Areas of specialism

Fracture mechanics; Mechanical testing; Fracture toughness testing; Finite element analysis; Structural assessment

My qualifications

Ph.D. in Mechanical Engineering
Study of Crack Tip Opening Displacement (CTOD) in Single Edge Notched Bend (SENB) specimens.
Brunel University
BEng in Mechanical Engineering (sandwich) w/ Honours
Brunel University

Affiliations and memberships

Institute of Physics
Committee member of the Applied Mechanics group


Research interests

Research collaborations

Indicators of esteem


    Weeliam Khor, Anil R. Ravindran, Raj B. Ladani, Manatsawee Limprapuwiwattana, Pete Whitton, Charlotte Meeks, Andrew D. Foreman, Francesco Ciampa (2023)Material-enabled damage inspection of multifunctional shape memory alloy tufted composite T-joints, In: NDT and E International: Independent Nondestructive Testing and Evaluation (NDT and E International)

    The through-the-thickness reinforcement of carbon-epoxy composite joints with shape memory alloy (SMA) tufts has shown significant improvement of the mechanical strength, fracture toughness, and delamination resistance. This study explores the thermal-electric properties of SMA filaments tufted in composite T-joints to exhibit multiple functionalities including material-enabled thermographic inspection and structural health monitoring via in-situ strain sensing. Infrared thermography image analysis was performed on both pristine and damaged T-joint specimens subject to pull-off testing. Experimental results showed that the heat generated by SMA tuftsmeasured by an infrared camera provided accurate indication of delamination perpendicular to the tuft direction. SMA tufts were also used as strain sensors embedded within the T-joint. Local changes of the electrical resistance in SMA filaments, both separately and within the joint, were observed during pulling loads. Digital Image Correlation measurements exhibited good correlation between electrical resistance variations and the opening of delamination. These results pave the way for the development of multifunctional composite joining systems combining enhanced through-the-thickness damage tolerance and self-sensing capabilities.

    W Khor, P L Moore, H G Pisarski, C J Brown (2018)Determination of the rigid rotation plastic hinge point in SENB specimens in different strain hardening steels, In: Journal of Physics: Conference Series1106012015 IOP Publishing

    According to some standards, fracture toughness tests loaded under bending are assumed to deform around a fixed plastic hinge point within the ligament ahead of the notch tip. The rotation factor,rp, defines the proportion of the ligament ahead of the crack tip to where this hinge point is located. In this paper, the concept of an SENB specimen bending about a fixed rotational point under loading was investigated. Experimental SENB tests were carried out on three different strain hardening steels, and the geometrical point of rotation was determined experimentally throughout the tests using a double clip gauge and the similar triangles principle. The experimental results were then used to develop and validate a series of different strain hardening property numerical models. By extracting the rotational factor from the different strain hardening property models, a relationship between strain hardening and a strain hardening corrected rotational factor, rp sh was established. This corrected rotational factor function was used to propose an improved equation for the calculation of CTOD and CTOD R-curves, which gave good estimations of CTOD when compared to values measured experimentally from sections through silicone replicas of the specimen crack-tip. The improved R-curve equation will be proposed for future amendments to the ISO 12135 standard.

    Weeliam Khor, Raj Ladani, GEOFFREY KNOTT, Thibaut Buns, Andrew D. Foreman, Charlotte Meeks, Alan Steele, Tim Cooper, Adrian P Mouritz, Francesco Ciampa (2023)Multifunctional Shape Memory Alloy Tufted Composites

    Multifunctional fibre reinforced polymer (FRP) composites combine multiple properties that can include mass efficiency, damage resistance, damage tolerance, self-repair, in-service health monitoring and ease of inspection. This paper describes a new type of multifunctional FRP composite material that enables large improvements to the interlaminar fracture toughness and damage tolerance whilst also allowing rapid self-sensing and material-enabled thermography capabilities. The composite material is reinforced in the through-thickness direction using shape memory alloy (SMA) wires inserted by tufting.Tufting is a cost-effective manufacturing process that uses commercially available automated systems to insert yarns in the through-the-thickness direction of dry fabric preforms [1]. Tufting uses a single needle to penetrate the fabric stack, and requires access only from a single side of the preform. As shown in Fig. 1, thin and flexible SMA filaments made of nitrol (Ni-Ti alloy) were tufted into six layers of 0˚/90˚ non-crimp carbon fabric using a KSL RS 522 tufting machine mounted on a KUKA KR240–2 robotic arm. The tufted fabric was infused with epoxy resin using the resin transfer moulding (RTM) process. The final cured composite panel was cut into double cantilever beam (DCB) coupons to perform mode I interlaminar fracture toughness tests according to the ASTM D5528-01 specification.

