Dr David Jesson
Fellow of the Institute of Materials, Minerals and Mining - Elected 2015
Member of the Institute of Physics- Elected 2005Chartered as an Engineer and Scientist through the IoM3 from 2011
PhD title- The Interaction of Nano-Composite Particles with a Polyester Resin and the Effect on Mechanical Properties
- Modification of composite systems
- The role of the interface and the interphase in controlling mechanical properties
- Natural fibres and resin systems for composite materials
- Mechanical Performance of Engineering Materials
Current collaborations include:• Dstl• NPL• Thames Water Utilities Limited• TW
CIVIL ENGINEERING APPLICATIONS,
have the potential to be used in civil engineering
applications where a level of ductility is required to
avoid brittle failures. However uncertainties remain
regarding mechanical performance, physical
properties, shrinkage and durability. In the present
work, specimens containing cement powder and
admixtures have been manufactured following two
different processes and tested mechanically.
Multiple matrix cracking has been observed in both
tensile and flexural tests and this leads to ?strainhardening?
behaviour. The results have been
correlated with sample density and porosity and it is
suggested that higher levels of porosity do not
necessarily lead to a loss of the strain hardening
capacity. Shrinkage has been investigated and it is
shown, consistent with the literature, that shrinkage
can be reduced both by controlling the initial
environment to which the material is exposed and by
the use of additives. Durability was assessed by
flexure testing of beams specimens aged for
different times. Initial testing (up to one year)
indicates that the specimen retain ductility, although
the initial cracking threshold increases with time ?
which may have implications for longer aging times.
to manage it. However, a lack of sufficient information on the quantities and types of
material in the waste stream can make sustainable waste management difficult. Since
waste in one sector can be valuable as a resource in another, there is a need to
understand the distribution of materials within the resource stream, especially those
that go to landfill. Current work is seeking to address this; whilst much material is
already recycled, this is not the only management option and there remain several
problematic materials/components to be removed from residual waste. This paper, the
first of two case studies, presents a more comprehensive waste composition
specification in order to better manage municipal waste. In developing this approach,
waste composition specifications currently in use have been reviewed and compared
with the solid municipal (household) waste collected at community recycling centres
and from the kerbside. Key primary and secondary descriptors for the better
management of resources arising from municipal waste have been determined, and
the impact of these changes on the information arising from composition analysis is
can develop on the exit face as a consequence of through-thickness penetration of the panel; such
flaps can also be seen in impact tests. The flaps develop as four triangles, with the apex of each triangle at
the point of impact. In this work, thin panels of CFRP with a 0/90 configuration have been subjected to
quasi-static indentation tests and the development of the flaps has been monitored. The results show that
the dependence of the flap compliance is proportional to the square of the flap length, which is in agreement
with theoretical predictions. The determination of the compliance/crack-length relationship
enables a toughness value for fracture of the composite panel to be derived that is directly relevant to
through-thickness penetration of the panel.
Waste is intricate to manage. With greater attention now being paid to the use of waste as a resource, there is an increasing need to develop sustainable and secure management options for the most complex material resource streams. In order to achieve this, it is necessary to look to those materials, which due to their complex structure have not traditionally been recycled, and so remain in the residual waste stream.
This paper presents a methodology that has been developed to enable local authorities, or their equivalents, to assess the environmental and economic feasibility of collecting complex material streams separately, in order to improve their management of municipal solid waste. The methodology utilises available data from a number of sources, to determine the feasibility of options available.
The methodology is applied to a case study in Surrey, England, in relation to the management of Absorbent Hygiene Products. Currently this waste is collected as part of the residual stream, and dealt with either through landfill or energy from waste. The result of applying the new methodology suggests that the optimum solution is the separate collection of Absorbent Hygiene Products and subsequent the sterilisation and recycling.
mechanical properties of a polyester resin has been investigated. For materials produced
on such a fine scale, surface properties are known to dominate the manner in which they
This thesis presents results from two complementary areas of study: surface analysis and
mechanical testing. The surface properties of the nano-particles and the interactions of
the nano-particles with a polyester and adsorbed water have been investigated. These
analyses have led to the development of a model which shows that the small organic
groups grafted to the silica surface (methyl, ethyl and vinyl) are able to pack
comparatively densely at the surface, effectively forming a continuous monolayer. This
layer is sufficiently thick to prevent interaction of retained silanol groups with the
polyester resin. When the silica is modified with phenyl functionality, however, the
larger size leads to a more dispersed organic coverage that cannot be considered as a
complete monolayer. Hence this layer reduces, but will not completely prevent interaction
of the matrix with retained silanols of the silica.
