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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.

An automated multiaxial cyclic loading pressure testing rig was developed as an alternative to the existing short-term test procedure specified by ISO 14692 and ASTM D2992. Conventionally, 14 months are required to estimate the residual properties at the end of expected life (20–50 years). The test periods and costs associated with this long-term test are high. To resolve this, a novel rig was developed based on the ultimate elastic wall stress (UEWS) algorithm, allowing five multiaxial stress ratios to be tested. The test involved the cyclic pressurizing of the pipe with 1-min of pressure and 1-min of zero pressure. The test rig was tested under five stress ratios using glass-epoxy composite pipes with winding angles of [±45°]4, [±55°]4 and [±63°]4. The rig is capable of testing both static and cyclic pressure loading, thereby reducing the test period and related costs. The results provide a more realistic failure envelope.

Summary The structural performance of polymer composites reinforced with plant fibres when exposed to fire was experimentally evaluated and compared against an E-glass fibre laminate. Fire testing under combined one-sided radiant heating and static tensile loading revealed that flax, jute, or hemp fibre composites experience more rapid thermal softening and fail within much shorter times than the fibreglass laminate, which is indicative of vastly inferior structural performance in fire. The plant fibre composites soften and fail before the onset of thermal decomposition of the plant fibres and polymer matrix, whereas the E-glass fibres provide the composite with superior tensile properties to higher temperatures and higher applied tensile stresses. The tensile performance of the three types of plant fibre composites in fire was not identical. When exposed to the same radiant heat flux, the flax fibre composite could withstand higher tensile stresses for longer times than the hemp and jute laminates, which showed similar performance.

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 effects of Napier filler on the compressive properties of an unsaturated polyester polymer were studied at various temperatures. Polyester resins with Napier filler contents of 1, 3 and 5wt-% were prepared using three different mixing methods (hand mixing, water shaker bath and hot plate stirrer). Static uniaxial compression tests were conducted to investigate the compressive stress–strain response, failure mechanisms and damage characteristics of the neat and Napier filled polyester. The results show that the elastic modulus and compressive strength of the Napier modified polyesters were improved, without significantly reducing the failure strain, by increasing the Napier content. The samples prepared by the hot plate stirrer method yielded the highest compressive strength. The strength and Young's modulus of the Napier filled polyester decreased as the temperature increased. This result suggests that the Napier filler introduced additional mechanisms of energy absorption, improving the compressive p...

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.

Analytical models have been evaluated for chitosan nanocomposites reinforced by needle-like hydroxyapatite (HA) and globule-like polyhedral oligomeric silsesquioxane (POSS) particles. The particle elastic stress distribution was investigated for the case of high loads with the matrix deforming plastically and the particle pull-out energy during matrix crack propagation was modelled. Model predictions, over a range of reasonable interfacial shear stress values and particle aspect ratios, show contrasting behaviour between the two types of nanoreinforcement. In HA particles, the axial stress is distributed fairly uniformly, whereas, with POSS it is concentrated towards the centre of the particle. The radial stress at the HA particle surface was found to be uniformly distributed, whereas in POSS it increased non-linearly to a high (theoretically infinite) value with distance from the particle centre to the end. For particles bridging a travelling matrix crack, the model predicts that the pull-out energy dens...

This paper presents the stress–strain response and general lifetime damage modelling of glass fibre reinforced epoxy (GRE) composite pipes subjected to multi-ratios stress loadings at room temperature (RT). This particular modelling work was developed to predict the non-linear stress– strain response caused by the fatigue static and cyclic loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. Although the UEWS procedure is not a standard protocol used for qualification of GRE pipes, it appears to offer an option to existing procedures delineated in ASTM D2992. The ply properties initially expressed as a function of crack density was computed as a function of increasing stress and strain using shear lag approximation. In general lifetime damage model, the effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The predictions from both models are found to be in good agreement with the data from the multiaxial UEWS tests of i55u filament wound GRE pipes. These models thus enable for the long term performance prediction of the pipes under combined loadings.

This paper describes the acoustic emission (AE) monitoring of multiaxial ultimate elastic wall stress (UEWS) tests of filament wound glass fibre-reinforced epoxy composite pipes under hydrostatic, pure axial and pure hoop loadings at room temperature. The purpose of AE monitoring is to quantitatively identify and characterise damage inception and evolution, which leading to different failure mechanisms via an analysis of AE parameters. AE parameters such as counts and energy released were plotted against time, and changes of these AE activities were monitored. A 3D correlation plot between AE amplitude and duration against time for each loading condition was produced and analysed. The AE measurement of both hydrostatic and pure axial loading suggested that matrix cracks were initiated early in the tests and possible had progressed into delamination failure just before UEWS point was reached at 200 MPa of hoop stress and 63 MPa of axial stress, respectively. No clear damage initiation and progression was o...

