy MS, Clough AS, Liljedahl CDM, Crocombe AD (2006) Using a scanning microbeam and a CdZnTe array for nuclear reaction measurements of water diffusion into an adhesive resin, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 249 pp. 406-408 ELSEVIER SCIENCE BV
This paper presents a study of moisture absorption-desorption effects in single lap adhesive joints. Experiments were carried out to characterise the moisture uptake of the single part epoxide adhesive, FM73. Tensile testing of single lap joints manufactured from aluminium alloy 2024 T3 and O and FM73 adhesive was carried out after the joints were exposed to different conditioning environments. The experimental results revealed that the failure strength of the single lap joints with 2024 T3 adherends progressively degraded with time when conditioned at 50 °C, immersed in water. However, the joint strength almost completely recovered after moisture was desorbed. The single lap joints with 2024 O adherends showed decreased strength for 28 days of conditioning, after which strength recovered, reaching a plateau after 56 days. Again, strength almost completely recovered on desorption of moisture. The strength recovery of the joints, after desorption of moisture, showed that the degradation of the adhesive was largely reversible. Analysis of the failure surfaces revealed that the dry joints failed cohesively in the adhesive layer and that the failure path moved towards the interface after conditioning. The failure mode then reverted back to cohesive failure after moisture desorption. © 2009 Elsevier Ltd. All rights reserved.
Kamat YD, Crocombe A, Bradley WN (2014) The eburnated bone-cement interface, Current Orthopaedic Practice 25 (5) pp. 484-487
© 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins.Background: The cement-bone interface has been well studied as the weakest link where initiation of long-term aseptic loosening occurs in cemented arthroplasty. During total knee replacement, one is often confronted with eburnated bone in patients with severe arthritis. We aimed to study shear strength of the eburnated cement-bone interface and the effect of varied surface topology of eburnated bone on this interface strength. Methods: We used blocks of ebony wood to simulate eburnated bone. They were engineered to produce three surface topologies: smooth, drill holes, and cross-hatch pattern. These were cemented to metal (steel) blocks. Each specimen was then mounted onto a loading machine that created a shear force at the simulated cement-bone interface. Force displacement curves were recorded for all specimens until interface failure. Results: The smooth surfaced blocks were found to fail at the cement-wood (bone) interface at an average force of 0.5 MPa. Both the other surface topology alterations resulted in an increased ability to withstand force (average 3.7 MPa) before failure. Examination of the failed specimens revealed a combination of failure at both interfaces as well as cement deformation. Conclusions: One must alter the smooth surface of eburnated bone when dealing with bone defects in cemented arthroplasty. The pattern employed does not make a difference to the strength of the construct. The resulting mechanical bond of the cement with bone is as strong as any component in the metal-cement-bone construct.
Crocombe AD, Hua YX, Loh WK, Wahab MA, Ashcroft IA (2006) Predicting the residual strength for environmentally degraded adhesive lap joints, INTERNATIONAL JOURNAL OF ADHESION AND ADHESIVES 26 (5) pp. 325-336 ELSEVIER SCI LTD
Shenoy V, Ashcroft IA, Critchlow GW, Crocombe AD (2010) Fracture mechanics and damage mechanics based fatigue lifetime prediction of adhesively bonded joints subjected to variable amplitude fatigue, Engineering Fracture Mechanics 77 (7) pp. 1073-1090
The first part of the paper describes an investigation into the behaviour of adhesively bonded single lap joints (SLJs) subjected to various types of variable amplitude fatigue (VAF) loading. It was seen that a small proportion of fatigue cycles at higher fatigue loads could result in a significant reduction in the fatigue life. Palmgren-Miner's damage sum tended to be less than 1, indicating damage accelerative load interaction effects. In the second part of the paper, fracture mechanics (FM) and damage mechanics (DM) approaches are used to predict the fatigue lifetime for these joints. Two FM based approaches were investigated, which differed with respect to the cycle counting procedure, however, both approaches were found to under-predict the fatigue lifetime for all the types of spectra used. This was attributed to the inability of the FM based models to simulate the crack initiation phase. A DM based approach was then used with a power law relationship between equivalent plastic strain and the damage rate. Good predictions were found for most of the spectra, with a tendency to over-predict the fatigue life. © 2010 Elsevier Ltd.
This paper presents a methodology for predicting moisture concentration in an epoxy adhesive under cyclic moisture absorption-desorption conditions. The diffusion characteristics of the adhesive were determined by gravimetric experiments under cyclic moisture conditions and the dependence of diffusion coefficient and saturated mass uptake on moisture history was determined. Non-Fickian moisture absorption was observed during absorption cycles while moisture desorption remained Fickian. The diffusion coefficient and saturated moisture content showed variation with absorption-desorption cycling. A finite element-based methodology incorporating moisture history was developed to predict the cyclic moisture concentration. A comparison is made between the new modelling methodology and a similar method that neglects the moisture history dependence. It was seen that the concentration predictions based on non-history dependent diffusion characteristics resulted in over-prediction of the moisture concentration in cyclic conditioning of adhesive joints. The proposed method serves as the first step in the formulation of a general methodology to predict the moisture dependent degradation and failure in adhesives.
Crocombe AD, Sofocleous K, Ogin SL, Tsakiropoulos P, Le-Page BH (2006) Controlled impact testing of shape memory alloy composites,
Wahab MMA, Hilmy I, Ashcroft IA, Crocombe AD (2011) Damage Parameters of Adhesive Joints with General Triaxiality Part I: Finite Element Analysis, JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 25 (9) pp. 903-923 BRILL ACADEMIC PUBLISHERS
Thozhur SM, Crocombe AD, Smith PA, Cowley K, Mullier M (2007) Cutting characteristics of beard hair, JOURNAL OF MATERIALS SCIENCE 42 (20) pp. 8725-8737 SPRINGER
Crocombe AD, Wang R, Richardson G, Underwood CI (2006) Estimating the energy dissipated in a bolted spacecraft at resonance, COMPUTERS & STRUCTURES 84 (5-6) pp. 340-350 PERGAMON-ELSEVIER SCIENCE LTD
Loosening and migration of tibial prostheses have been identified as causes of early total knee replacement (TKR) failure. The problem is made more complex when defects occur in the proximal tibia compromising fixation and alignment. Clinical studies using metal augments have shown these to be an alternative to other means of defect treatment. Finite element (FE) analysis can be used to identify regions that may be prone to loosening and migration. In the current work, 3D FE models of TKR uncontained type-2 defects treated with block augments have been constructed and analysed. It has been shown that a metal augment is the most suitable. The use of bone cement (PMMA) to fill proximal defects is not considered suitable as stresses carried by the cement block exceed those of the fatigue limit of bone cement. It has been shown that the stresses in the proximal cancellous bone of block-augmented models are significantly below levels likely to cause damage due to overloading. Furthermore, the use of stem extensions has been shown to reduce the cancellous bone stresses in the proximal region thus increasing the likelihood of bone resorption. Given this, it is recommended that stem extensions are not required unless necessary to mitigate some other problem.
Liljedahl CDM, Crocombe AD, Wahab MA, Ashcroft IA (2006) Damage modelling of adhesively bonded joints, INTERNATIONAL JOURNAL OF FRACTURE 141 (1-2) pp. 147-161 SPRINGER
Solana AG, Crocombe AD, Wahab MMA, Ashcroft IA (2007) Fatigue initiation in adhesively-bonded single-lap joints, JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 21 (14) pp. 1343-1357 BRILL ACADEMIC PUBLISHERS
Topal S, Ogin S, Crocombe A, Potluri P (2014) Finite element modelling of 3D orthogonal non-CRIMP woven composites, 11th World Congress on Computational Mechanics, WCCM 2014, 5th European Conference on Computational Mechanics, ECCM 2014 and 6th European Conference on Computational Fluid Dynamics, ECFD 2014 pp. 3504-3512
This paper presents the results of a preliminary finite element analysis conducted for a 3D orthogonal non-crimp woven composite which explicitly, and for the first time, incorporates the through thickness z-binder yarns. A representative volume element (RVE) of the composite has been created to fully model the microstructural arrangement of yarns. The continuously changing material orientations in the z-binder yarns have been incorporated into the finite element software, ABAQUS, by means of input files generated with an open source code program, TEXGEN. The behaviour of the composite has been inspected for the cases of loading in warp and fill (weft) directions. The results show that the fill which is adjacent to the z-binder yarn will fail prior to the warp yarns due to the material's low transverse tensile strength. This phenomenon has been reported in the literature as transverse cracks in fill yarns for the case of loading in warp direction. Furthermore, only modest values of tensile stresses have been evaluated on the surfaces of z-crowns, which explain why no initial crack formation could be observed at those regions in experiments. With these results, better understanding of the micromechanical events occurring inside the 3D orthogonal non-crimp woven composite in case of loadings in warp and fill directions has been provided.
