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The effect of hydrothermal ageing on the mechanical behaviour and fatigue response of a hybrid (bolted/bonded) aluminium alloy (AA7075) and glass fibre reinforced epoxy (GRE) hybrid composite single lap joints (SLJs) were carried out in this work. This effect was investigated using hybrid joints as a joint configuration. An adhesive layer of Araldite epoxy and mechanical fasteners of Huck bolt were attached between the adherends as primary and secondary attachments, respectively. Three types of joint were exposed to a humid environment at 50 °C for long-term immersion (20, 40, 60, 80, 100, and 120 days) periods. Composite laminates (i.e. glass fibre epoxy GRE) and metal (i.e. aluminium alloy AA7075) were used as joint adherends. Quasi-static and fatigue tests were carried out to evaluate the evolution of the mechanical performance and the damage mechanisms of hybrid joints during the ageing exposition. The dissimilar-AA7075/GRE hybrid SLJ showed the highest joint strength and the longest failure strain. Moreover, the hybrid joint with dissimilar-AA7075/GRE achieved 83% and 30.2% higher fatigue strength than similar adherends of AA7075 and GRE composites, respectively. As for the damage mechanisms, shear specimens experienced a typical bearing mode.

A Pennisetum purpureum/glass-reinforced epoxy (PGRE) hybrid composites was comprehensively characterised to assess its impact response behaviour at room temperature (RT), under moisture exposure, and elevated temperatures. The untreated, 5 and 10% alkali-treated PGRE composites were fabricated using hybridised Pennisetum purpureum/woven E-glass fibres and epoxy resin. An instrumented IMATEK IM10 drop weight impact tester was utilised to characterise the impact responses of the prepared hybrid composites. The specimens were subjected to water exposure for 50, 100, 200, and 400 h and before arranged with a low-velocity impact test. In addition, the tests were repeated at 40, 60, and 80 °C to examine the effects of elevated temperatures. The results indicate that the untreated PGRE composite yielded the highest peak load impact response at all energy levels. The stiffness of the composites found to decrease substantially with increasing temperatures, which increases the absorbed energy and peak deflection causing extensive damage to the specimens.

ObjectivesTo report the volume of surgical activity and the number of cancelled surgical procedures during the COVID-19 pandemic.Design and settingAnalysis of electronic health record data from the National Health Service (NHS) in England and Wales.MethodsWe used hospital episode statistics for all adult patients undergoing surgery between 1st January 2020 and 31st December 2020. We identified surgical procedures using a previously published list of procedure codes. Procedures were stratified by urgency of surgery as defined by NHS England. We calculated the deficit of surgical activity by comparing the expected number of procedures from the years 2016-2019 with the actual number of procedures in 2020. We estimated the cumulative number of cancelled procedures by 31st December 2021 according patterns of activity in 2020.ResultsThe total number of surgical procedures carried out in England and Wales in 2020 was 3,102,674 compared to the predicted number of 4,671,338. This represents a 33.6% reduction in the national volume of surgical activity. There were 763,730 emergency surgical procedures (13.4% reduction), compared to 2,338,944 elective surgical procedures (38.6% reduction). The cumulative number of cancelled or postponed procedures was 1,568,664. We estimate that this will increase to 2,358,420 by 31st December 2021.ConclusionsThe volume of surgical activity in England and Wales was reduced by 33.6% in 2020, resulting in over 1,568,664 cancelled operations. This deficit will continue to grow in 2021.Summary boxesWhat is already known on this topicThe COVID-19 pandemic necessitated a rapid change in the provision of care, including the suspension of a large proportion of surgical activitySurgical activity has yet to return to normal and has been further impacted by subsequent waves of the pandemicThis will lead to a large backlog of casesWhat this study adds3,102,674 surgical procedures were performed in England and Wales during 2020, a 33.6% reduction on the expected yearly surgical activityOver 1.5 million procedures were not performed, with this deficit likely to continue to grow to 2.3 million by the end of 2021This deficit is the equivalent of more than 6 months of pre-pandemic surgical activity, requiring a monumental financial and logistic challenge to manage

ObjectivesTo confirm the incidence of perioperative SARS-CoV-2 infection and associated mortality after surgery.Design and settingAnalysis of routine electronic health record data from National Health Service (NHS) hospitals in England.MethodsWe extracted data from Hospital Episode Statistics in England describing adult patients undergoing surgery between 1st January 2020 and 31st October 2020. The exposure was SARS-CoV-2 infection defined by ICD-10 codes. The primary outcome measure was 90-day in-hospital mortality. Data were analysed using multivariable logistic regression adjusted for age, sex, Charlson co-morbidity index, index of multiple deprivation, presence of cancer, surgical procedure type and admission acuity. Results are presented as n (%) and odds ratios (OR) with 95% confidence intervals.ResultsWe identified 1,972,153 patients undergoing surgery of whom 11,940 (0.6%) had SARS-CoV-2. In total, 19,100 (1.0%) patients died in hospital. SARS-CoV-2 infection was associated with a much greater risk of death (SARS-CoV-2: 2,618/11,940 [21.9%] vs No SARS-CoV-2: 16,482/1,960,213 [0.8%]; OR: 5.8 [5.5 – 6.1]; pConclusionsThe low incidence of SARS-CoV-2 infection in NHS surgical pathways suggests current infection prevention and control policies are highly effective. However, the high mortality amongst patients with SARS-CoV-2 suggests these precautions cannot be safely relaxed.Summary boxesWhat is already known on this topicHigh mortality rates have been reported amongst surgical patients who develop COVID-19 but we don’t know how this compares to the concurrent surgical population unaffected by COVID-19.Strict infection prevention and control procedures have substantially reduced the capacity of surgical treatment pathways in many hospitals.The very large backlog in delayed and cancelled surgical procedures is a growing public health concern.What this study addsFewer than 1 in 100 surgical patients are affected by COVID-19 in the English National Health Service.Elective surgical patients who do develop COVID-19 are 30 times more likely to die while in hospital.Infection prevention and control procedures in NHS surgical pathways are highly effective but cannot be safely relaxed.

