Constant stress triaxiality using displacement

[bigmanrunning]

Hi Guys,

I am using a spring to apply a force to the surface of a cube in the z axis direction. The surface nodes are tied together, so the pressure/stress applied is S = Force_spring/Area_surface.

I want to apply another stress/pressure in the y and x directions that is related to the z direction stress/pressure by a stress triaxiality factor T defined as the ratio between hydrostatic stress and equivalent von mises stress. This stress triaxiality must be satisfied during every increment. I can't use kinematic coupling because of anisotropy in the material model. I know I can use an user element to achieve what I want and I can also apply pressure loads that ramp linearly over the simulation thereby preserving the stress T, but is there a method that doesn't need user elements that will allow me to apply the stress using displacement?

Thanks