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Lists research papers in the volumes 39 and 40 of the "Journal of Materials Science". "Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials," by A. Baldan; "Thermo-mechanical fatigue of shape memory alloys," by E. Hornbogen; "Role of entropy of fusion in phase transformation and self-diffusion," by G.P. Tiwari, J.M. Juneja and Y. Illjima.

In this paper, an accurate formula for calculating the thermal residual stress field in a particle-reinforced composite are presented. Numerical examples are given to show r-variations of the thermal residual stresses. The increase in fracture toughness of matrix predicted by the thermal residual stress field is compared well with the experimentally measured increase. [ABSTRACT FROM AUTHOR]

In this paper, the mixed-mode interlaminar fracture behaviour of woven carbon-epoxy composite was investigated based on experimental and numerical analyses. A modified version of Arcan specimen was employed to conduct a mixed mode fracture test using a special loading device. A full range of mixed-mode loading conditions including pure mode-I and pure mode-II loading were created and tested. This test method has a simple procedure, clamping/unclamping the specimens are easy to achieve and only one type of specimen is required to generate all loading conditions. Also, finite element analysis was carried out for different loading conditions in order to determine correction factors needed for fracture toughness calculations. Interlaminar fracture toughness was determined experimentally with the modified version of the Arcan specimen under different mixed-mode loading conditions. Results indicated that the interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading condition. Response of woven carbon-epoxy composite was also investigated through several criteria and the best criterion was selected. The interlaminar fracture surfaces of the carbon-epoxy composite under different mixed-mode loading conditions are examined by scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

The notched Izod impact properties of polypropylene (PP) filled with hollow glass beads (HGB) have been measured at room temperature to identify the effects of the particle contents, size and its distribution on them in the present paper. The mean diameters of the particles were 11, 35, and 70 μm, and named TK10, TK35 and TK70 respectively. The surface of the particles was pretreated with silane coupling agent. The results showed that the notched Izod impact strength ( σ I) of the filled systems increased gently with increasing the volume fraction ( φ f) of the fillers when φ f was less than 15%, and then it decreased. When φ f was 10%, σ I decreased with an increase of the mean diameter of the particles. Furthermore, the impact fracture surface of the specimens was observed by using a scanning electron microscope (SEM). The improvement of the impact toughness of the composites might be mainly attributed to the shear yielding first of the matrix around the beads to absorb relevant deformation energy under impact load. [ABSTRACT FROM AUTHOR]

Composite materials demonstrate a considerable extent of heterogeneity. A non-uniform spatial distribution of reinforcement results in variations of local properties of fibrous laminates. This non-uniformity not only affects effective properties of composite materials but is also a crucial factor in initiation and development of damage and fracture processes that are also spatially non-uniform. Such randomness in microstructure and in failure evolution is responsible for non-uniform distributions of stresses in composite specimens even under externally uniform loading, resulting, for instance, in a random distribution of matrix cracks in cross-ply laminates. The paper deals with statistical features of a distribution of carbon fibres in a transversal cross-sectional area in a unidirectional composite with epoxy matrix, based on various approaches used to quantify its microscopic randomness. A random character of the fibres’ distribution results in fluctuations of local elastic moduli in composites, the bounds of which depend on the characteristic length scale. A lattice model to study damage and fracture evolution in laminates, linking randomness of microstructure with macroscopic properties, is discussed. An example of simulations of matrix cracking in a carbon fibre/epoxy cross-ply laminate is given. [ABSTRACT FROM AUTHOR]

The fracture process of composite laminates subjected to static or fatigue tensile loading involves sequential accumulation of intra- and interlaminar damage, in the form of transverse cracking, splitting and delamination, prior to catastrophic failure. Matrix cracking parallel to the fibres in the off-axis plies is the first damage mode observed. Since a damaged lamina within the laminate retains certain amount of its load-carrying capacity, it is important to predict accurately the stiffness properties of the laminate as a function of damage as well as progression of damage with the strain state. In this paper, theoretical modelling of matrix cracking in the off-axis plies of unbalanced symmetric composite laminates subjected to in-plane tensile loading is presented and discussed. A 2-D shear-lag analysis is used to determine ply stresses in a representative segment and the equivalent laminate concept is applied to derive expressions for Mode I, Mode II and the total strain energy release rate associated with off-axis ply cracking. Dependence of the degraded stiffness properties and strain energy release rates on the crack density and ply orientation angle is examined for glass/epoxy laminates. Suitability of a mixed mode fracture criterion to predict the cracking onset strain is also discussed. [ABSTRACT FROM AUTHOR]