A dynamic mechanical analysis was undertaken to determine the influence of moisture on the mechanical properties of interwoven hemp/polyethylene terephthalate (PET) hybrid composites. Composite laminates were fabricated using vacuum infusion process; form epoxy resin reinforced with interwoven hemp and PET fibres. Woven hemp, woven PET, and interwoven hemp/PET hybrid composites were produced. The hybrid hemp/PET composites yielded the highest final residue % due to the PET fibres which improved the thermal stability. The glass transition temperatures of the woven hemp, woven PET, and interwoven hemp/PET hybrid composites were 68, 67, and 69 °C, respectively. Water absorption tests were conducted, and tensile and flexural tests were conducted on the wet and dry specimens. The water uptake of the hemp/PET hybrid composite was half that of the woven hemp composites. The tensile and flexural strengths of the interwoven hemp/PET hybrid composites were 4% and 22% greater than those of the woven hemp composites, respectively.

The absorption behaviour of water and its effect on the tensile and flexural properties of interwoven cellulosic fibres were investigated. Hybrid composites consisting of interwoven kenaf/jute and kenaf/hemp yarns were prepared by an infusion process that used epoxy as the polymer matrix. The water absorption characteristics of the fibres were obtained by immersing the composite samples in tap water at room temperature, until reaching their water content saturation point. The dry and water-immersed woven and interwoven hybrid composite samples were subjected to tensile and flexural tests. To study the effect of water penetration in the fibre/matrix interface, fractured samples were examined using field emission scanning electron microscopy (FESEM). The study shows that the mechanical and water-resistant properties of the kenaf, jute, and hemp fibres were improved through hybridization. However, as a result of water penetrating the fibre/matrix interface, longer water-immersion times reduced the tensile and flexural strength of the composites.

In this study, the fire structural properties of a basalt fibre reinforced polymer laminate under compressive loading were investigated analytically and experimentally, and compared against an E-glass fibre composite with the same fibre content, ply orientation and polymer matrix. A thermal-mechanical model was used to compute the softening rate and failure stress of basalt fibre laminates which collapse, when loaded in compression, by either global buckling or material failure when exposed to fire. Fire structural measurements involving one-sided radiant heating with axial compressive loading were also performed. The measurements revealed that the softening behaviour and failure stress of the basalt fibre laminate were inferior to those of the glass fibre composite. Furthermore, the fire reaction properties, such as heat release rate and smoke density, were also less favourable for the basalt laminate. This appears to be mainly due to the thermal absorptivity of the basalt fibre laminate being higher, which causes it to heat up at a faster rate and reach higher temperatures when exposed to a radiant heat flux.

The effects of hydrothermal ageing on the crushing behaviour of glass fibre-reinforced epoxy (GRE) pipes are discussed. Pipes with three different winding angles (±45°, ±55°, ±63°) were manufactured by filament winding process. The pipes were then hydrothermally aged in tap water at a constant temperature of 80 °C for periods of 500, 1000, and 1500 h. Uniaxial compressive tests were conducted on the virgin and aged samples using a universal testing machine in accordance with ASTM D695 -10. The tests were also performed at temperatures ranging from room temperature (RT) at 25 °C to 45 °C and 65 °C to study the response of the pipes at elevated temperatures. Scanning electron microscopy (SEM) images were captured and the relationship between the ageing period and strength of the GRE pipes was determined. The results indicate that the strength of the GRE pipes significantly decreases with increase in the temperature and ageing period. On the contrary, the strength increases as the winding angles decrease. The compressive strength of the pipes was also predicted using a Berbinau’s based model and was found to correlate well with the earlier obtained experimental results yielding a maximum variation of less than ∼25%.

The thermal behaviour and dynamic mechanical analysis of Pennisetum purpureum/glass-reinforced hybrid composites were investigated. Hybrid composite laminates were fabricated using untreated, 5%, or 10% alkali-treated P. purpureum fibres with woven E-glass fibres and epoxy resin. The composites were manufactured using a vacuum infusion process; the volume fractions of the P. purpureum, glass fibre, and epoxy resin were 24%, 6%, and 70%, respectively. Thermogravimetric analysis (TGA) demonstrated that the amount of residue of the hybrid composites decreased as the concentration of the alkali used to treat the P. purpureum fibres increased. The glass transition temperature values of the neat epoxy, and hybrid composites with the untreated, 5%, and 10% alkali-treated P. purpureum fibres were 64, 64, 67, and 63 °C, respectively as determined by dynamic mechanical analysis (DMA). When tested at room temperature (RT), the maximum tensile and flexural strengths were recorded for the hybrid composites with the 5% alkali-treated P. purpureum fibres. At >60 °C, as the temperature approached Tg, debonding of the fibre and matrix occurred, which resulted in a reduction of the tensile and flexural strengths. The fractured surface morphologies of the samples indicated that improved fibre–matrix interfacial bonding was achieved for the 5% alkali-treated P. purpureum/glass hybrid composites.

