Low-temperature behaviour of epoxy-rubber particulate composites

Toughness and mechanical property data are presented for a carboxyl-terminated acrylonitrile butadiene (CTBN) rubber-modified epoxy resin in the temperature range 20 to – 110° C. A toughening model based on ultimate strain capability and tear energy dissipation of the rubber, present as dispersed microscopic particles in an epoxy matrix, is used to explain the suppression of composite toughness (G _Ic ) below – 20° C. The toughness loss is attributed to a glass transition in the rubber particles, and to a secondary transition in the epoxy resin, both occurring in the range – 40 to – 80° C. Strain-tofailure and modulus measurements on bulk rubber-epoxy compounds, formulated to simulate rubber particle compositions, confirm a decrease in rubber ductility coincident with the onset of composite toughness loss. An increase in rubber tear energy associated with its transition to a rigid state can explain the observation that even at low temperatures composite toughness generally remains significantly higher than that of pure epoxy. Although the low-temperature epoxy transition reduces molecular mobility in the matrix phase, residual ductility in, and energy dissipation by, the rubber particles determine the extent of composite toughness suppression. The low-temperature data bear out the particle stretching-tearing model for toughening.     

Mechanical behavior of mycelium-based particulate composites

This work investigates the mechanical behavior of mycelium composites reinforced with biodegradable agro-waste particles. In the composite, the mycelium acts as a supportive matrix which binds reinforcing particles within its filamentous network structure. The compressive behavior of mycelium composites is investigated using an integrated experimental and computational approach. The experimental results indicate that the composite mimics the soft elastic response of pure mycelium at small strains and demonstrates marked stiffening at larger strains due to the densification of stiff particles. The composite also exhibits the characteristic stress softening effect and hysteresis under cyclic compression previously observed for pure mycelium. To gain further insight into the composite behavior, a three-dimensional finite element model based on numerical homogenization technique is presented. Model validation is performed by direct comparison with experiments, and a parametric study of the effect of mycelium density and particle size is discussed.     

Low cycle fatigue behaviour of particulate reinforced metal matrix composites

The low cycle fatigue (LCF) resistance of two different 6061 Al/20 vol% alumina particulate metal matrix composites (MMCs) in a peaked-aged condition has been evaluated under fully reversed strain control testing. Test results were combined with scanning electron and optical microscopy investigations to determine the effects of reinforcement particles and strain amplitude on the LCF behaviour of these MMCs. Both materials show three stages of response to LCF: initial fast hardening or softening in the first few cycles; gradual softening for most of the fatigue life; and a rapid drop in the stress carrying capability prior to failure. Both MMCs exhibit short LCF life which follows a Coffin-Manson relationship. All tested specimens demonstrate ductile fracture morphology at final failure. The experimental results are discussed in respect of strain amplitude, matrix composition and reinforcement shape and crack initiation.     

Mechanical behaviour of nickel aluminide–zirconia transformation-toughened particulate composite

The fracture toughness and strength behaviour of nickel aluminide toughened by partially stabilized as well as by non-stabilized zirconia dispersoids were investigated in the range of zirconia content up to 40 vol%. The temperature dependence of the mechanical properties of the composite with an optimal zirconia content was examined. A considerable increase both in fracture toughness and in bending strength was achieved compared to the base nickel aluminide. To reveal the nature of the toughening and strengthening effects, X-ray diffraction measurements were performed before and after fracture. Residual stresses imposed on zirconia particles were evaluated. Trends in mechanical behaviour have been discussed in terms of microstructure development. This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical properties of cast lead alloy/silicon carbide particulate composites

This paper describes a study of the mechanical properties of cast lead-antimony alloy composites containing silicon carbide (SiC) particles of size 90–150 μm and of contents ranging from 0% to 5% by weight. The ‘vortex method’ of production was employed in which the SiC particles were poured into the vortex created by stirring the molten metal at 400°C by means of a mechanical agitator. The results of this study revealed that as SiC composition was increased, there were significant increases in the ultimate tensile strength (UTS), hardness, torsional strength and impact strength of the composite, accompanied by a reduction in its ductility. An attempt is made in the paper to provide explanations for these phenomena.     

Mechanical and microstructural behaviour of a particulate reinforced steel for structural applications

Abstract

Low density, high modulus, and potentially improved wear resistance are the major benefits of a ferrous composite material. A BS S.156 (4%NiCrMo)gear steel reinforced with 15 vol.-% titanium diboride particles has been demonstrated for possible high performance structural applications. This composite has been produced by a powder metallurgy/mechanical milling processing route, to give a homogeneous distribution of fine reinforcement particles. The composite tensile strength was 90% of the matrix in the fully heat treated condition, with ductility of up to 6%. However, martensite formation and hence the hardenability was found to be suppressed in the composite. A fatigue study indicated that the titanium diboride particles did not appear to contribute to crack initiation in the composite.     

Ageing behaviour and toughness of silicon carbide particulate reinforced Al-Li-Cu-Mg-Zr metal matrix composites

The effects of lithium content on the ageing characteristic and notched tensile properties of particulate reinforced Al-Li-Cu-Mg-Zr based metal matrix composites (MMCs) have been investigated. MMC sheet containing 20 wt% silicon carbide particulate produced by a conventional powder metallurgy route aged at a similar rate as unreinforced sheet, and the highest strengths were achieved in samples containing 2–2.5 wt% Li. A proprietary processed 8090 Al-Li alloy MMC sheet aged more rapidly, however, and gave considerably higher strengths. The toughness of Al-Li-Cu-Mg-Zr MMC sheet, as indicated by the notched tensile behaviour, can be improved by reducing the lithium content albeit at the expense of strength.     