This paper studies the influence of Ni3AI intermetallic particles on the fracture behaviour of aluminium matrix (2014) composite materials. Intermetallics were obtained by mechanical alloying and by atomisation. The composite materials were manufactured by mixing, uniaxial compacting of a preform, and subsequent extrusion without canning or degassing. The study considered materials in extruded state and after T6 heat treatment. Assessments were made from the viewpoint of microstructure (by means of optical and scanning electron microscopy), and studying the reactions between the matrix and the reinforcement. These reactions produce a highly copper-enriched interphase. The influence of the reinforcement and state of the alloy on the fracture behaviour of the composite materials was studied through scanning electron microscopy. [ABSTRACT FROM AUTHOR]

The newly derived relationship between the closure traction and the crack opening displacement by the modified shear-lag model is used to investigate the tensile failure behaviors of unidirectional fiber reinforced ceramics. The critical stress for matrix cracking and the critical stress to fracture the fiber are calculated for various crack configurations. Then, the failure of composite initiates as the applied stress exceeds the smaller of the matrix cracking stress and the fiber fracture stress. The differences of results between the present analysis and Marshall and Cox are discussed. Finally, the possible tensile failure modes and the transition conditions between different failure modes are summarized in this paper. [ABSTRACT FROM AUTHOR]

Niobium particle reinforced aluminum oxide (Al2O3) dispersion strengthened copper composite is an attractive and emerging engineered material for applications requiring high strength, high thermal and electrical conductivities and resistance to softening at elevated temperatures. In this paper, the microstructure, tensile deformation and fracture behavior of the composite is examined. The strength of the material decreases with an increase in temperature with a concomitant improvement in ductility. The composite microstructure maintains a high value of yield strength/ultimate tensile strength ratio. The factors contributing to increased strength and the intrinsic mechanisms governing fracture characteristics of the composite are examined in light of intrinsic microstructural effects, nature of loading and deformation characteristics of the matrix. [ABSTRACT FROM AUTHOR]

We developed a facile and low-cost approach to prepare lightweight and high-strength magnesium-matrix composites with a nacre-inspired laminated structure. First, lamellar Mg2B2O5 whisker (Mg2B2O5w) scaffolds with initial solid loadings of 10, 15 and 20 vol% were prepared by ice templating. The wettability between a molten AZ91D alloy and the Mg2B2O5w scaffold was greatly improved by the incorporation of nano-SiO2 sol in the aqueous slurry, making the preparation of nacre-mimetic AZ91D/Mg2B2O5w composite by way of pressureless infiltration feasible. The SiO2 content in the Mg2B2O5w scaffold has a significant effect on the processing and the microstructure and properties of the composites. The optimum SiO2 content was about 6-8 wt% of the total ceramic loading. A lower SiO2 content resulted in incomplete infiltration, while a higher content led to the formation of a large quantity of Mg2Si in the composite. The flexural strength of the composites seemed independent of the initial ceramic loading (10-20 vol%), whereas the compressive strength and elastic modulus increased considerably and the crack-growth fracture toughness decreased with increasing ceramic content. The mechanism for such variations was addressed. [ABSTRACT FROM AUTHOR]

SPS-processed alumina and reaction-bonded boron carbide ceramic composite (RBBC) were joined with Al10SiMg alloy by spark plasma sintering and tested in a series of planar impact experiments designed to measure dynamic tensile (spall) strength of the joints. The results of the impact testing, together with postmortem inspection of the fractured samples, confirmed the applicability of this approach for testing joint strength. The measurements show that in the case of an RBBC/metal joint, the dynamic tensile strength of the joint exceeds that of the ceramic part, and that fracture of the shock-loaded ceramic-metal pair occurred in the ceramic portion. The dynamic tensile strength of the interface between alumina and Al10SiMg alloy virtually coincides with that of the metal part, with the fracture occurring exactly at the interface. The coincidence may be explained based on the recently published results of atomistic calculations of the structure of an alumina-aluminum interface. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced plastic composites (GFRPs) are often suffered to impact loadings; it is essential to improve its damage-resistant properties and understand the energy absorption mechanisms. In this work, the low-velocity impact behaviors of GFRPs were investigated in consideration of epoxy resins modified with 0, 0.4, and 0.75 % multi-walled carbon nanotubes (MWCNTs) by weight content and pre-stretched fabric at 0, 1.27, and 2.47 kg weight. In comparison with pure GFRPs sample, MWCNT-modified specimens are effective in improving the impact resistance under impact energies at 9, 16, and 22 J in terms of reduced damage factor and enhanced perforation threshold. Microscopic fractographic analysis indicated that the incorporation of MWCNTs in epoxy matrix offered additional mechanisms through breakage, bridging, and pull-out of carbon nanotubes to favor load transfer effect, prevent crack propagation, and thus dissipate more energy. The dynamic thermo-mechanical analysis proved that MWCNTs improved the storage modulus and glass transition temperature of the composites. In addition, the pre-stretched GFRP composites showed more impact resistant than the non-stretched ones through instant load transfer effect. [ABSTRACT FROM AUTHOR]

