Showing papers in "Journal of Materials Science in 1991"

Particulate reinforced metal matrix composites — a review

Abstract: The physical and mechanical properties that can be obtained with metal matrix composites (MMCs) have made them attractive candidate materials for aerospace, automotive and numerous other applications. More recently, particulate reinforced MMCs have attracted considerable attention as a result of their relatively low costs and characteristic isotropic properties. Reinforcement materials include carbides, nitrides and oxides. In an effort to optimize the structure and properties of particulate reinforced MMCs various processing techniques have evolved over the last 20 years. The processing methods utilized to manufacture particulate reinforced MMCs can be grouped depending on the temperature of the metallic matrix during processing. Accordingly, the processes can be classified into three categories: (a) liquid phase processes, (b) solid state processes, and (c) two phase (solid-liquid) processes. Regarding physical properties, strengthening in metal matrix composites has been related to dislocations of a very high density in the matrix originating from differential thermal contraction, geometrical constraints and plastic deformation during processing.

Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies

Abstract: The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.

Deformation mechanisms in negative Poisson's ratio materials : structural aspects

Abstract: Poisson's ratio in materials is governed by the following aspects of the microstructure: the presence of rotational degrees of freedom, non-affine deformation kinematics, or anisotropic structure. Several structural models are examined. The non-affine kinematics are seen to be essential for the production of negative Poisson's ratios for isotropic materials containing central force linkages of positive stiffness. Non-central forces combined with pre-load can also give rise to a negative Poisson's ratio in isotropic materials. A chiral microstructure with noncentral force interaction or non-affine deformation can also exhibit a negative Poisson's ratio. Toughness and damage resistance in these materials may be affected by the Poisson's ratio itself, as well as by generalized continuum aspects associated with the microstructure.

Statistical properties of Weibull estimators

Abstract: The Weibull parameters were estimated for data produced by Monte Carlo simulations using three different approaches: linear regression, moments method, and maximum likelihood method. The last of these was shown to be the most appropriate approach for the whole range of sample sizes of 4 to 100 for estimating the Weibull parameters of a brittle material. In each simulation 10000 estimators were produced. Using these values histograms of the estimators were created, which showed the asymmetry of the Weibull modulus distribution. The integrals of these density functions were directly used to determine confidence intervals for the estimated Weibull moduli. Furthermore it was reaffirmed that a minimum of 30 samples are required for a good characterization of the strength of a brittle material.

The fabrication of metal matrix composites by a pressureless infiltration technique

Abstract: A novel technique for fabricating metal matrix composites by the spontaneous (pressureless) infiltration of filler preforms with molten aluminium alloys is described. Numerous reinforcing materials, including Al2O3 and SiC of various configurations, such as particles, agglomerates, and fibres, have been incorporated as fillers. The effects of processing variables, such as alloy chemistry, process temperature, and filler material, on the infiltration kinetics and resultant microstructures are discussed. Comparisons with existing infiltration technology and preliminary composite properties are presented.

Exact theory of fibre fragmentation in a single-filament composite

Abstract: An exact theory is developed to describe the evolution of fibre fragmentation in a single-filament composite test as a function of the underlying fibre statistical strength and fibre/matrix interfacial shear stress, τ. The fragment distribution is a complicated function of fibre strength and τ because the stress around breaks which do occur recovers to the applied value, σ, over a length δ(σ) determined by τ. Therefore, no other breaks can occur within δ (σ) of an existing break. To account for this effect, the fibre fragment distribution is decomposed into two parts; fragments formed by breaks separated by more than δ (σ) at stress σ, and fragments smaller than δ (σ) which were formed at some prior stress σ′ < σ when a smaller δ(σ′) < δ(σ) prevailed. The distribution of fragments larger than δ (σ) is identical to that of a fibre with a unique non-statistical strength σ and is known exactly. The distribution of fragments smaller than δ(σ) can then be determined from the distribution of the longer fragments. Predictions of the theory are compared to simulations of fibre fragmentation for several common models of stress recovery around fibre breaks with excellent agreement obtained. The present theory can be utilized to thus derive both thein situ fibre strength at short gauge lengths ≃ δ and the τ from experimentally obtained fragment distributions, and an unambiguous inversion procedure is briefly discussed. The application of the theory to other multiple-cracking phenomena in composites is also discussed.