Rheological behaviour of SiC (particulate)-borosilicate composites at elevated temperatures

Journal of Materials Science Letters -     

Mechanical behaviour of carbon and glass hybrid fibre reinforced polyester composites

Mechanical behaviour of carbon fibre/glass mat/polyester resin hybrid composites of sandwich construction is studied through tension, flexure, impact and post-impact tension tests. Tensile and flexural strength, modulus and failure strain values are compared to the calculated values. Total impact fracture energy and residual (after impact) tensile strength values of hybrid composites are analysed with regard to corresponding values of carbon/polyester composites. Failure of tested coupons was analysed by visual inspection and observation by scanning electron microscopy.     

Evaluation of dielectric behaviour of particulate composites consisting of polymeric matrix and conductive filler

Abstract

Extension of the logarithmic law of mixtures enables equations to be formulated which describe the dielectric behaviour of particulate polymeric composites containing conductive particles. These equations give the permittivity and dielectric loss of the composite as a function of the permittivity of the polymeric matrix, the volume fraction and aspect ratio of the inclusions, and the frequency of the applied field. The proposed equations were tested with experimental data obtained over a wide range of frequencies and temperatures from composites consisting of epoxy resin and aluminium powder. Satisfactory agreement was observed when the volume fraction of the inclusions was small, but at higher values discrepancies appeared which are attributed to the intrinsic weakness of the logarithmic law of mixtures, on which the proposed equations are based.

MST/3167     

Fracture of particulate composites

A thermodynamic analysis of the process of fracture in elastically deformable composites is formulated. The critical dimensions leading either to particle fracture or to matrix-particle decohesion are identified. Fracture in plastically deformable composites is discussed in the light of the experimental evidence regarding void or cavity nucleation. Models of void growth under the application of stress and the role of void growth in causing failure are described in brief.     

Mechanical and tribological behaviour of nano scaled silicon carbide reinforced aluminium composites

ABSTRACT

This work assesses the impact of the presence of Nano scaled silicon carbide on the Mechanical & Tribological behavior of aluminium matrix composites. Aluminium matrix composites containing 0, 0.5, 1, 1.5, 2 and 2.5 wt.%-nano scaled silicon carbide was set up by a mechanical stirrer. The trial comes about to demonstrate that the inclusion of Nano silicon carbide brings about materials with progressively high elastic modulus and likewise brings about expanded brittle behavior, fundamentally lessening failure strain. Shear modulus and flexural shear modulus likewise increases with silicon carbide increase. The presence of Nano scaled silicon carbide in the aluminium matrix diminishes subsurface fatigue wear and increases wear resistance, because of silicon carbide lubricant activity. Wear testing, microstructure & morphological, density & void testing, hardness, flexural and tensile test of the readied composites were investigated and outcomes were analyzed which demonstrated that including nano-SiC in aluminum (Al) matrix increased wear resistance, tensile strength, and 2 wt. % of nano scaled SiC for Al MMC indicated maximum wear resistance, tensile strength, and an optimum balanced mix of both Tribological and Mechanical properties. Microstructural observation uncovered uniformand homogeneous distribution of SiC particles in the Al matrix.     

Mechanical and water absorption behaviour of banana/sisal reinforced hybrid composites

The tensile, flexural, impact and water absorption tests were carried out using banana/epoxy composite material. Initially, optimum fiber length and weight percentage were determined. To improve the mechanical properties, banana fiber was hybridised with sisal fiber. This study showed that addition of sisal fiber in banana/epoxy composites of up to 50% by weight results in increasing the mechanical properties and decreasing the moisture absorption property. Morphological analysis was carried out to observe fracture behaviour and fiber pull-out of the samples using scanning electron microscope.     

Mechanical behaviour of SiC fibre-reinforced titanium/titanium aluminide hybrid composites

The viability of developing an SiC fibre-reinforced titanium/titanium aluminide hybrid matrix composite was explored. The hybrid composites are expected to be used at temperatures beyond those attainable in conventional titanium matrix composites while improving the damage tolerance of the titanium aluminide matrix composites. The room-temperature mechanical characteristics studied were tensile strength, fracture toughness, low-cycle fatigue life and fatigue crack growth rate. The mechanisms of damage initiation and propagation under various loading conditions were also characterized. The directions for developing a satisfactory composite with hybrid titanium/titanium aluminide matrix are also addressed.     

Mechanical and corrosion behaviour of powder metallurgy stainless steel based metal matrix composites

Abstract

Stainless steel matrix composites were manufactured using powder metallurgy techniques. Matrixes of AISI 316L stainless steel were reinforced with yttria or alumina particles. Chromium diboride was added in some cases and boron nitride in others to obtain steels with densities close to theoretical, using reactive (liquid phase) sintering techniques. The composites showed very good densification and better hardness than the 316L stainless steel without additions. The 316L steel reinforced with 4 wt-% yttria chromium diboride showed the highest density and strength, with an acceptable corrosion resistance.     

Mechanical behaviour of chemical vapour infiltration-processed two- and three-dimensional nicalon/SiC composites

The effect of two different fibre architectures on the mechanical properties of the Nicalon fibre-reinforced SiC composites processed by chemical vapour infiltration has been investigated. The microstructure, flexural strength, fracture toughness and failure mechanisms of both two-dimensional woven laminate and three-dimensional braided composites were characterized. It was found that the fibre placement in the preform will not only affect the infiltration of the SiC matrix, but also the mechanical property and failure behaviour of the composite. A strong, tough and damage-tolerant SiC matrix composite can be fabricated through the combination of a three-dimensional braided integrated fibre network and chemical vapour infiltration processing.