Crocombe AD, Ogin SL, Reed GT, Thorne AM, Palaniappan J, Capell T, Wang H, Mohanty L, Tjin SC (2007) An optical method, based on chirped fibre Bragg gratings, for the non-destructive evaluation of disbonding in bonded composite joints,
Hua Y, Crocombe AD, Wahab MA, Ashcroft IA (2007) Continuum damage modelling of environmental degradation in joints bonded with E32 epoxy adhesive, JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 21 (2) pp. 179-195 BRILL ACADEMIC PUBLISHERS
Hilmy I, Wahab MMA, Ashcroft IA, Crocombe AD (2008) A Finite Element Analysis of Scarf Joint for controlling the Triaxiality function in Adhesive Bonding., ADVANCES IN FRACTURE AND DAMAGE MECHANICS VII 385-387 pp. 17-20 TRANS TECH PUBLICATIONS LTD
The measurement of fatigue damage in adhesive bonding has been investigated. Bulk adhesive was used in this study for two reasons: the stress distribution of adhesives in bulk is simpler to investigate than adhesives in joints; and the specimen dimensions met fatigue test standards. Bulk adhesive was made from a film type of epoxy resin. In general, the characteristics and the behaviour of bulk adhesive may differ from adhesive in joint because of the presence of voids and the constraints imposed by the substrates. Low cycle fatigue tests with a load amplitude ratio of 0.1 at a frequency of 5 Hz were performed to determine the damage as a function of the number of cycles. Damage curves, i.e., the evolution of the damage variable as a function of number of cycles, were derived and plotted using an isotropic damage equation. Damage was evaluated using the decrease of stress range during the lifecycles of a constant displacement amplitude test. It was found that the damage curves were well fitted by a low cycle, fatigue damage evolution law equation. This equation was derived from a dissipation potential function. Curve fitting was performed using the robust least square technique rather than ordinary linear least square technique because damage curves have extreme points (usually near the failure point). It was found that the fitting process would not converge for adhesive fractures at high cycle values (Nf > 9000). Two damage constants A and ² were found from the fitting process. Each fatigue set of data, at a certain level of von-Mises stress range for the undamaged state or at the stabilized hardened state, (Ãeq*), had a different set of damage parameters A and ². Linear regression of these points was used to express A and ² as a function of Ã eq*. Using these expressions, damage curves for different levels of Ãeq* could be predicted. © Koninklijke Brill NV, Leiden, 2010.
Crocombe AD, Khoramishad H, Katnam K, Abdel Wahab MM, Ashcroft IA (2008) Fatigue damage study of adhesively bonded joints on thick laminated substrates,
Crocombe AD, Ashcroft IA (2008) Modelling Fatigue in Adhesively Bonded Joints, In: Silva LFMD, Öchsner A (eds.), Modeling of Adhesively Bonded Joints 7 pp. 183-223 Springer Verlag
The book proposed intends to provide the designer with the most advanced stress analyses techniques in adhesive joints to reinforce the use of this promising ...
The present study is focused on the fatigue failure initiation at bimaterial corners by means of a configuration based on the Brazilian disc specimens. These specimens were previously used for the generalized fracture toughness determination and prediction of failure in adhesive joints, carried out under static compressive loading. Under static loading, local yielding effects might affect the asymptotic two-dimensional linear elastic stress representation under consideration. Fatigue loading avoids this fact due to the lower load levels used. The present tests were performed using load control; video microscopy and still cameras were used for monitoring initiation and crack growth. The fatigue tests were halted periodically and images of the corner were taken where fatigue damage was anticipated. Damage initiation and subsequent crack growth were observed in some specimens, especially in those which presented brittle failure under static and fatigue tests. These analyses allowed the characterization of damage initiation for a typical bimaterial corner that can be found in composite to aluminium adhesive lap joints. © 2012 © 2012 Taylor & Francis.
Stem tip pain following revision total knee arthroplasty is a significant cause of patient dissatisfaction, which in the presence of an aseptic well-fixed component has no widely accepted surgical solution. A definitive cause of stem tip pain remains elusive, however it has been suggested that high stress concentrations within the region of the stem tip may play a role. This paper reports a finite element study of a novel clinical technique where a plate is attached to the tibia within the region of the stem tip to reduce stem tip pain. The results demonstrate that the plate reduces stress concentrations in the bone at the stem tip of the implant. The magnitude of stress reduction is dependent upon plate location, material and attachment method.
In recent years, cohesive elements based on the cohesive zone model (CZM) have been increasingly used within finite element analyses of adhesively bonded joints to predict failure. The cohesive element approach has advantages over fracture mechanics methods in that an initial crack does not have to be incorporated within the model. It is also capable of modelling crack propagation and representing material damage in a process zone ahead of the crack tip. However, the cohesive element approach requires the placement of special elements along the crack path and is, hence, less suited to situations where the exact crack path is not known a priori. The extended finite element method (XFEM) can be used to represent cracking within a finite element and hence removes the requirement to define crack paths or have an initial crack in the structure. In this article, a hybrid XFEM-cohesive element approach is used to model cracking in the fillet area using XFEM where the crack path is not known and then using cohesive elements to model crack and damage progression along the interface. The approach is applied to the case of an aluminium-epoxy single lap joint and is shown to be highly effective. © 2014 Copyright Taylor & Francis Group, LLC.
Crocombe AD, Capell T, Ogin SL, Reed GT, Thorne AM, Palaniappan J, Tjin SC, Mohanty L (2007) The use of thermal mismatch stresses to detect disbond initiation and propagation in metal/composite bonded joints using a CFBG fibre optic sensor,
Capell TF, Palaniappan J, Ogin SL, Thorne AM, Reed GT, Crocombe AD, Tjin SC, Wang Y, Guo Y (2009) Detection of defects in as manufactured GFRP-GFRP and CFRP-CFRP composite bonded joints using chirped fibre Bragg grating sensors, PLASTICS RUBBER AND COMPOSITES 38 (2-4) pp. 138-145 MANEY PUBLISHING
Lijedahl CDM, Crocombe AD, Wahab MA, Ashcroft IA (2007) Modelling the environmental degradation of adhesively bonded aluminium and composite joints using a CZM approach, INTERNATIONAL JOURNAL OF ADHESION AND ADHESIVES 27 (6) pp. 505-518 ELSEVIER SCI LTD
The present paper is concerned with modelling damage and fracture in notched woven fabric composites. Previous experimental work has shown that damage at a notch in a variety of GFRP and CFRP composites based on woven fabric reinforcement comprises matrix damage and fibre tow fracture along the plane of maximum stress. It is these experimental observations that inform the failure modelling developed here, in which a cohesive zone approach is used within a 2- D finite element framework. The cohesive zone parameters are based on previously reported experimental measurements for the strength and toughness of the woven fabric materials under investigation. The approach is shown to provide predictions of notched strength that are in very good agreement (less than 11% discrepancy) with experimental results from the literature for a range of GFRP and CFRP woven fabric systems. © (2014) Trans Tech Publications, Switzerland.
Crocombe AD, Palaniappan J, Ogin SL, Thorne AM, Reed GT, Tjin SC, Mohanty L (2007) Disbond detection in composite-composite bonded joints using embedded chirped fibre bragg gratings,
Experimental studies have been undertaken investigating the effect of moisture on the fatigue response of adhesively bonded monolithic single lap joints and laminated doublers loaded in bending, both made of the same materials. The joints were aged in deionised water at a temperature of 50 °C for up to 2 years exposure. The backface strain technique was employed to monitor damage initiation and propagation in the joints. The test results show that the fatigue life degraded with increasing moisture content and tended to level off when approaching saturation. The failure surfaces were cohesive in the adhesive. Numerical fatigue modelling has been undertaken to predict the fatigue response of these joints utilising a strain-based fatigue damage law integrated with a bilinear traction-separation cohesive zone model. The residual stresses due to thermal and swelling strain were included in the model. Good agreement was found between the predicted fatigue response and the experimental results. © 2012 Elsevier Ltd. All rights reserved.