Conversion mechanisms of a polycarbosilane precursor into an SiC-based ceramic material

Abstract: The pyrolysis of a PCS precursor has been studied up to 1600 °C through the analysis of the gas phase and the characterization of the solid residue by thermogravimetric analysis, extended X-ray absorption fine structure, electron spectrocopy for chemical analysis, transmission electron microscopy, X-ray diffraction, Raman and Auger electron spectroscopy microanalyses, as well as electrical conductivity measurements. The pyrolysis mechanism involves three main steps: (1) an organometallic mineral transition (550 < T p < 800 °C) leading to an amorphous hydrogenated solid built on tetrahedral SiC, Si02 and silicon oxycarbide entities, (2) a nucleation of SiC (1000 < T p < 1200 °C) resulting in SiC nuclei (less than 3 nm in size) surrounded with aromatic carbon layers, and (3) a SiC grain-size coarsening (T p > 1400 °C) consuming the residual amorphous phases and giving rise simultaneously to a probable evolution of SiO and CO. The formation of free carbon results in a sharp insulator-quasimetal transition with a percolation effect.

Crosslink Density and Fracture Toughness of Epoxy Resins.

Abstract: A series of networks of diverse crosslink density were prepared using bifunctional epoxide prepolymers of different molecular weight, crosslinked with diamine diphenyl sulphone, and their fracture behaviour investigated. The same set of resins was also modified with a reactive rubber. The fracture toughness regularly decreased on increasing the crosslink density for all formulations. The addition of the rubber gave rise to a marked increase in toughness, though it magnified the influence of the molecular weight of the prepolymer. Tests performed with blunt notches showed that the fracture toughness was maximum at medium crosslink densities. A dispersion of rubber particles caused a toughness increase through the formation of microcavities ahead of the crack tip. Failure was preceded by a rapid volume increase caused by void coalescence.

Fracture mechanics and cavitation in rubber-like solids

Abstract: Conditions for propagation of a pressurized crack within a rubber-like solid are derived in terms of the elastic properties of rubber, the fracture energyGc and the initial radiusro of the crack. A previously proposed criterion, that the critical internal pressurePc for crack growth is given by 5E/6, whereE is the tensile (Young) modulus of elasticity, is shown to be inadequate both for small cracks, when the stiffening of rubber at high strains must be taken into account, and for large cracks, when the critical degree of inflation is so small that the assumptions leading toPc=5E/6 do not apply. However, this simple criterion is found to remain a useful guide for cracks having initial radii lying in an intermediate range, such thatroE/Gc lies between about 0.0005 and 1. For representative rubber-like solids, this corresponds to the rangero=0.5 μm to 1 mm.

Processing techniques for particulate-reinforced metal aluminium matrix composites

Abstract: The critical need for high strength, lightweight and high stiffness materials has, in recent years, resurrected much interest in discontinuously reinforced powder metallurgy metal matrix composites. These hybrid materials have combined both standard wrought alloys of aluminium and a wide variety of discontinuous reinforcements such as particulates and whiskers of ceramic materials. Renewed interest in these materials as attractive candidates for use in the aerospace and transportation industry has resulted from an attractive and unique combination of physical and mechanical properties, and an ability to offer near isotropic properties coupled with the low cost of these materials when compared with existing monolithic materials. In this paper, the primary processing categories for discontinuously-reinforced metal-matrix composites are highlighted and the salient features of the various techniques in each category are discussed. The variables involved in each processing technique are examined, and the influence of alloy chemistry highlighted. Novel processing techniques for these materials such as the variable co-deposition method is presented as a means to process these novel engineering materials in order to improve their overall mechanical performance.

Microfailure behaviour of randomly dispersed short fibre reinforced thermoplastic composites obtained by direct sem observation

Abstract: The microfailure behaviour of thermoplastic polyamide 6,6 composites reinforced with randomly dispersed short glass fibres was studied. Scanning electron microscopy was carried out on the surface of the composites under load to observe directly the behaviour. The microfailure proceeds following the steps (1) interfacial microfailure occurs at the fibre tips, (2) the microfailure propagates along the fibre sides, (3) plastic deformation bands of the matrix occurs from the interfacial one, (4) crack opening occurs in the band and the crack grows slowly through the band, (5) finally a catastrophic crack propagation occurs through the matrix with pulling-out fibres from the matrix. A model for the microfailure mechanism of the composites is proposed and some methods to improve the mechanical properties of the composites are discussed on the basis of the mechanism.

