Exjobbsförslag från företag

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Förslaget inkom 2004-12-08

Micromechanical modelling of time-dependent compressive relaxation of particle reinforced thermosets in joints for automotive applications

Background: Screw joints with high clamping forces are widely used in structures. For coated materials, the screw forces of the joint decrease with time which could subsequently lead to slippage and fatigue cracking. The force reduction is primarily due to creep deformations in the coating. If the mechanisms leading the stress relaxation were better understood, measures could be taken to reduce the unwanted decrease of load. This project is intended to shed light on the link circumscribed by the red dotted line in the appended figure of length scales. The other areas are treated in an ongoing PhD project at Scania in Södertälje and KTH Fibre and Polymer Technology.

Tasks: Modelling of constitutive time-dependent properties of unit cells of particle reinforced polymers (elastic particles in a linear viscoelastic matrix). The ABAQUS finite element software will be used. A parametric study will be carried out to provide deeper understanding which microstructural features that are important for the compressive relaxation of the coatings. Input data from experimental tests on the mechanical behaviour of the constituents will be used (values taken from literature or backed out from indentation tests). A comparison with simple analytical models, e.g. the one suggested by Hashin for spherical particles, will be made. The model will be validated by comparing predictions with trends regarding the effect of the geometry and volume fraction of reinforcement observed in experiments. The most important factors are filler content and thermoset properties. Literature values for ¿extreme case¿ polymers (e.g. polypropylene and densely cross-linked epoxy) will be used in a macroscopic model of a joint. Finally, a report should be written in English, and oral presentations should be given at Scania and KTH. Close collaboration with the Ph.D. project will be maintained throughout the M.Sc. thesis project. A realistic goal is that the outcome of the simulations should be of sufficiently high quality to be used in an article for peer-reviewed scientific journal.


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