Microstructure and mechanical behaviour of a SiC particles reinforced Al-5Cu composite under dynamic loading

The mechanical behaviour of a composite of Al–5Cu matrix reinforced with 15% SiC particles was studied at different strain rates from 1×10−3 to 2.5×103 s−1 using both a conventional universal testing machine (for low strain-rate tests) and a split Hopkinson bar (for tests at dynamic strain rates). Whilst the yield stress of the composite increases as the strain rate increases, the maximum flow stresses, 440 MPa for compression and 450 MPa for tension, are independent of strain rate. The microstructures and defect structures of the deformed composite were studied with both scanning electron microscopy and transmission electron microscopy and were correlated to the observed mechanical behaviour. Fracture surface studies of samples after dynamic tensile testing indicates that failure of the composite is controlled by ductile failure of the aluminium matrix by the nucleation, growth and coalescence of voids.

Interfacial microstructure and mechanical behaviour in laser clad TiCp/Ni alloy coatings

Coatings of TiCp reinforced composite have been produced by laser cladding. Two kinds of coating with different TiCp origins were investigated, i.e. undissolved TiCp and in situ TiCp. For undissolved TiCp, epitaxial growth of TiC, precipitation of CrB, and a chemical reaction occur at phase interfaces, and nanoindentation loading curves show pop in marks caused by the plastic deformation associated with crack formation or debonding of TiCp from the matrix. As for in situ TiCp, no pop in mark appears. Meanwhile, in situ TiCp produces hardness and elastic modulus values that are higher than those produced by the coating that contains undissolved TiCp.

Molecular Dynamics Study Of Mechanical Behaviour Of Screw Dislocation During Cutting With Diamond Tip On Silicon

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are calculated. A screw dislocation is introduced into workpiece Si. It is found that motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocation is far below the yield strength of Si.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

Mechanical modeling of grain boundary sliding of polycrystals

Using a variational method, a general three-dimensional solution to the problem of a sliding spherical inclusion embedded in an infinite anisotropic medium is presented in this paper. The inclusion itself is also a general anisotropic elastic medium. The interface is treated as a thin interface layer with interphase anisotropic properties. The displacements in the matrix and the inclusion are expressed as polynomial series of the cartesian coordinate components. Using the virtual work principle, a set of linear algebraic equations about unknown coefficients are obtained. Then the general sliding spherical inclusion problem is accurately solved. Based on this solution, a self-consistent method for sliding polycrystals is proposed. Combining this with a two-dimensional model of an aggregate polycrystal, a systematic analysis of the mechanical behaviour of sliding polycrystals is given in detail. Numerical results are given to show the significant effect of grain boundary sliding on the overall mechanical properties of aggregate polycrystals.

Optical fringe multiplication technique with TEM nano-moiré method

In this paper, a nano-moiré fringe multiplication method is proposed, which can be used to measure nano-deformation of single crystal materials. The lattice structure of Si (111) is recorded on a film at a given magnification under a transmission microscope, which acts as a specimen grating. A parallel grating (binary type) on glass or film is selected as a reference grating. A multiplied nano-moiré fringe pattern can be reproduced in a 4f optical filter system with the specimen grating and the prepared reference grating. The successful results illustrate that this method can be used to measure deformation in nanometre scale. The method is especially useful in the measurement of the inhomogeneous displacement field, and can be utilized to characterize nano-mechanical behaviour of materials such as dislocation and atomic bond failure.

Micromechanics analysis of particulate-reinforced composites and their failure mechanisms

Stress fields and failure mechanisms have been investigated in composites with particles either surface treated or untreated under uniaxial tension. Previous experimental observation of failure mechanisms in a composite with untreated particles showed that tensile cracks occurred mostly at the polar region of the particle and grew into interfacial debonding. In a composite with surface-treated particles, however, shear yielding and shear cracking proceeded along the interphase-matrix interface at the polar area of the matrix and thus may improve the mechanical behaviour of the material. The finite element calculations showed that octahedral shear stress at the polar and longitudinal areas of the particle treated by coupling agents is much larger than that of materials with untreated particles, and the shear stress distribution around the interface is sensitive to the interphase property. The results suggest that a th ree-phase model can describe the composites with surface-treated fillers.