Therapeutic use of high-amplitude pressure waves, or shock wave therapy (SWT), is emerging as a popular method for treating musculoskeletal disorders. However, the mechanism(s) through which this technique promotes healing are unclear. Finite element models of a shock wave source and the foot were constructed to gain a better understanding of the mechanical stimuli that SWT produces in the context of plantar fasciitis treatment. The model of the shock wave source was based on the geometry of an actual radial shock wave device, in which pressure waves are generated through the collision of two metallic objects: a projectile and an applicator. The foot model was based on the geometry reconstructed from magnetic resonance images of a volunteer and it comprised bones, cartilage, soft tissue, plantar fascia, and Achilles tendon. Dynamic simulations were conducted of a single and of two successive shock wave pulses administered to the foot. The collision between the projectile and the applicator resulted in a stress wave in the applicator. This wave was transmitted into the soft tissue in the form of compression-rarefaction pressure waves with an amplitude of the order of several MPa. The negative pressure at the plantar fascia reached values of over 1.5 MPa, which could be sufficient to generate cavitation in the tissue. The results also show that multiple shock wave pulses may have a cumulative effect in terms of strain energy accumulation in the foot.
Crocombe AD, Khoramishad H, Katnam K, Ashcroft IA (2009) Damage modelling of adhesively bonded joints subjected to fatigue loading at different load ratios,
Crocombe AD, Reed GT, Ogin SL, Thorne AM, Palaniappan J, Capell TF, Tjin SC, Mohanty L (2009) The use of chirped fibre Bragg grating sensors to monitor disbond growth,
Hua Y, Crocombe AD, Wahab MA, Ashcroft IA (2006) Modelling environmental degradation in EA9321-bonded joints using a progressive damage failure model, JOURNAL OF ADHESION 82 (2) pp. 135-160 TAYLOR & FRANCIS LTD
The behaviour of adhesively bonded lap joints subjected to fatigue loading is still not well understood. In this paper strength degradation of joints during fatigue cycling is measured experimentally and related to damage evolution. Strength wearout (SW) measurements carried out under constant amplitude fatigue loading of single lap joints are presented and correlated with in situ measurements of back-face strain (BFS) and estimations of damage progression from fracture surfaces and sectioning of partially fatigued samples. Residual strength was found to decrease non-linearly with respect to the number of fatigue cycles and this corresponded to non-linear increases in the BFS and damage measurements. In particular it was noted that fatigue damage accelerated very quickly towards the end of the fatigue life of a joint. A non-linear SW model is proposed and was found to agree well with the experimental results. This model can be used to predict the residual strength of a joint after a period of fatigue loading once a single empirical constant has been determined. © 2008 Elsevier Ltd. All rights reserved.
In this paper, the backface strain (BFS) measurement technique is used to characterise fatigue damage in single-lap adhesive joints subjected to constant amplitude fatigue loading. Different regions in the BFS plots are correlated with damage in the joints through microscopic characterisation of damage and cracking in partially fatigued joints and comparison with 3D finite element analysis (FEA) of various crack growth scenarios. Crack initiation domination was found at lower fatigue loads whereas crack propagation dominated at higher fatigue loads. Using the BFS and fatigue life measurement results, a simple predictive model is proposed which divides the fatigue lifetime into different regions depending upon the fatigue load. The model can be used with experimental BFS measurements to determine the residual life of the joint in different regions of damage progression during the fatigue life. © 2008 Elsevier Ltd. All rights reserved.
Crocombe AD, Palaniappan J, Wang H, Ogin SL, Thorne A, Reed GT, Tjin SC (2006) Disbond growth detection in bonded composite joints using a fibre bragg grating,
This article is the second part of a two-part article looking at carcass deflections, contact pressure and shear stress distributions for a steady-rolling, slipping and cambered tyre. In the first part, a previously described and validated finite-element (FE) model of a racing-car tyre is developed further to extract detailed results which are not easily obtainable through measurements on an actual tyre. Generally, these results aid in the understanding of contact patch characteristics. In particular, they form a basis for the development of a simpler physical tyre model, which forms the focus of this part of the article. The created simpler tyre model has the following three purposes: (i) to reduce computational demand while retaining accuracy, (ii) to allow identification of tyre model features that are fundamental to an accurate representation of the contact stresses and (iii) to create a facility for better understanding of tyre wear mechanisms and thermal effects. Results generated agree well with the physically realistic rolling-tyre behaviour demonstrated by the FE model. Also, the model results indicate that an accurate simulation of the contact stresses requires a detailed understanding of carcass deformation behaviour.
Crocombe AD, Agarwal Y, Frehill B, Cirovic S, Bradley N (2009) Stability of Tibial Implants in Augmented Knee Arthroplasty,
Crocombe AD, Ashcroft IA, Jumbo F, Abdel Wahab MM (2007) Modelling Environmental Ageing in Bonded Joints,
The durability of adhesive joints is of special concern in structural applications and moisture has been identified as one of the major factors affecting joint durability. This is especially important in applications where joints are exposed to varying environmental conditions throughout their life. This paper presents a methodology to predict the stresses in adhesive joints under cyclic moisture conditioning. The single lap joints were manufactured from aluminium alloy 2024 T3 and the FM73-BR127 adhesive-primer system. Experimental determination of the mechanical properties of the adhesive was carried out to measure the effect of moisture uptake on the strength of the adhesive. The experimental results revealed that the tensile strength of the adhesive decreased with increasing moisture content. The failure strength of the single lap joints also progressively degraded with time when conditioned at 50C, immersed in water; however, most of the joint strength recovered after drying the joints. A novel finite element based methodology, which incorporated moisture history effects, was adopted to determine the stresses in the single lap joints after curing, conditioning, and tensile testing. A significant amount of thermal residual stress was present in the adhesive layer after curing the joints; however, hygroscopic expansion after the absorption of moisture provided some relief from the curing stresses. The finite element model used moisture history dependent mechanical properties to predict the stresses after application of tensile load on the joints. The maximum stresses were observed in the fillet areas in both the conditioned and the dried joints. Study of the stresses revealed that degradation in the strength of the adhesive was the major contributor in the strength loss of the adhesive joints and adhesive strength recovery also resulted in recovered joint strength. The presented methodology is generic in nature and may be used for various joint configurations as well as for other polymers and polymer matrix composites. © 2011 Taylor & Francis Group, LLC.
The hypothesis of this study is that all-polyethylene (APE) tibial implants offer a biomechanical profile similar to metal-backed tray (MBT). There are significant financial implications, in selected patient groups, if APE can be deemed to perform as well as MBT.Using a finite element analysis of CAD models provided by DePuy (Leeds), stress distributions were investigated for both an APE and MBT tibial implant. The performance was assessed for cancellous bone at 700 MPa (normal) and at 350 MPa (less stiff). Plots were recorded along the length of the tibia, showing the loads carried by the bone (cortical and cancellous), the implant interface, cement interface and the stem. von Mises stress distributions and percentage volumes were used to assess bone resorption and hence potential for failure (fracture).Higher stress shielding (resorption) occurred around the keel and stem of the MBT revealing greater potential for bone loss in these areas. APE had no areas of bone resorption (being more flexible resulting in less stress shielding). The stiffer MBT carries a higher proportion of the load down the stem. MBT stress in cancellous bone is lower than APE, as load is distributed to the cortical rim. APE has a marginally favourable strain state in cancellous bone and spreads loads more at the cement interface than MBT.Modern-day APE bearings may be superior to previously designed implants due to improvements in manufacturing. In the correct patient group, this could offer substantial cost savings.
Crocombe AD, Xu DH, Xu W (2007) A Study of Strain Related Bone Remodelling of the Osseointegrated Patient,
Palaniappan J, Wang H, Ogin SL, Thorne A, Reed GT, Crocombe AD, Tjin SC (2005) Structural health monitoring of bonded composite joints using embedded chirped fibre Bragg gratings, ADVANCED COMPOSITES LETTERS 14 (6) pp. 185-192 ADCOTEC LTD
The aim of this research was to develop numerical modelling techniques for simulating the simultaneous effects of moisture, elevated temperature, and applied load on the performance of adhesively bonded joints. Associated experimental data are also reported. The degradation process of the joints was modelled using a fully-coupled approach, with the moisture concentration affecting the stress distribution and the stress state affecting the moisture diffusion analyses simultaneously. Further, the stress analysis contains a moisture-dependent creep model to accommodate viscous effects, and both swelling and thermal strains were included in the simulation. The governing parameters adopted in the modelling procedure were determined from experimental work based on the bulk adhesive. The joint response was monitored throughout the ageing process and good correlation was found between the experimental and numerical results. Copyright © 2014 Taylor & Francis Group, LLC.