One of the typical failure modes of composite repairs in oil and gas pipelines is the formation of a blister underneath the repair. Exceeding the critical pressure, and therefore the critical energy release rate ( GC) for crack propagation, will result in failure of the repair. Knowing the magnitude of the energy release rate ( G) is therefore key to understanding the interfacial debonding between a steel pipe and a composite repair. This paper describes two approaches for calculating the value of G for crack advance: (a) a purely analytical evaluation and (b) finite element analysis computation using the pressure–volume method (PVM). The design guidance by ASME and ISO standards for correct dimensioning is also presented, incorporating the most recent changes, which are derived from the work presented here.

The post-fire integrity of pultruded phenolic/glass and polyester/glass floor gratings, of the type used offshore and elsewhere, was investigated. The aim was to determine whether glass/phenolic gratings may be safely walked on, post-fire, by offshore workers and fire-fighting teams. The load to be resisted was identified as equivalent to a running person carrying a load, the combined mass being 150 kg. The maximum resulting dynamic strains were determined by strain gauges on the undersides of the individual beam elements of gratings. This enabled target values of post-fire bending resistance to be identified. Individual beam elements from the gratings were exposed to heat fluxes of 12.5, 37.5 and 100 kW/m2 using a propane burner, for periods up to 16 min, after which the residual strength was measured. Phenolic gratings showed longer ignition times, with lower flame and smoke emission, as well as greater post-fire strength compared to polyester ones. At the lowest flux, 12.5 kW/m2, all gratings remained serviceable beyond 16 min. At higher heat fluxes, the phenolic gratings retained some post-fire strength, assisted by the formation of a carbonaceous char binding the fibres. However, this was somewhat below the target level. A study of the effect of testing speed indicated that fire-exposed gratings are not especially strain-rate sensitive.

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 article presents relationships for the through-thickness elastic constants of composite laminates, needed for modelling three-dimensional stress problems. Using the individual ply elastic constants together with the in-plane laminate elastic constants (from laminate theory) results in explicit relationships for, ν13, ν23, E3, G13 and G23. The Poisson’s ratio and Young’s modulus expressions apply to all laminate types. The shear modulus relationships apply to balanced laminates, but are extendable to other laminate types. Relationships are developed here for angle-ply, cross-ply and quasi-isotropic laminates. Results are presented for glass/epoxy and carbon/epoxy laminates, above and below the resin Tg. The importance of coupling stresses and their influence on ν13, ν23 and E3 is underlined. It is shown, for instance, that equating the laminate through-thickness modulus to the individual ply value can result in a significant under-estimate.

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 article presents an experimental study of fusion-bonded polypropylene (PP) glass composite joints in the context of small craft manufacture. The objective is to investigate the manufacturing of lap joints and T-joints as a structural part of a small boat and study their properties, because a joining technique is a fundamental requirement of any boat construction technology. Results show that PP interlayers improve bond quality for both lap joints and T-joints and that woven precursor materials are preferred for T-joint manufacturing. It was also found that this technique produces higher lap shear strength values than adhesives and resistance welding, and that pull-out strength values were comparable with those of thermosetting designs, demonstrating that fusion bonding is a suitable joining technique for thermoplastic composite craft.

This paper discusses the characterization and modeling of thermoplastic and thermosetting matrix composites under load in fire. Small-scale tests were found to provide a cost-effective means of characterizing load-bearing behavior of composites in fire and a useful framework for materials development. This paper demonstrates the modeling of thermal and decomposition behavior during the test and the extension of this modeling to include mechanical response and failure behavior. The work necessitated measurement of strength and stiffness over a wide temperature range, with interesting results up to the point of resin decomposition. The approach was applied to three 12 mm thick glass reinforced systems: vinyl ester, polyester, and polypropylene. The laminates were subjected to a one-sided 50 kW·m−2 heat flux, using a propane burner. Thermal behavior was modeled using a simplified version of the Henderson equation to predict the evolution of temperature and residual resin content through the thickness. These parameters were then used, along with a material model, to predict the mechanical response in fire.

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.

