Imperial College London

Prof Ambrose Taylor

Faculty of EngineeringDepartment of Mechanical Engineering

Professor of Materials Engineering
 
 
 
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Contact

 

+44 (0)20 7594 7149a.c.taylor Website

 
 
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Assistant

 

Miss Valerie Crawford +44 (0)20 7594 7083

 
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Location

 

515City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

188 results found

Terry JS, Taylor AC, 2021, The properties and suitability of commercial bio-based epoxies for use in fiber-reinforced composites, Journal of Applied Polymer Science, Vol: 138, Pages: 1-12, ISSN: 0021-8995

Environmental concerns about fiber composites are leading manufacturers to consider bio‐based alternatives to petroleum‐derived epoxies. Such a substitution is hindered by a lack of information, so commercially available bio‐based epoxy systems have been compared, their mechanical properties measured, and fiber composites produced by vacuum infusion. Most high bio‐based content resins for infusion use conventional curing agents. Bio‐based content is generally added using Epicerol, but also other bio‐based precursors. A diglycidyl ether of bisphenol A system produced using Epicerol achieves 20 % bio‐based content, but achieves higher contents when Epicerol is used in diluents. Fully bio‐based monomers can be deleterious to the mechanical properties and glass transition temperature (Tg), so are used sparingly. The most‐promising systems (28 % to 43 % bio‐based) compare well to conventional epoxies, possessing good strength, stiffness, toughness, and a reasonable Tg. These partially bio‐based epoxies offer an immediate lower‐carbon alternative for vacuum‐infused composites in marine, sports equipment, and wind energy.

Journal article

Charalambides M, Zhang R, Taylor A, Balint D, Wood J, Young Cet al., 2021, A numerical investigation of interfacial and channelling crack growth rates under low-cycle fatigue in bi-layer materials relevant to cultural heritage, Journal of Cultural Heritage, Vol: 49, Pages: 70-78, ISSN: 1296-2074

In traditional and modern paintings on canvas or wood, two crack types have been identified, these are: (i) delamination between two of the many layers and (ii) channelling through the paint layer, terminating at the paint-substrate interface. One cause of this damage can be attributed to environment-induced low-cycle fatigue, specifically through relative humidity and temperature fluctuations. We present novel 2D as well as 3D finite element models that, for the first time, identify the time for each type of crack to initiate under a variety of realistic relative humidity (RH) cycles, as well as the corresponding crack growth rates. The focus is on modern paintings that have some layers executed in alkyd paint, found to be a vulnerable layer in a relatively short period of time. The paintings are idealised as a two-layer construction with a visco-hyperelastic alkyd paint layer on a linear elastic (acrylic) primed canvas substrate. Cracks, both interfacial and channelling, are represented using cohesive elements. To simulate the damage caused by a relative humidity cycle, a fatigue damage parameter was incorporated in the traction-separation law using a user-defined field. It was found that channelling cracks initiate slightly earlier than interfacial cracks for all the environmental conditions studied. Specifically, for an RH cycle of 35%–90%, channelling cracks initiate at 2.2 years and grow at an accelerating rate, while the interfacial crack initiates at 2.6 years and grows at a stable rate of approximately 0.1 mm/year. Narrower RH cycles lead to longer crack initiation times, e.g. the channelling crack initiates at 13.9 years under 40%–65% RH, and when the RH cycle was further narrowed to 45%–55%, the initiation time increased to 86 years. Our models are applicable to other painted or coated cultural heritage objects and can be used to inform preservation and environmental control strategies.

Journal article

Sorce FS, Ngo S, Lowe C, Taylor ACet al., 2021, The effect of structure-property relationships on the formability of pigmented polyester coatings, Progress in Organic Coatings, Vol: 154, Pages: 1-12, ISSN: 0300-9440

Pre-painted metal sheet (PPM) is used in applications from domestic appliances to architectural cladding. The coating provides excellent aesthetics and corrosion protection, but must possess excellent formability to not fail due to the large strains applied during the folding and hemming processes used to produce components. Therefore it is important to understand how the coating formulation affects the free-film properties and formability of a coating system. Polyester coatings crosslinked with hexa(methoxymethyl)melamine (HMMM) with a Tg of ∼ 40 °C were used, pigmented with TiO2. The glass transition temperature was increased by increasing the crosslinker content (from 5 % to 30 %), decreasing the adipic acid content (from 24 % to 12 %) and decreasing the molecular weight (from Mn = 3300 g/mol to Mn = 1500 g/mol). The chemical structure of the resin had little effect on the formability of the coatings when the test temperature was normalised with respect to Tg. The formability measured using the Erichsen cupping and T-bend tests is related to the tensile properties of the free-films. The damage induced by the T-bend is greater than that by the Erichsen cupping test due to the higher applied deformation rates in T-bend tests. Increasing the apparent yield and fracture stress increases the likelihood of damage at lower deformation levels, whilst increasing the strain to failure decreases the likelihood of damage in both the T-bend and Erichsen cupping tests. The strength of these correlations reduces with an increase in T-bend level as the magnitudes of the strains applied are reduced. This work takes a holistic approach to correlate structure and tensile properties with formability in both the Erichsen cupping test and T-bend test for the first time, enabling industry to improve coating performance significantly but cost-effectively.