Hydration/dehydration characteristics of struvite and dittmarite pertaining to magnesium ammonium phosphate cement systems

Abstract: Struvite, an important reaction product in magnesium ammonium phosphate cement systems, was synthesized in the laboratory. The elevated-temperature dehydration and then roomtemperature hydration characteristics of the dehydrated products were studied by thermogravimetric analyses and X-ray diffraction techniques. From isothermal experiments, struvite is found to be thermally unstable in air at temperatures above 50 ‡C. Struvite can lose part or all of its ammonia and water molecules depending on the time and temperature of heat treatment, ultimately forming magnesium hydrogen phosphate. This decomposed product is X-ray amorphous and upon room-temperature rehydration can form struvite, unknown hydrates or newberyite, alone or in combination with each other, depending on the amount of ammonia left in the structure. However, when struvite is heated in excess water, it only loses its water of crystallization to form the monohydrate, dittmarite. Dittmarite is thermally more stable than struvite and like struvite also forms magnesium hydrogen phosphate on decomposition. At room temperature and in the presence of excess water, dittmarite can slowly transform to the hexahydrate, struvite. The consequence of structural similarities between struvite and dittmarite and conditions under which they may be present in cured cements are described.

Weibull strength statistics for graphite fibres measured from the break progression in a model graphite/glass/epoxy microcomposite

Abstract: Recent statistical theories for the failure of fibrous composities focus on the initiation and growth of clusters of broken fibres within the composite. These theoreis require the probability distribution for fibre strength at the length scale of micromechanical load transfer around a cluster of broken fibres. Such lengths are of the order of 10 to 150 fibre diameters, and thus the associated strengths have previously been unmeasurable by direct means. Using Weilbull/weakest-link rules, researchers have resorted to extrapolation of tension test results from gauge lengths two orders of magnitude longer. In this paper, a technique is developed to study the break progression of a single graphite fibre in an epoxy microcomposite tape, where the graphite fibre is flanked by two, proof-tested, glass fibres. These results are interpreted using a Weibull/Poisson model of the break progression, the number of breaks in the graphite fibre as a function of applied strain, which accounts for stress decay at the fibre ends. It is shown that such extrapolations of tension test data are too optimistic. In addition, different fibres from the same yarn cross-section, apparently have different flaw populations, unlike that which occurs at longer gauge lengths.

Impedance spectra of hydrating cement pastes

Abstract: Complex impedance spectra were obtained over the frequency range 5 Hz to 13 MHz on Portland cement pastes with water/cement ratios of 0.3, 0.35, and 0.4 at various hydration times from 6 h to 24 days. Features of the spectra which could be associated with the bulk material and which could be separated from the electrode arc, were studied. The overall bulk resistance of each paste was thereby determined as a function of hydration time. Bulk features evolved from a simple high-frequency intercept to an intercept with a single arc, then an intercept with two overlapping arcs, and back to an intercept with a single arc. A plausible equivalent circuit was developed involving an electrodeR/C network and constant phase element in series with one or two bulkR/C networks and a bulk resistor. Possible physical interpretation is discussed but assignment of equivalent circuit elements to microstructural features and/or processes will require microstructural characterization and a knowledge of pore-phase chemistry and properties.

Solid lubricants for applications at elevated temperatures

Abstract: Relative motion between mating surfaces at elevated temperatures often causes substantial material degradation due to friction and wear. Conventionally, solid lubricants have been used to reduce wear damage and friction drag under extreme conditions where liquid lubricants do not function properly. The recent trend towards higher operating temperatures in advanced power generating systems, i.e. turbomachinery, gas turbines, and hot adiabatic diesel engines, has imposed severe limitations on the currently available solid lubricants. The unusually aggressive conditions in these systems phased out most conventional solid lubricants and gave impetus to the search for more efficient materials. This paper discusses the lubricating characteristics of four different groups of materials known to provide lubricity under elevated temperature conditions. These groups are polymers, laminar solids, metal fluorides and metal oxides. Polymer lubricants are efficient lubricants within the range from room temperature to about 300 °C. Laminar solids extend that range to about 450 °C. Graphite, also a laminar solid, is an exception since it can offer excellent lubricity beyond 450 °C in the form of gaseous oxidation products. Stable fluorides and metal oxides are useful lubricants between 500 and 1000 °C, though their performance is rather poor at lower temperatures.