Procedures for qualifying fibreglass pipes are discussed here in relation to industry needs. The ultimate elastic wall stress (UEWS) test appears to provide an efficient means of rating pressure pipe, and indeed vessels, for the case where weepage failure occurs resulting from the accumulation of matrix cracks. The principle behind the UEWS test is to identify, from the pressure–strain response, a pressure level below which damage growth is either negligible or at least sufficiently low to avoid failure within the design life. The version of the UEWS test most often used involves the application of groups of 10 one-minute pressure cycles at increasing pressure values, recording the hoop or axial strain. The onset of non-linearity in the pressure–strain relationship can be accurately determined and enables a safe long term pressure level to be identified. The UEWS test appears to provide a desirable alternative to the currently used procedure laid down in ISO 14692, which involves an expensive series of long term constant pressure tests, as described in ASTM 2992, running for a period in excess of 10 000 h. It is shown here that the UEWS test reflects the cyclic fatigue behaviour of fibreglass pipe, but further work on the relationship between cyclic and static behaviour would be desirable. It has been shown that a Miner’s law approach is effective in modelling damage due to combined static and cyclic effects, and that damage can be directly related to matrix crack growth. This approach could form the basis of a future procedure for describing lifetime behaviour of glass reinforced epoxy pipes under any required combination of static, fatigue, hydrostatic and non-hydrostatic (multiaxial) loading.

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 discusses the recycling of thermoplastic composite materials in the context of boatbuilding. Work was carried out on the recycling of an experimental thermoplastic composite rigid inflatable boat, originally built by BVT Surface Fleet and tested in service by the Royal National Lifeboat Institution. It was found that a range of useful injection moulding materials could be prepared from the hull material of the craft, demonstrating that structural thermoplastic composites are recyclable in practice as well as in principle, and confirming that they are a sustainable alternative to thermosets.

Delamination damage occurs in carbon fibre reinforced plastic (CFRP) as a result of fire exposure, followed by extensive resin decomposition and charring. The initial delaminations are detectable using portable ultrasonic equipment and appear to coincide with the onset of resin decomposition, as measured by thermogravimetric analysis (TGA). However, further work is needed to determine the exact temperature for permanent damage. The spread of delaminations through the structure correlates with a reduction in compressive strength which can be described using the 'two-layer' model. Temperature-dependent thermal properties, including anisotropic values of thermal conductivity, enabled the 3-D temperature field to be modelled using a finite element (FE) package. The high in-plane thermal conductivity of CFRP can result in indirect thermal damage in regions adjacent to the zone of fire exposure.

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 new model has been developed for the prediction of thermal profiles for fibre reinforced plastic composites exposed to high one sided heat flux. The model involves expressing the thermal diffusivity of the composite as a function of temperature. Apparent thermal diffusivity (ATD) can take into account the decomposition of the resin, which is endothermic, as well as the consequent changes in specific heat capacity and thermal conductivity of the composite. This offers the possibility of significantly simplifying computational procedures needed for modelling thermal behaviour with decomposition. Temperature profiles were measured at different depths through the thickness of a chopped strand mat/polyester composite and compared with the results obtained with the ATD model. The results were also compared with predictions of the COM_FIRE model, a previously developed heat transfer model for fibre reinforced composites in fire, based on the Henderson equation.

A thermal-mechanical model is presented for calculating the residual compressive strength of flammable sandwich composite materials in fire. The model can also estimate the time-to-failure of the laminate face skin to sandwich composites exposed to fire. The model involves a two-stage analysis: thermal modeling and mechanical modeling. The thermal component of the model predicts the temperature profile and amount of decomposition through sandwich composites exposed to one-sided heating by fire. The mechanical component of the model estimates the residual compressive strength of the sandwich composite and the onset of skin failure. The model is tested for sandwich composite materials with combustible glass/ vinyl ester skins and balsa core. Experimental fire tests are performed on the sandwich composites under combined compressive loading and one-sided heating at constant heat flux levels between 10 kW/m 2 (Tmax · 250°C) and 50 kW/m2 (·600°C). The model predicts that the time-to-failure increases with the skin thickness and decreases with an increase to the applied compressive stress or heat flux. The predictions are supported by experimental data from fire-under-load tests. It is envisaged that the model can be used to design sandwich composite materials with improved compressive load capacity in fire.