Journal article

Mulakkal M, Castillo Castillo A, Taylor A, Blackman B, Balint D, Pimenta S, Charalambides Met al., 2021, Advancing mechanical recycling of multilayer plastics through finite element modelling and environmental policy, Resources, Conservation and Recycling, Vol: 166, ISSN: 0921-3449

Plastics are attracting negative publicity due to the scale of current pollution levels, yet they are irreplaceable in several applications such as food packaging, where different types of plastics are combined in laminate form to produce multilayered packaging (MLP) materials which extend the life of food items packaged within them. Increased plastic recycling is urgently needed, however for MLP it is particularly difficult. For the first time, this study combines engineering tools with environmental policy towards developing solutions for current single use plastic packaging. This study investigates recycling challenges for MLP and emerging melt-blending based mechanical recycling solutions as this is the main current method for material recovery of conventional plastics. Melt-blending of MLP with compatibilisers is explored, and the current lack of models addressing the influence of compatibilisers is identified. This gap in knowledge is addressed using novel engineering models based on the finite element (FE) micromechanical modelling technique to estimate the mechanical properties of recycled blends. Our model output is compared with experimental data available in literature and the good agreement highlights its predictive ability, providing a fast and cost-effective novel method for optimising recycled plastics. The policy aspect proposes the introduction of twenty policies based on mission-oriented innovation strategy to enable deployment of the recycling technologies studied whilst improving the viability of recycling of material currently not recycled. Implementation of these measures by the stakeholders will enable adoption of new MLP recycling techniques, create demand for recycled materials from MLP and incentivise MLP collection to mitigate pollution.

Journal article

Zhang R, Stannard A, Street G, Taylor AC, Charalambides MNet al., 2021, Towards optimisation of rolling process of potato dough: Effect of processing on the microstructure and the mechanical properties, Journal of Food Engineering, Vol: 291, ISSN: 0260-8774

The quality of potato chips is highly dependent on the mechanical properties of the dough sheet produced prior to frying. It has been well established that poor mechanical properties result in fragile dough sheets and associated high product wastage. However, the effect of the rolling process on the mechanical properties of the dough is unknown so the optimum rolling process can only be obtained via a trial and error approach. This work reports for the first time the effects of dry flake size and rolling parameters on the mechanical performance of potato dough sheets. The laboratory scale rolling setup used a 10 cm roller diameter with a 0.2 mm gap height. Furthermore, an experimental method was developed enabling rigorous tensile testing of fragile potato dough sheets. The mechanical performance of the potato dough sheets was anisotropic, as the Young's modulus and strength were 35% and 57% higher across the rolling direction than those along the rolling direction, respectively. The formability, i.e. the ability to form a coherent sheet of the potato dough is improved by using smaller dry flakes (<500 μm). However, further decrease in the flakes size had no effect on the mechanical behaviour of potato dough sheets, i.e. flakes with diameter smaller than 212 μm showed similar tensile response to flakes smaller than 500 μm. Rolling the dough increases the coherence and the strength of the potato dough sheets, but also introduces defects orientated across the rolling direction which decrease the strength if the dough is rolled too many times. For example, sheets rolled for seven passes showed over 100% improvement in failure stress comparing to sheets rolled for five passes, but when the sheets were rolled for the eighth pass, the failure stress dropped by 17%. Due to the viscoelasticity of the dough, both the tensile modulus and strength of the sheets are higher when tested at higher strain rate. In addition, at higher strain rate, the defects in the shee

Journal article

Sorce FS, Ngo S, Lowe C, Taylor ACet al., 2021, Quantification and analysis of coating surface strains in T-bend tests, International Journal of Advanced Manufacturing Technology, Vol: 113, Pages: 1-18, ISSN: 0178-0026

Pre-painted sheet metal (e.g. coil coated with polyester-melamine) undergoes large deformations when formed into architectural cladding or white goods. The coatings provide protection and superior aesthetics, so must withstand failure by cracking or delamination during forming. The T-bend test is an industry standard test used to qualitatively compare the formability of coatings and mimics the conditions experienced during hemming processes. The failure of coatings during forming is strain governed, so understanding the surface strains in the T-bend test is of great interest to manufacturers. For the first time, the maximum surface strains experienced during the T-bend test have been predicted using finite element modelling (FEM) and verified experimentally using digital image correlation. The experimental shapes of the deformed blank are compared with the FEM results for further verification. In addition, a novel analytical model is proposed to determine the maximum surface strains. It is shown that strains of up to ~ 225% are applied during a 0T test (bent around a zero thickness spacer) reducing to ~ 23% at 4T (bent around a four times sheet thickness spacer). The finite element model, experimental data and new analytical model show excellent agreement and indicate that behaviour is independent of the substrate thickness or material used. Understanding the strain behaviour quantifies the formerly qualitative T-bend. This will improve the efficacy of the test, allowing metal formers and coating developers to better understand the performance requirements, to reduce waste and to develop better coatings.