Open pore description of mechanical properties of ceramics

Abstract: A dependence of Young's modulus of elasticity on open porosity in ceramics is derived from an open-porosity model, which in the literature, is applied to salinity conductivity and fluid permeability in rocks. A random distribution of grain and pore size is assumed. The relation developed,E(p)=E o(1−"p)m, whereE is the modulus of elasticity of the porous ceramic,E o is the theoretical elastic modulus,p is the porosity andm is an exponent dependent on the tortuosity of the structure of the ceramic, adequately describes the dependence of the modulus of elasticity on porosity. The model is applied to the experimental data from several ceramics such as alumina, silicon nitride, silicon carbide, uranium oxide, rare-earth oxides, and YBa2Cu3O7−δ superconductor, and the value ofm is obtained for each case. We have shown thatm has a value of nearly 2 for sintered ceramics, unless sintering aids or hot pressing have been used during fabrication of the ceramic. Such additional procedures approximately double the magnitude ofm.

Some properties of Sb2Te3−xSex for nonvolatile memory based on phase transition

Abstract: Composition dependence of properties of Sb2Te3−xSex in the range 0⩽x<3 were studied using differential thermal analysis and X-ray diffraction. Sb2Te3−xSex form solid solution for 0

Self-propagating high-temperature synthesis of molybdenum disilicide

Abstract: Molybdenum disilicide was synthesized from elemental reactants in argon and vacuum atmospheres by utilizing the exothermicity of the reaction using self-propagating high temperature synthesis. Experiments were carried out using powdered reactants and compacts with varying densities. The reaction front propagated at a finite velocity depending upon the atmosphere, the diameter of the pellet and the particle sizes of the reactants. The exothermicity of the reaction between molybdenum and silicon raised the temperature of the product to 1886 K, which is close to the theoretical adiabatic combustion temperature, 1900 K. X-ray diffraction analysis of the product confirmed the product to be a single phase MoSi2 crystallizing in a tetragonal structure. Microstructural examination revealed melting of Si and its capillary flow, and chemical analysis indicated that the product is much purer than the reactants.

Low temperature degradation of Y-TZP materials

Abstract: Seven yttria-tetragonal zirconia polycrystal (TZP) materials were examined to determine if they were susceptible to low temperature degradation. Flexure specimens were exposed to approximately 800 Pa of water vapour pressure for 50 h between 200 and 400 °C. Only one of the TZPs was unaffected by these low temperature treatments. Three underwent catastrophic degradation after all the low temperature treatments, while the final three had property losses of varying degrees, depending on the treatment temperature.

Contribution to the study of reactive wetting in the CuTi/Al2O3 system

Abstract: The wetting (kinetics of spreading and stationary contact angles) of CuTi alloys on monocrystalline alumina under high vacuum, at a temperature of 1373 K, by the sessile drop technique was investigated. The morphological and chemical characteristics of the metal-ceramic interface were determined by scanning electron microscopy and microprobe analysis. When the results are analysed, three distinct effects of the Ti solute on wetting can be identified and evaluated semi-quantitatively: (a) a reduction in the solid-liquid interfacial tension by adsorption into the liquid side of the interface; (b) a reduction in this tension by formation of a TiO metallic-like oxide layer in the solid side of the interface; (c) a contribution to the wetting driving force due to the free energy released at the interface by the reaction between Ti and Al2O3.

Elastic constants of TiAl3 and ZrAl3 single crystals

Abstract: The elastic stiffness constants, c ij, were measured from the velocity of ultrasonic waves for TiAl3 and ZrAl3 single crystals with tetragonal D022 and D023 structures, respectively. The value of c 11 for the 〈1 0 0〉 direction was approximately equal to that of c 33 for the 〈0 0 1〉 direction in both TiAl3 and ZrAl3. Young's modulus for a single crystal was the highest in the 〈1 1 0〉 direction in which titanium or zirconium atoms and aluminium atoms were arranged in the closest packed manner, although it was not so high in 〈0 1 2〉 and 〈0 1 4〉 directions which showed the other closest packed array of the constituent atoms for TiAl3 and ZrAl3, respectively. The elastic constants, such as Young's modulus, shear modulus and Poisson's ratio, were approximately estimated for ideal polycrystalline TiAl3 and ZrAl3 from the stiffness constants and the compliance constants for single crystals. The Poisson's ratio of these materials was about 0.16 and 0.19 for TiAl3 and ZrAl3, respectively, and these values are much lower than those of ordinary metals and alloys. Debye temperatures were estimated at room temperature from the average velocity of ultrasonic waves and were 681 and 577 K for TiAl3 and ZrAl3, respectively.

