Learning Forum

[Yspartan]

Hello,

I am trying to simulate a box drop made of Polypropylene. What material model will be best for capturing the softening behavior of the Polyproylene. I know Multilinear kinematic hardening model does not take in negative slopes and therefore is not suitable. Is there even a way to go about it? I see Bergstorm-Boyce is one of the models that have been previously considered for polycarbonates. I do have the capability to all the required testing, I just need to understand the best material model choice and how to go about it. Thank you!

[Yspartan]

hoping you see this !

[peteroznewman]

There are different material data needs for static analysis compared with dynamic analysis for an impact study. In statics, rate-dependent properties are unimportant, but in an impact problem, rate-dependent properties are very important. While there may be a negative slope (softening) in a quasi-static material test, there may be a much higher stiffness during impact.
ANSYS Help in the Mechanical APDL section has a Material Reference section and Chapter 4.5 is on Rate-Dependent Plasticity material models. Take a look at some of those. Perhaps others will reply with advice on which one to choose.
Take a look at the Explicit Dynamics material library. There are material models called Equation of State. I don't know how to create that kind of material model, but I see it is used frequently in the Explicit Dynamics material library.
What are the design requirements for the drop box? What is the peak acceleration that you are trying to stay below during impact? What is the mass inside the box?

[Yspartan]

Hello Peter, thank you very much for replying. The fea model that I am trying to create is of an existing product. The actual drop tests performed on the box have revealed plastic deformations in certain regions. I am trying to get the model to predict that. The box is dropped from 3ft height and impacts the surface at around 3.6m/s. The tests involves empty and 3kg weight drop test. I have been unsuccessful in finding appropriate literature on this.

[peteroznewman]

Thanks for that information. The purpose of the drop box is to reduce the peak acceleration on impact. What is an acceptable level of acceleration? If you can't answer that question, it is difficult to design a drop box.