Morphologies and physical properties of PA1010/HIPS/HIPS-g-MA ternary blends

The effect of the content of a copolymer consisting of high impact polystyrene grafted with maleic anhydride (HIPS-g-MA) on morphological and mechanical properties of PA1010/HIPS blends has been studied. Blend morphologies were controlled by adding HIPS-g-MA during melt processing, thus the dispersion of the HIPS phase and interfacial adhesion between the domains and matrices in these blends were changed obviously. The weight fractions of HIPS-g-MA in the blends increased from 2.5 to 20, then much finer dispersions of discrete HIPS phase with average domain sizes decreased from 6.1 to 0.1 mu m were obtained. It was found that a compatibilizer, a graft copolymer of HIPS-g-MA and PA1010 was synthesized in situ during the melt mixing of the blends. The mechanical properties of compatibilized blends were obviously better than those of uncompatibilized PA1010/HIPS blends. These behaviors could be attributed to the chemical interactions between the two components of PA1010 and HIPS-g-MA and good dispersion in PA1010/HIPS/HIPS-g-MA blends. Evidence of reactions in the blends was seen in the morphology and mechanical behaviour of the solid. The blend containing 5 wt % HIPS-g-MA component exhibited outstanding toughness. (C) 1999 Kluwer Academic Publishers.

Studies on morphology and crystallization of polypropylene/polyamide 12 blends

Scanning electron microscopy (SEM) and an image analyser are used to study morphologies of the fractured surface, etched by hot phenol, of polypropylene/maleated polypropylene/polyamide 12 PP/PP-MA/PA12) = 65/10/25 blend and PP-MA/PA12 = 75/25 blend. The particle dimension and its distribution of PA12 dispersed phase in these blends are much lower and narrower than that of the PP/PA12. blends. Especially, most of the particles in the PP-MA/PA12 = 75/25 blend are smaller than 0.1 mu m. The effect of the morphology of PP/PA12 blends on their crystallization behaviour is studied using differential scanning calorimetry and SEM. PA12 dispersed phase coarsens during annealing in the PP/PP-MA/PA12 = 65/10/25 blend. The mechanism of coarsening of the PA12 dispersed phase is a coalescence process. The intense mixing between the PP component and the PA12 component through reaction of PP-MA and PA12 leads to a change of dynamic mechanical behaviour of the components. A separation method is used to separate the polyolefin parts (precipitated from hot phenol), from PA12 parts (hot phenol filtrate). Of PP/PP-MA/PA12 = 65/10/25 blend, infra-red measurements and elementary analysis show that the precipitate has a lower PA12 content than the feed, whereas the filtrate has a higher PA12 content. From PP-MA/PA12 = 75/25 blend, PA12 contents in the precipitate and the filtrate are the same as in the feed. This implies that all PA12 has reacted with all PP-MA in the latter case while not in the former case. Using the method of interface exposure, interfacial reaction of PP-MA with PA12 is studied by X-ray photoelectron spectrometry (X.p.s.). Copyright (C) 1996 Elsevier Science Ltd.

COMPATIBILIZING EFFECT OF POLY(ETHYLENE OXIDE)-B-POLYSTYRENE-B-POLY(ETHYLENE OXIDE) IN PHENOLPHTHALEIN POLY(ETHER ETHER KETONE) POLY(2,6-DIMETHYL-1,4-PHENYLENE OXIDE) BLENDS

The morphology and mechanical behaviour of phenolphthalein poly(ether ether ketone) (PEK-C)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends has been investigated. A poly(ethylene oxide)-b-polystyrene-b-poly(ethylene oxide) (PEO-PS-PEO) triblock copolymer was used as compatibilizer. It was found that PEO-PS-PEO has a compatibilizing effect on the PEK-C/PPO blends. The addition of PEO-PS-PEO to the blends greatly improves phase dispersion and interfacial interfacial adhesion and also enhances the ultimate tensile strength and Young's modulus at compositions ranging from 30 to 70% PEK-C. However, all the values of the ultimate tensile strength within the whole composition range are lower than those expected by simple additivity, probably owing to the poor mechanical properties of PEO-PS-PEO copolymer.

