The solution of elasticity problems for the half-space by the method of Green and Collins

The paper reviews the method of complex potential functions developed by Green and Collins as applied to axisymmetric mixed boundary value problems in elasticity for the half-space. It is shown how the method can be applied to problems in several coupled potential functions such as adhesive and frictional contact problems, to problems involving annular regions and to problems in thermoelasticity. Attention is given to the question of choosing a formulation which leads to a well-behaved numerical solution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41802/1/10494_2004_Article_BF00386216.pd

Strain rate sensitivity of sintered silver nanoparticles using rate-jump indentation

Nanoindentation experiments were performed at room temperature on pressure-less sintered silver nanoparticles (AgNP) samples. Two representative die attach solder materials: sintered electrically conductive silver adhesive and conventional Sn-3.0Ag center dot 0.5Cu solder were investigated. A novel technique of multiple strain-rate jumps is adopted accompanied by the continuous stiffness measurement, which can effectively determine the strain rate sensitivity (SRS) with good accuracy. Different strain rates and indentation depths are considered to obtain the nanomechanical properties such as hardness and Young's modulus. Compared with Young's modulus of sintered AgNP, the effect of applied strain rate is more influential to the hardness. In the loading stage, the SRS exponent decreases due to a smaller variation of hardness at a greater indentation depth. In the holding stage prior to the unloading of the applied indentation force, the creep displacement is relatively insensitive to the applied strain rate, however, the creep strain rate decays exponentially and the corresponding stress exponents are determined. (C) 2018 Elsevier Ltd. All rights reserved

Annealing effect on residual stress of Sn-3.0Ag-0.5Cu solder measured by nanoindentation and constitutive experiments

In this study, residual stress in Sn-3.0Ag-0.5Cu lead-free solder after annealing at varying temperature and duration was investigated by nanoindentation and uniaxial tensile experiments. Based on the unloading response of load-penetration depth, the contact stiffness was theoretically calculated and found to be decreased with increasing annealing duration especially at the annealing temperature of 210 degrees C. Additionally, the effect of residual stress on constitutive behaviour at strain rates of 1 x 10(-3) s(-1), 5 x 10(-4)s(-1) and 1 x 10(-4) s(-1) was consistently observed. By correlating residual stress and elastic indentation recovery, it was confirmed that greater contact stiffness is induced by greater compressive residual stress. Therefore, the optimal annealing condition of SAC305 solder is 210 degrees C for 12 h, which is believed to minimize the residual stress and stabilize the mechanical property of annealed solder.</p

Characteristics of stress relaxation kinetics of La60Ni15Al25 bulk metallic glass

The 0 relaxation typically plays an important role in the plastic deformation of glassy materials. Compared with amorphous polymers, most of the metallic glasses do not show evident beta-relaxation based on mechanical spectroscopy. However, La60Ni15Al25 bulk metallic glass (BMG) exhibits a prominent beta relaxation process, which could be an ideal model alloy to investigate the correlation between the beta relaxation and mechanical behavior of metallic glasses. In this work, compressive properties and stress relaxation at high temperature (below glass transition temperature T-g) were studied. Stress relaxation of La60Ni15Al25 BMG was measured by uniaxial compressive tests and mechanical spectroscopy around both a and beta relaxation temperature domain. At higher temperatures and sufficiently low strain rate, the flow behavior of the La50Ni15Al25 BMG could be simulated by a master curve, showing that the behavior is independent of temperature, especially on the proximity of the beta relaxation process. Because the existence of the beta relaxation, a high value of the activation volume for the plastic deformation could be ascribed to the existence of a specific atomic arrangement in the La(60)Nt(15)Al(25) BMG. It is found that compressive stress relaxation kinetics parameter remains temperature independent below T-g. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Irreversible matter creation in inflationary cosmology

Irreversible matter creation is investigated in a two-component (scalar field and ordinary matter) cosmological fluid in a homogeneous spatially flat and isotropic Friedmann-Robertson-Walker (FRW) inflationary Universe during its reheating era. The thermodynamics of open systems as applied together with the gravitational field equations to the two-component cosmological fluid leads to a generalisation of the elementary reheating theory in which the decay (creation) pressures are explicitly considered as parts of the fluid stress-energy tensor. Particular models describing coherently oscillating scalar waves and leading to a high particle production at the beginning of the oscillatory period are considered too.link_to_subscribed_fulltex