The particles have been dispersed in a polyester resin successfully. The dispersion
process is an important step in producing viable nano-composites. Mechanical testing of
such nano-composites has found a significant improvement in the toughness properties of
the phenyl ormosil modified polyester, compared with the unmodified resin, whilst the
other modified polyesters show smaller improvements. When considered with the surface
analysis investigation, it is argued that the improvement is a result of a reduction of the
strength of the interface (with reference to a commercial nano-silica) between the
particles and the matrix. The phenyl ormosil is more strongly bonded than the other
ormosils. Whilst these other ormosils are able to contribute to toughness through a crack
pinning mechanism, the phenyl ormosil absorbs energy through debonding and promotes
plastic deformation in the matrix, around and between particles, mechanisms which lead
to a greater toughness enhancement.
on the mechanical properties of the resulting composite material. The interface can
be studied by a number of surface analysis techniques and the interaction modelled.
Such studies, and such modelling, can help understanding of the mechanisms which
composites undergo during their lifetime. The current review discusses the role of the
interface and the methods by which it can be studied; two case studies are presented
which illustrate these methods and the value that such knowledge of the interface has
brought to larger investigations.
results from the manufacture of fibre reinforced polymer matrix composites using commercially available resin systems are discussed.
The fibre is a commercially available viscose rayon of similar imensions to E-glass and in a continuous form. Whilst there are significant inputs in terms of the mechanical work and chemical
treatments that are applied to biomass in order to produce the fibre,
the fibre has the potential to produce composite laminates with higher fibre volume fractions and can be adopted easily into current fibre processes that utilise continuous synthetic fibres. Whilst the stiffness of the fibre is comparatively low (compared with carbon or glass) the strain to failure is much higher, which requires the use of a resin system
with a similar strain to failure. Two such resin systems are considered (with and without the use of a coupling agent). Data are presented
for the mechanical properties of the resultant composite materials.
Whilst the properties are comparatively modest compared to glass and carbon based systems, they are potentially useful. Further, it is noted that the composite has the ability to recover, to some extent, from plastic yielding.
Keywords: graphitic corrosion, cast iron, water distribution, EIS, chlorides.
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.
a fresh supply of water. Many of these networks are comprised of pipes made from grey cast iron and may
have been in service for up to 150 years. Despite their age, some parts of these networks continue to operate
with little degradation, whereas in other areas they degrade rapidly: more recently laid pipes are being outlived by their forerunners. In such networks, it is the trunk mains (pipes between 12-60? [300 mm to 1500 mm] in diameter) that are of great concern, since they pose the greatest risk of failure and are already bursting more frequently.
Accurate NDE is required to enable the mains in poor health with the highest risk of failure to be identified
and replaced before they burst. A review of the published literature has shown that whilst there are many NDE
techniques to choose from, many are not practical for application to the mains. The review process also
highlighted the kinds of defects present in grey cast iron and an initial stress analysis using strength models
and material data published in the literature has suggested defect sizes approaching 5 mm must be able to be detected to prevent catastrophic pipe failure.
Ultrasonic inspection has been investigated and shown to work effectively on uncorroded cast iron. Speed of
sound values between 4100 ? 4600 m s-1 have been observed across several pipes. A speed of sound of 2950 ± 80 m s-1 has been measured for graphitic corrosion, however, inspection on corroded main has not been possible.
A complementary magnetic technique, with the potential to scan pipe rapidly in order to identify mains in need
of further investigation, as well as providing supplementary condition data, has been trialled and shown to detect corrosion layers up to 6 mm thick.
A methodology using a 3D scanner to accurately determine the ?ground truth? pipe condition has been developed. This methodology proved to be successful and provided corrosion measurements that were in-keeping with those obtained through standard pit depth measurements. Further, the data showed that traditional pit depth measurements do not always find the deepest external corrosion pits, particularly where the surrounding geometry is complicated.
This methodology was used in a live comparison exercise of two, commercially available techniques. This
comparison highlighted problems with the surface preparation required by some techniques, which can be
quite damaging, and with some proprietary post-processing algorithms ? the raw data can be more useful.
From this assessment process, it has been possible to specify very detailed schedule for the testing of new NDE
techniques in the future.