Ashcroft IA, Shenoy V, Critchlow GW, Crocombe AD (2010) A comparison of the prediction of fatigue damage and crack growth in adhesively bonded joints using fracture mechanics and damage mechanics progressive damage methods, Journal of Adhesion 86 (12) pp. 1203-1230
Chirped fibre Bragg grating (CFBG) sensors embedded within composite materials have been shown to be able to monitor delamination growth in adhesively bonded single-lap joints, whether the sensors are embedded within a composite adherend or within the adhesive bondline itself. The relative ease of interpretation of CFBG reflected spectra with regard to delamination growth is a consequence of the relationship between the spectral bandwidth of the reflected spectrum (typically 20 nm) and physical locations along the sensor length (typically 60 mm). When the sensor is embedded in, or bonded to, a composite material subjected to a tensile uniform strain, all the grating spacings are increased and the entire spectrum shifts to higher wavelengths-just as for a uniform FBG sensor. However, if the strain field is perturbed by damage in the composite (such as a matrix crack or a delamination), so that the smooth linear increase in the grating spacing is disrupted, then a perturbation appears in the reflected spectrum that can be used to determine the physical location of the damage. In this paper, results on monitoring delamination/disbond growth will be discussed with regard to sensor location, together with the possibility of using the sensors to monitor repaired composite structures. © 2012 Taylor & Francis Group, London.
This work is concerned with investigating the residual static strength of adhesively bonded joints after long-term exposure to a combined mechanical-hygro-thermal environment. Associated experimental data are also reported. The degradation process of the joints was modelled using a fully-coupled approach, with the moisture concentration affecting the stress distribution and the stress state affecting the moisture diffusion analyses simultaneously. A bilinear cohesive zone model was then used to implement the progressive damage FE analysis of the quasi-statically loaded joints following the ageing phase. This model is degraded using the damage factors (creep strain and moisture uptake) accumulated over the ageing process and calibrated against the experimental results from static tests on the bulk adhesive. Predicted and experimentally-measured quasi-static responses for the aged adhesive joints were found to be in good agreement. © 2014 Elsevier Ltd.
Scarf repairs are often used for damaged composite structures in order to recover the mechanical properties of the original structure. During service, there is the possibility that damage will occur in the repaired region and hence it would be useful to be able to monitor such repairs. This work investigates the use of chirped fibre Bragg grating (CFBG) sensors to monitor the development of damage initiation and growth in the repaired region. The experimental part of the work uses a model system consisting of a scarf-repaired, transparent GFRP beam. During fatigue loading, damage in the form of cracks initiate at the interface between the scarf-repair and the parent material on the tensile face of the beam, and grows within this region. The modulus reduction as a consequence of crack growth has been monitored and finite-element analysis (FEA) has been used to predict this reduction, with reasonable agreement between experiment and modelling. Using the FEA analysis, predictions have been made of the strain changes in the vicinity of the growing damage and the effect that these would have on reflected spectra recorded by a chirped fibre Bragg grating sensor bonded across the scarf repair. The predictions suggest that as the damage develops within the scarf repair, the strain changes will modify the reflected spectra in such a way that the initiation of damage can be detected and the growth of fatigue cracks associated with the scarf repair can be monitored. The predictions are in good qualitative agreement with experimental results. © 2012 Taylor & Francis Group, London.
The damage parameters for crack initiation in a single lap joint (SLJ) are determined by combining continuous damage mechanics, finite element analysis (FEA) and experimental fatigue data. Even though a SLJ has a simple configuration, the stresses in the adhesive region are quite complex and exhibit multi-axial states. Such a condition leads to the need to introduce a general value for the triaxiality function in the damage evolution law rather than using a triaxiality function which equals unity, as in the case of a uni-axial stress state, e.g., the bulk adhesive test specimen presented in Part 1 of this paper. The effect of stress singularity, due to the presence of corners at edges, also contributes to the complex state of stress and to the variability of the triaxiality function along the adhesive layer in a SLJ. The damage parameters A and ² determined in Part 1 for bulk adhesive are now extended to take into account the multi-axial stress state in the adhesive layer, as calculated from FEA. © Koninklijke Brill NV, Leiden, 2010.
A unified model is proposed to predict the fatigue behaviour of adhesively bonded joints. The model is based on a damage mechanics approach, wherein the evolution of fatigue damage in the adhesive is defined as a power law function of the micro-plastic strain. The model is implemented as an external subroutine for commercial finite element analysis software. Three dimensional damage evolution and crack propagation were simulated using this method and an element deletion technique was employed to represent crack propagation. The model was able to predict the damage evolution, crack initiation and propagation lives, strength and stiffness degradation and the backface strain during fatigue loading. Hence the model is able to unify previous approaches based on total life, strength or stiffness wearout, backface strain monitoring and crack initiation and propagation modelling. A comparison was made with experimental results for an epoxy bonded aluminium single lap joint and a good match was found. © 2010 Elsevier Ltd. All rights reserved.
The aim of this research is to investigate the effect of moisture on the static response of adhesively bonded monolithic single lap joints and laminated doublers loaded in bending. All joints were made of aluminium alloy Al 2024-T3 bonded using epoxy film adhesive FM 73M OST. The joints were aged in deionised water at a temperature of 50°C for up to 2 years exposure. The use of different widths of specimen (5 mm for monolithic single lap joints and 15 mm for laminated doublers) allowed both full and partial saturation of the adhesive layer. The bulk adhesive has been characterised to obtain the coefficient of moisture diffusion, the coefficient of thermal and moisture expansion and the moisture dependent mechanical properties. The testing results showed that the mechanical properties degraded in a linear way with the moisture content. The residual strength after exposure decreased with increasing moisture content (exposure time) and tended to level off towards saturation. The damage evolution and failure of the joint has been successfully monitored using the backface strain technique and in-situ video microscopy. Progressive damage finite element modelling using a moisture dependent, bilinear traction-separation law has been undertaken to predict the residual strength. Residual stresses due to thermal and swelling strains in the adhesive layer have been included; however their effect on the predicted static strength was not significant. Good agreement was found between the predicted residual strength and the experimental result. © 2012 Elsevier Ltd.
Adediran OA, Abdel Wahab MM, Xu W, Crocombe AD (2012) Application of FE model updating for damage assessment of FRP composite beam structure, Conference Proceedings of the Society for Experimental Mechanics Series 6 pp. 385-398
The FRP composite beam structure that is intended to represent deck prototype used in civil engineering construction is investigated. FRP composite material may have possible damage, which affect vibration structural integrity and reliability. To overcome this problem, vibration data from experiments can be used to assess such damage accurately. The FE mode updating process is demonstrated in parameter identification as well as structural damage identification. It is used to minimise the difference between experimental and numerical data. The updated parameters are the modified parameters selected in the FE model with aim of correcting modelling errors and/or damage detection. In this FE model updating procedure, model physical characteristics are changed so that the differences between experimental and numerical dynamic properties are reduced. The FE model updating is carried out using optimisation tools in ANSYS software. Only the first three natural frequencies will be considered in this work. The FE model updating procedure brings the numerical results of the FRP structure in proper correlation to the experimental results, according to an objective function, by changing the FE model parameters. The test results of the structure under intact and damage states are presented. It is suggested that there is damage at the unbounded joint when there is significant change in fixed parameters of the structure beyond acceptable degree. © The Society for Experimental Mechanics, Inc. 2012.
Crocombe AD, Katnam KB, Khoramishad H, Sugiman S, Ashcroft IA (2009) Environmental-Fatigue Damage Model for Adhesively Bonded Laminated Joints,
Liljedahl CDM, Crocombe AD, Wahab MA, Ashcroft IA (2006) Modelling the environmental degradation of the interface in adhesively bonded joints using a cohesive zone approach, JOURNAL OF ADHESION 82 (11) pp. 1061-1089 TAYLOR & FRANCIS LTD
Quasi-static tests have been carried out to characterise mixed-mode fracture using a Double Cantilever Beam (DCB) specimen. The DCB consists of equal thickness mild steel adherends bonded with FM-73M epoxy adhesive and is tested under pure mode I, pure mode II and a range of mode-mixity conditions, using a relatively simple loading fixture. The test method is analysed using closed-form and finite element methods, which agree well provided that the adhesive deformation is considered. The strain energy release rate components at fracture are presented in a conventional GI (mode I)-GII (mode II) failure plot using closed-form Linear Elastic Fracture Mechanics (LEFM) methods reported previously in the literature. The results showed that the strain energy release rate is enhanced in the situation of the mode II (in-plane shearing) dominated mixed mode condition as compared to the mode I (opening mode) dominated mixed mode. © 2010 Elsevier Ltd.
