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The effect of water absorption on the fire structural resistance of a sandwich composite is investigated. A sandwich material consisting of E-glass/vinyl ester laminate skins and balsa wood core was environmentally aged in hot (70 °C) and humid (85% relative humidity) conditions for an increasing period up to and exceeding the saturation time. The face skins displayed Fickian diffusion behaviour in the absorption of water whereas the core exhibited significant mass loss due to water causing hydrolysis of bioorganic compounds in the wood. Water absorption decreased the fire structural resistance of the sandwich composite under tensile loading. The saturated sandwich composite exposed to fire failed at lower tensile stresses and within shorter times compared to the dry composite. The reduction in fire resistance was primarily due to moisture-induced weakening of the laminate skins. The reduction to the fire structural resistance caused by water absorption was predicted using a thermal–mechanical model.

An experimental and numerical study into the intrinsic scatter in the fire structural resistance of aluminium plate supporting tension loads is presented. Small-scale simulated fire structural tests performed on two aluminium alloys (AA5083 and AA6061) show for the first time a large amount of scatter in the tensile deformation rate and rupture stress. Multiple simulated fire tests conducted under identical heat flux exposure and tensile load conditions reveal scatter in the softening behaviour of the two aluminium alloys; there is large variability in the deformation rate, rupture stress and time-to-rupture, particularly at low stresses when creep dominates the softening process. Finite element analysis (incorporating elastic, plastic and creep softening effects) and elevated temperature material testing reveals that the scatter is caused mainly by variability in creep properties such as creep activation energy. A probability density function is used to quantify the scatter in the creep activation energy, and the finite element model using Monte Carlo simulations computes the scatter in the fire structural resistance of aluminium, which is not possible with existing deterministic models.

A thermal–mechanical model for calculating the residual stiffness and strength of fire-exposed sandwich composite structures is presented. The model computes the unsteady-state heat flow and decomposition of a sandwich composite exposed to one-sided radiant heating representative of a fire scenario. The model also computes the residual tension and compression properties of a fire-exposed sandwich composite at room temperature. The accuracy of the model is assessed using post-fire stiffness and failure stress property data for a sandwich composite beam consisting of face skins of E-glass/vinyl ester laminate and a core of balsa wood. Experimental testing reveals that the residual tension and compression properties of the sandwich composite decrease rapidly due mainly to thermal decomposition to the fire-exposed skin. It is demonstrated that the model can accurately predict the residual stiffness and strength properties of fire-exposed sandwich composites. The model reveals that the post-fire tension properties are controlled by char damage to the entire sandwich composite whereas the post-fire compression properties are only dependent on charring to the front skin, resulting in a more rapid loss in stiffness and strength than the tension properties.

A thermal–mechanical model is presented for calculating softening and failure of flammable sandwich composites under combined tension loading and one-sided unsteady-state heating by fire. The thermal model calculates the temperature rise of the sandwich composite when exposed to fire. The mechanical model computes the reduction to the tensile modulus and strength of the laminate face skins caused by thermal softening of the fibre reinforcement and polymer matrix and weakening of the core. The numerical accuracy of the model was assessed using data obtained from fire structural tests performed on a combustible sandwich composite consisting of thin woven glass–vinyl ester laminate skins and a thick core of balsa wood. Tests were performed at different tension stress levels and heat fluxes. The model can determine the temperature rise, tensile failure stress and failure mechanism of the sandwich composite in fire. The experimental results presented in the paper also provide new insights into the structural survivability of tension-loaded sandwich composites in fire.

This paper presents an experimental study into the use of z-pins to improve the compression fatigue properties of quasi-isotropic carbon fibre-epoxy composite containing barely visible impact damage (BVID). The study investigates the effect of increasing volume content of z-pins (up to 4%) on the barely visible impact damage resistance, post-impact compression fatigue properties, and fatigue damage mechanisms of a quasi-isotropic carbon-epoxy material. The study reveals new insights into the impact damage resistance of z-pinned composites. Z-pins induce different responses in the compression fatigue properties of the quasi-isotropic composite following low or high-energy impact loading. Z-pins proved ineffective at increasing the fatigue properties when the quasi-isotropic composite contained low-energy BVID. However, z-pins were effective at improving the fatigue performance of the composite with high-energy BVID, with the post-impact fatigue life and fatigue endurance limit increasing with the pin content. The improvement in fatigue performance is due solely to the increased resistance against high-energy impact damage imposed by the z-pins. It is also found that z-pins do not affect the fatigue mechanism or fatigue damage growth rate of the composite containing BVID.