The effects of accelerated hydrothermal ageing on the behaviour of composite tubes under multiaxial stress were experimentally investigated. A set of [±55°] 4 tubes were hydrothermally aged at 80 °C for 1500 h. An indigenous automated test rig was fabricated to accommodate five stress ratios—0H:1A, 1H:1A, 2H:1A, 4H:1A, and 1H:0A. The cyclic test involved, pressurising the tube with 1-min pressure and 1-min no-pressure cycles. The first ply failure points were determined from the axial and hoop stresses. Failure envelopes were constructed at the aforesaid five stress ratios. Fourier transform infrared results show an increase in the intensity of absorbance peaks of the OH stretching bands at the interphase. The scanning electron microscopy micrographs of aged samples show clear debonding between the epoxy resin and the glass fibres, which is a cause of failure. Moisture uptake by the epoxy leads to matrix osmotic cracking, resulting in damage.

This study proposes a novel approach to determine the fibre volume fraction in composites using vibration based non-destructive technique with a neural network. Currently, the volume fraction of a glass fibre/matrix based composite material is assessed using destructive techniques. Instead of changing or destroying the structure, a new non-destructive approach based on vibration analysis is proposed. Complete experimental protocols were developed to capture the vibration pattern. An auto-regressive model was developed as a feature extraction tool to classify the fibre volume fractions and as a pole tracking algorithm. The classification performances were within the range of 90–98%. For NDT method to be efficient, the classification results were then compared with destructive burn-out technique. The results of non-destructive test showed good agreement with those obtained through destructive test suggesting that the proposed method is an alternative to ASTM D2584-11 for determining the volume fraction of a glass fibre/matrix composite.

The effect of moisture absorption on untreated and alkaline-treated Napier grass fibre-reinforced polyester composites was evaluated. Under room-temperature immersion, the water absorption behaviour of the Napier grass fibre composites conformed to the Fickian diffusion mechanism. Compared with the untreated fibres, the treated fibres absorbed less water due to the removal of lignin and hemicelluloses. The tensile and flexural strength of the Napier grass composites decreased with increased water absorption. SEM analysis showed that the treated Napier grass fibre composites contained fewer fibre pull-outs and splits compared with the untreated composites, which supports the improved performance.

The effect of moisture absorption on the mechanical degradation of hybrid Pennisetum purpureum /glass–epoxy composites was investigated. The hybrid P. purpureum /glass–epoxy composites plates were manufactured by the vacuum infusion method using epoxy resin as a matrix. Following 50 h of water immersion, the hybrid composite specimens were tested. The moisture content reduced as the glass fibre content increased. The wet and dry hybrid composite specimens were subjected to tensile and flexural tests. The incorporation of the glass fibre into the P. purpureum –epoxy composites enhanced their tensile and flexural strength, as well as their modulus. The tensile and flexural strengths of the hybrid P. purpureum /glass–epoxy composites (24/6–70 vol%) were 43 and 60 MPa, respectively. However, the tensile and flexural properties significantly degraded under wet conditions. Using field emission scanning electron microscopy (FESEM), morphological analysis was performed to observe the fracture behaviour of the specimens and the effect of water molecules.

The mechanical properties of Napier grass fibre-reinforced composites were characterised. Napier grass fibres were extracted through water retting process. The effect of alkali-treatment on the tensile properties and morphology of the fibres was investigated. The fibres were alkali-treated using NaOH solutions of various concentrations and subjected to single fibre testing. The morphology of the fibres was observed using scanning electron microscopy. The 10% alkali-treated Napier grass fibres yielded the highest strength. To fabricate the polymer composites, Napier grass fibre and polyester resin were used as the reinforcing material and polymer matrix, respectively. The tensile and flexural properties of the composites were studied. In general, up to a certain threshold value, the tensile and flexural strengths of the composites increased as the fibre volume fractions increased, following which, there was a reduction in strength. The maximum tensile and flexural strengths of the composites were obtained at 25% fibre loading.

The design of composite repairs of corroded oil and gas pipelines must take into account the strength of the interface adhesion between composite and metal. A shaft-loaded blister test is a common method to measure interface fracture toughness and energy release rate. The study aimed on evaluating shaft-loaded blister tests as replacements for more complex pressure blister tests. Specimens investigated were thick fibre-reinforced plates bonded on metal disks as substrates containing a circular through-hole defect. This paper presents the influence of different punch head geometries on the resulting energy release rates and compares the results with blister tests using fluid pressure. Test and simulation results are presented and analytical solutions were derived and evaluated to establish best fitting formulations. It was shown, that significant variations between the different means of loading exist.