Crocombe AD, Frehill B, Agarwal Y, Bradley N (2010) Stability of conical augments in the treatment of contained proximal tibial defects,
Ali AM, Wahab MMA, Crocombe AD, Ashcroft IA (2007) Damage assessment of adhesively bonded FRP Beams using modal parameters, Damage Assessment of Structures VII 347 pp. 525-530 TRANS TECH PUBLICATIONS LTD
Crocombe AD, Ashcroft IA, Wahab MA (2008) Environmental Degredation, In: Silva LFMD, Öchsner A (eds.), Modeling of Adhesively Bonded Joints 8 pp. 225-241 Springer Verlag
The book proposed intends to provide the designer with the most advanced stress analyses techniques in adhesive joints to reinforce the use of this promising ...
Yang Y, Rahmanivahid P, Xu W, Crocombe AD (2011) A finite element analysis and experimental study of human edentulous mandible, Proceedings of the Third Annual Conference of the Biomedical Science and Engineering Center
By the means of finite element analysis (FEa), biomechanical behaviors of human mandible have been widely studied over decades. Many different types of simulation of muscle forces have been employed in studies to increase the reality of mastication environment. Among these studies, Cruz et al (2003)'s calculation of muscle forces was well accepted. However, these simulations have not been verified experimentally as seen in literatures. In this study, a three dimensional (3D) finite element model of human mandible was created from CT images of a cadaver mandible bone. 4 pairs of muscle forces was applied to this 3D model based on a calculation by using Cruz et al (2003)'s method. The exact cadaver bone was used in an experimental testing rig to evaluate strain distribution and, hence, to verify the results of FEa. A set of different sizes of loads which matches with the one used in FE study was applied to the cadaver bone. Strain gauges were employed to gain data of strain distribution on the bone. The experimental result shows that the trend of stress/strain during increase or decrease of muscle forces coincides with FE result. This verifies the masticator muscle force calculation of Cruz et al (2003) to be correct.
This paper presents a methodology to predict the strength of adhesive joints under variable moisture conditions. The moisture uptake in adhesive joints was determined using a history dependent moisture prediction methodology where diffusion coefficients were based on experimental cyclic moisture uptake of bulk adhesive samples. The predicted moisture concentrations and moisture diffusion history were used in a structural analysis with a cohesive zone model to predict damage and failure of the joints. A moisture concentration and moisture history dependent bilinear cohesive zone law was used. The methodology was used to determine the damage and failure in aluminium alloy - epoxy adhesive single lap joints, conditioned at 50 °C and good predictions of failure load were observed. The damage in the adhesive joints decreased the load carrying capacity before reaching the failure load and a nonlinear relationship between the load and displacement was observed. Changes in crack initiation and crack propagation were also observed between different types of joints. The presented methodology is generic and may be applied to different types of adhesive joint and adhesive. © 2011 Elsevier Ltd.
Crocombe AD, Ashcroft IA (2008) Simple Lap Joint Geometry, In: Silva LFMD, Öchsner A (eds.), Modeling of Adhesively Bonded Joints 1 pp. 3-23 Springer Verlag
The book proposed intends to provide the designer with the most advanced stress analyses techniques in adhesive joints to reinforce the use of this promising ...
Woodland S, Crocombe AD, Chew JW, Mills SJ (2011) A New Method for Measuring Thermal Contact Conductance-Experimental Technique and Results, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 133 (7) ARTN 071601 ASME-AMER SOC MECHANICAL ENG
Xu W, Xu DH, Crocombe AD (2006) Three-dimensional finite element stress and strain analysis of a transfemoral osseointegration implant, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE 220 (H6) pp. 661-670 PROFESSIONAL ENGINEERING PUBLISHING LTD
Ogin SL, Sanderson AR, Crocombe AD, Gower MRL, Lee RJ, Tjin SC, Lin B (2011) Monitoring crack growth in a DCB test using a surface-bonded chirped FBG sensor,
Delamination growth within transparent, unidirectionally reinforced glass fibre/epoxy doublecantilever beam (DCB) specimens has been monitored using a surface-mounted chirped fibre Bragg grating (CFBG) sensor. The specimens were tested using a constant displacement rate, with the delamination length being measured using (i) surface-mounted CFBG sensors, (ii) in situ photography, and (iii) surface-mounted strain gauges. The DCB specimens showed characteristics typical of such material, with the development of extensive fibre bridging and pronounced R-curve behaviour. A distinct perturbation in the reflected spectra, when monitoring the delamination growth using the CFBG sensors, was indicative of the location of the delamination front during the test. The in situ photographs and the surface strain measurements provided by the strain gauges were used to predict the experimentally determined CFBG reflected spectra, with good agreement between prediction and experiment. These results enabled the delamination length to be measured using the CFBG sensor technique to within 4 mm over the 60 mm sensor length.
Sanderson AR, Ogin SL, Capell TF, Crocombe AD, Gower MRL, Barton E, Lee RJ, Hawker J (2012) Monitoring the disbonding of a CFRP plate-bonded reinforcement of a structural beam using a chirped FBG sensor, ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials
A surface-mounted CFBG sensor has been used to monitor disbond growth of a CFRP platebonded reinforcement of a structural box-section beam, bonded using a room-temperature cure structural adhesive. These tests are part of a programme to determine whether disbonding of such a plate could be monitored by ambient thermal fluctuations alone with the aid of thermal mismatch strains. Disbonds were introduced by physically cutting the structural adhesive and a range of different disbond lengths and temperatures have been investigated. When monitoring the disbond growth using the CFBG sensors, a distinct peaktrough perturbation in the reflected spectra was indicative of the location of the disbond front during the test. A prediction of the reflected spectrum was in good agreement with the experimentally-determined results, enabling the disbond lengths to be measured using the CFBG sensor technique to within about 3 mm.
Wenman MR, Price AJ, Steuwer A, Chard-Tuckey PR, Crocombe A (2009) Modelling and experimental characterisation of a residual stress field in a ferritic compact tension specimen, INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING 86 (12) pp. 830-837 ELSEVIER SCI LTD
The present paper is concerned with modelling damage and fracture in notched woven fabric composites. Previous experimental work has shown that, under tensile loading, damage at a notch in a variety of glass fibre reinforced plastic (GFRP) and carbon fibre reinforced plastic (CFRP) composites based on woven fabric reinforcement comprises matrix damage and fibre tow fracture along the plane of maximum stress. It is these experimental observations that inform the failure modelling developed here, in which a cohesive zone approach is used within a two-dimensional extended finite element method framework. The traction-separation parameters used in the extended finite element method implementation are based on previously reported experimental measurements for the strength and toughness of the woven fabric materials under investigation. The approach is shown to provide predictions of notched strength that are in very good agreement with experimental results from the literature for a range of glass fibre reinforced plastic and carbon fibre reinforced plastic woven fabric systems and also agree well with results obtained from closed form analytical models, which require calibration. © Institute of Materials, Minerals and Mining 2013.
Crocombe AD, Jo SI, Onoufriou T (2008) Effect of corrosion on the reliability of a bridge based on Response Surface Method,
Shao F, Xu W, Crocombe A, Ewins D (2007) Natural frequency analysis of osseointegration for trans-femoral implant, ANNALS OF BIOMEDICAL ENGINEERING 35 (5) pp. 817-824 SPRINGER
This paper is concerned with modelling damage and fracture in woven fabric CFRP single-lap bolted joints that fail by net-tension. The approach is based on the assumption that damage (matrix cracking, delamination and fibre tow fracture) initiates and propagates from the hole in a self-similar fashion. A traction-separation law (based on physically meaningful material parameters) is implemented within an Extended Finite Element Method (XFEM) framework and used to predict the joint strength. Reasonable agreement between model and experiment was obtained for test configurations covering different weave types and lay-ups, a range of joint geometries (two hole diameters and a range of normalised joint widths) and finger-tight and fully torqued clamp-up conditions. The greatest discrepancies were for situations where the tensile fracture mechanisms were more complex, and hence not captured fully in the model or when bearing failure occurred. © 2014 Elsevier Ltd. All rights reserved.
Hilmy I, Wahab MMA, Ashcroft IA, Crocombe AD (2006) Measuring of damage parameters in adhesive bonding, Fracture and Damage Mechanics V, Pts 1 and 2 324-325 pp. 275-278 TRANS TECH PUBLICATIONS LTD
Ahmad H, Crocombe AD, Smith PA (2011) Failure modelling of woven GFRP bolted joints under quasi-static loading, ICCM International Conferences on Composite Materials
A 2-D finite element model has been developed to simulate crack growth (net-tension and shear-out failures) in composite bolted joints. Results from the model have been compared with a similar approach from the literature and experimental data for a woven fabric system. Agreement is reasonable in each case.
