Hi,

I am trying to create a constitutive model for a TPU material, I have identified the following coefficients for the Arruda Boyce model but when testing the material in a tensile test simulation I appear to be getting the wrong response, could someone please suggest what the issue might be please.

Arruda Boyce coefficients: mu:2.5MPa, lambda_m: 3.5, D: 0

Strain rate: 0.013/s

Gauge length of specimen: 15mm

Step time: 230s

Displacement load: 45mm

Max strain: 300% 

Below is the stress strain response I am getting from the simulation, I have tested the Ogden model also and recieved same response.

Any suggestions are welcome, thanks in advance