Mechanical stability of sol-gel films

Abstract: The relationship between film cracking and film thickness has been studied experimentally for films of ceria gel deposited by spinning on to stainless steel substrates from an aqueous ceria sol. A critical film thickness below which films were crack-free was observed at about 0.6 μm. For films thicker than the critical thickness the crack spacing was approximately ten times the film thickness. Existing models for the mechanical stability of the films were examined to explain the observations, encompassing different forms of relaxation of the stress in the vicinity of a crack through the film. The model in best accord with the experimental observations is one in which stable delamination cracks are formed at the film-substrate interface on both sides of a crack through the film. However, for the model to be applicable some rather restrictive conditions must be assumed to be satisfied.

A map for wear mechanisms in aluminium alloys

Abstract: A quantitative wear map for aluminium and its alloys has been constructed using normalized test variables and the physical modelling approach proposed by Lim and Ashby for steels. New model equations based on a different state-of-stress criterion suitable for aluminium alloys have been developed and found to match well with reported experimental wear data on aluminium alloys. The field boundaries between various interfacing wear mechanisms were constructed by using critical values of experimental wear data which manifest themselves in discontinuities in the slope of wear curves. However, within a given wear regime, the model equations developed here agreed fairly well with the reported wear data. The wear mechanisms successfully modelled here include oxidation dominated wear, delamination wear, severe plastic deformation wear, and melt wear.

Composite PTCR thermistors, utilizing conducting borides, silicides, and carbide powders

Abstract: Ceramic-polymer composite thermistors using conducting boride, silicide, and carbide powders that include TiB2, ZrB2, NbB2, NbSi2, WSi2, MoSi2, and TiC have been fabricated. Percolation and subsequent PTCR effects were observed for all the powders in both semi-crystalline (polyethylene) and amorphous (epoxy) polymer matrix materials, however, as found for carbon black and metal fillers, both niobate powders did not exhibit a PTCR effect in the amorphous polymer. Results indicate that percolation and PTCR behaviour are related to the powder characteristics (size/distribution), composite microstructure and ceramic-polymer interface. Composite thermistors with room temperature resistivities as low as 1 Ω cm and a nine-order of magnitude change (Δϱ) at 1 kHz (12 Δϱ at d.c.) were achieved.

Processing-morphology relationships of compatibilized polyolefin/polyamide blends

Abstract: The emulsifying effect of a polyethylene-based ionomer on the phase size/composition relationship was studied for polypropylene/polyamide and polyethylene/polyamide blends. The particle size measured for the uncompatibilized blends increased with minor phase concentration, particularly as the region of dual phase continuity was approached. This relationship was less pronounced when ionomer was added, and the dimensions of the dispersed phase were significantly reduced. A narrowing of the region of dual phase continuity was observed due to the addition of ionomer. An increase in the torque measured during melt blending in a Brabender mixing chamber resulted when ionomer was added, due to the increase in the interactions at the interface. The particle size determined for the uncompatibilized blends increased with viscosity ratio. The effect was also less pronounced for the compatibilized blends. From these observations, it was possible to conclude that the effect of interfacial modification on morphology predominates over that of composition and viscosity ratio. The effects were interpreted in terms of the reduction of interfacial mobility due to the compatibilization.

Synthesis of molybdenum silicides by the self-propagating combustion method

Abstract: The synthesis of the silicides of molybdenum (Mo3Si, Mo5Si3, and MoSi2) by the self-propagating combustion method is investigated. Only the reactants corresponding to the last phase can be reacted in a self-sustaining mode without preheating. The product of such a reaction is single-phase MoSi2. Although reactant mixtures corresponding to the other two silicides can react in a self-sustaining mode with prior heating, the products of combustion were multi-phase. The dependence of the combustion temperature and velocity on the stoichiometry of the silicide was determined. The activation energy for the combustion synthesis of MoSi2 determined in this investigation, 139.4 kJ mol−1, is considerably lower than activation energies reported for the diffusion of silicon in molybdenum or in MoSi2.