This chapter discusses the cyclic stress fatigue behaviour of textile polymer composites with three-dimensional (3D) fibre architectures. The fatigue properties of 3D woven, stitched, tufted, z-anchored and z-pinned composites are discussed, and compared to 2D textile laminates. The chapter discusses the in-plane fatigue properties, delamination fatigue properties and fatigue strengthening mechanisms of 3D textile composites. Also discussed is the fatigue response of 3D textile joints. Gaps in the understanding of the fatigue response of 3D textile composite materials and structures are discussed.

The structural response of welded aluminium in fire is computationally and experimentally analysed. A finite element (FE) model is developed to compute the deformation and failure of gas metal arc welded (GMAW) aluminium plate under combined loading and one-sided unsteady-state heating representative of fire. The FE model predicts the deformation of the weld, heat-affected zone and parent plate based on the combined effects of elastic softening, plastic softening and creep. The effects of residual stresses in the weld and thermal expansion on the deformation response are also analysed. The numerical accuracy of the model is rigorously evaluated using a large amount of deformation and failure stress data obtained from fire structural tests performed with welded AA5083-AA5083, AA5083-AA6061 and AA6061-AA6061 plates. Good agreement is found between results computed with the FE model and experimental testing. The results reveal that GMAW welds do not reduce the structural performance of aluminium in fire unless the maximum temperature remains below the recrystallisation temperature.

This paper examines changes to the abrasive wear resistance of aluminium-based composites when heat-treated to different ageing conditions. The composites studied were the age-hardenable aluminium alloys 2014 Al or 6061 Al reinforced with 3 μm or 20 μm SiC particles. The materials were aged at temperatures between 50°C and 250°C, and changes to the wear resistance were measured using a pin-on-drum machine. When aged at the lowest temperatures (between ≈50–150°C), transmission electron microscopy revealed the presence of the solute clusters (e.g. GP zones) and small coherent precipitates in the aluminium alloy matrices, and these were easily sheared by mobile dislocations. Consequently, the hardness and abrasive wear resistance of these under-aged composites were measured to be relatively low. Raising the ageing temperature to ≈200°C increased the hardness and abrasion resistance of the composites to the peak-aged condition, and this was associated with the precipitation of small intermetallic compounds which were incoherent with the crystal structures of the aluminium alloy matrices. At 250°C the composites were over-aged, and this resulted in a reduction in hardness and wear resistance due to the coarsening of the intermetallic precipitates. The composites containing 20 μm SiC particles were slightly more wear resistant than those containing 3 μm SiC.

An overview is presented into polymer matrix composites with three-dimensional fibre reinforcement. The applications, manufacturing processes, microstructure, mechanical and other properties of 3D fibre composites are reviewed. The materials examined are composites with three-dimensional woven, stitched, braided, z-pinned, tufted or z-anchored fibre reinforcements. Progress in the modelling and experimental characterisation of the material properties of 30 fibre composites is described, including delamination toughness, impact damage tolerance, in-plane mechanical properties, and joint properties. Progress in the characterisation of other properties, including thermal conductivity, electrical resistivity and environmental durability, is also examined.

Metal matrix composites (MMC) are attractive candidate materials for structural applications where high strength and stiffness combined with low weight are required, such as in some load-bearing components in automobiles, aircraft and maritime structures. As the number of possible applications for MMCs increases it is important that their mechanical properties are thoroughly understood. Many studies have been devoted to examining the mechanical properties of MMCs, including their tensile and compressive strength, creep and fatigue resistance, impact toughness and hardness. It is only recently, however, that the Bauschinger effect in composites has been examined, and there are many features of the effect that are not completely understood.

