Modeling the deformation behavior of a Sn-Pb solder alloy using the simplified viscoplasticity theory based on overstress (VBO)

Stress-strain diagrams showing the influence of strain rate at five differe nt high homologous temperatures for a Sn-Pb solder alloy are used to determ ine the material parameters in a minimal version of the viscoplasticity the ory based on overstress (VBO), accounting for static recovery effects. VBO is a "unified" state variable theory that does not use a yield surface and has three state variables with appropriate growth laws. It is shown that th e effects of strain rate can be modeled well by this theory that requires e ight material parameters to describe the inelastic behavior. The behavior i n tensile and cyclic strain-controlled loadings, ratcheting, and creep is p redicted. The results compare very well with the experiments for tensile an d cyclic loading. For the other tests no comparisons were made due to the l ack of proper experimental data. The model is formulated in tensorial form and can be used for inelastic stress analyses of solder joints.