This thesis explores the topics of ecological modernisation, employee engagement and sustainability-oriented innovation, grounded by a case study of Interface, a global manufacturing company. The work helps to build an understanding of the practicalities of organisation-level ecological modernisation, corporate sustainability and innovation in practice. It makes use of a case study research strategy combined with a grounded theory methodological approach. Three themes; ecological modernisation, employee engagement and sustainability-oriented innovation, are discussed and are applied to the analysis of the case material.
The following key findings emerge:
" Ecological modernisation, a theory typically applied and discussed at the macro-sociological level, is explored at the level of a single organisation, where it is used to contextualise the actions of Interface which contribute to wider, system-level sustainable disruptions. This is found to be a useful unit of analysis compared with typical explorations of EM, and reveals a number of interesting pathways by which EM organisations might impact upon the wider system in which they operate;
" Social dimensions of EM theory are discussed and explored. By considering Interface at the centre of a larger, interconnected network of actors, it is found that there are numerous dynamics at play, including the role of employees and their levels of engagement, the role of competitors and the wider industry, the role of customers and the role of suppliers;
" Temporal dimensions of EM are revealed and discussed, and several barriers are shown to emerge for Interface as it progresses further into a 20-year journey towards sustainability. Most strikingly, the low-hanging fruit is no longer available, and Interface finds itself in the ?tall canopy? in seeking further reductions in emissions and waste;
" Net-Works, a radical, innovative recycling project is presented and compared with other, less successful innovations from Interface. The contextual factors that gave rise to Net-Works are a combination of a radical goal, deliberate adoption of a social goal, and a safe failure space. Success is owed to developed capabilities, incorporation into an existing product, and partnering with an NGO and academia for accountability and credibility.
The current work focusses on stainless steel and titanium alloy. The lap shear bond strength for both metals increased significantly after a cold atmospheric plasma (CAP) treatment and was in line with the chemical etching processes. The durability of both metals demonstrated that the plasma treatment increases the performance. For stainless steel the durability is similar to the chemical etch process. For titanium the durability performance is increased, but does not reach the level of the chemical treatment process.
A combination of surface science techniques has revealed that there are three mechanisms which lead to an increased bond strength. These are: a reduction in hydrocarbon contamination, shown using X-ray photoelectron spectroscopy (XPS) and time of flight\,-\,secondary ion mass spectrometry (ToF-SIMS). The growth of the surface oxide layer, analysed using an XPS sputter depth profile, and functionalisation of the oxide layer, which has been probed using ToF-SIMS, both lead to an increase in lap shear bond strength.
The feasibility of the process rests on two factors. The first is achieving equivalent mechanical properties, the second factor is the energy, resources and time required for a given treatment. The first has been satisfied in this work, the second has been investigated using a life cycle analysis approach which found that plasma treatment had a higher impact on the environment when compared to oxalic acid etching. but this assumed that the acid is 100\% efficient, which is far from the case. When simulated in a `real world' scenario, there is nearly parity between the two treatments
Based on the data presented in this work, including analysis of the process life cycle, CAP has the potential as a first multi material pre-treatment for structural adhesive bonding.
wood products : aspects of the interaction of i
socyanates with stainless steel and wood.,
adhesive commonly used in the manufacturing process of composite wood panels. Its
use has constantly been increasing over the past years driven by the great performance
that this resin offers in terms of moisture resistance, durability and strength. However,
the use of isocyanate-based adhesives carry some challenges related to the composite
wood production which need to be improved. In particular, the adhesion of these resins
to the stainless steel press platens during the production process. The strong adhesion
between the glue and the press platens results in production issues forcing the
production to stop. There are a number of methodologies to overcome the production
issues, however, all of them incur additional costs or have associated health and safety
issues. Therefore, this study aims to expand the understanding of the interfacial
chemistry and processes occurring at the press platen/pMDI-wood interface to help to
develop approaches to achieve release of isocyanate-based adhesives.
In order to achieve the aim of this project, surface analysis techniques, in particular Xray
photoelectron spectroscopy (XPS) and time of flight secondary ion mass
spectrometry (ToF-SIMS), were used. In the first stage of this project, the surface characterisation of pine wood and its extractives, pMDI and the stainless steel used for
the manufacture of composite wood panels was carried out. Then, the study of the
pMDI/metal interface was performed obtaining important information related to the
bonding of pMDI to steel. The interface between the stainless steel/pMDI-wood
system was also investigated. The results of this study showed that the pine wood
extractives compounds have a significant impact in the adhesion of wood to stainless
steel. These findings allowed us to inform strategies which could lead to the release of
isocyanate-based adhesives from the steel during the composite wood panel
The overall objective of this research is to quantify errors associated with the use of DIC in different (non-ideal) locations and, associated with this, to find methods of limiting the effect of the potential error sources.
