Hi,

In my simulation, I use two different sets of material properties and define the constitutive relation using vumat. The material properties and the vumat have been tested individually and they work fine.

When, I use two different sets of material properties simultaneously in simulation, I get the following error

***ERROR: Bad Material definition in element number 136 instance MERGE-1: zero or negative initial dilatational modulus caused by bad material data. Please check your material input and any initial conditions if necessary.

The dilatation modulus (= (stressNew-stressOld)/strainInc for both sets material parameters at t=0 is greater than zero. So i am not really sure, why this error would occur.

I would really appreciate inputs to tackle this problem.

Thanks