Crocombe AD, Hafiz TA, Smith PA, Abdel Wahab MM (2009) The Development of an experimental technique to characterise mixed-mode fracture in adhesively bonded joints,
Topal S, Baiocchi L, Crocombe AD, Ogin SL, Potluri P, Withers PJ, Quaresimin M, Smith PA, Poole MC, Bogdanovich AE (2015) Late-stage fatigue damage in a 3D orthogonal non-crimp woven composite: An experimental and numerical study, COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING 79 pp. 155-163
ELSEVIER SCI LTD
Arastu MH, Partridge R, Crocombe A, Solan M (2010) Determination of optimal screw positioning in flexor hallucis longus tendon transfer for chronic tendoachilles rupture, Foot and Ankle Surgery 17 (2) pp. 74-78
Palaniappan J, Ogin SL, Capell TF, Thorne AM, Reed GT, Crocombe AD, Tjin SC, Mohanty L (2007) Reflected spectra predictions for chirped fibre bragg gratings used for disbond detection in composite/composite joints, ICCM International Conferences on Composite Materials
In this paper it is shown that a chirped fibre Bragg grating sensor embedded within a composite adherend can be used to monitor disbond initiation and propagation in an adhesively bonded single lap-joint. Characteristic changes in the reflected spectra from the sensor indicate both disbond initiation and the current position of the disbond front to within about 2 mm (a distance which depends on adherend material and sensor position in relation to the adhesive bondline). When the sensor extends the full overlap length, disbond initiation from either end of the overlap can be monitored. The results have been modelled using a combination of finite-element analysis and commercial software for predicting FBG spectra; the predicted spectra are in very good agreement with experiment. The CFBG sensor technique could provide the basis for monitoring a wide range of bonded joints and structures where one adherend is a composite material.
Experimental and numerical studies have been undertaken on metal laminate (ML) doublers and hybrid fibre-metal (aluminium-Glare) laminate (FML) doublers to investigate their static and fatigue response under tension loading. Inevitably sheets in these laminates butt together and these butts can affect the joint strength. Progressive damage modelling, including the damage in the adhesive bondline, the butt, the metal and the fibre has been undertaken in both static and fatigue loading. This modelling was found to be in good agreement with the experiment data in terms both of the strength and the failure mechanisms. In ML, the butt influenced the static and fatigue response. In hybrid FML, the specimens either have the fibres parallel to the loading direction (spanwise) or perpendicular to the loading direction (chordwise). The spanwise specimen was found to have the highest strength followed by chordwise specimens without butts and finally chordwise specimens with butts. The most critical position for a butt was found to be adjacent to the doubler end. Without butts the static strength for spanwise and chordwise specimens was controlled by the failure in the Glare layer whilst the fatigue failure was precipitated by failure in the aluminium sheet. © 2012 Elsevier Ltd.
Frehill B, Crocombe A, Cirovic S, Agarwal Y, Bradley N (2010) Initial stability of type-2 tibial defect treatments, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE 224 (H1) pp. 77-85
PROFESSIONAL ENGINEERING PUBLISHING LTD
A surface-mounted chirped fibre Bragg grating (CFBG) sensor has been used for the first time to monitor delamination growth within a composite material (a transparent, unidirectionally reinforced glass fibre/epoxy resin double-cantilever beam (DCB) specimen). The specimens were tested using a constant displacement rate, with the delamination length being measured using complementary techniques: (i) in situ photography, (ii) surface-mounted strain gauges, and (iii) the surface-mounted CFBG sensors. The unidirectionally reinforced DCB specimens showed characteristics typical of such material which complicate the curvature of the beams, i.e. the development of extensive fibre bridging and pronounced R-curve behaviour. To validate the interpretation of the CFBG reflected spectrum, the experimentally determined strains from the surface-mounted strain gauges have been used, together with in situ photographs of the position of the delamination front. Using the CFBG sensor technique, the delamination length was measured to within about 4 mm over the 60 mm sensor length.
Sampo' E, Sorniotti A, Crocombe AD (2010) Chassis Torsional Stiffness: Analysis of the Influence on Vehicle Dynamics, Tire and Wheel Technology and Vehicle Dynamics and Handling, 2010
The current paper is concerned with modelling damage and fracture in woven fabric composite double-lap bolted joints that fail by net-tension. A 3-D finite element model is used, which incorporates bolt clamp-up, to model a range of CFRP bolted joints, which were also tested experimentally. The effects of laminate lay-up, joint geometry, hole size and bolt clamp-up torque were considered. An Extended Finite Element (XFEM) approach is used to simulate damage growth, with traction-separation parameters that are based on previously reported, independent experimental measurements for the strength and toughness of the woven fabric materials under investigation. Good agreement between the predicted and measured bearing stress at failure was obtained. © 2013 Elsevier Ltd. All rights reserved.
Crocombe AD, Agarwal Y, Frehill B, Bradley N (2010) Stability of augmented total knee replacement,
Crocombe AD, Mubashar A, Ashcroft IA, Critchlow GW (2009) Strength Recovery in Epoxy Adhesive Joints under Cyclic Moisture Conditioning Environment,
Woodland S, Crocombe AD, Chew JW, Mills SJ (2008) A NEW METHOD FOR MEASURING THERMAL CONTACT CONDUCTANCE EXPERIMENTAL TECHNIQUE AND RESULTS, PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 4, PTS A AND B pp. 627-634 AMER SOC MECHANICAL ENGINEERS
Crocombe AD, Frehill B, Cirovic S, Agarwal Y (2008) Application of Bone Remodelling Algorithms to Knee Arthroplasty,
In pre-stressed concrete structures, consideration is being given to replacing the steel tendons with CFRP rods. One of the challenges associated with this is to develop a suitable anchorage for the CFRP rods. A bonded anchorage was investigated, where the CFRP is potted in a steel tube using epoxy adhesive. Experimental static tests of different configurations were undertaken with failure occurring in the bond. A set of numerical simulations were carried out with different adhesive material models to investigate the static response of the bonded anchorage and its failure mechanism. The adhesive was modelled with linear elastic properties, von Mises plasticity, Drucker-Prager plasticity and progressive damage. A cohesive zone model with progressive damage in the bonded joint was found to be in reasonable agreement with the experimentally recorded data. Also, an analytical formulation was developed (and validated) in order to provide an approximate distribution of shear stress in the bonded joint for circular anchors for adhesives with mainly elastic behaviour. © 2014 Elsevier Ltd. All rights reserved.
Fatigue tests have been carried out to investigate mixed mode fatigue crack growth behaviour in FM73 epoxy adhesive using double cantilever beam (DCB) specimens. The DCB configuration used consisted of equal thickness mild steel adherends bonded with FM73 adhesive. The joints were tested under pure mode I and a range of fatigue mixed-mode conditions using a relatively simple, variable-mode loading fixture developed in previous work . The fatigue testing was carried out in displacement control, with an initial load ratio (R) of 0.1. The fatigue load decreased as the fatigue crack grew and this load was recorded. Crack growth was monitored and measured using a video microscope. The results suggest that crack initiation in the test specimens is controlled by the mode I strain energy release rate, GI component. The fatigue crack growth rates were characterised using a Paris law approach, from which it appears that the total strain energy release rate range, G Total, is a more dominant factor in controlling crack growth than the mode I component of strain energy release rate range, GI. For a quantitative description of the mixed-mode fatigue crack growth, generalised forms of the Paris relation are developed. © 2012 Elsevier Ltd.
Crocombe AD, Frehill B, Cirovic S, Agarwal Y (2009) Long-term stability analysis of augmented knee arthroplasty using bone remodelling algorithms,
Thozhur SM, Crocombe AD, Smith PA, Cowley K, Mullier N (2006) Structural characteristics and mechanical behaviour of beard hair, JOURNAL OF MATERIALS SCIENCE 41 (4) pp. 1109-1121 SPRINGER
Crocombe AD, Graner Solana A, Abdel Wahab MM, Ashcroft IA (2008) Fatigue behaviour in adhesively-bonded single lap joints,
Osseointegrated trans-femoral implant is a relatively new orthopaedic anchoring method for connecting a stump with a prosthesis. Through a follow-up study of a patient over six years, significant bone remodelling has been observed. Finite element (FE) simulations were carried out to investigate the relationship between the bone remodelling and the strain re-distribution around the trans-femoral osseointegrated implant system. An initial FE model representing the original status of the femur-implant assembly was created from CT scans of the subject prior to osseointegration. Follow-up X-ray images were acquired at various stages post-surgery, which allowed the changes in bone wall thickness to be measured. By updating the bone thickness in the initial model, a series of follow-up FE models were created. Representative load associated with the subject's body weight was applied to the models, and the strain re-distributions were calculated. The results showed that in order to minimise the adverse effect of bone remodelling, an osseointegration implant made by functionally gradient materials are preferred over homogeneous materials.