Journal article

Cheong Z, Sorce FS, Ngo S, Lowe C, Taylor ACet al., 2021, The effect of substrate material properties on the failure behaviour of coatings in the Erichsen cupping test, Progress in Organic Coatings, Vol: 151, Pages: 1-13, ISSN: 0300-9440

Pre-painted sheet metal produced by coil coating is subjected to large deformations during manufacture of white goods and architectural cladding. The thermosetting polyester coatings must resist failure by cracking, and their formability can be assessed qualitatively using the industry-standard Erichsen cupping test. However, this only provides strains much smaller than the coatings can withstand, and hence does not discriminate between coating behaviour. Finite element (FE) modelling has been used to show that the applied strain governs the failure of coil coatings during forming, and to demonstrate how increased surface strains can be achieved by altering key parameters to make the Erichsen cupping test discriminating and quantitative. The surface strains are increased by increasing the coefficient of friction between the indenter and the substrate, and by increasing the thickness of the substrate. A parametric study on substrate properties showed that a smaller strain hardening exponent (i.e. more plastic behaviour) gave higher surface strains. There was no variation in the surface strains over a temperature range of -60 °C to 60 °C. Understanding how the test conditions and substrate properties influence the surface strains improves the efficacy of the Erichsen cupping test. The surface strains applied to a coating can be varied by changing the substrate properties, which allows for greater differentiation between coatings and for the coating failure strains to be determined quantitatively. This provides a data-driven approach to develop and formulate better coatings using a single, efficient and easy test.

Journal article

Kopsidas S, Olowojoba G, Kinloch A, Taylor Aet al., 2021, Examining the effect of graphene nanoplatelets on the corrosion resistance of epoxy coatings, International Journal of Adhesion and Adhesives, Vol: 104, Pages: 1-12, ISSN: 0143-7496

Graphene due to its two-dimensional structure, large surface area and high impermeability is regarded as an excellent functional filler for the development of anti-corrosive coatings by creating a natural barrier to the diffusion of electrolytes. Epoxy polymers are widely used as protective coatings, and in the present study, commercially-available graphene nanoplatelets (GNPs) were dispersed into an epoxy resin using three-roll milling (3RM). The GNP-modified epoxy was coated onto mild steel substrates, and cured. The coated panels were immersed into a corrosive environment of 3.5 wt% NaCl aqueous solution for 4–5 days. The adhesion of the coatings to the substrate was then measured using a cross-cut test. The addition of higher loadings of GNPs resulted in a deteriorating corrosion performance, with the 1.5 wt% and 3 wt% coatings exhibiting 53% and 91% damage, respectively, after the cross-cut tests. The unmodified epoxy and low GNP content coatings (≤0.5 wt%) demonstrated 0% damage. This shows that the corrosion behaviour of GNP/epoxy coatings is not dominated by barrier effects but by electrochemical factors. The addition of GNPs is only effective at low loadings, as higher contents result in electrically-conductive coatings that facilitate the conduction of corrosion currents.

Journal article

Sorce F, Ngo S, Lowe C, Taylor Aet al., 2020, The effect of varying molecular weight on the performance of HMMM-crosslinked polyester coatings, Progress in Organic Coatings, Vol: 149, ISSN: 0300-9440

Thermosetting polyester coatings crosslinked with hexa(methoxymethyl)melamine (HMMM) are ubiquitous for the pre-painted metal sheet used in white goods and architectural cladding. The coatings are typically 20 μm thick and must have superior resistance to cracking during the forming process to maintain their excellent aesthetics and corrosion resistance. Hence, understanding their structure-property relationships is key to design durable coatings with good formability. The thermo-mechanical properties of clear and TiO2-pigmented polyester-HMMM free-films with varying number average molecular weight (MW) from Mn =1500 g/mol to 3300 g/mol and a constant crosslinker content of 20 % have been determined, and this work provides a fundamental investigation into the effects of varying the MW for the first time. Increasing the MW decreases the glass transition temperature (Tg) as the crosslink density reduces due to fewer functional chain ends. The Young’s modulus and yield stress decrease with an increase in MW at low temperatures, and the strain to failure increases around Tg. The TiO2 pigment increases the stiffness of the coatings and reduces the strain to failure around Tg, but has a toughening effect at higher temperatures. All the coatings show comparable behaviour in the Erichsen cupping test; however, increasing the MW reduces the damage during the T-bend test as the coatings are able to withstand higher applied strains. Thus controlling the MW allows a balance of properties to be achieved, as increasing the MW reduces the Tg and modulus while increasing the strain to failure and formability of the coating. Such an understanding of the structure-property relationships allows for better formulating and targeted coating design, reducing cost and increasing performance in the coil coating industry.