The diffusion of water in an isophthalic polyester glass reinforced composite laminate, typical of marine applications, has been studied through accelerated water uptake tests involving total immersion in seawater at 40 and 60°C. Gravimetric analysis has shown that at 40°C, a Fickean type diffusion is operative with a saturation level of 0·8% whereas at 60°C, a two stage Langmuir type diffusion is operative. The nuclear magnetic resonance technique has also been used in an attempt to image the diffused water and determine its position within the composite. This has revealed that the water concentrates on the fibre/matrix interface and the concentration there is twice that of bulk of the matrix. The diffusion process appears to be aided by 'wicking' along the fibre/matrix interface.

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.

The failure of polyester and phenolic pultrusions under tensile and compressive load and a one sided heat flux of 50 kW m 22 has been studied. A thermal/mechanical model, based on the Henderson equation and laminate theory, has been used to model their behaviour. In tension, significant load bearing capacity was retained over a period of 800 s, due to the residual strength of the glass fibres. However, pultruded composites are susceptible to compressive failure in fire, due to the loss of properties when the resin Tg is reached. The fire reaction properties reported here showed the phenolic pultrusions to perform better than polyesters in all fire reaction properties (time to ignition, heat release, smoke and toxic product generation). The measurements under load in fire showed that the phenolic system decayed at a slower rate than the polyester, due mainly to the very shallow glass transition of the phenolic, but also the char forming characteristic of the phenolic. The behaviour described here for phenolic pultrusions is superior to that reported for some phenolic laminates, the main reason probably being their lower water

The present paper describes a creep rupture investigation on aramid fibre yarns (Twaron 1000 and Kevlar 29) supplied by Teijin and Du Pont respectively. The ISO 9080 extrapolation procedure, which was developed for thermoplastic pipe materials, was used to model and interpret the results. The 4 parameter version of this procedure fitted the results well and gave useful predictions of the long term stress rupture behaviour, lending confidence to existing qualification procedures for the use of aramid fibre in reinforced thermoplastic pipe (RTP), and other applications involving continuous high tensile loads. Creep strain measurements on yarns showed a near constant degree of creep deformation per decade. Although they may involve some of the same mechanisms the creep and stress rupture processes appear to operate independently and on different time scales. It was found that creep deformation in aramid yarns is unlikely to be a significant problem at stress levels corresponding to a 20 year lifetime.

The Cole–Cole (C–C) and Havriliak–Negami models respectively, have been identified as suitable for the parametric modelling of time and temperature behaviour of composites with symmetrical and asymmetrical retardation time spectra. For C–C a shortcut method is proposed to enable the prediction of creep behaviour from dynamic mechanical and thermal analysis (DMTA) data. The C–C plot provides a method of characterising the retardation time distribution, independently of any time–temperature equivalence relationship. The isophthalic polyester resin and composites examined in the present study all showed symmetrical retardation time spectra (in log time) and their DMTA behaviour was well modelled using C–C, with the added assumption of Arrhenius relaxation kinetics. The proposed creep model also worked well for these materials.

This paper presents a model for the stiffness terms of composite sandwich panels with structured cores (referred to as ‘z-core’ panels). Truss-cores, corrugated-cores and double-corrugated cores containing a polymeric foam were considered. The model was validated, both through finite element simulation and through comparison with the results of experimental three point bend tests on panels. A parametric study was performed to assess the performance of the different reinforced panel configurations.

A thermal-mechanical model is presented to calculate the tensile strength and time-to-failure of glass fiber reinforced polymer composites in fire. The model considers the main thermal processes and softening (mechanical) processes of fiberglass composites in fire that ensure an accurate calculation of tensile strength and failure time. The thermal component of the model considers the effects of heat conduction, matrix decomposition and volatile out-gassing on the temperature—time response of composites. The mechanical component of the model considers the tensile softening of the polymer matrix and glass fibers in fire, with softening of the fibers analyzed as a function of temperature and heating time. The model can calculate the tensile strength of a hot, decomposing composite exposed to fire up to the onset of flaming combustion. The thermal-mechanical model is confined to hot, smoldering fiberglass composites prior to ignition. Experimental fire tests are performed on dry fiberglass fabric and fiberglass/vinyl ester composite specimens to validate the model. It is shown that the model gives an approximate estimate of the tensile strength and time-to-failure of the materials when exposed to one-sided heating at a constant heat flux. It is envisaged the model can be used to calculate the tensile softening and time-to-failure of glass—polymer composite structures exposed to 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.