Recent work has shown that a simple rule-of-mixtures approach may be used to predict the stress strain behaviour of a cross-ply metal matrix composite (MMC) laminate. However, the low-strain behaviour was not predicted accurately, probably because thermal residual stresses are obviously not included in such an approach. To increase the understanding of the limitations of the rule-of-mixtures approach for predicting the stress-strain response, the residual strain-state of the fibre reinforcement has been determined using an etching technique (henceforth referred to as the ?total etch removal method?), and results have been compared both with finite element modelling and with thermal residual strain measurements derived from stress-strain curves. The results show that the residual strain distribution in a cross-ply composite may be more complex than previously thought, with the fibres in internal 00 plies having considerably higher thermal residual strains than fibres in external plies. The results confirm that the rule-of-mixtures approximation can be used, with some reservations with regard to the low strain behaviour.
This paper presents an experimental and numerical study on the structural health monitoring of composite patch repairs using chirped fibre Bragg grating (CFBG) sensors. The repair consisted of bonding a pre-cured patch of the same, but thinner, material to a parent GFRP panel containing a machined hole, with the sensors embedded in the bond-line. The repaired coupons were subjected to four-point flexural loading in fatigue. Bond-line delamination cracks (disbonds) initiated at both ends of the patch repair and grew towards the centre of the repair. Predictions of the strain distributions enabled the reflected spectra obtained during damage growth to be predicted with good agreement between theory and experiment. For practical applications when using CFBG sensors to monitor patch repairs, the results suggest that two sensors should be included within the bond-line so that both vulnerable edges of the repair can be monitored using the low-wavelength end of a sensor.
Improved walking comfort has been linked with better bio-mimicking of the prosthetic ankle.
This study investigated if a hydraulic ankle/foot can provide enough motion in both the sagittal
and frontal planes during level and camber walking and if the hydraulic ankle/foot better
mimics the biological ankle moment pattern compared with a fixed ankle/foot device. Five
active male unilateral trans-femoral amputees performed level ground walking at normal
and fast speeds and 2.5Ê camber walking in both directions using their own prostheses fitted
with an ªEchelonº hydraulic ankle/foot and an ªEspritº fixed ankle/foot. Ankle angles and the
Trend Symmetry Index of the ankle moments were compared between prostheses and
walking conditions. Significant differences between prostheses were found in the stance
plantarflexion and dorsiflexion peaks with a greater range of motion being reached with the
Echelon foot. The Echelon foot also showed significantly improved bio-mimicry of the ankle
resistance moment in all walking conditions, either compared with the intact side of the
same subject or with the ªnormalº mean curve from non-amputees. During camber walking,
both types of ankle/foot devices showed similar changes in the frontal plane ankle angles.
Results from a questionnaire showed the subjects were more satisfied with Echelon foot.
Digital Image Correlation (DIC) can be used to obtain full-field strain information on specimens under load. Through analysis of the resultant strain-contours, defects such as delaminations in composite materials can be detected, based on their effect on the deformation behaviour. This work focusses on the use of the DIC technique and two variations of active thermography (lock-in thermography and pulse thermography) for determining the lengths of delaminations in ?milled-slot? specimens; for each technique, the measured delamination lengths have been compared with visually observed (i.e. photographed) delaminations grown under fatigue loading in transparent woven fabric GFRP specimens. In addition, the DIC results have been interpreted with the aid of a finite element model of the strain distribution in the milled-slot specimens.
It has been found that the DIC technique provides a reasonably good method for measuring the length of the fatigue-grown delaminations after an empirical fit is applied, with the aid of the FE analysis, to overcome complications caused by fibre-bridging. On the other hand, the results using both lock-in and pulse thermography showed reasonable correlations with the visually observed (i.e. photographed) delamination lengths without the need for an empirical fit, although some post-processing of the data was required. For both thermography techniques, there were difficulties in determining the delamination lengths close to the edge of the milled slot.
This paper describes progress towards developing design guidelines for a number of composite bonded joints in aerospace applications. The premise of a universal failure criterion is impractical given the number of adherend-adhesive configurations and layups available. However, for a finite number of joint configurations, design rules can be developed based on experimental test data and detailed finite element (FE) modelling. By using these techniques rather than the traditional overly conservative knock down factors, more of the performance of composite bonded joints can be accessed. The work presented here experimentally studied the effect of the substrate layup, adhesive type and adhesive thickness on double-lap joint (DLJ) strength. The corresponding failure surfaces were analysed and failure modes identified. Following this, detailed FE models were developed to identify the trends associated with altering joint parameters. Finally, the stresses and strains within the adhesive and substrate were analysed at the joints respective failure loads to identify critical parameters. These parameters can provide an insight as to the stress state of the joint at failure or near failure loads, and hence its true performance.
Continuous reinforcement metal matrix composites (MMCs) have yet to become widely used within
the aerospace industry. Despite the high stiffness and strength of unidirectional MMCs, the
complexity and inherent cost of manufacture are major factors that have prevented the widespread
uptake of these advanced materials.
Furthermore, the relatively poor mechanical performance of unidirectional MMCs subjected to
transverse loads has largely precluded their use in structures which experience complex loading
(with the notable exception of bladed compressor discs in gas turbines). Recently, TISICS has been involved in projects with two major aerospace companies to investigate the use of titanium and aluminium matrix composites. In both projects it was necessary to examine the properties of less conventional cross-ply composites and the work undertaken by the author in conjunction with these projects forms the basis of this EngD thesis.
A range of MMC layups were tested in tension, compression and shear and detailed microscopy was
undertaken to investigate the failure processes. A simple rule-of-mixtures approach was found to
show good agreement with the unidirectional tensile test results. Subsequently, a more complex
approach taking ?weighted? averages for biaxial and multiaxial laminates at a ply level was developed
and this enabled full tensile response of the composites to be modelled, albeit with some limitations
in low strain response.
Part of the work which was conducted to increase the understanding of cross-ply composites
involved the determination of residual stresses. Although cross-ply MMCs were thought to have
greater axial residual stresses than unidirectional MMCs, the variation of residual stresses
throughout the eight ply laminates was found to change significantly (from 0.37% in the innermost
to 0.23% in the outermost plies) depending on the sub-laminate sequence. Finite element modelling
predictions were compared to the experimental residual stress determination techniques and it was
found that the FE modelling underestimated the strains in cross-ply composites.
Both aluminium and titanium pressure vessels were manufactured and tested; the mechanical data
from pressurisation was compared to simple analytical modelling and macroscale FEA.
Metallographic samples studied from the failed vessels showed deficiencies in manufacture and a
rudimentary form of acoustic emission showed that damage was incurred at relatively low strains,
but did not propagate to failure during the proof test cycles. This suggests that with adequate
provisions, the development of damage within a cross-ply layup does not need to rule out its use in a
non-critical tank application.
A prosthetic socket used by a lower limb amputee should accommodate the patient?s geometry and
biomechanical needs. The creation of a geometrically accurate subject-specific finite element model can be
used to provide a better understanding of the load transfer between socket and limb. There has been a
limited number of finite element studies of trans-femoral sockets with all current models only including the
femur and ignoring the pelvis. This study looked to evaluate the effect that including the pelvic bone as
well as the femur in a finite element model has on the contact interface between the prosthetic socket and
residual limb. This was done by creating a finite element model from a computerised tomography scan of a
trans-femoral amputee. This model included three-dimensional geometry, nonlinear material properties and
frictional contact between the residual limb and prosthetic socket. It was found that without the pelvic bone
the contact pressures peaked at the distal end region of the residual limb (peak of 95 kPa). However by
including the pelvic bone the contact pressures were instead concentrated at the ischial loading region
(peak of 364 kPa). The shear stresses experienced on the socket-residual limb interface were also
simulated. The results obtained in this study can be used to provide more of an understanding of the
loading on the residual limb for the design and creation of future trans-femoral sockets.
Two polymeric foams have been characterised to develop a simple calibration process for extracting the parameters which are required by the material
model available in the commercial FE package Abaqus. Indentation tests with DIC were conducted to study the validity of the proposed method.