Journal article

He S, Carolan D, Fergusson A, Taylor ACet al., 2020, Mechanical and fracture properties of epoxy syntactic foams modified with milled carbon fibre

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. Syntactic foams are lightweight but brittle materials typically used as the core for sandwich composite panels. Foams comprising of ∼60 vol% hollow glass microspheres (GMS) in an epoxy matrix were modified by the addition of milled carbon fibre (MCF). Weight ratios of up to 30% MCF:GMS were used. The tensile modulus of the foams increased from 3.36 GPa up to 4.82 GPa with the addition of 30% weight ratio of MCF. The tensile failure strength of the syntactic foam decreased with low loadings of MCF, which is attributed to low load transfer capacity among the fibres due to poor fibre population. The tensile failure strength recovers when more MCF particles are added. The fracture energy of the syntactic foam showed an increase of 217%, from 182 J/m2 to 396 J/m2, due to the addition of 30% weight ratio of MCF. Toughening mechanisms were identified as crack deflection, debonding and subsequent plastic void growth, and fibre pull-out.

Conference paper

Deng X, Kinloch AJ, Pimenta S, Schueneman GT, Sprenger S, Taylor AC, Teo WSet al., 2020, Toughening epoxy composites using nano- And microcellulose modifiers

The fracture properties and toughening mechanisms of cellulose- and cellulose-rubber hybrid-modified epoxy polymers and glass-fibre (GF) composites are investigated. The cellulose modifiers used are microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC), and the rubber modifiers are carboxyl-terminated butadiene-acrylonitrile (CTBN) and core-shell rubber (CSR). The toughening mechanisms of the MCC-epoxy and CNC-epoxy were identified to be crack deflection, shear band yielding, particle rupture or pull-out and debonding of the cellulose particles, which was followed by plastic void growth. An additive toughening effect is observed for the hybrid polymers. Analytical modelling of the fracture energies showed that the particle pull-out toughening contribution is negligible for CNC-epoxy, and the particle debonding and rupture toughening contributions are negligible for MCC-epoxy. The GF composites were manufactured using the wet-layup process. Cellulose modifiers did not increase the composite propagation fracture energy (GC,prop) but slight increases in GC,prop occurred for the CNC hybrids. Increases in the fibre-matrix adhesion reduced the fibre toughening mechanisms in the composites that were modified with only MCC or CNC. The crack tip deformation zone is smaller than the MCC particles, reducing their toughening ability in the GF composites.

Conference paper

He S, Carolan D, Fergusson A, Taylor ACet al., 2020, Mechanical and fracture properties of epoxy syntactic foams modified with milled carbon fibre

Syntactic foams are lightweight but brittle materials typically used as the core for sandwich composite panels. Foams comprising of ∼60 vol% hollow glass microspheres (GMS) in an epoxy matrix were modified by the addition of milled carbon fibre (MCF). Weight ratios of up to 30% MCF:GMS were used. The tensile modulus of the foams increased from 3.36 GPa up to 4.82 GPa with the addition of 30% weight ratio of MCF. The tensile failure strength of the syntactic foam decreased with low loadings of MCF, which is attributed to low load transfer capacity among the fibres due to poor fibre population. The tensile failure strength recovers when more MCF particles are added. The fracture energy of the syntactic foam showed an increase of 217%, from 182 J/m2 to 396 J/m2, due to the addition of 30% weight ratio of MCF. Toughening mechanisms were identified as crack deflection, debonding and subsequent plastic void growth, and fibre pull-out.

Conference paper

Deng X, Kinloch AJ, Pimenta S, Schueneman GT, Sprenger S, Taylor AC, Teo WSet al., 2020, Toughening epoxy composites using nano- And microcellulose modifiers

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. The fracture properties and toughening mechanisms of cellulose- and cellulose-rubber hybrid-modified epoxy polymers and glass-fibre (GF) composites are investigated. The cellulose modifiers used are microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC), and the rubber modifiers are carboxyl-terminated butadiene-acrylonitrile (CTBN) and core-shell rubber (CSR). The toughening mechanisms of the MCC-epoxy and CNC-epoxy were identified to be crack deflection, shear band yielding, particle rupture or pull-out and debonding of the cellulose particles, which was followed by plastic void growth. An additive toughening effect is observed for the hybrid polymers. Analytical modelling of the fracture energies showed that the particle pull-out toughening contribution is negligible for CNC-epoxy, and the particle debonding and rupture toughening contributions are negligible for MCC-epoxy. The GF composites were manufactured using the wet-layup process. Cellulose modifiers did not increase the composite propagation fracture energy (GC,prop) but slight increases in GC,prop occurred for the CNC hybrids. Increases in the fibre-matrix adhesion reduced the fibre toughening mechanisms in the composites that were modified with only MCC or CNC. The crack tip deformation zone is smaller than the MCC particles, reducing their toughening ability in the GF composites.

Conference paper

He S, Carolan D, Fergusson A, Taylor ACet al., 2020, Mechanical and fracture properties of epoxy syntactic foams modified with milled carbon fibre

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. Syntactic foams are lightweight but brittle materials typically used as the core for sandwich composite panels. Foams comprising of ∼60 vol% hollow glass microspheres (GMS) in an epoxy matrix were modified by the addition of milled carbon fibre (MCF). Weight ratios of up to 30% MCF:GMS were used. The tensile modulus of the foams increased from 3.36 GPa up to 4.82 GPa with the addition of 30% weight ratio of MCF. The tensile failure strength of the syntactic foam decreased with low loadings of MCF, which is attributed to low load transfer capacity among the fibres due to poor fibre population. The tensile failure strength recovers when more MCF particles are added. The fracture energy of the syntactic foam showed an increase of 217%, from 182 J/m2 to 396 J/m2, due to the addition of 30% weight ratio of MCF. Toughening mechanisms were identified as crack deflection, debonding and subsequent plastic void growth, and fibre pull-out.

