I learn a lot from this great website. Thank you very much! Now its for me to ask the stupid question as follows: 😆
I am working on a project involving high velocity impact on braided composites, and I try to do some micromechanics analysis. One step is I need the material law for matrix. In my case, the matrix is toughened epoxy, such as 977-2, And I have tension, compression and shear data at the different strain rates (from low 10-5/s to high 500 /s). However, I dont have any unloading data for those materials. Can you give me some suggestion on how to model this material?
1. I already programmed a UMAT based on the combination of Drucker-Prager yielding model and Bodners state variable theory in LSDYNA. And I use explicit method. In the one element test, the simulation can simultaneously match test data in shear and tension at different strain rates using one group of material parameters, but I need to adjust parameters for compression. (is this strange?) The more serious thing is I do multi-axial simulation, the simulation results are very very 🙄 strange, such as softening. What could cause the above problem?
2. Whats kind of unloading curve shape should be for toughened epoxy? In my understanding, epoxy is thermosets, my stupid question is whether thermosets have plastic deformation from the viewpoint of micromechanics? 😥 The idea using Drucker-Prager model is from other researchers work on thermoplastics.