Learning Forum

[karun00162]

Hello,

I am using multi-linear material property for TPU (thermoplastic polyurethane) polymer up to 70% of strain. As stress-strain curve for TPU is non-linear after 10% strain, I used Linear elastic (Isotropic elasticity) and Plasticity (Multilinear Isotropic hardening). Would this be correct ? as I do not need to use hyper-elastic models due to some constraints. I used Young's modulus of 20 MPa and Poisson's ratio 0.48. 

[Bhargava Sista]

Thermoplastics are challenging to model as they tend to have nonlinear elastic behavior followed by compressible plastic deformation. There are no off-the-shelf material models for such behavior but depending on the application, one may use multilinear plasticity models (which are meant for metal plasticity). However, make note of one major limitation: the plastic deformation in metals is incompressible which is not the case in thermoplastics. This may not be a problem at moderate deformation but at very large deformations you may start seeing that the material becomes unstable (force reaction drops upon further loading). 

To make the long story short: yes, you can use the multilinear plasticity model for thermoplastics but do verify the results especially at large strains.

[karun00162]

Thank you 

[karun00162]

Hello sir,

I am trying to study interface crack fracture toughness between linear elastic (material 1) and non-linear elastic (material 2). 

Well, using multilinear isotropic hardening material model (for material 2) gives higher J-integral values but using bilinear isotropic hardening does give lower and expected J-integral values. As J-integral can be used or approximated for non-linear elastic models, then would bilinear isotropic hardening model would be the right fit for material 2 ?

The doubt I am having is that as bilinear isotropic hardening model asks for Yield strength and Tangent modulus, in actual stress-strain graph of material 2, no yielding occurs up to 100% strain (and the actual whole part is also below 100% strain). I am just curious to know that how does this bilinear isotropic hardening material model interpret J-integral values ?

Thanks.

[SK Abdul Alim]

Hi, I am a newbie working on Ansys. I am also trying to add TPU as material. Can you please tell me how you did it?