Conference paper

Sorce F, Lowe C, Ngo S, Taylor Aet al., 2019, The effect of HMMM crosslinker Ccntent on the thermal-mechanical properties of polyester coil coatings, Progress in Organic Coatings, Vol: 137, ISSN: 0300-9440

The thermosetting polyester-based coatings crosslinked with hexa(methylmethoxy)melamine (HMMM) used for coil coating sheet metal experience large deformations when formed into architectural cladding and white goods. Cracking of the 20-μm-thick coatings must not occur during forming, to prevent corrosion of the steel substrate, so the relationship between the composition and the thermal-mechanical properties is critical to develop highly formable and durable coatings, and to choose suitable forming conditions. Free films of coatings with 5 % to 30 % crosslinker content have been analysed. Dynamic mechanical analysis (DMA) showed that the glass transition temperature (Tg) and crosslink density increase with crosslinker content. Differential scanning calorimetry (DSC) has been used to measure the Tg from the thermal response, based solely on the chemical structure, and agrees well with the DMA.Tensile tests were performed at temperatures as a function of DSC Tg (Tg - 40 °C to Tg + 50 °C). There was little variation in Young’s modulus and strain to failure in the glassy region where the intermolecular forces dominate, but in the rubbery region governed by the covalent bonds a lower crosslinker content gave lower values. This indicates that the failure mechanism undergoes a transition with increasing temperature from being controlled by the brittle fracture stress to the yield stress. The addition of TiO2 pigment increased the modulus and apparent yield stress at low temperatures in the glassy region, and increased the strain to failure and failure stress in the rubbery region. Failure envelopes, normalising the tensile data with the DSC Tg and the crosslink density, show the dependence on crosslinker content and pigmentation. This allows the behaviour of coatings to be predicted from their structure, and enhanced coatings to be developed based on the required mechanical properties.

Journal article

Tsang WL, Taylor AC, 2019, Fracture and toughening mechanisms of silica- and core–shell rubber-toughened epoxy at ambient and low temperature, Journal of Materials Science, Vol: 54, Pages: 13938-13958, ISSN: 0022-2461

The highly cross-linked thermosetting polymers used as adhesives and as the matrices of fibre composites for the construction of lightweight vehicles are very brittle, and finding effective toughening solutions for such engineering applications is a long-standing problem. An anhydride-cured thermosetting epoxy polymer has been modified by the addition of different wt% of silica nanoparticles, core–shell rubber particles and hybrids with equal wt% of both. The fracture energy was measured at ambient and low temperature (− 40 °C and − 80 °C) to understand the brittle fracture behaviour. The fracture and toughening mechanisms were identified by scanning electron microscopy of the fracture surfaces. Analytical models were used to predict the modulus and fracture energy; the predictions agreed very well with the measured values. Toughening using silica nanoparticles is especially efficient at low particle contents. This shows how epoxies can be toughened successfully for use in industrial and transport applications.

Journal article

Tsai S-N, Taylor A, 2019, Vibration behaviours of single/multi-debonded curved composite sandwich structures, Composite Structures, Vol: 226, ISSN: 1879-1085

Sandwich structures, which are light but have high strength, are extensively used in automobile, marine and aircraft structures. However, core/facesheet debonding can occur and reduce the stiffness of the structures and hence result in the failure of the structures, whilst affecting the vibration behaviours. Hammer impact tests and finite element simulations were conducted on flat and curved sandwich structures, which were composed of carbon fibre reinforced polymer (CFRP) facesheets and epoxy cores, to analyse how the vibration behaviours were affected by debonding and other factors. The 15°- and 30°-curved structures showed only slight differences in the natural frequencies of bending and torsional modes. However, significant difference in the lateral modes were found as the mode shape merged with torsional movement and hence the natural frequencies increase. Debonding resulted in the reduction in the natural frequencies, an 80 mm debonded region reduced the natural frequency of the flat and 30°-curved structures by 57.0% and 56.6%, respectively. Change of natural frequencies can make a structure resonate and lead to failure, therefore how the debonded regions affect the vibration of sandwich structures is important for applications.

