What is the ratio of bending stress on Copper busbar due to short circuit to that for Aluminium busbar?

Bending stress between two parallel copper busbar due to short circuit current in panel boards. I know it for Copper busbar but need to know how much will it be for Aluminium busbar. If I know the ratio, I can easily calculate it. For this i think I‘ll need ratio of strength of Copper Aluminium.Thanks!