Pennisetum purpureum (PP) fibres were comprehensively characterised to assess their potential as reinforcing materials in polymer composites. The fibres were treated with 5, 7, 10, 12, and 15% sodium hydroxide wt.% concentration for 24 h. The fibres were subjected to single fibre tensile tests, thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The average diameter of the untreated fibres was 0.24 ± 0.02 mm, and the treated fibres had an average diameter of less than 0.21 ± 0.03 mm, yielding a 12–45% reduction in the diameter. The moisture content of the treated fibres decreased as the concentration of the alkali increased. The morphological observation demonstrated that as the alkali concentration increased, the fibre becomes more compressed due to collapse the cellular/lumen structure, the void content decreased, and its surface became rougher. The 5% alkali-treated fibre achieved an average maximum ultimate tensile stress of 141 ± 24 MPa. Young's modulus on the other hand, decreased from an average of 5.68 ± 0.14 GPa for untreated fibre to only 0.55 ± 0.17 GPa as the alkali concentrations increased from 5 to 15%. Keywords: Pennisetum purpureum fibre, Mechanical properties, Infrared spectroscopy, Thermogravimetric analysis, Natural fibre

This study investigated the effects of water ageing and low-velocity impact loadings on E-glass fibre/epoxy composite pipes subjected to monotonic internal pressure. The pipes, which consisted of six antisymmetric layers with (±55°)3 winding angles, were manufactured by the filament winding process. The specimens were cut from the pipes to the required test length. The specimens were then subjected to the ageing process by being immersed in 80 °C tap water for time intervals of 500, 1000, and 1500 h. Impact loadings of three different energy levels (5 J, 7.5 J, and 10 J) were applied, which were followed by monotonic burst tests. Scanning electron microscopy images were captured and the correlation between the ageing time and the level of impact energy on the pipes' burst strength was identified. The results indicated that the peak force and displacement increased as the impact energy increased. The monotonic burst test results revealed that the specimens that had been aged and were impacted by higher energy yielded lower burst strength. Weepage and eruption failures were observed depending on the applied impact energies. Keywords: Filament winding, GRE composite pipe, Ageing, Impact loading, Monotonic burst test

This paper presents a modelling approach to analyse the protection provided by passive and intumescent surface coatings on glass fibre reinforced laminate substrates exposed to fire. The modelling involves a multi-stage analytical approach: (i) thermal analysis of heat transfer from the fire through the surface insulation coating, which includes decomposition and expansion in the case of an intumescent material; (ii) thermal–chemical analysis of heat transfer through the fibreglass laminate substrate (beneath the fire protective coating), including decomposition of the polymer matrix; and (iii) thermal–mechanical analysis of softening and failure of the laminate under in-plane tension or compression loading. The modelling approach is validated using experimental temperature and strength data from fire structural tests performed on woven glass–vinyl ester laminates insulated with passive (ceramic fibre mat) or organic intumescent surface coatings.

This paper presents a new modelling approach to analyse the fire structural response of fibre–polymer laminates protected with an intumescent surface coating. The model is designed to predict the temperature, decomposition, softening and failure of laminates with an intumescent coating in fire. The modelling involves a three-stage analytical approach: (i) thermal-chemical analysis of the intumescent coating, (ii) thermal-chemical analysis of heat transfer through the laminate substrate (beneath the intumescent coating), and (iii) thermal-mechanical analysis of the softening and failure of the laminate under tension or compression loading. Fire structural tests were performed on a woven glass/vinyl ester laminate coated with an organic intumescent material to validate the modelling approach. It is shown the model can predict with good accuracy the temperature distribution and swelling of the intumescent coating with increasing exposure time to a constant heat flux. The model can approximate the temperature, softening and failure of the laminate substrate.

This paper presents an experimental investigation of the behaviour of filament wound glass fibre reinforced epoxy (GRE) composite pipe under hydrostatic and biaxial load conditions at temperatures up to 95 °C. The format of the experiments has been chosen to be compatible with the Future Pipe Industries (FPI) procedure using the ultimate elastic wall stress (UEWS) concept in the qualification and production control of GRE. The test appears to provide an attractive alternative to the current 1000 hour test procedure detailed in ASTM D2992 for the detection of manufacturing changes and reconfirmation of the design basis of the pipe. Six different stress ratios ranging from pure axial loading 0:1, 0.5:1, 1:1, 2:1, 4:1 and pure hoop 1:0 loading were tested. Three distinct failure modes were observed: tensile axial failure at pure axial loading, weepage at axial dominated loading from 0.5:1 to 2:1 and localized leakage failure under hoop dominated loading of 4:1 and 1:0. Full tensile–tensile UEWS and leakage based failure envelopes have been developed at a range of temperatures from 20 °C (RT) to 95 °C. Both showed a strong dependence on stress ratio and test temperatures. It was also shown that the UEWS based failure envelope at elevated temperatures generally degraded, except for the 2:1 loading where the UEWS strength increased.

This paper investigates the effects of temperature, heating time and atmosphere on the tensile modulus and strength of thermally-treated E-glass fibres. The heating conditions that were investigated are identical to those used in thermal recycling of waste polymer matrix composite materials, and therefore this study determines the effects of the recycling process conditions on the properties of reclaimed fibreglass. The loss in fibre strength is dependent on the temperature and time of the thermal process, and large strength loss occurs under the heating conditions used for high temperature incineration of polymer composites. A phenomenological model is presented for the residual fibre strength for the temperatures and heating time of the thermal recycling process. The reduction in fibre strength is dependent on the thermal recycling atmosphere under low temperature or short heating time conditions, but at high temperatures the strength loss is the same, regardless of furnace atmosphere (ambient air, dry air or inert gas). Quantitative fractographic analysis of the fibres shows that fracture for all heat treatments is caused by surface flaws. The strength loss is most probably due to structural relaxation during thermal annealing and a secondary effect of adsorbed surface water attacking the glass by thermally-activated stress-corrosion. It is shown that large reductions in fibre strength due to thermal recycling are not recovered during composite manufacture, therefore resulting in composite materials with significantly lower strength. The reduced strength of the composite matches the reduced fibre strength following thermal recycling.