Journal article

Wood J, Gauvin C, Young C, Taylor A, Balint D, Charalambides Met al., 2019, Reconstruction of historical temperature and relative humidity cycles within Knole House, Kent, Journal of Cultural Heritage, Vol: 39, Pages: 212-220, ISSN: 1296-2074

It is essential for the preservation of cultural heritage that the effects of climate change are investigated. With this in mind, the daily temperature and relative humidity (RH) cycles within the Brown Gallery at Knole House, Kent, have been reconstructed for the period 1605 – 2015 enabling the study of low-cycle environmental fatigue on a set of 17th century panel paintings. By establishing a relationship between the temperature in the Brown Gallery and the Hadley Centre Central England Temperature (HadCET) dataset over a sixteen year period (2000 – 2015), it is possible to use the full HadCET dataset to obtain the daily minimum and maximum temperatures in the Brown Gallery for the period 1878 – 2015. Using a Fourier series to fit the periodic data it is then possible to extrapolate back to 1605. Furthermore, correction factors derived using the HadCET average daily temperature in the period 1772 – 1877 and average monthly temperature in the period 1659 – 1771 are applied to the temperature data to increase the model accuracy. The daily minimum and maximum RH for the period 1605 – 2015 are obtained using the Brown Gallery maximum and minimum temperatures respectively, and assuming that the daily dew point temperature at Knole is calculated by subtracting a monthly-dependent constant from the daily minimum temperature at Knole, thus enabling the calculation of the daily actual water vapour pressure of air. Changes in RH are a result of the daily temperature cycle changing the saturation vapour pressure of air in the gallery. This data is valuable as it enables a study of the effects of low-cycle fatigue on the 17th century panel paintings housed in the Brown Gallery at Knole House, Kent due to these temperature and relative humidity cycles. Furthermore, the method presented offers a technique that can be utilised to replicate the internal environment for any unheated monument building so that the effects of past and future temper

Journal article

Tsai SN, Carolan D, Sprenger S, Taylor ACet al., 2019, Fracture and fatigue behaviour of carbon fibre composites with nanoparticle-sized fibres, Composite Structures, Vol: 217, Pages: 143-149, ISSN: 0263-8223

Fibre composites with thermoset polymer matrices are widely used. However, thermosets are very brittle, which can limit the applications of fibre composites. In this work, silica nanoparticles (SNPs) were used to modify two fibre sizings to improve the toughness of carbon fibre composites. Mode I interlaminar fracture and fatigue crack growth tests were conducted on the composites made using the silica nanoparticle-sized fibres. There was no significant change in the fatigue crack growth rate with the addition of SNPs. However, the addition of SNPs to either sizing increased the composite toughness. The fracture energy was significantly increased from 166 J/m 2 to 220 J/m 2 (increased by 33%) with only 0.89 wt% on fibre weight of SNPs. This is significantly more efficient than adding SNPs into the matrix, which can require addition of up to 20 wt% of SNPs [1], to achieve the same improvement in toughness.

Journal article

He S, Carolan D, Fergusson A, Taylor ACet al., 2019, Toughening epoxy syntactic foams with milled carbon fibres: mechanical properties and toughening mechanisms, Materials and Design, Vol: 169, Pages: 1-15, ISSN: 0264-1275

Syntactic foams comprising hollow glass microspheres (GMS) in an epoxy matrix are critical materials for lightweight structures, being extensively used in marine and aerospace as cores for composite sandwich panels. They are buoyant and crush resistant, but their use is limited by their brittleness. Milled carbon fibres (MCF) were used to increase toughness, by introducing energy absorption mechanisms, to foams comprising ∼60 vol% GMS. Weight ratios of up to 40% MCF:GMS were used. The tensile modulus of the foams increased from 3.36 GPa to 5.41 GPa with the addition of 40% weight ratio of MCF. The tensile strength of the syntactic foam decreased with low loadings of MCF, but then recovers when more MCF particles are added, and the mechanisms responsible are explained for the first time. The fracture energy of the syntactic foam increased by 183%, from 182 J/m2 to 516 J/m2, due to the addition of 40% weight ratio of MCF. Toughening mechanisms were identified as crack deflection, debonding and subsequent plastic void growth, and fibre pull-out. Thus, the simple and cheap addition of MCF greatly increases the toughness of the syntactic foams, enabling lighter or more damage-resistant structures to be produced.

Journal article

Sorce F, Ngo S, Lowe C, Taylor Aet al., 2019, Quantification of coating surface strains in Erichsen cupping tests, Journal of Materials Science, Vol: 54, Pages: 7997-8009, ISSN: 0022-2461

Thermosetting polyester-based coatings are used to produce pre-painted metal in the coil coating industry. The coated steel sheet is formed into white goods and architectural cladding, which involves large deformations of the metal and results in large strains in the coating. The Erichsen cupping test is a standard method used to assess the formability, ductility and adhesion of coatings, which induces similar strains to those experienced during forming. It is a qualitative and robust quality control method, but the behaviour of coatings during the test has never been previously studied quantitatively. Failure of coatings on sheet metal during forming is a strain-governed process, so understanding the behaviour of a coating in the Erichsen cupping test will allow the formability, material properties and chemical structure of the polymer to be linked more closely, enabling the development of better coatings. A finite element model has been developed to calculate the coating surface strains for any level of indentation during the test, and has been validated using the surface strains during cupping measured by digital image correlation. A master curve of the maximum strain versus the indentation depth (Erichsen index) has been determined. This allows the strain to failure of the coating on a substrate, a critical material property which is otherwise difficult and laborious to obtain, to be simply determined from the Erichsen test for the first time. The relationship between the Erichsen index and maximum surface strain presented here enables users to obtain this material property both from future tests and from the results of historic tests (as many coating suppliers and users have extensive databases of Erichsen test results stretching back many years). This novel framework provides a quantitative method to analyse the performance of coatings used in the coil industry, redeveloping a century-old technique.