The Bauschinger effect in SiC/Al composites has been attributed to a number of possible mechanisms. Numerous studies have suggested that relatively high residual tensile stresses in the aluminum matrix are the principal cause of the Bauschinger effect. These stresses are produced by the large difference in the coefficients of thermal expansion between the SiC and Al phases. Arsenault and Taya measured stresses as high as 408 MPa in the aluminium phase of a SiC whisker (5% volume fraction)/6061 Al composite using x-ray diffraction techniques, while Withers et al. measured strains of about 7 [times] 10[sup [minus]4] in a similar composite using neutron diffraction. Due to the presence of tensile stresses in the matrix, Arsenault et al. and Taya et al. suggest that the Bauschinger effect arises because the flow stress of the composite is reduced when pre-straining is performed in tension and is raised when performed in compression. They also believe that other mechanisms such as differences in the dislocation configurations that may form as a result of pre-straining in tension or compression are not likely to contribute significantly to the Bauschinger effect. However, Withers et al. and Warner et al. suggest that relaxation processes such as diffusion and plasticmore » flow in the aluminium matrix may contribute to the Bauschinger effect. This paper describes the results of a preliminary study of the Bauschinger effect in particulate Al[sub 2]O[sub 3]/Al composites, and compares their behavior to some SiC/Al composites.« less

The abrasive wear of carburized and uncarburized low-alloy steels has been studied under conditions of combined rolling and sliding motion against a range of composite counterfaces containing a high proportion of silica particles in an epoxy resin binder. The system simulates some aspects of abrasion by natural rocks. The wear rates of the steels depended strongly on the compressive strengths of the composites: increasing the strength of the composite reduced the wear rate of the steel. The extent of sliding motion had little effect on the wear rates per unit sliding distance. The wear rates of the composites also varied widely, and depended not only on their bulk strength butr also on the porosity level and filler/matrix bond strength. Removal of material from the composite counterface, leading to the exposure of fresh abrasive particles, occurred more readily for the weaker composites and led to the higher wear rate of the steel. On the stronger composites an accumulation of metallic debris contributed to reduced wear rate in the steel. The mechanisms and rates of degradation of the composites were very important in determining the abrasive wear rates of the steel specimens.

Composites containing a high proportion of hard inert filler particles in a cold-curing polymer resin are relatively inexpensive materials, easily cast to shape and with mechanical strength and durability suitable for use as flooring and grouting compounds. They are also used.in the mineral-handling and mining industries as abrasion-resistant materials, to line plant handling or processing rocks, coal or ores, either dry or in slurry form [1]. Materials of this type are also useful to simulate some of the properties of natural sedimentary rocks, such as sandstones and limestones, for experimental purposes. For example, in studying the abrasive wear of steels against natural sandstone and limestone [2] it is not possible to obtain reproducible samples of rock with independently varied values of interparticle bond strength, porosity and binder strength. Silica-filled epoxy resins, however, can be made which behave in many respects like sandstones, with similar contents of silica particles, values of compressive strength and with the potential for controlled variation of their microstructure and properties. Previous work has shown that the addition of hard filler particles to an epoxide resin generally leads to increased elastic modulus and compressive strength, although the tensile strength may be reduced [3]. Compressive strength is a particularly important property for some applications, including the simulation of abrasive natural rocks, but only limited information is available about the effect on the compressive strength of composites with high proportions of particulate filler of the properties of the matrix material itself, the porosity of the composite or the strength of the bonding between the filler particles and the matrix. A systematic investigation was therefore made of the effects of these variables on the uniaxial compressive strengths of composites containing a constant high volume fraction (72%) of silica sand particles in an epoxy resin matrix.

The effect of z-pinning on the tensile strength, fatigue life and failure mechanisms of single lap joints is experimentally investigated. Under tensile loading, the tensile load to initiate delamination cracking in the adhesive bond-line to a lap joint can be reduced slightly by z-pinning, however the ultimate failure strength and elongation limit are improved by z-pins bridging the bond-line. Z-pinning is also highly effective in extending the tensile fatigue life of lap joints by the crack bridging mechanism. Transitions in the failure mechanisms were observed from joint debonding in the absence of pins to pull-out and/or shear failure of pins or tensile failure of the laminate, depending on the volume content and diameter of the z-pins. It is shown that under certain z-pinning conditions, bond-line delamination of the joint can be suppressed and the failure mechanism is changed to rupture of the composite laminate.