Environmental effect on mechanical properties of recrystallized L12-type Ni3(Si,Ti) intermetallics

Abstract: The environmental effect on the mechanical properties of boron-doped and undoped Ni3(Si, Ti) polycrystals was investigated by tensile testing in air from room temperature to 1073 K, and the results were compared with those obtained previously by tensile testing in vacuum. The environmental effect for the Ni3(Si, Ti) alloys was significant at ambient temperatures whereas that for the boron-doped Ni3(Si, Ti) alloys was considerable at elevated temperatures. When these samples at associated temperatures were tensile tested in air and also at low strain rate, intergranular fracture was dominant. It was suggested that the environmental embrittlements at low and high temperatures were due to hydrogen and oxygen absorbed from the air, respectively, and were caused by the weakening of the grain-boundary cohesion. It was proposed that boron competing with hydrogen, for site occupation or for its effectiveness at grain boundaries, has the effect of suppressing hydrogen embrittlement, whereas it was suggested that the low-melting phases, consisting of boron and oxygen (and/or constituent atoms), may be responsible for the ductility loss in the boron-doped Ni3(Si, Ti) alloys.

High-temperature materials — a general review

Abstract: Materials that allow operation at high temperature are essential in many industries from material producing and processing to transportation and power generation. After brief comments on typical operating environments, high-temperature aluminium alloys, steels and nickel alloys are discussed, referring to alloy types, characteristics and applications. Future development possibilities are indicated. The engineering ceramics silicon nitride and silicon carbide are discussed with particular emphasis on defect tolerance considerations. The various forms and applications of high-temperature carbon, including carbon-carbon composite, are included and a discussion on “engineered materials” concepts, such as thermal insulators and ablative materials, concludes the review.

Nitridation reactions of molten Al-(Mg, Si) alloys

Abstract: The isothermal nitridation of magnesium- and silicon-doped aluminium melt at 1273 K was investigated. With increasing Mg/Si ratio and decreasing oxygen content in the nitriding atmosphere, four major reaction mechanisms may be separated: (i) a passivating surface nitridation, (ii) a volume nitridation with precipitation of isolated AlN in the aluminium matrix, (iii) a volume nitridation resulting in a three-dimensionally interconnected AlN/Al composite microstructure, and (iv) a break-away nitridation with complete conversion of aluminium to AlN. The behavioural transition of the nitridation mechanism is reflected by the growth direction and the crystal morphology of AlN which change from inward (mechanisms i, ii) to outward (mechanisms iii, iv) growth of the reaction product with [0 0 0 1] as the dominating growth direction. Attempts are made to define the critical magnesium and silicon contents for the regime of controlled AlN/Al composite growth (mechanism iii) at 1273 K, in order to develop novel AlN/Al composite materials.

Fibre orientation and mechanical behaviour in reinforced thermoplastic injection mouldings

Abstract: Process variables, fibre orientation distribution and mechanical properties were inter-related for injection-moulded short-glass fibre-reinforced polypropylene and polyamide and long-glass fibre-reinforced polyamide. The properties of the reinforced grades were also contrasted with those of the base polymer. A rectangular mould with triple pin-edge gates on the same side to facilitate a single melt flow-front or double flow-front advancing adjacently, was employed. Mouldings were evaluated for fibre orientation distribution, and tensile, dynamic mechanical and fracture properties. The relative magnitudes of the shell and the core fibre-orientation persuasions depended on the melt and the mould temperatures, and the injection ram speed. An increase in G c, K c, ultimate tensile strength (UTS) and elastic moduli values and a decrease in tan δ values were observed with fibre reinforcement. The properties showed marked sensitivity to the position of the specimens in the moulding because of the associated variations in the fibre orientation. The prediction of UTS based on a rule of mixture relationship for strength and the Halpin-Tsai equations for elastic moduli had limited success. The predictions were improved by employing measured data representative of regions of high fibre orientation, e.g. knit-line. The estimation was weakened in the material systems containing significant production-induced voids. An inference of the fracture toughness values was that the composites contained flows of the order of 0.2 mm in size, which is conceivable, either as voids or as defects introduced in the machining of the specimens.