Journal article

Tsai S-N, Taylor AC, 2019, Vibration behaviours of single/multi-debonded composite sandwich structures with nanoparticle-modified matrices, Composite Structures, Vol: 210, Pages: 590-598, ISSN: 0263-8223

Sandwich structures with carbon fibre reinforced plastic (CFRP) facesheets are widely used in aerospace and marine structures because they have high strength, stiffness and light weight. However, debonds between the facesheets and the core can reduce greatly the stiffness and the strength of the structures, whilst affecting the vibration behaviours. Hammer impact tests and finite element simulations were conducted to analyse the vibration behaviours of sandwich structures with single and double debonded regions, different matrix modifiers and facesheet stacking orientations. The debonded regions reduced the natural frequencies of sandwich structures, an 80 mm debonded region reduced the natural frequency by 57 %. The natural frequencies in bending modes of the structures with facesheets were more sensitive to debonds; while structures with facesheets were more sensitive in torsion modes. When the debonds were present in the same location for both upper and lower facesheets, there was a greater reduction in the natural frequencies of the bending modes than for other debond arrangements. Reductions in the natural frequency can cause a structure to vibrate at resonance and cause structural failure, therefore understanding of how debonded regions affect the vibration of sandwich structures is critical.

Journal article

He S, Carolan D, Fergusson A, Taylor ACet al., 2019, Toughening epoxy syntactic foams with milled carbon fibres: Mechanical properties and toughening mechanisms

Syntactic foams comprising hollow glass microspheres (GMS) in an epoxy matrix are critical for lightweight structures, being extensively used in marine and aerospace as cores for composite sandwich panels. They are buoyant and crush resistant, but their use is limited by their brittleness. Milled carbon fibres (MCF) were used to increase toughness, by introducing energy absorption mechanisms, to foams comprising ∼60 vol% GMS. Weight ratios of up to 40% MCF:GMS were used. The tensile modulus of the foams increased from 3.36 GPa to 5.41 GPa with the addition of 40% weight ratio of MCF. The tensile strength of the syntactic foam decreased then increase when more MCF particles are added, and the mechanisms responsible are explained for the first time. The fracture energy of the syntactic foam increased by 183%, from 182 J/m2 to 516 J/m2, due to the addition of 40% weight ratio of MCF. Toughening mechanisms were identified as crack deflection, debonding and subsequent plastic void growth, and fibre pull-out. Thus, the simple and cheap addition of MCF greatly increases the toughness of the syntactic foams, enabling lighter or more damage-resistant structures.

Conference paper

Wood JD, Gauvin C, Young CRT, Taylor AC, Balint DS, Charalambides MNet al., 2018, Cracking in paintings due to relative humidity cycles, 22nd European Conference on Fracture (ECF) - Loading and Environmental Effects on Structural Integrity, Publisher: Elsevier B.V., Pages: 379-384, ISSN: 2452-3216

A numerical study is performed using the finite element method to consider the effects of low-cycle fatigue, specifically induced through relative humidity cycles on paintings. It has been identified that there are two major crack types in paintings, these being (i) an interfacial crack (delamination) between paint and support and (ii) a through-thickness (channel) crack in the paint layer itself, arresting on the interface. Therefore a 2D plane strain model for each type of crack has been created, which both consist of an alkyd paint modelled using a visco-hyperelastic material model and a primed canvas which is assumed to behave in a linear elastic manner. To account for fatigue damage in both models, cohesive elements located along the interface or through the film thickness respectively, are used and the traction-separation law has been modified to incorporate a fatigue damage parameter. It is possible to expose the models to the same relative humidity cycles, which would typically be seen in museums, enabling the prediction of time to first crack and which crack type is more readily grown in the painting.

Conference paper

Guild F, Kinloch AJ, Masania K, Sprenger S, Taylor Aet al., 2018, The fracture of thermosetting epoxy polymers containing silica nanoparticles, Strength, Fracture and Complexity, Vol: 11, Pages: 137-148, ISSN: 1567-2069

An epoxy resin, cured with an anhydride, has been modified by the addition of silica nanoparticles. The particles were introduced via a sol-gel technique which gave a very well dispersed phase of nanosilica particles, which were about 20 nm in diameter, in the thermosetting epoxy polymer matrix. The glass transition temperature of the epoxy polymer was unchanged by the addition of the anoparticles, but both the modulus and toughness were increased. The fracture energy increased from 77 J/m2 for the unmodified epoxy to 212 J/m2 for the epoxy polymer containing 20 wt.% of nanosilica. The fracture surfaces were inspected using scanning electron and atomic force microscopy, and these microscopy studies showed that the silica nanoparticles (a) initiated localised plastic shear-yield deformation bands in the epoxy polymer matrix and (b) debonded and allowed subsequent plastic void-growth of the epoxy polymer matrix. A theoretical model for these toughening micro mechanisms has been proposed to confirm that these micromechanisms were indeed responsible for the increased toughness that was observed due to the presence of the silica nanoparticles in the epoxy polymer.