An experimental and modeling study is conducted on the vacuum consolidation of commingled glass/thermoplastic composites as part of a larger project on manufacturing large monolithic structures from these precursors. Two polyethylene terephthalate (PET) matrices are employed: semicrystalline PET and an amorphous PET copolymer. Samples of commingled fabric are processed into consolidated composites by means of both a convective oven, as will be used in practice, and a small-scale experimental characterization rig, designed to measure consolidation accurately. The samples are then cooled to room temperature. In this article, the thermal and consolidation characterization of these fabrics is reported. Thermally induced consolidation is observed to occur in two stages: a low temperature solid state de-bulking near to Tg, followed by full melt impregnation at a higher temperature. Both stages are modeled separately using an empirical model based on the Kamal equation. The measured consolidation versus time profiles suggest a rapid impregnation and wetting of the fibers, occurring near to the melting point of the semicrystalline polymer. The PET melting endotherm and crystallization exotherm have little effect on the observed thermal profiles, suggesting that these effects can possibly be neglected when modeling the process.

The present study discusses the possibilities offered by ramp pressure loading tests to generate data for determining the long term load-bearing characteristics of plastic pipe systems. In addition to ramp pressure loading, procedures are also considered where the pressure is held at a constant value for a period of time, after which the product is subjected to a ramped pressure burst test. The method discussed relies on the material in question obeying Miner's Law in its static fatigue behaviour. The pipe system to which the procedure has been applied is Reinforced Thermoplastic Pipe (RTP), in which the reinforcement is aramid fibre. However, the results are expected to apply to any polymeric system where there is evidence of conformity to Miner's Law. A set of ramp loading tests, and constant pressure plus burst tests are reported and compared with the results of conventional 'constant pressure' stress rupture tests and a method is proposed for converting these results into 'equivalent' constant pressure values. The results obtained on RTP using this new approach lie close to those generated using constant pressure.

The present study describes the results of a pilot study to carry out the initial development and testing of a new class of high-pressure all thermoplastic pipe, using recycled PET as reinforcement. A prototype pipe design has been manufactured and initial qualification testing carried out demonstrating a new high added value product application for recycled materials.

Laminate analysis is used to model a loaded composite plate under one-sided heat flux. The input to the laminate analysis comes from a thermal/ablative model, which predicts the temperature evolution through the thickness. It also gives the profile of residual resin content, which reflects the extent of thermal damage. Relationships are proposed to enable the computation of the elastic constants and other mechanical properties as functions of temperature and resin content. The model was applied to a 12 mm thick woven glass/polyester laminate exposed to a heat flux of 75 kW m 2. The laminate A, B, and D matrices were modeled, along with the variation of failure loads in compression and tension. The predictions agreed well with experimental values for compression of a constrained plate. Both the local buckling load, which is proportional to √D1 D2, and the compressive failure load fall rapidly on exposure to heat flux. The bending/tensile coupling matrix, B, which is zero initially, becomes finite due to the asymmetric thermal profile, then declines as the thermal front progresses. For tensile loading, the residual properties after fire were accurately modeled, but the fall in tensile failure load was somewhat over-predicted.

This paper reports on changes to the mechanical properties of woven glass laminates with polyester, vinyl ester and phenolic resins during fire exposure. Two sets of experiments were carried out. First, unstressed laminates were exposed to a constant one-sided heat flux (50 kW m 2) for various times, and the residual post-fire strength at room temperature was reported. In a second series of experiments, laminates were tested under load. The times corresponding to a given loss of properties were 2-3 times shorter than in the previous case. It was found in both cases that modes of loading involving compressive stress were more adversely affected by fire exposure than those involving tension. A simple ‘two-layer’ model is proposed, in which the laminate is assumed to comprise (i) an unaffected layer with virgin properties and (ii) a heat-affected layer with zero properties. For residual properties after fire, the ‘effective’ thickness of undamaged laminate was calculated using this model and compared with measured values. A thermal model was employed to predict the temperature and the residual resin profile through the laminate versus time. Comparing the model predictions with the measured values of effective laminate thickness enabled simple criteria to be developed for determining the position of the ‘boundary’ between heat-affected and undamaged material. For post-fire integrity of unloaded laminates, this boundary corresponds to a Residual Resin Content (RRC) of 80%, a criterion that applies to all the resin types tested. For polyester laminate under load in fire, the boundary in compressive loading (buckling failure) appears to correspond to the point where the resin reaches 170 C. In tensile loading, significant strength is retained, because of the residual strength of the glass reinforcement. The model was used to produce predictions for ‘generic’ composite laminates in fire.