Non-stoichiometric curing effects on the fracture toughness behaviors of nanosilica particulate-reinforced epoxy composites were experimentally investigated in this study by comparing them with bending strengths to take into consideration the effect of interaction between nanoparticles and network structures in matrix resins. The matrixes were prepared by curing them with an excess mixture of diglycidyl ether of bisphenol A-type epoxy resin as the curing agent for the stoichiometric condition. The volume fractions of the silica particles with a median diameter of 240 nm were constantly 0.2 for all composites. The neat epoxy resins and the composites were cured non-stoichiometrically to change the crosslinking densities of the neat epoxy resins and the matrix resins of the composites within 2740-490 mol/m. The fracture toughnesses and bending strengths of the composites and the neat epoxy resins strongly depended on the crosslinking densities in the resins. Although the fracture toughness decreased monotonously from that of the stoichiometrically cured resins as the crosslinking density decreased, the fracture toughnesses of composites were largest at a slightly lower crosslinking density of approximately 2490 mol/m from the stoichiometric condition of 2740 mol/m. The fracture toughness and the bending strength were improved for crosslinking densities higher than 2000 mol/m by adding particles. At crosslinking density lower than 2000 mol/m, the particles worked against the mechanical properties as defects in matrix resins. [ABSTRACT FROM AUTHOR]

The tensile properties and fracture behavior of polyacrylonitrile (PAN)- and pitch-based hybrid carbon fiber/polyimide composites with several types of nanoparticles (25 nm C, 20-30 nm β-SiC, 130 nm β-SiC, 80 nm SiO, and 300 nm SiO) added to the matrix were investigated. The tensile stress-strain curves of PAN- and pitch-based hybrid carbon fiber/polyimide composites with 25 nm C, 20-30 nm β-SiC, and 80 nm SiO nanoparticles have complex shapes (jagged trace), whereas the tensile response of hybrid carbon fiber/polyimide composites with 130 nm β-SiC and 300 nm SiO nanoparticles indicates an instantaneous failure. The stress after the initial failure in hybrid carbon fiber/polyimide composites improves by adding 25 nm C, 20-30 nm β-SiC, and 80 nm SiO nanoparticles to the matrix and correlates with the fracture toughness of the polyimide matrix. [ABSTRACT FROM AUTHOR]

A model has been formulated to determine the work of pull-out, U, of an elastic fibre as it shear-slides out of a plastic matrix in a fractured composite. The fibres considered in the analysis have the following shapes: uniform cylinder and ellipsoidal, paraboloidal or conical tapers. Energy transfer at the fibre–matrix interface is described by an energy density parameter which is defined as the ratio of U to the fibre surface area. The model predicts that the energy required to pull out a tapered fibre is small because the energy transfer at the fibre–matrix interface to overcome friction is small. In contrast, the pull-out energy of a uniform cylindrical fibre is large because the energy transfer is large. The pull-out energies of the paraboloidal and ellipsoidal fibres lay between those for the uniform cylindrical and the conical fibres. With the exception of the uniform cylindrical fibre which yields a constant energy density, tapered fibres yield expressions for the energy density which depend on the fibre axial ratio, q. In particular, the energy density increases as q increases but converges at large q. By defining the critical axial ratio, q0, as the limit beyond which u is independent of the fibre slenderness, our model predicts the value of q0 to be about 10. These results are applied to explain the mechanisms regulating fibre composite fracture. [ABSTRACT FROM AUTHOR]