The influence of stitches on the deformation properties and mechanisms of triaxial non-crimp fabrics during dome forming is experimentally investigated. The dome forming properties are improved by minimising the line-tension on the stitches because this lowers the resistance against tow sliding, which is identified as an important deformation mechanism. Lowering the stitch tension also reduces the forming loads and amount of tow crimp damage to the fabric. Stitch location also affects the amount of tow crimping. Stitches located to the sides, rather than through, the tows provide less resistance to tow sliding and thereby cause less fabric damage. The number of stitches in the fabric was found not to affect the forming properties.

This article provides information on the potential applications of fiber-reinforced polymer (FRP) composites for maritime craft and offshore drilling platforms. The key benefits gained from using FRP materials together with an examination of the drawbacks and major issues impeding the more widespread use of composites in marine structures are presented.

The effect of thermal damage on the mechanical properties of glass-reinforced polyester (GRP) composites is investigated. GRP panels underwent surface heating to high temperature (750-800° C) in a cone calorimeter to create localised regions of thermal damage having a circular, oval, square, diamond or irregular shape. The size of the heat-affected region ranged from 10% to 100% of the panel width. The heat damage consisted mostly of char from combustion of the polyester matrix and delamination cracks. After heating in the cone calorimeter, the GRP was cooled to room temperature and then the residual tension and compression properties were determined. Increasing the size and depth of the fire damage zone caused reductions to the stiffness and strength of the GRP. It was found that the shape of the heat-damaged region did not affect the mechanical properties. A model is presented for accurately determining the tension and compression properties of composites with localised heat damage of any shape.

In many mining operations ( e.g. excavation, drilling, tunnelling, rock crushing), metallic components are forced against abrasive rocks in a complex motion. This study examines the relative importance of combined rolling and sliding motion in the two-body abrasive wear of a low carbon tempered martensitic steel against rock counterfaces. A novel wear test rig has been used to vary the amount of rolling and sliding motion between a rotating steel cylinder and a counter-rotating sandstone (highly abrasive) or limestone (much less abrasive) disc. Weight loss measurements reveal that the wear rate of the steel increases as the amount of motion against the rock counterface is reduced from pure sliding to about 50% sliding (and about 50% rolling). With further reductions in the amount of sliding motion, the wear rate of the steel is reduced because of the formation of corrugations on the sandstone and limestone rock surfaces. Scanning electron microscopy shows that when the amount of motion is reduced from pure sliding to about 50% sliding, the topographical and subsurface physical properties of the worn steel and rock surfaces are modified. Following large amounts of sliding motion (70–80% sliding), the worn steel surface is heavily deformed by shearing in the sliding direction and many of the minerals in the worn rock counterface are crushed and compacted. Reducing the motion to 50% sliding leads to a reduction in the depth of the plastically sheared layer in the worn steel, and the rock surface shows a considerable reduction in the amount of mineral crushing and compaction, with many of the abrasive grains maintaining some angularity. It is concluded, therefore, that the increasing wear rate of the steel with the amount of rolling motion, until the onset of rock surface corrugations, probably results from the rock counterface retaining a higher proportion of angular abrasive minerals.

Rutherford backscattering, ion channeling and optical absorption techniques have been used to study the lattice damage and impurity distributions in sapphire implanted with He+, Zn+, In+ and Pb+ ions at room temperature. Implantation at low damage densities is found to result in the formation of point defects and point defect clusters. Increasing the ion dose and mass can result in the formation of more complex defects, until eventually the lattice becomes amorphous at a critical damage density. Optical absorption techniques appear to be quite sensitive to the presence of a thin amorphous layer in sapphire, and can be usefully employed for qualitative measurements of such layers. Both the removal of implantation induced damage and substantial impurity loss (by diffusion to the Al2O3 surface) were observed on annealing, in an argon atmosphere, of Zn +, In+ and Pb+ implanted sapphire. The retained concentration of these implanted metals appears to be independent of both the implanted dose and phase diagram considerations.