Energy Education Science and Technology Part A: Energy Science and Research, vol.30, no.SPEC .ISS.1, pp.123-130, 2012 (Scopus)
Viscoplasticity theory based on overstress (VBO) is a state variable theory that does not use yield surface and has three state variables with appropriate growth laws which are in the form of stiff ordinary differential equations (ODE).Monotonic loading-unloading, cyclic hardening, cyclic softening, relaxation and creep can be simulated with the same material constants. In this paper, thermomechanical (TVBO) constitutive equations are implemented for solder alloy which is an important element used in electronics industry and frequently subjects to thermal cyclic loading. After validation of numerical equations with respect to experimental results for isothermal modeling, uniaxial stress-strain deformation behavior of Sn63Pb37 solder alloy has been investigated by DGEAR ODE solver for linearly increasing, linearly decreasing and constant temperature rates for various strain rates. It is shown that decreasing (increasing) strain rate and temperature rate by the same ratio do not yield the same stress-strain curve; however both follow the same trend. The results also indicate nonpatological behavior where a threshold exists for increasing temperature rates to yield a decrease in stress values. The thermomechanical model is suggested to be implemented for further use in inelastic finite element analysis of electronics structures. © Sila Science.