Fiber-reinforced cement composites were produced in Brazil using blast furnace slag cement reinforced with pulped fibers of sisal originated from agricultural by-products. Thin pads were produced by slurring the raw materials in water, followed by de-watering and pressing stages. Studies of mechanical behavior included observations of stable crack growth behavior under monotonic loading (resistance-curve behavior), followed by scanning electron microscopy (SEM) analysis of the fracture surfaces. Reinforcement with cellulose fibers resulted in improved fracture toughness, even after 9 months in laboratory environment. Microscopic analysis indicated a considerable incidence of crack bridging and fiber pull-out in the composite. The shielding contributions from crack bridging are estimated using a fracture mechanics model, before comparing with the measured resistance-curve behavior. [ABSTRACT FROM AUTHOR]

A model is presented herein for predicting the evolution of numerous cracks on multiple length scales, the objective of such a model being to develop the capability to predict failure of structural components to perform their intended tasks. Such a capability would then be useful as a predictive tool for designing structural components so as not to fail, but rather to succeed in performing their intended tasks. The model developed herein is somewhat involved, being based in continuum mechanics and thermodynamics, but is nevertheless expected to be cost effective (wherever sufficient accuracy permits) when compared to more costly experimental means of determining component life. An essential ingredient within the context of the model is that cracks must develop on widely differing length scales. Where this is observed to occur in nature, which is surprisingly often, there are potential simplifications over more generally described but practically untenable approaches, that can lead to (at least partly) computational multiscale algorithms capable of assimilating failure due to multiple cracking with a high degree of accuracy. The model presented herein will be briefly described within a mathematical framework, and an example problem will be presented that is representative of certain currently relevant technologies. [ABSTRACT FROM AUTHOR]

Hybrid composite systems consisting of liquid crystalline polymer (LCP), short glass fibers and toughened nylon in varied ratios were studied. Dynamic mechanical results indicated that, elastomeric phase in toughened nylon 6,6 promoted a better compatibilization between nylon 6,6 and LCP in a hybrid system containing short glass fibers in comparison with one without glass fibers. Improved compatibility facilitated fibrillation of LCP phase in the skin region of the hybrid composite, thereby providing superior tensile strength. Without the presence of LCP, glass fiber reinforced toughened nylon 6,6 exhibited the least tensile strength. J-integral analysis and essential work of fracture (EWF) method were used to compare the fracture behavior of composites. Results showed that specific essential work of fracture were consistent with the critical J-integral. Matrices reinforced by LCP alone showed the best crack initiation and propagation toughnesses, followed by glass fiber reinforced and hybrid composites. The better compatibility between nylon 6,6 and LCP appeared to inhibit the interfacial debonding process, resulting in brittle fracture. [ABSTRACT FROM AUTHOR]

The damage process in composite laminates subjected to cryogenic cooling was monitored employing a thermo-acoustic emission (AE) technique. The thermo-AE signals processed with a short-time Fourier transform could be classified into three different types which were correlated with individual microfracture processes. In the initial stage of cryogenic cooling, very strong AE signals with low and high frequency bands were dominantly detected showing that large cracks accompanying fiber breakages were developed mainly. With an increase in the cooling time, weak emissions with low frequency bands became prevalent indicating the propagation of microfractures in the matrix and/or fiber-matrix interface. Similar types of AE signals, however, having weak amplitudes, were also observed for the cryogenically-treated specimens during thermal heating and cooling load cycles. Thus, analysis of thermo-AE behavior through the thermal load cycle led to the nondestructive evaluation for the cryogenic damage of composites. [ABSTRACT FROM AUTHOR]

Models for the strain energy release rate in crack extension and tunnelling are taken from the literature with minor modification to take account of the compressive stresses in multi-layer ceramic tubes or composites. These models are applied to predict the potential for crack development in co-extruded tubes fabricated from combinations of alumina, zirconia (fully and partially stabilized) and zirconia toughened alumina. Experimental results show that the models predict the failure in the composites closely and thus form useful tools in the design of such structures. The main aspect of the predictive capacity is in the selection of the layer numbers and the layer thicknesses to prevent failure. The significance of crack-free layers is improved mechanical properties, in particular strength, and potential improvement in fracture toughness and device performance. [ABSTRACT FROM AUTHOR]