The choice of the materials used for the core and skin of a sandwich structure plays an extremely important role in the skin-core interfacial behaviour. In
this paper, three PMI foams are used as core material and the effect of foam type in the skin-core interfacial response is examined.
Slope ambulation is a challenge for trans-femoral amputees due to a relative lack of knee function. The assessment of prosthetic ankles on slopes is required for supporting the design, optimisation, and selection of prostheses. This study assessed two hydraulic ankle-foot devices (one of the hydraulic ankles is controlled by a micro-processor that allows real-time adjustment in ankle resistance and range of motion) used by trans-femoral amputees in ascending and descending a 5-degree slope walking, against a rigid ankle-foot device. Five experienced and active unilateral trans-femoral amputees performed ascending and descending slope tests with their usual prosthetic knee and socket fitted with a rigid ankle-foot, a hydraulic ankle-foot without a micro-processor, and a hydraulic ankle-foot with a micro-processor optimised for ascending and descending slopes. Peak values in hip, knee and ankle joint angles and moments were collected and the normalcy Trend Symmetry Index of the prosthetic ankle moments (as an indication of bio-mimicry) were calculated and assessment. Particular benefits of the hydraulic ankle-foot devices were better bio-mimicry of ankle resistance moment, greater range of motion, and improved passive prosthetic knee stability according to the greater mid-stance external knee extensor moment (especially in descending slope) compared to the rigid design. The micro-processor controlled device demonstrated optimised ankle angle and moment patterns for ascending and descending slope respectively, and was found to potentially further improve the ankle moment bio-minicry and prosthetic knee stability compared to the hydraulic device without a micro-processor. However the difference between the micro-processor controlled device and the one without a micro-processor does not reach a statistically significant level.
The range of applications for composite materials is growing, but understanding of the effect of defects is limited, as is the ability to detect them. Versatile non-destructive testing (NDT) techniques, that can be deployed rapidly and reliably, to detect and monitor damage in composite components are vital to the continued growth of this sector.
This research investigates the application of Digital Image Correlation (DIC) as an NDT technique for monitoring delamination defects in Fibre Reinforced Polymer (FRP) composites. The research has matched physical experiments with Finite Element (FE) modelling. Four types of glass-fibre reinforced epoxy matrix composite structural elements were designed and manufactured to assess this application of DIC. The first two types of structural elements were flat coupons containing fully embedded delaminations, artificially introduced using two different methods. It was found that by placing these specimens in three-point bending, near surface delaminations, one ply below the surface being monitored, would cause a plateau in the surface strains. This plateau in strains was used to measure the embedded defect sizes. The size of the delamination was consistently overestimated from the interpretation of the strain fields. This was improved with the assistance of FE modelling to identify the relationship between the feature and the delamination. Pulse thermography was found to be a better technique for measuring the size of these defects.
The third type of specimen was a flat coupon containing a milled-slot, which was fatigued to grow a delamination at the foot of the milled slot, and the delamination measured visually. For this specimen, the DIC results showed good correlation with the visually determined delamination lengths with an empirical fit applied to the strain results. Both lock-in thermography and pulse thermography were used to measure the delamination size of the same specimens and showed reasonable correlation with the visually determined delamination lengths.
Finally, tubular specimens containing embedded PTFE delamination-defects were fatigued at different ratios of tension and torsion. DIC of the specimens loaded at the fatigue load ratio at which the delaminations were grown could not be used to quantify the size of the delaminations.
The work has shown that DIC can be used to monitor delaminations in some structural elements, however the type of loading needs to be considered to ensure sufficient influence on the surface strains to enable strain features that can be used to measure the size of delamination
Slope ambulation is a challenge for trans-femoral amputees due to relative lack of knee function. The assessment of prosthetic ankles on slopes is required for supporting prostheses design, optimisation, and selection. This study assessed two hydraulic ankle-foot devices (one of the hydraulic ankles is controlled by a micro-processor that allows real-time adjustment in ankle resistance and range of motion) used by trans-femoral amputees in ascending and descending a 5-degree slope walking against a rigid ankle-foot devices. Five experienced and active unilateral trans-femoral amputees performed ascending and descending slope tests with their own prostheses fitted with a rigid ankle-foot, a hydraulic ankle-foot without micro-processor, and a hydraulic ankle-foot with micro-processor optimised for ascending and descending slopes. Peak values in hip, knee and angle joint ankles and moments were collected and the normalcy Trend Symmetry Index of the prosthetic ankle moments (as an indication of bio-mimicry) were calculated for assessment. Particular benefits of the hydraulic ankle-foot devices were better bio-mimicry of ankle resistance moment, greater range of motion, and improved passive prosthetic knee stability according to the greater mid-stance knee flexor moment (especially in descending slope) compared to the rigid design. The micro-processor controlled device demonstrated optimised ankle angles and moments for ascending and descending slope respectively, and was found to further improve the ankle moment bio-minicry and prosthetic knee stability compared to the hydraulic device without a micro-processor .
Polymeric foams are used extensively as the core of sandwich structures in automotive and aerospace industries. Normally, several experiments are necessary to obtain the required properties to model the response of crushable foams using finite element analysis (FEA). Hence, this research aims to develop a simple and reliable calibration process for extracting the physical parameters which are required by the material model available in the commercial FE package Abaqus. To do this, a set of experimental tests, including uniaxial compression, uniaxial tension and shear punch tests, is proposed. All the experimental tests were also simulated, and generally, good correlations between experiments and numerical models were obtained. The validity of the overall approach was finally demonstrated using an indentation test in which the foam was subjected to a more complex mixed mode loading. During these indentation tests, digital image correlation was used to observe full-field strain distribution in the foam under the indenter. Good agreement between the experimental results and the numerical predictions was found for load?displacement response, failure mode and strain distribution.
Debonding between the skins and the core in a sandwich structure is a critical failure mode in automotive applications; once debonding occurs, the load carrying capacity of a sandwich structure drastically decreases. In the present paper, the effect of using three core materials, with different cell characteristics, on the interfacial strength between the foam cores and a CFRP skin is investigated through mechanical testing and numerical modelling. A key finding is that foams with a coarse cellular structure favour a high resin uptake at the interface during the manufacturing process, which results in a stronger interfacial bonding between the foam and the CFRP. During Mode I loading, the thick resin layer at the interface postpones crack initiation and kinking in the core, whilst under Mode II, this resin layer delays the collapse in compression of foam cells under the crack tip. Thus, the importance of including this thick resin layer in the FE modelling was demonstrated. Finally, as the CZM was shown to be unable to predict the unstable crack propagation within the core, an alternative approach was suggested which has the significant benefit of not requiring experimental testing of the interface between the skin and the core.
Debonding between the skins and the core in a sandwich structure is a critical failure mode in automotive applications where the energy absorption capability is a key property for crashworthiness. Once debonding occurs, the load carrying capacity of a sandwich structure, and therefore its energy absorption capability, drastically decreases. Debonding between a Carbon Fibre Reinforced Polymer (CFRP) skin and a foam core depends on many factors, including skin layup, foam material properties and skin-core thickness ratio.
This research investigates the effect of using various core materials, with different cell characteristics, on the interfacial strength between a cellular foam and a CFRP skin. A key finding was that foams with a coarse cellular structure favoured a high resin uptake at the interface during the manufacturing process. The role of this resin layer was well-defined with the experimental tests, where it was shown to postpone crack initiation and kinking on samples subjected to Mode I loading and to delay the collapse of foam cells under the crack tip in compression on samples under Mode II loading.
The research has matched physical experiments with Finite Element (FE) modelling. Initially, the work presented in this thesis focused on gaining a deep understanding of two of the most used numerical techniques to model interfacial failure: the Cohesive Zone Method (CZM) and the Virtual Crack Closure Technique (VCCT). However, limitations of these two techniques were found when modelling skin-core debonding in sandwich specimens. Experimentally, debonding in a foam-cored pre-cracked specimen was seen to initiate at the interface but to propagate within the foam core, growing in an unstable manner under both Mode I and Mode II loading. Both CZM and VCCT were not capable of capturing the stick-slip behaviour resulting from the unstable crack propagation. Therefore, a new method was suggested in order to accurately simulate debonding; this included the modelling of foam failure with an element deletion mechanism.
This was the first time a failure criterion-based method was used to model debonding in foam cored sandwich specimen. The suggested modelling technique was also validated comparing the FE predictions to the experimental results obtained performing three-point bending tests on sandwich panels with three different configurations. As a result, the work has shown that debonding in foam-cored sandwich structures can be modelled as foam failure instead of as interface failure, decreasing the computational time and the pre-processing efforts.