Temperature and strain rate dependent simulation of high speed tests before yielding
Martin Keuerleber, Nina Woike, Bernhard Möginger, Peter Eyerer
Universität Stuttgart, Institut für Kunststoffpruefung - IKP
Germany
Keywords: tensile tests, DMA, Maxwell
Present market forces dictates that the automotive industry must shorten development time and increase safety standards and crash-security. Therefore, FEA-Methods such as crash-simulations are increasingly important in the development process. For reliable simulation results, it is necessary to provide material data by high speed tensile tests at varying strain rates and temperatures. These tests are time consuming and expensive so a new and efficient way has to be found for generating these data.
The aim of this study is to compare the results gathered by DMA and compression tests with the elasticity modulus (E) measured in tensile tests to minimise the testing effort for complete material characterisation before yielding.
Therefore, DMA experiments at varying frequencies and temperatures were carried out with isotactic polypro-pylene (i-PP) MOPLEN HP 500 L. The storage moduli (G') were shifted over the frequencies to produce a mas-ter curve. The shifting factors of the master curve can be described by an arcus-tangent function (instead of WLF or Arrhenius). The loss moduli (G'') in combination with the storage moduli (G') are the base to generate pa-rameters for a generalised Maxwell model. To complete the necessary data for simulation the temperature de-pendent compression modulus (K) is measured.
For comparison, tensile tests at varying strain rates (10-4 s-1 to 102 s-1) and temperatures (-30°C to +40°C) are investigated. Thereby, the glass transition temperature is well inside the temperature range.
Simulation of high speed tensile tests are done by finite element analysis (FEA) with the software MARC based on the results of the DMA and compression tests. The results are compared with the experimental tensile tests. This is done to prove the equivalence of the described tests below and above glass transition at different strain rates