The reference test sample is a thin-walled shell into which defects can be introduced at specified locations, thus disturbing the local strain field.
A portable test rig, which makes use of an internal vacuum, to cause a pressure differential on the component, has been designed and deployed to explore the potential of using DIC as a method of non-destructive evaluation. Preliminary results have been conducted in a laboratory setting to ensure that the strain data correlate with finite element analysis. Following from initial experimentation, successive investigations into the effects of possible external error sources have been conducted. These include: ground vibrations, increased airflow and changes in ambient lighting. Each experiment is repeated five times to allow for random error of the testing process.
DIC has been shown to be a powerful tool in identifying the strain perturbation associated with the presence of defects. Initial results indicate that environment conditions have the potential to lead to perturbation of results, but that these may be identified and minimised and/or corrected if care is taken.
This investigation analysed the possibility of using a pre-speckled bag to encase and load multiple components of complex geometries, via the evacuation of internal air. Each coupon within the bag was either originally white in colour, or spray painted with a matt white acrylic paint. The reason for this was to increase contrast between the component and the black speckles upon the bag.
Results suggested that using the speckled bag, the algorithm was confident of strain mapping accurately for subsets larger than 31 pixels and could plot strain profiles for geometrically complex objects.
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
Worldwide, a significant proportion of trunk mains are still made of aging cast iron material. Remarkably, these aging assets have in some cases outlived the pipes that replaced deteriorated parts of the network. Even so, many cast iron pipes are beginning to approach, or have already exceeded, their design life: consequently, out of a large population of pipes, some are failing whilst some still have considerable residual life.
Asset management, in this context focussing on the targeted replacement of degrading main, requires tools and models for the prediction of the future performance of the network. Several mechanistic deterioration models have been developed in recent years, which attempt to predict the condition of cast iron pipes, but few methodologies have specifically targeted water trunk mains. Nevertheless, the requirement has remained for a robust deterioration and failure model for cast iron trunk mains, worldwide.
This project, being part of a wider, collaborative project between Thames Water Utilities and the University of Surrey, has reviewed existing failure models for cast iron trunk mains and sought to modify these based on information arising from other areas of the project. This has included, new understanding of the corrosion of cast iron trunk main, the use of fracture mechanics to predict failure and non-destructive evaluation data gathering techniques has provided significant insight into improvements that can be made to failure models.
In particular, the present research has shown how traditional loss-of-section approach to the residual strength of corroded pipes can be used alongside a fracture mechanics approach, in order to provide boundaries to the failure ?envelope?. This novel methodology has been incorporated as part of an enhanced modelling framework, which has shown to improve the failure predictions across the network. The enhanced model also enables more detailed analysis of sections of the pipes that have been surveyed on site.
Wood fibers are of the order of a few millimeters in length and a hundred micrometers in width, which makes it difficult to mechanically characterize them using standard methods, such as tensile testing. This work, builds on the development of a novel method to evaluate the stiffness of wood fibers, which uses the cantilever of an atomic force microscope (AFM) to carry out three-point bending. This is done by placing the fibers across a two millimeter trench, whereupon the AFM engages to the center and both applies loads and records the resulting displacements. Testing using this method has been confined to a single species of wood, pinus sylvestris (Scots pine), but there is a significant spread in the modulus of the fibres tested. This is not entirely surprising as a sample of wood consists of several different types of fibre, including, for example, heartwood and sapwood, early wood and latewood. These different fibres vary slightly in size and wall thickness.
Here, Weibull statistics is used to investigate the correlation between samples in a dataset, and describe the magnitude of the correlation, in order to distinguish between fibre types and to provide greater clarity of the modulus associated with different types of fibre.
wood fibres, hollow tube like elements which are responsible for both water transport and load bearing within
trees, (Ansell, 2015). The fibres can be separated from bulk timber in a process known as defibrilation, a key
industrial process for the production of Medium Density Fibreboard (MDF). MDF is a composite material
formed of fibres and adhesive, which is used widely in the construction industry among innumerable others.
