In Explicit Dynamics system, by default all geometric bodies must have the same initial temperature, i.e., room temperature in Johnson Cook material model to start with. The initial temperature is the Environmental Temperature specified in the Explicit Dynamics system. If user wants to have different initial body temperatures for each body or each element, user could use External Data to read the temperature distribution and then map the temperature to the materials in Explicit Dynamics system. Please be aware that due to thermal softening, the yield stress may be different from element to element based upon the temperature that the element has.