Enhanced Measurements of Large Deformations of Thermoplastics

The purpose of this study is to evaluate a numerical material model for thermoplastics developed at SIMLab, NTNU. Several experimental tests, using both HDPE and PVC, were conducted in order to have a basis for calibrating the material model. The focus of this thesis has been on optimizing the methods for retrieving the results of the experimental tests and numerical simulations.3D digital image correlation (DIC) was used to obtain the strains from the experimental tests. This proved very successful for the tension tests, but did not work well for longitudinal strains of the compression tests, which had to be calculated from the displacement. The 3D DIC analysis also allows for test specimens with circular cross sections to be used. These specimens proved to get better results than the quadratic specimens used in previous studies.Obtaining the strains from the numerical simulations was done by two different methods. One method was getting the strains directly from all the elements in one cross section; the other was calculating the strains from the displacement of the nodes on the surface of the specimen. This last method is equivalent to the DIC analysis, and resulted in a better match between the experimental and simulation results of the tension tests.The numerical model was largely able to reproduce the results of the experimental tests. The biggest problem seems to stem from the simulations having a higher strain rate than the experimental tests