    W. L. Khor, P. Moore, H. Pisarski, C. Brown (2017)Comparison of methods to determine CTOD for SENB specimens in different strain hardening steels, In: Fatigue & Fracture of Engineering Materials & Structures41(3)pp. 551-564 Wiley Publishing Ltd.

    Methods for determining crack tip opening displacement (CTOD) given in national and international standards are compared for steels with a range of strain hardening characteristics. Crack tip opening displacement measurements were made from single‐edge notched bend notches using a silicone rubber casting method. The finite element model produced good agreements with predictions of these CTOD measurements. The versatility of the finite element model enabled CTOD from the original crack tip and the 45° intercept method to be compared. The 45° CTOD generally underestimates the origi nal crack tip CTOD, and is less useful for conditions with stable crack extension. Apart from the high strain hardening material, CTOD calculated using BS 7448‐1, WES 1108 (JWES), and ASTM E1820 was slightly lower than the values determined from silicone measurements and modelling, which is conservative. ASTM E1820 gave the largest underestimation of CTOD, whilst BS 7448‐1 may be unsuitable for higher strain hardening steels, where the standard predicts higher CTOD than measured from the replica. JWES gives the most consistent estimation of CTOD for steels with a wide range of strain hardening values.

    W Khor, P L Moore, H G Pisarski, M Haslett, C J Brown (2016)Measurement and prediction of CTOD in austenitic stainless steel, In: Fatigue & Fracture of Engineering Materials & Structures39(11)pp. 1433-1442 John Wiley & Sons Ltd

    Variation of Crack Tip Opening Displacement (CTOD) test values can have a significant effect on the Engineering Critical Assessment of a structure. This paper examines the development of CTOD with increasing load in an austenitic stainless steel. The silicone replication method giving variation of CTOD across the specimen thickness, and Digital Image Correlation (DIC) are compared to each other, and in turn to clip gauge measurements from tests. Results from Finite Element models are also presented. Estimations of CTOD from BS 7448‐1, ISO 12135 and ASTM E1820, and a proposed modification from JWES are compared to the experimental data from the crack cast in silicone compound – assumed to be the actual CTOD. The DIC measurement showed consistency with crack replicas, and a formula is given to estimate CTOD using DIC. For high strain hardening austenitic stainless steel, both the JWES and ASTM E1820 estimations provide adequate accuracy for CTOD.

    Crack tip opening displacement (CTOD) from national and international standards was shown to give different values. This paper investigates the feasibility of CTOD determined based on the concept of rigid rotational factor in single‐edge notched bend (SENB) specimens. Based on validated modelling methods, finite element (FE) models were simulated for crack ratios 0.3 ≤ a0/W ≤ 0.7 and yield‐to‐tensile ratio 0.44 ≤ σys/σuts ≤ 0.98. This covers cases of shallow to deeply cracked specimens and a wide range of strain hardening properties. CTOD obtained from the FE models was used as the basis of a newly implemented strain hardening corrected rotational factor, which considers the effects of crack tip blunting due to strain hardening, rp sh. An improved equation considering strain hardening was implemented based on the rp sh. The equation gives accurate estimation of CTOD from the FE models compared with the equation from BS 7448‐1, ASTM E1820, and WES 1180.

    Weeliam Khor, Anil R. Ravindran, Francesco Ciampa, Raj B. Ladani, Manatsawee Limprapuwiwattana, Pete Whitton, Andrew D. Foreman, Charlotte Meeks, Alan Steele, Tim Cooper, Andrew Rider, Adrian P Mouritz (2023)Improving the damage tolerance of composite T-joints using shape memory alloy tufts, In: Composites Part A: Applied Science and Manufacturing168107474

    This paper presents a novel approach to improve the structural properties and damage tolerance of fibre-reinforced polymer composite joints via tufting using shape memory alloy (SMA) filaments. T-shaped joints made of carbon-epoxy composite material were reinforced with thin SMA (Ni-Ti nitinol) tufts. Experimental testing and finite element (FE) modelling reveal that the ultimate load, ultimate displacement and absorbed energy capacity of the T-joint increase with the areal density of SMA tufts. Improvements of over 110% in strength and 450% in absorbed energy capacity were achieved by SMA tufting. Under certain conditions, the shape memory effect of the tufts can be activated via electrical resistance heating to partially or completely close cracks in the T-joint caused by over-loading. The novel use of SMA tufts both to improve the resistance against cracking and to close cracks when they occur is a unique approach to improving the damage tolerance of composite structural joints.

