Discussion Forum

Hello everyone,

I am modeling a thernal shock process of a Ag-SnO2 composite on a representative cell. The zero stress state starts from 800 C, and then cooling to room temperautre.

As the CTE of Ag and SnO2 are very different, the thermal stress induces. The SnO2 is considered always in elastic, while the Ag is considered as plastic. For simplify the model, I use the perfect plasticity, with a von mises stress yield function and a constant initial yield stress (55e6).

The model runs convergely, as the volume shrinks during the cooling.

However, as I processing the average von mises stress of the Ag, the pattern does not increase smoothly but in a sawtooth shape. Meanwhile, the volumetric plastic strain does not increasely, but grows in a repeating step-grow pattern as shown in the images.

In principle, the von mises and the volumetric plastic strain should increase gradually, at least not increase by steps. I find the principle stretchs are growing gradually, but the directions of the principle stretchs in space is changing. So I wander if the changing directions of the principle stretch is related to this strange behaviors.