Effect of strain rate on continuum and pre-cracked polymer failure

Sammanfattning: The main intention of this thesis work was to investigate the effect of strain rate on continuum and pre-cracked polymer failure. Low-Density Polyethylene (LDPE) was chosen to study experimentally and numerically. In order to cover wide range of strain rates, four specific strain rates were selected for the uniaxial tensile tests. To perform the tests, cyclic loading and unloading with relaxation was utilized in the room temperature for continuum specimen and for pre-cracked specimen monotonic tensile test till failure was utilized. Through Digital Image Correlation (DIC) the local strain distribution was assessed through the specimen and the deformation was compared with simulation results. Based on the extensive literature review of material models from PolyUMod library among Viscoplastic models, the Three Network Viscoplastic (TNV) model was selected to proceed with the calibration. The motivation behind choosing TNV model is it's capability of capturing load-unload curves, different strain rates as well as non-linear responses. Furthermore, it was seen that among Viscoplastic models, TNV has the lowest average errors which plays a vital role in this case as the accuracy of FE simulation directly depends on the calibration results. From the experimental results it was safe to say that with increasing strain rates LDPE films tend to get stiffer and stronger both in continuum and pre-cracked. Through the calibration it was seen that the predicted curves were in reasonable agreement with experimental ones. Hence,the calibrated model was exported as python script into Abaqus CAE to perform the simulations. The comparison was done and discussed in details between the simulation and experimental data in three orientations; MD (Machine Direction), CD (Cross Direction) and 45 direction.