This paper reports elevated temperature mechanical property measurements on woven glass fibre/polypropylene composites. Tensile and compressive stress rupture measurements were made on 12 mm thick laminate exposed to 50 kW m−2 heat flux. Behaviour was qualitatively similar to that of thermosetting laminates, but compressive behaviour was significantly inferior, due to a poorer resin–matrix bond, and to the loss of compressive properties at temperatures above the melting point. COM-FIRE, a finite difference implementation of the Henderson Equation, was able to model the thermal and residual resin profiles in the laminate during fire exposure. The thermal predictions were used, in conjunction with the measured mechanical property data, to model changes in elastic properties and stress rupture behaviour in fire. Because of the non-linearity of the tensile stress–strain curves, a 3-parameter model was needed to describe behaviour. In contrast the compressive response could be modelled by a simpler 2-parameter or saw-tooth model.

This paper presents a critical review of research progress in modelling the structural response of polymer matrix composites exposed to fire. Models for analysing the thermal, chemical, physical, and failure processes that control the structural responses of laminates and sandwich composite materials in fire are reviewed. Models for calculating the residual structural properties of composites following fire are also described. Progress towards validation of the models by experimental characterisation of the structural properties of composites during and following fire is assessed. Deficiencies in the fire structural models are identified in the paper, which provide the focus for future research in the field.

A small-scale loading frame was used to apply tensile and compressive stresses to glass vinyl ester and glass polyester laminates in a cone calorimeter under a heat flux of 75kW m−2. It was found, for the first time, that stress has a small but significant effect on the fire reaction properties. Increasing tensile stress increased heat release rate and smoke production, while shortening the time-to-ignition. Compressive stress had the reverse effect. This was attributed to the fact that tensile stress promotes the formation of matrix microcracks, facilitating the evolution of flammable volatiles. This hypothesis is further supported by the observation that stress has the greatest effect on the early heat and smoke release peaks, with a lower effect on the final ‘run-out’ values.

This paper evaluates the structural performance of flame resistant phenolic matrix composites exposed to fire. Experimental fire tests were performed on a glass-phenolic composite under combined static loading and one-sided radiant heating. The reduction to the tension and compression failure strengths of the phenolic composite was measured in these tests for heat flux conditions ranging from 10 kW/m2 (225 °C) to 75 kW/m2 (700 °C). It was discovered that the failure strengths of the phenolic composite decreased rapidly in the event of fire, particularly under compressive loading when failure occurred more rapidly than under tensile loading. The phenolic composite, despite having high flame resistance, loses strength more rapidly and fails sooner than a more flammable vinyl ester composite. The study shows that greater flammability resistance does not necessarily result in better structural performance in fire. The poor structural performance of the phenolic composite was due to explosive delamination damage and cracking caused by vaporisation of water in the matrix phase. It is shown that removing water from phenolic composites by natural or artificial ageing reduces the incidence of delamination cracking and thereby improves the materials' structural performance in fire. It is concluded that phenolic composites do not provide good structural performance in fire, even though they have low flame and smoke properties. However, reducing the water content in the matrix phase below about 10% can greatly improve the structural performance of phenolic composites during fire.

Fatigue behavior of polyvinylidiene fluoride (PVDF) pipes is investigated under low temperatures to characterize the temperature effects. The analysis included experimental evaluation of fatigue life for test samples taken directly from the manufactured pipes used for service as opposed to compression molded compact tension samples used in previous works. In this test, short sections from an extruded pipe are used to better represent the material service conditions. A compact test chamber was designed to control the test temperature. The samples were loaded into the test rig and allowed to cool for 30 min ensuring a constant and even temperature distribution. Cooling was done in a sealed test chamber using carbon dioxide gas. Two test temperatures of −20 °C and −10 °C were chosen since they represent typical temperature during which failure occurs during actual pipe service in cold environments. Fractured surfaces were inspected and fatigue data were analyzed using a standard procedure for calculation of fatigue life with a semi-elliptical surface crack assumption was performed; from which parameters of the Paris law for fatigue fracture were obtained. Comparing the results with previous works it is found that they capture the trend of the PVDF material behavior for high temperature.

A theoretical and experimental study is presented into the thermal decomposition, softening and failure of polymer matrix laminates under combined compressive loading and one-sided heating to high temperature. A thermo-mechanical model is presented for predicting the time-to-failure of laminates supporting a static compressive stress during one-sided heating. The thermal component of the model predicts the mass loss due to polymer decomposition and through-thickness temperature profile of the hot laminate. The mass loss and temperature predictions are validated against measured data, and the agreement is good. The thermal analysis is coupled to a mechanics-based model that calculates the loss in compressive strength with increasing temperature. The model can also predict the time-to-failure of the hot laminate supporting a static compressive load. The accuracy of the model is evaluated using failure times measured in fire-under-compression load tests on a woven E-glass/vinyl ester laminate. The experimental time-to-failure values decreased with increasing heat flux (temperature) and applied compressive stress, and the model can accurately predict these failure times. The paper also examines the dimensional expansion, out-of-plane distortion and failure mechanism of laminates under combined compressive loading and heating. It is envisaged that the thermo-mechanical model is a useful tool to estimate the failure time of compressively loaded composite structures exposed to high temperature or fire.