    WeeLiam Khor, Jeffery Farrow, Mike Mulheron, David A Jesson (2021)FEA on Grey Cast Iron Assets: A Case Study on Penstocks in the Waste Water System, In: Infrastructure asset management ICE Publishing

    Penstocks have been used in the water industry for flow control since the Victorian expansion and consolidation of clean and waste water networks. However, the Victorians were the first to use grey cast iron (GCI) castings to manufacture large scale penstocks. Most of these ageing assets are still in operation, however engineering assessments are necessary to determine a structure’s fitness-for-service. Even today, penstocks in the sewer system tend to be made from GCI, due to ease of manufacturing, resistance to corrosion and cost. One characteristic property of grey cast iron is the graphite flake structure in the material, contributing to its low toughness, inconsistency in material strength and brittle behaviour, despite exhibiting slight hardening properties. Finite element analysis (FEA), is a numerical method which allows the analysis of complex structures by splitting it into finite parts and solving them with a computer processor. Despite the versatility of FEA, appropriate considerations and assumptions are necessary due to the difficulty to obtain data from inspection and unique material behaviour of GCI. The article shows concerns for an analysis of GCI penstocks using FEA, which extends into the application of fracture mechanics approaches for defect assessments.

    Philippa L. Moore, Wee Liam Khor (2018)The Effect of Material Strain Hardening on the Determination of CTOD R-Curves Using SENB Specimens, In: Volume 3: Operations, Monitoring, and Maintenance; Materials and Joining3 American Society of Mechanical Engineers (ASME)

    In ductile materials the fracture toughness is usually characterised by a tearing resistance curve, or R-curve, plotting the fracture toughness in terms of J or CTOD against crack extension. Recent research has evaluated the methods to determine CTOD in engineering alloys with a wide range of yield to tensile (Y/T) ratios for single point CTOD. This work develops the investigation into R-curves, and reviews the assumptions about SENB specimens deforming under rigid rotation, the evaluation of CTOD from J for R-curves, and the nature of tearing initiation in low Y/T ratio stainless steel, from comparisons against a series of silicone replicas cast from the SENB specimen notch during fracture toughness tests. For CTOD R-curves, the methods based on CTOD from J in ISO 12135 and ASTM E1820 gave lower and less accurate R-curves than the rigid rotation methods in BS 7448-4 and WES 1108. However, the accuracy of the BS 7448-4 formula varied for the different strain hardening materials, and overestimated the R-curves in the low tensile ratio stainless steel. Investigations into the effect of the assumption about rigid rotation in different strain hardening materials led to a rotational factor function of tensile ratio, rp sh, to be developed from numerical modelling. When this function was substituted into standard equations in place of the fixed value of rp an improvement in the accuracy of BS 7448-4 R-curves compared to replica measurements was seen for the range of strain hardening investigated, but it did not significantly improve the accuracy of the WES 1108 formula, which accounts for strain hardening in other parameters. A combination of the elastic CTOD part of the WES 1108 formula, with the plastic CTOD incorporating the modified rotational factor, was concluded to offer the optimum method to determine CTOD R-curves for a range of strain hardening materials.

    W. Khor, D. Jesson (2019)Loading on plate with different tension-compression strength, In: Proceedings of The BSSM's 14th International Conference on Advances in Experimental Mechanics British Society for Strain Measurement

    Whilst superseded by other materials, there are many instances of engineering structures in use today that are formed of grey cast iron. These aging assets need to be assessed for their abilities to continue to function, and to predict performance in the event of engineering works being carried out on the asset, or nearby. Grey cast iron does not exhibit an obvious elastic regime when loaded in tension and is often classified in terms of minimum guaranteed tensile strength. Grey cast irons typically fail in brittle cleavage with a strain limit of

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