More reliable numerical simulation of impact loading of plastics
The performance of polymeric materials subjected to mechanical impact is of increasing interest, as these materials are frequently used in critical applications. The response to impact loads is of particular interest for automotive components with a role in passenger and pedestrian safety.
The present thesis considers the most common polymer material family used in cars, namely polypropylene-based materials. The thesis reports advances in experimental testing and numerical simulation, improving the understanding and prediction of the mechanical behavior of this class of materials. The PhD work was performed at SINTEF in Oslo, in collaboration with Plastal AS (Raufoss) and the University of Oslo.
The thesis addresses some of the challenges with these materials, both in terms of testing and simulation: The materials are highly ductile and special optical methods were used to obtain the true stress-strain up to large strains. Also, the mechanical properties are sensitive to the strain rate and the stress state (tension, compression, shear), and they are also affected by the processing (injection moulding in our case). Due to the complex mechanical response of these polypropylene-based materials, it is challenging to find an adequate material model which can be used by e.g. the automotive industry. The model should not require too much mechanical testing and data analysis, and it should not be too computation-intensive. Some of the challenges are related to uncertainties in the mechanical response and the testing, while some are related to limitations of the models.
The contribution of this thesis has been to improve the understanding of material performance and to address the challenges of material modelling for numerical simulations. As part of this, test methods and test specimen geometries have been analyzed. Finally, a material model specially developed for ductile polymers was calibrated with data from the thesis, and results from simulations were compared to experimental data for various loading cases.
After the defence: Hamid Daiyan (no 4 from the left) together with (from the left) Julio C. Viana (opponent from the University of Minho, Portugal), Erik Andreassen (principal supervisor, SINTEF), Einar L. Hinrichsen (research manager, polymer and composite materials, SINTEF), Harald Osnes (supervisor, University of Oslo) and Arild H. Clausen (opponent, NTNU). The third supervisor, Frode Grytten (SINTEF), was not present when the photo was taken.