Thermo-mechanical models are presented for predicting the time-to-failure of polymer laminates loaded in tension or compression and exposed to one-sided radiant heating by fire. Time-to-failure is defined as the time duration that a polymer laminate can support an externally applied load in a fire without failing. The models predict the temperature rise and through-thickness temperature profile in a hot decomposing laminate exposed to fire. Using this thermal data, mechanics-based models based on residual strength analysis are used to calculate the time-to-failure. A preliminary evaluation of the accuracy of the models is presented using failure times measured in fire-under-load tests on a woven glass/vinyl ester laminate. The model was evaluated at temperatures between ∼250 and 800 °C by testing the laminate at heat flux levels between 10 and 75 kW/m2. It was found that the time-to-failure of the laminate decreased with increasing heat flux and increasing applied stress for both the compression and tension load conditions. The tests also revealed that the failure times were much shorter (by about one order of magnitude) when the laminate was loaded in compression. The models can predict the time-to-failure with good accuracy for both compression and tension loading for certain heat flux levels. However, because the models have only been evaluated for one type of laminate (woven glass/vinyl ester), further evaluation is necessary for other laminate systems. The paper also presents new experimental insights into the strengthening mechanisms of laminates at high temperature.

This paper describes the experimental and modelling results of a study on the vacuum consolidation of commingled thermoplastic composites. Samples of Twintex® glass/polypropylene (GFPP) fabric were melted, consolidated and cooled to room temperature by different cooling routes. The temperature field and the occurrence of a plateau in the through-thickness cooling profiles were modelled by coupling a non-isothermal crystallisation kinetics model with the energy equation, solved numerically using temperature-independent thermal properties for the resin. The model correctly predicted the onset of crystallisation and the degree of undercooling over a range of cooling rates. Predictions for the crystallisation rate, half-time, and temperature range agreed well with the literature data available.

The relationship between heat release rate and other fire reaction properties of fibre reinforced polymer composite materials is investigated. The heat release rate and fire reaction properties of thermoset matrix composites reinforced with combustible fibres (aramid, extended-chain polyethylene) or non-combustible fibres (glass, carbon) were determined over a range of heat flux levels using the oxygen consumption cone calorimeter technique. The fire reaction properties that were measured were time-to-ignition, smoke density, carbon monoxide yield, carbon dioxide yield, mass loss rate and total mass loss. It is discovered that these reaction properties (apart from ignition time) are linearly related to the heat release rate for composites containing non-combustible fibres. When the reinforcement is combustible, however, the heat release rate only appears to be related to the carbon monoxide yield, mass loss rate and (in some cases) smoke density. This study clearly shows the importance of the relationship between heat release rate with smoke density and carbon monoxide yield, the two reaction properties that influence the survival of humans in fire.

A series of tests has been conducted to investigate the effect of sea water absorption on fatigue damage accumulation in a glass fibre reinforced polyester laminate of the type widely used in the marine and offshore industries, using four-point bend flexural loading to ensure peak strain in the outer layers of the material most subject to seawater absorption. Pre-exposure was found to reduce the flexural strength and enhance damage accumulation in fatigue by stimulating matrix cracking, fibre debonding and delamination. Acoustic emission (AE) was used to characterise damage accumulation. These results were found to correlate well with independent measurements of changing bending stiffness and with microstructural observations of the damaged sections.

The thermal response of laminated glass fibre reinforced panels to severe fire conditions has been investigated by furnace fire testing and thermal modelling. Excellent fire resistance has been demonstrated for several matrix materials and the materials response has been modelled to a high degree of accuracy. The thermal resistance properties are due to a combination of low thermal conductivity, good structural integrity and significantly, the endothermic decomposition of the matrix, which slows down the heat transmission through the laminate.

This paper discusses the axisymmetric squeeze flow of concentrated transversely isotropic fibre suspensions in a power-law matrix and relates to the processing of composite materials such as sheet moulding compounds (SMCs) and glass mat thermoplastics (GMTs). A solution to the squeeze flow problem for a transversely isotropic power-law fluid is presented first, followed by a more detailed micromechanical analysis. In the first part of the paper a variational approach is applied to the interpretation of squeeze flow behaviour. This gives a simple expression for the total pressure, which enables the contributions due to extension and shear to be separated. Applying the procedure to GMT data suggests that the dissipation is predominantly extensional, except at very low plate separations. In the second part, a non-local constitutive equation is derived based on a simple drag law for hydrodynamic interactions. This is then used to model the pressure distribution when the effective length of the fibres is comparable to or determined by the dimensions of the squeeze flow plates. The model is shown to describe the observed squeeze flow stresses in both long and short fibre systems and to relate behaviour to the underlying resin flow properties.

The compression moulding flow of SMC has been investigated by squeeze flow testing between parallel circular plates at room temperature and at elevated temperatures of 30 and 70°C. A model based on a variational approach was adopted to characterise the squeeze flow of SMC. The present results indicate that dissipation in the squeeze flow of SMC at 30 and 70°C is predominantly extensional with shear dissipation only becoming significant at very small plate separations. Measurements of the pressure distribution across the plate also confirm that the flow is predominantly extensional. The presence of edge effects due to fibre length is also evident. The strong dependence of the compression moulding flow characteristics of SMC with temperature is demonstrated by changes in the flow parameters.

