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In this study, medium-carbon steel was subjected to warm deformation experiments on a Gleeble 3500 thermosimulator machine at temperatures of 550°C and 650°C and strain rates of 0.001 s-1 to 1 s-1. The warm deformation behavior of martensite and the effects of strain rate on the microstructure of ultrafine grained medium-carbon steel were investigated. The precipitation behavior of Fe3C during deformation was analyzed and the results showed that recrystallization occurred at a low strain rate. The average ultrafine ferrite grains of 500 ± 58 nm were fabricated at 550°C and a strain rate of 0.001 s-1. In addition, the size of Fe3C particles in the ferrite grains did not show any apparent change, while that of the Fe3C particles at the grain boundaries was mainly affected by the deformation temperature. The size of Fe3C particles increased with the increasing deformation temperature, while the strain rate had no significant effect on Fe3C particles. Moreover, the grain size of recrystallized ferrite decreased with an increase in the strain rate. The effects of the strain rate on the grain size of recrystallized ferrite depended on the deformation temperature and the strain rate had a prominent effect on the grain size at 550°C deformation temperature. Finally, the deformation resistance apparently decreased at 550°C and strain rate of 1 s-1 due to the maximum adiabatic heating in the material. [ABSTRACT FROM AUTHOR]

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Abstract: We elucidate here the biomechanical response and large strain deformation behavior of silicone containing dispersion of different forms of nanostructured carbon, which adapt favorably to the functional requirements of joints during soft tissue reconstruction or replacement. The behavior of hybrid silicone systems is compared with standalone silicone. The key biomechanical properties, contact stiffness, reduced modulus and hardness were studied in vitro using nanoindentation approach in a simulated physiological environment under conditions of slow and rapid mechanical loading. Based on the biomechanical analysis, it is proposed that handheld indentation devices can be appropriately used during clinical practice for determination of stiffness of artificial soft tissues. However, while nanoindentation is a sensitive technique for quantitative evaluation of biomechanical properties of soft tissues, it is, important that the test procedure is standardized. Also, discussed are the basic physical mechanisms that govern elastic recovery and large strain deformation in terms of molecular theory. [Copyright &y& Elsevier]

Abstract: The study described here is in sequel to our studies on the mechanics of microscale deformation in thermoplastic materials where a perspective of deformation processes occurring over different strain–strain rate regimes was obtained. The specific aim here is to enhance our fundamental understanding from microscale to nanoscale deformation in polymeric material systems containing dispersion of nanoparticles, considering the growing use of polymeric materials as functional materials. A Berkovich nanoindenter was used to induce surface damage using a load of 0.5–1mN and scratch velocity of 1μm/s. The secondary objective is to investigate the commonality in surface deformation behavior between nano- and microscale deformation to reinforce the underlying fundamental principles governing surface deformation. Combining electron microscopy with nanoscale surface deformation experiments enabled us to extend the understanding of microscale deformation to nanoscale deformation. In the intercalated polypropylene-nanoclay system, the susceptibility to surface deformation was significantly reduced because of the shift of von Mises stress from the surface to the sub-surface region, with consequent reduction in the maximum tensile stress induced by the nanoindenter. This conclusion was consistent with electron microscopy observations and theoretical analysis. [Copyright &y& Elsevier]

Abstract: The objective of the study is to understand the nanoscale near-surface deformation response of two polymer nanocomposite systems with significant differences in ductility during nanoscratching with a Berkovich indenter using a load of 1mN and a scratch velocity of 1μms−1. An accompanying objective is to investigate the commonality in surface deformation behavior between nano- and microscale deformation to reinforce the underlying fundamental principles governing surface deformation. An understanding of surface deformation response is accomplished through determination of physical and mechanical properties, structural characterization and electron microscopy analysis of surface deformation tracks and residual plastically deformed structures. The study suggests for the first time that the understanding derived from microscale surface deformation studies can be extended to nanoscale surface deformation. The microscale response in a polypropylene-based system is characterized by periodic multiple ripple-type deformation tracks that form via a mechanism identical to the periodic single-ripple-type tracks during nanoscale deformation. Similarly, in a less ductile polyethylene-based system, the periodic parabolic tracks and ironing mode of deformation during microscale deformation tend to be significantly reduced in intensity, with ironing being the primary deformation mechanism at the nanoscale. The surface deformation topography suggests that both micro- and nanoscale response is material specific. Additionally, the study suggests that reinforcement of polymers with nanoclay is a viable route to significantly decrease the susceptibility of polymeric materials to micro- and nanoscale deformation and can be discussed in terms of physical and mechanical properties of materials notably percentage crystallinity and elastic recovery. [Copyright &y& Elsevier]

