Bug with PressureDependentElastic3D material

[david4utd]

Hi,
I've noticed that the source code for the PressureDependentElastic3D material may have a problem in it. If I'm not mistaken, OpenSees takes compression as negative just as in conventional continuum mechanics, but the way the cut off pressure is set in the code will give you the wrong elastic modulus because it states if p is smaller than p_cut (positive), then p=p_cut, which would totally do the opposite to what we would want it to do. I don't know if I'm mistaken or maybe a newer version has changed this piece, but simple calculation results indicate that this is probably wrong.

The part of the code goes:
double p = p_n;
if (p <= p_cutoff)
p = p_cutoff;
double Eo = E * pow(p/p_ref, exp0);