Fatigue Injection Moulded Short Fibre Reinforced Polymers

University essay from KTH/Hållfasthetslära (Inst.)

Author: Axel Eriksson; [2019]

Keywords: ;

Abstract: In order to keep up with the increasing demand of fuel-efficiency in the transportationindustry, the interest of making the vehicles as lightweight as possible is steadilyincreasing. One of the ways of reducing the weight is to introduce an anisotropicmaterial as Short Fibre Reinforced Polymers (SFRP) as a replacement for structuralparts made out of metals. To meet the modern vehicle design process which strivestowards a more simulation driven workflow, the need for accurate simulations offibre reinforced composites is of importance.This thesis aims to evaluate and find a working process for fatigue analysis of injectionmoulded SFRP components. To evaluate the fatigue analysis procedure anexisting SFRP component has been studied. The component is the front bracket thatmounts the roof air deflector to the roof on Scania trucks. To correlate the fatigue lifeestimation from the fatigue analysis, experiments were performed at ÅF Test Centerin Borlänge.The anisotropic behaviour is modelled using the commercial software Digimat togetherwith an injection simulation provided by Scania, to estimate the fibre orientationand thereby the material behaviour of the SFRP component. The fatigue analysiswas conducted by performing a coupled structural analysis between Digimat-Abaqus and then import the resulting stress- and strain-fields into the fatigue postprocessornCode DesignLife. The stress is then cyclic tested towards experimentallydetermined S-N curves determined in Digimat.Due to restriction of available fatigue data for the plastic in the front bracket, a fatiguematerial model for a plastic containing the same fibres and matrix but witha different fibre amount was implemented. The fatigue data were scaled using theUTS method to get a good characterisation of the real-life material behaviour of theplastic of the front bracket component.From the correlation between the fatigue analysis and performed experiments, itwas shown that the simulated fatigue life was conservative compared to the fatiguelife determined from the experiments. However, the correlation between the fatigueanalysis and experiments is not fully captured but gives a better estimation of thefatigue life compared to performing the fatigue analysis using an isotropic materialmodel.

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