Abstract: The mechanical response of calcium carbonate-reinforced high density polyethylene nanocomposite is investigated and the behavior compared with the unreinforced polyethylene processed under similar conditions. The reinforcement of high density polyethylene with nanocalcium carbonate retains adequately high strength in the temperature range of −40 to +20°C. The positive influence of reinforcement on the impact strength is reflected in the fracture characteristics and is attributed predominantly to the nucleating effect of calcium carbonate in decreasing the spherulite size. The achievement of high impact strength is accompanied by increase in modulus and no loss in yield strength. The reinforcement of neat high density polyethylene (HDPE) with nanocalcium carbonate alters the deformation micromechanism from crazing–tearing in HDPE to fibrillated fracture in polymer nanocomposite. [Copyright &y& Elsevier]

The article examines the mechanically-induced surface damage introduced during scratching of polyethylene-clay nanocomposites using electron microscopy. The role of clay in reducing the susceptibility to surface deformation is estimated from the characteristics of surface morphology and the scratch deformation parameters. The scratch deformation behavior is explained in terms of tensile modulus, percentage crystallinity, elastic recovery and scratch hardness.

Abstract: The study describes the surface deformation behavior and susceptibility to surface damage in two clay-reinforced intercalated polymer nanocomposite systems that have significant differences in ductility. Neat polybutene (PB) experiences a severe and distinct ‘quasi-periodic psiloma-type’ deformation process that was absent on reinforcement with clay. In clay-PB nanocomposite system, ‘ironing,’ a less severe surface damage mechanism is dominant. While in the less ductile polymethylpentene (PMP) polymer system, ploughing–tearing and micro-voiding constitute the surface deformation mechanism. Both the clay-reinforced polymer nanocomposite systems experience significantly reduced stress whitening and is characterized by a lower change in gray level. The optical transparency of the polymeric systems is governed by the micromechanism of deformation and is greater for the ductile PB system. The difference in the susceptibility to surface deformation behavior is discussed in terms of mechanical properties and clay-induced structural changes. The reinforcement of polymers with nanoclay has a positive overriding positive influence on the modulus and yield strength that increases the resistance to surface deformation. [Copyright &y& Elsevier]

Abstract: There are many microvoids in alloy materials and the many microvoids are spherical in these materials. A spherical void cell model is presented. The microscopic stain field and the increment of the intrinsic time measure of the model are derived from its microscopic velocity field. They are used for obtaining the equation of the void evolution and the softening function related to void evolution. After the softening function is embedded to elastoplastic constitutive equations based on a simple mechanical model, the constitutive equations considering void evolution are obtained. The corresponding numerical algorithm of the constitutive equations are put forward and applied to the computation of the deformation and damage of a pearlitic alloy steel. It shows that the computed result is well consistent with the experimental data. [Copyright &y& Elsevier]

Abstract: The near surface deformation during scratching of neat polypropylene (PP) and polymer nanocomposites (PP–clay) at loads of 0.2–6kgf is described in terms of characteristics of scratch morphology and scratch deformation parameters. In neat PP, the application of higher loads introduces severe ironing deformation, disrupting the periodic parabolic nature of scratch tracks such that the material plastically flows along the ironing zone. Under identical test conditions, the severity of surface deformation in PP–clay nanocomposites, which leads to stress whitening is significantly reduced. At lower loads, the periodic nature of tracks is retained together with ironing, while at higher loads, ploughing occurred. The resistance to scratch deformation is discussed in terms of modulus, elastic recovery, and scratch hardness. [Copyright &y& Elsevier]