Summary Background Ataxia is the commonest neurological manifestation of coeliac disease. Some individuals with genetic susceptibility to the disease have serological evidence of gluten sensitivity without overt gastrointestinal symptoms or evidence of small-bowel inflammation. The sole manifestation of disease in such patients may be ataxia. We describe the clinical, radiological, and neurophysiological features of this disorder. Methods Patients with ataxia attending the neurology outpatient clinics at the Royal Hallamshire Hospital, Sheffield, UK, were screened for gluten sensitivity as shown by the titre of antibody to gliadin. Those with other causes of ataxia were excluded. We carried out clinical, neurophysiological, neuroradiological, and, in two cases, neuropathological examinations. Findings 28 patients with gluten ataxia were identified. All had gait ataxia and most had limb ataxia. Those with more severe gait ataxia had longer disease duration. No patient had tremor or other extrapyramidal features. 19 patients showed some form of peripheral neuropathy on neurophysiological examination. 16 patients had no gastrointestinal symptoms. Distal duodenal biopsy showed lymphocytic infiltration in two patients, and changes compatible with coeliac disease in 11. Six patients had evidence of cerebellar atrophy on magnetic-resonance imaging. Necropsy was done on two patients who died; there was lymphocytic infiltration of the cerebellum, damage to the posterior columns of the spinal cord, and sparse infiltration of the peripheral nerves. Interpretation Gluten sensitivity is an important cause of apparently idiopathic ataxia and may be progressive. The ataxia is a result of immunological damage to the cerebellum, to the posterior columns of the spinal cord, and to peripheral nerves. We propose the term gluten ataxia to describe this disorder.

The paper describes low-velocity impact tests on square panels made from two polymer composite sandwich constructions, namely woven glass vinyl ester skins with Coremat core and woven glass epoxy pre-preg skins with honeycomb core. The impact velocity was up to 8 m s -1 with an impact mass of up to 30 kg giving a maximum impact energy of 882 J. This maximum energy gives full perforation of the panels. The panels were 0.5 m by 0.5 m with clamped but free to pull in boundary conditions. The impactor geometry considered was a 50 mm diameter hemisphere. Results are expressed in the form of energy and failure mode plots and it is shown that the energy absorbing capabilities of the panels increase with the velocity of impact. The increase in energy absorption is attributed to an increase in the core crush stress and skin failure stress at high strain rates. Some discussion is given on the influence of the energy absorbing capabilities of constituent materials on the overall energy absorption behaviour of the panel. Suggestions have also been made for increasing panel perforation energy.

A consolidation model is applied to powder-impregnated composites. The model predicts the time evolution of the void volume fraction as a function of the applied pressure during consolidation. The applied pressure is considered to be composed of resin pressure obtained from a solution of the flow of resin along a channel formed by three parallel fibres. Micrographs support the geometrical assumptions of the model. Good correlation is achieved with experimental data produced from consolidated polyphenylene sulfide glass fibre (PPS/GF) laminates pultruded using the dry powder impregnation technique. Void measurements were taken at three points during processing and are seen to increase linearly with the final fibre volume fraction of the composite. Flexural and interlaminar shear stregth tests are used to correlate the mechanical properties with respect to the impregnation quality, in particular the void content, of the laminates.

The anisotropic flow behaviour of glass fibre/polypropylene glass mat thermoplastic (GMT) has been investigated using axisymmetric squeeze flow testing between parallel circular plates. The material has a continuous swirled fibre mat construction and is manufactured by the melt-impregnation technique. Constant plate velocity squeeze flow tests have been carried out under isothermal conditions to cover a range of strain rates. Modelling of squeeze flow behaviour has been based on two simple expressions: one assumes pure shear flow during testing, while the other assumes pure biaxial extension (plug flow). The modelling results suggest that biaxial extension dominates the isothermal squeeze flow process, with apparently negligible shear flow effects.

The static and dropped weight impact performance of polymer composite sandwich beams has been investigated in a three-point bend configuration. The skin materials examined included woven fabrics of glass, carbon and aramid fibre, as well as glass chopped strand mat. The core materials were Coremat ™ (resin-impregnated non-woven polyester) and Aeroweb ™ aluminium honeycomb. Polyester and epoxy resin matrices were used. The static failure modes of beams with various core and skin combinations are discussed. The dominant failure modes for both glass/Coremat and glass/Aerolam ™ beams involved upper skin failure in the vicinity of the penetrator. The dropped weight impact performance of the latter two types of beam, at impact speeds of up to 7.5 m s −1 , was investigated. The Coremat-cored beams showed marked rate dependence effects, with failure energies reducing to a minimum at a given drop height and then increasing again with increasing drop height. The honeycomb-cored beams showed only slight rate dependence. The dynamics of the beam tests are discussed in terms of mass spring models and times to failure in the upper skins highlighted.

An experimental and theoretical investigation was carried out into the collapse behaviour of filament wound glass fibre/epoxy cylinders under combinations of external pressure and axial loading in the third quadrant of the stress plane. Samples were tested with length-to-diameter ratios from 2·5 to 20 and diameter-to-thickness ratios in the approximate range of 20 to 40. Four ratios of hoop to axial stress were employed: ∞, 2, 1 and 0·5. The theoretical study employed a special purpose finite element program to calculate first ply failure (FPF) and buckling loads for shells of revolution made from multi-layered orthotropic materials. In all cases the experimental collapse pressure was strongly influenced by the predicted buckling failure mode. For those samples predicted to fail by buckling, agreement between the model and the experimental results was excellent. With the samples predicted to undergo FPF prior to buckling it was found that the residual strength was often sufficient to permit the buckling load to be approached.