An in situ reaction was proposed and investigated to produce Mo(Si1 − xAl x)2-SiC composites. The starting powders were MoSi2, Al and C. A direct current hot pressing (DCHP) method was used to prepare these composites. When the mixed powder was hot pressed at temperatures lower than 1500°C, the phase composition was Mo(Si,Al)2 and β-SiC. When the hot pressing temperature was higher than 1600°C, however, Nowotny phase Mo≦5Si3C≦1 appeared. The chemical stoichiometry of the proposed in situ reaction becomes difficult because of the formation of solid solution among these phases and the appearance of Mo5Si3C phase. The in situ formed SiC phase in the x = 0.3 sample was partly in whisker shape. However, the SiC phase in x = 0.15 sample was in particle shape. These in situ formed SiC particles and whiskers acted as crack deflection and bridging elements and improved the fracture toughness. The Vickers hardness and fracture toughness of the x = 0.3 sample hot pressed at 1700°C for 60 min in vacuum were 15.6 GPa and 5.39 MPa · m1/2, respectively. [ABSTRACT FROM AUTHOR]

The effect of static and cyclic loading conditions on the stress corrosion cracking of unidirectional glass reinforced polymer (GRP) rods used in composite high voltage insulator has been investigated. A series of stress corrosion experiments have been performed on unidirectional E-glass/modified polyester composite rods. The rods have been subjected to mechanical tensile static and cyclic stresses in the presence of a nitric acid solution. The stress corrosion fracture process in the rods was monitored using acoustic emission techniques. The experimental loading conditions simulated possible in-service loadis for composite suspension insulators. The results obtained in this study showed that the brittle fracture process can be generated in the rods when subjected to relatively low tensile stresses in the presence of a nitric acid solution. The morphology of the experimentally generated brittle fracture cracks in the rods closely resemble those from in-service failed composite suspension. It has also been shown in this research that low frequency, low amplitude vibrations in tensile loads can significantly accelerate the fracture process. It appears that the brittle fracture cracks in the rods generated under cyclic loads are less planar in nature in comparison with the cracks formed under static conditions. It has also been found that the acoustic emission generated during the stress corrosion fracture process in the rods is sensitive to the placement of the transducers. However, reasonably good correlation between the stress corrosion crack growth rates and acoustic emission has been attained. [ABSTRACT FROM AUTHOR]

The fatigue life behaviour and the underlying micromechanisms have been studied in two different Types of unidirectional carbon-fibre-reinforced plastics loaded in tension-tension along the fibre direction. The carbon fibres (AS4) were the same in the two composite systems. One thermoplastic matrix (polyetheretherketone, PEEK) and one thermosetting matrix (epoxy toughened with a thermoplastic additive) were used. The macroscopic fatigue behaviour was characterised by fatigue life diagrams. Surface replicas were taken intermittently during the course of the fatigue tests to monitor the active fatigue damage micromechanisms. The thermoset based composite showed a higher fatigue resistance with few microcracks initiated at distributed fibre breaks growing at a decelerating rate. The thermoplastic composite had a more pronounced fatigue degradation with a steeper fatigue life curve, which was caused by widespread propagating debonds and matrix cracks. The use of a tougher and more ductile matrix results in an inferior fatigue life performance, due to a more widely distributed accumulation of damage that propagates at a higher rate. [ABSTRACT FROM AUTHOR]

Unidirectional carbon fibre reinforced SiC composites were prepared from four types of carbon fibres, PAN-based HSCF, pitch-based HMCF, CF50 and CF70, through nine cycles or twelve cycles of impregnation of polycarbosilane and subsequent pyrolysis at 1200°C. The polycarbosilane-derived matrix was found to be β-SiC with a crystallite size of 1.95 nm. The mechanical properties of the composites were evaluated by four-point bending tests. The fracture behavior of each composite was investigated based on load-displacement curves and scanning electron microscope (SEM) observation of fracture surfaces of the specimens after tests. It was found that CF50/SiC and CF70/SiC exhibited high strength and non-brittle fracture mode with multiple matrix cracking and extensive fibre pullout, whereas HSCF/SiC and HMCF/SiC exhibited low strength and brittle fracture mode with almost no fibre pullout. The differences in the fracture modes of these carbon fibre/SiC composites were thought to be due to differences in interfacial bonding between carbon fibres and matrix. Values of flexural strengths of CF70/SiC and CF50/SiC were 967 MPa and 624 MPa, respectively, which were approximately 75% and 38% of the predicted values. The relatively lower strength of CF50/SiC, compared with CF70/SiC, was mainly attributed to the shear failure of CF50/SiC during bending tests. [ABSTRACT FROM AUTHOR]