Journal article

Selimov A, Jahan SA, Barker E, Dackus P, Carolan D, Taylor A, Raghavan Set al., 2018, Silane functionalization effects on dispersion of alumina nanoparticles in hybrid carbon fiber composites, APPLIED OPTICS, Vol: 57, Pages: 6671-6678, ISSN: 1559-128X

Journal article

Taylor AC, Selimov A, Jahan SA, Barker E, Dackus P, Carolan D, Raghavan Set al., 2018, Silane functionalization effects on dispersion of alumina nanoparticles in hybrid carbon fiber composites revealed through photo-luminescence spectroscopy, Applied Optics, Vol: 57, Pages: 6671-6678, ISSN: 1559-128X

Hybrid carbon fiber reinforced polymer composites are a new breed of materials currently being explored and characterized for next-generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties—fracture toughness, for example—and stress-sensing capabilities can be achieved. However, problems with manufacturing can arise resulting from the inherent variability of the manufacturing techniques along with the tendency for the nanoparticles to agglomerate. Photoluminescence spectroscopy is used to investigate the effects of adjustments to manufacturing processes and silane functionalization on particle dispersion and sample consistency between samples of the same type. This work finds that application of surface treatments on the nanoparticles improved their dispersion, with the reactive treatment providing for the most consistency among samples. Improvements to dispersion and increased consistency resulting from specific changes in manufacturing processes were shown numerically. Findings provide a manufacturing recommendation to achieve optimum dispersion and mechanical properties of the composite.

Journal article

Kinloch AJ, Uhlig C, Bauer J, Bauer M, Kahle O, Taylor ACet al., 2018, Influence of backbone structure, conversion and phenolic co-curing of cyanate esters on side relaxations, fracture toughness, flammability properties and water uptake and toughening with low molecular weight polyethersulphones, Reactive and Functional Polymers, Vol: 129, Pages: 2-22, ISSN: 1381-5148

The effect of backbone structure and conversion of polycyanurate networks on solid state properties has been studied and compared to co-curing with bisphenol-A. Dynamic mechanical behaviour, density, flammability properties, fracture toughness and long-term water uptake were investigated. The intensity of the γ-relaxation increases, room temperature density decreases with increasing conversion, both due to increasing free volume with increasing conversion. A brittle-ductile transition was detected by precise fracture toughness measurements; above a critical conversion the fracture toughness rises suddenly from extremely low values to a plateau or maximum: Networks with higher toughness show a maximum, those with lower toughness a plateau. Bisphenol-A modification causes intrinsic toughness variations. Toughening of two different cyanate esters with polyethersulphones synthesized with various molecular weights between 3000 and 10,500 (Mn) was investigated. Significant toughening effects can be achieved already with intermediate molecular weights lower than those of commercially-available high-Tg amorphous thermoplastics. Long-term water uptake measurements at 28 °C, 50 °C and 70 °C over two years show a non-Fickian part of the water uptake for all cyanate esters even at temperatures as low as 28 °C. The effects of backbone structure, conversion and storage temperature are discussed in detail.

Journal article

Awang Ngah S, Taylor AC, 2018, Fracture behaviour of rubber- and silica nanoparticle-toughened glass fibre composites under static and fatigue loading, Composites Part A: Applied Science and Manufacturing, Vol: 109, Pages: 239-256, ISSN: 1359-835X

The crosslinked polymers used in fibre composites are very brittle, and require toughening for structural applications. Research over many years has increased the fracture energy, but the fatigue resistance of these toughened polymers is very poor, limiting the optimisation of structures. This work reports the first successful use of hybrid toughening to increase both the quasi-static interlaminar fracture energy, GIC, and the fatigue threshold strain-energy release-rate, Gth. Amine-cured epoxy glass-fibre composites were toughened using carboxyl-terminated butadiene-acrylonitrile (CTBN) which forms micron-sized rubber particles and 20 nm-diameter silica nanoparticles. The toughening mechanisms were identified as cavitation of rubber particles and debonding for the silica nanoparticles, followed by plastic void growth. The CTBN greatly increases GIC, and the nanoparticles increase Gth. Combining both particles as a hybrid has a synergistic effect on the fatigue resistance. This demonstrates the effectiveness of hybrid toughening, enabling the design of optimised composites by combining micro- and nanoparticles.

Journal article

Taylor AC, 2018, Adhesives with nanoparticles, Handbook of Adhesion Technology: Second Edition, Pages: 1677-1702, ISBN: 9783319554105

The increased commercial availability and the reduced prices of nanoparticles are leading to their incorporation in polymers and structural adhesives. This chapter outlines the principal types of nanoparticles, and the methods that may be used to disperse the particles in a polymer matrix. It discusses how nanoparticles can alter the mechanical properties (e.g., stiffness), electrical properties (e.g., conductivity), functional properties (e.g., permeability, glass transition temperature), and fracture performance of thermoset polymers. The effect of nanoparticles on joint performance is also discussed.

Book chapter

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