Thermal-mechanical interface crack behaviour of a surface mount solder joint

The effect of thermal-mechanical loading on a surface mount assembly with interface cracks between the solder and the resistor and between the solder and the printed circuit board (PCB) was studied using a non-linear thermal finite element analysis. The thermal effect was taken as cooling from the solder eutectic temperature to room temperature. Mechanical loading at the ends of the PCB was also applied. The results showed that cooling had the effect of causing large residual shear displacement at the region near the interface cracks. The mechanical loading caused additional crack opening displacements. The analysis on the values of J-integral for the interface cracks showed that J-integral was approximately path independent, and that the effect of crack at the solder/PCB interface is much more serious than that between the component and solder.

Morphology, mechanical properties and interfacial behaviour of PA1010/PP/PP-g-GMA ternary blends

Morphology, mechanical properties, and interfacial interaction of polyamide 1010/polypropylene (PA1010/ PP) blends compatibilized with polypropylene grafted with glycidyl methacrylate (PP-g-GMA) were studied. It was found that the size of the PP domains, tensile and impact strength of ternary blends, and adhesion fracture energy between two layers of PA1010 and PP were all significantly dependent on the PP-g-GMA contents in the PP layer. Correlations between morphology and related properties were sought. The improvements in properties have been attributed to chemical and physical interaction occurring between PA1010 and PP-g-GMA. (C) 1997 Elsevier Science Ltd.

Effect of structural relaxation on deformation behaviour of Zr-based metallic glass

Structural relaxation through isothermal annealing at tempertature below glass transition is conducted on Zr46.75Ti8.25Cu7.5Ni10Be27.5 (Vitreloy-4) bulk metallic glass. Defect concentration is correlated with the annealing time t according to differential scanning calorimetry thermalgrams. The effects of structural relaxation on mechanical properties and deformation behaviour are investigated by using instrumented nanoindentation. It is found that as-cast alloy exhibits pronounced serration flow during the loading process of nanoindentation, and the size and number of serrations decrease with the annealing time. The change of the deformation behaviour with structural relaxation is explained using a free volume model.

Analyses of the mechanical properties and microstructure of bamboo epoxy composites

Bamboo reinforced epoxy possesses reasonably good properties to waarrant its use as a structural material, and is fabricated by utilizing bamboo, an abundant material resource, in the technology of fibre composites. Literature on bamboo-plastics composites is rare. This work is an experimental study of unidirectional bamboo-epoxy laminates of varying laminae number, in which tensile, compressive, flexural and interlaminar shear properties are evaluated. Further, the disposition of bamboo fibre, the parenchymatous tissue, and the resin matrix under different loading conditions are examined. Our results show that the specific strength and specific modulus of bamboo-epoxy laminates are adequate, the former being 3 to 4 times that of mild steel. Its mechanical properties are generally comparable to those of ordinary glass-fibre composites. The fracture behaviour of bamboo-epoxy under different loading conditions were observed using both acoustic emission techniques and scanning electron microscopy. The fracture mode varied with load, the fracture mechanism being similar to glass and carbon reinforced composites. Microstructural analyses revealed that natural bamboo is eligibly a fibre composite in itself; its inclusion in a plastic matrix will help solve the problems of cracking due to desiccation and bioerosion caused by insect pests. Furthermore, the thickness and shape of the composite can be tailored during fabrication to meet specific requirements, thereby enabling a wide spectrum of applications.

The role of sense organs in the feeding behaviour of Chinese perch

Experiments were conducted to identify the rules of the individual sense organs in the feeding behaviour of Chinese perch Siniperca chuatsi by determining the consumption of natural food after selective removal or blocking of eyes, lateral lines and olfactory organs, and also by observing the behavioural response to visual, mechanical and chemical stimulation by artificial prey. Chinese perch were able to feed properly on live prey fish when either eyes or lateral lines were intact or functional, but could scarcely feed without these two senses. Chinese perch recognized its prey by vision through the perception of motion and shape, and showed a greater dependence on vision in predation when both visual and mechanical cues were available. Chemical stimulation by natural food could not elicit any feeding response in Chinese perch, and gustation was only important to the fish for the last stage of food discrimination in the oropharyngeal cavity. The sensory basis of Chinese perch in feeding is well adapted to its nocturnal stalking hunting strategy. and also explains its peculiar food habit of accepting live prey fish only and refusing dead prey fish or artificial diets. (C) 1998 The Fisheries Society of the British Isles.