I have spent a lot of time in my career studying CPVC (chlorinated polyvinyl chloride). It is a material that is similar to PVC, but has better ductility and maintains its stiffness better at high temperatures. CPVC is used in many applications, one common example is cold and hot water delivery pipes. Typically CPVC performs well in this environment, but the material can become brittle if exposed to certain chemicals for an extended period of time. I have worked on at least one legal case related to this embrittlement issue. In preparation for this article, I poked around the basement of my house and I was able to quickly locate CPVC pipes and other plumbing components made from CPVC. Fortunately, none of the pipe clamps that I could see introduced significant strains in the CPVC components. So I expect the lifetime of the parts to be excellent.
In this article I examine 7 different candidate material models for CPVC, and show that 2 material models are significantly better than the traditional plasticity model. Can you guess which 2 material models are the most accurate?
Experimental Data Used for the CPVC Material Model Study
Figure 1. Experimental data used in the study.
In the following sections I will go through 7 different candidate material models in order from worst to best!
Results #7: Bergstrom-Boyce Model
Figure 2. Comparison between the experimental data and predictions from the Bergstrom-Boyce (BB) model. The average error in the model predictions is 22.4%. No good.
Results #6: Abaqus PRF3YP
Figure 3. The Abaqus Parallel Rhelogical Framework (PRF) model is not able to accurately predict the response of the CPVC. Particularly the unloading behavior is poor. The average error is 15.9%.
Results #5: Isotropic Hardening Plasticity
Figure 4. The isotropic hardening plasticity model does not work well for CPVC. This to be expected – this type of plasticity model never predicts the unloading response of polymers accurately. The average error is 14.8%.
Results #4: Kinematic Hardening Plasticity
Figure 5. The Abaqus combined hardening plasticity model and the Ansys Chaboche models cannot accurately predict the response of CPVC. Again, the unloading response is poorly predicted. Average error: 13.9%.
Results #3: Johnson-Cook Plasticity
Figure 6. The Johnson-Cook plasticity model cannot either predict the unloading response with accuracy. The average error in the model predictions is 12.5%.