## General Mechanical

#### Adding plasticity and hardening rule in only one direction of orthotropic material

• Rodrigo28
Subscriber

Hi everyone!

I'm simulating the compressive behaviour perpendicular to the plane of cross-laminated timber panels for my master's thesis. I've done various experiments on my university, and now I want to validate a FEM model using this data.

I'm basing my study on a paper relating this issue, where plasticity and bilinear hardening has been applied only on the direction of the load , which is perpendicular to the plane (Z axis in my case), leaving other directions purely linear elastic. The author used user-programable features in Abaqus to accomplish this.

I thought that maybe I could replicate this using Hill's yielding criterion combined with isotropic bilinear hardening (already available in the GUI of Ansys). I'm trying to obtain the  same load-displacement curve of the aforementioned author, with the same elastic and plastic properties, load, etc.

For that, I chose Hill's yield stress ratios (Rij) equal to 1000 for every direction, except the normal Z one, which was equal to 1.

I combined that with isotropic bilinear hardening, defining 2,10 MPa and 3,0 MPa, the yield stress and linear hardening module (H) of wood in the radial direction (perpenicular to the panel plane), respectively. Therefore, the reference stress used in the yield criterion in ansys, is equal to 2,10 MPa.

Solving the problem, I get neither yielding or hardening, just a linear load-displacement result, along with a warning message saying that some Hill's constants were defined as non-positive, which could deliver a non-physical result. There constants are L, M, and N, which depend on Rxy, Ryz and Rxz. I then tried to assign them to unity, but nothing changed.

My question is, is there some way to use Hill's criterion to accomplish the behaviour I'm looking for, or any other GUI available option? Or is it only achievable via the usermat?

Thanks in advance for any help