This paper reviews the technology available for the impregnation of carbon and glass fibres with thermoplastic resins. Process models and the key material factors influencing the achievement of impregnation are outlined, then the processes by which impregnation is currently carried out are discussed. These techniques can be divided into three categories: direct melt, processes where there is intimate mingling of the solid constituents prior to melting of the resin, and operations where low resin viscosities are employed (solvent impregnation and processes involving reactive chain extension).

Darcy's law for the flow of fluids in porous media is frequently used to describe the flow of resins in beds of reinforcement. An extension is proposed, to permit the modelling of the longer range viscous forces which result from externally applied shear flows and other surface boundary conditions. This allows the decay of velocity perturbations due to tooling surface effects to be modelled. In profiles of thick section, decay of the velocity perturbation takes place exponentially over a characteristic distance equal to the square root of the Darcy permeability. The new model enables solutions to be obtained for the resin velocity profiles across the finite sections encountered in processes such as pultrusion and resin transfer moulding. However, the range of bed permeabilities and flow dimensions likely to be encountered in most real composite systems is such that the solutions obtained will, in nearly all cases, reduce to the simpler exponential decay solution. The model allows the equivalent resin film thickness at the mould interface to be calculated and could, in addition, form the basis of a new method for measuring permeability under processing conditions.

‘Long fibre’ ( lf ) injection moulding materials, which consists of parallel strands of reinforcement, well-impregnated with thermoplastic resin, enable products to be manufactured with a much higher residual fibre length than was previously possible. This paper compares the behaviour of lf nylon 66 moulding compounds with that of their short fibre ( sf ) counterparts and with that of the unfilled ( uf ) polymer. Despite their greater initial fibre length, lf materials are relatively easy to process by injection moulding, shear viscosity under moulding conditions being only a little higher than that of conventional sf thermoplastics. The extensional viscosity, which is important in injection moulding, is higher than with sf materials, but not has high as might be expected given the length of the fibres present. Fibres appear to be protected from breakage during flow because they remain locally parallel to one another, even in quite complex flow regimes. Flow appears to involve movement of domains of locally oriented fibre swirls, rather than of individual well-dispersed fibres. Clumps and bundles of oriented material even survive passage through the nozzle of a moulding machine, to appear in the core of the final product. LF injection mouldings have a layer structure, similar to that in sf mouldings, except that the central core is more disordered and much thicker.

External pressure tests on two 0·8 m diameter torispherical domed ends made from woven roving carbon fibre reinforced plastic (CFRP) pre-preg are discussed in the paper. The domes were made from 20 and 30 plies, respectively. The BOSOR 4 program was used to predict the stresses in the shells and their buckling pressures; the Tsai-Wu equation (in stress space) was adopted for the material failure criterion. In the test on the 20-ply dome, the first cracking noises occurred simultaneously with the collapse of the dome. The predicated first ply failure (FPF) pressure differed by about 10% from the experimental collapse pressure and was about two-thirds the theoretical buckling pressure of the dome (assumed to be perfect). The actual 20-ply dome had a slight flattening at its apex but, when this was incorporated into the buckling analyis, it had no effect on the theoretical buckling pressure. For the 30-ply dome, the FPF pressure again differed by about 10% from the experimental collapse pressure and was less than 60% of the theoretical buckling pressure. However, in this case, the first cracking noises were heard at a pressure which was about one-half the experimental collapse pressure. Between the two pressures, many cracking noises were heard. The test pressures at which first cracking was heard were not very different for the 20-ply and the 30-ply domes. However, the reason of the ‘first cracking’ pressure for the 30-ply being so much lower than its FPF pressure is not known at the moment. It is clear that, if CFRP domes are to be used in deep submersibles, then the ‘first cracking’ pressure for the 30-ply dome will have to be increased considerably. Changing the stacking sequence, the fabrication process or the shape of the dome might bring this about.

The dynamic shear behaviour of oriented linear polyethylene has been studied with particular reference to previous studies of the dynamic tensile modulus. First, it has been shown that the increase in the −50°C plateau shear modulus with draw ratio can be understood on a Takayanagi-type model in terms of an increase in crystal continuity. The crystal continuity is estimated from the longitudinal crystal thickness and the long period on the basis of the random crystalline bridge model. At a similar level of sophistication it is also possible to explain the cross-over in the ranking of samples of increasing draw ratio with change of temperature. The dynamic mechanical behaviour is then considered in terms of a simple extension of this Takayanagi model in which crystalline sequences which span two or more adjacent lamellae are regarded as the fibre phase in a short fibre composite. It can be shown that this model gives a satisfactory prediction of the changes in dynamic tensile modulus and loss with temperature, for a range of samples with different degrees of crystal continuity.

The model describes the contributions of extensional and shear flow to the pressure drop at convergences, such as die entries, nozzles and mould gates for reinforced melts under injection moulding conditions. Fibre and molecular orientation lead to high extensional viscosities and hence large pressure losses with reinforced polymers. The model treats the flowing melt as an anisotropic fluid with extensional and shear flow governed by independent power law relations. Use of the model with real systems is described and power law constants are given for some commercial reinforced polymers.