in the production of so-called environmentally friendly composite materials. However, whilst the
majority of systems consider complete replacement, another route is to look at the constituents that
are required to give certain properties, including the content of diluents; a third is to identify ?hot
spots? in manufacturing. This paper considers these three possibilities in the context of the production
of a resin system, and presents results from a life cycle assessment. The aim of this study was to
make qualitative assertions based on quantitative estimates. The current work provides a practical
assessment of the contribution of the manufacturing process of a multi-part resin formulation to a
range of environmental impacts. As a part of this, a multi-stage methodology, the first of its kind,
which is more relevant for the batch processes used to manufacture many structural thermosetting
polymer systems, was developed. This was applied to a range of resins, some of which include
bio-mass derived precursors. For the boundary conditions used, the indications are that the impacts
due to taking the constituents and processing them to produce the resin system are insignificant
compared with those due to producing the feedstocks in the first place. Surprisingly, whether the
feedstocks were from fossil resources or were bioderived was of little significance. As a consequence
of the analysis, it has been demonstrated that whilst a manufacturer can make significant savings
through careful management of plant and the supporting energy mix, significant improvements to
the environmental impacts of resin systems can be made through the choice of particular monomers.
The term 'waste' has long been associated with disposal, despite the fact that 44% of household waste in the UK is now recycled. By thinking of household waste as a resource, it may be possible to extract value. Items that householders no longer require should not simply be discarded as waste but instead should be appreciated for the inherent value they possess and the new products they can become. However, implementing this paradigm is complicated by the variety of different materials in the waste stream, and the number of stakeholders responsible for its management.
A central theme of the work presented in this thesis is the paradigm shift ?From Waste to Resource?. This is important both for issues of resource security and sustainability. Indeed, whilst the times of ?make do and mend? can appear to be in the past, there is a great deal of interest in reusing and recovering material resources, especially if components or assemblages can be refurbished or ?upcycled?.
This research has developed a decision-making tool ? The Local Authority Optimal Material Management Framework (LAOMMaF) ? which can enable local authorities to assess the best way of managing their household ?waste?. The LAOMMaF takes the user through the identification and quantification of the materials of interest, the determination of viable treatment options, and an options appraisal. The framework has been refined using five case studies: i) assessment of the optimal management of absorbent hygiene products, ii) quantification of waste as a material, through the development of a composition specification, iii) exploration of future waste and potential impacts on waste generation in Surrey, iv) assessment of management options for household wood waste using Multi-Criteria Decision-Making, and v) application of the revised LAOMMaF to assess the compliance of current collection systems in Surrey to the amended Waste Regulations (2011).
By understanding the composition, amount and value of waste available to them, local authorities can take a more proactive approach in the ?Waste Supply Chain? to prevent the implementation of ?sub-optimal? management practices and the loss of valuable resources.
Key Words: Waste, Resource, Local Authority, Decision-Making
The effects of coupon width, thickness, and mould coverage on apparent tensile strength and Young?s modulus were investigated. This found that strength increases when the coupon width reaches twice the length of the reinforcement. The strength was found to increase with thickness according to a logarithmic relationship, with non-significant differences occurring after the thickness had reached 4 mm thickness. The strength was found to decrease with increasing mould coverage for the mould coverages tested. The modulus was found to not correlate to coupon width, although there was a decrease in variation at 50 mm width. Similarly, the Young?s modulus was not found to change with increasing thickness, but the variance did decrease. The Young?s modulus increased with decreasing mould coverage. This allowed definition of the geometry of a tensile test coupon to increase the confidence in the determined mechanical properties for future test programmes.
Current assessment methodologies ensure safety standards are met, but detailed evaluation of components requires transportation from site. Minimising transport of equipment would reduce costs and fuel usage, and also save lives.
The current work considers the use of digital image correlation (DIC) for non-destructive evaluation (NDE), with a particular focus on the assessment of combat helmets.
To optimize component loading, the use of pressure differentials and single-point mechanical loading were trialed. Finite element analysis (FEA) suggests pressure differentials produce a greater likelihood for the detection of component damage via surface strain discontinuities. By contrast, single point loading produces highly concentrated strain in the region of contact, whilst minimal strains result for the rest of the component.
The optimization of component speckling has also been considered, leading to the development of a novel approach using customisable transfer paper, which can be printed with a pattern specific to a given test geometry. This allows greater standardization, faster application, and increased accuracy, compared with traditional approaches, such as spray painting a speckle pattern.
Following these experiments, NDE of an entire military helmet was investigated using a portable test rig. With the method for helmet loading in concept stage, proof that the technique can detect damage is presented via five case studies. The variety of materials and testing processes show the novel approach for component speckling has direct use for the completion of, and external to, the primary goal of the project: ?to develop a DIC technique with the potential for portable damage detection of helmets?.