Cyclic response of thermoplastics
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In the first part of this thesis, the focus is on describing what viscoelasticity is and what effects viscoelasticity cause in materials. Then several different material models are described and their constitutive relations are derived. The materials used in the laboratory tests reported herein, PEHD and PVC, were investigated and their structure and important properties were reported. Two constitutive models are then investigated. One of the models is a hyperelastic-viscoplastic model designed to model large deformation behavior. And one is a purely viscoelastic model, which means that it can only accurately model deformations in the elastic range. Both are made at SIMLab, NTNU and implemented as user-defined material models in LS-DYNA. In the last part of the thesis work these models are calibrated and validation tests are run in LS-DYNA to seehow the models perform compared to the laboratory tests.