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An investigation of the failure behaviour of fibre reinforced polymers under bi-axial loading conditions

Monday, 20 December, 2010 - 13:00
Campus: Brussels Humanities, Sciences & Engineering campus
Andreas Makris
phd defence

The last decade’s composite materials are being increasingly used in many industrial sectors. Their high specific strength, stiffness and corrosion resistance make these materials very attractive for applications in aviation, submarine, automotive and energy domains. However, for a more wide spread use of composites in every industrial sector the ability to confidently predict their response under various types of loading is of paramount importance.

Predicting or analysing the failure behaviour of fibre reinforced composites is not a simple problem. Their anisotropic behaviour makes the accurate prediction of their failure mechanism much more difficult than for an isotropic material. Unfortunately, the current practice of using uniaxial tests as a basis for failure predictions under multi-axial stress states has been proven insufficient. Results from bi-axial testing and comparisons with failure theories can lead to a better understanding of composite’s mechanical behaviour under complex loading and hence to a more efficient usage of them.

This Phd work focuses on the optimisation and instrumentation of an experimental set-up for bi-axial testing of fibre reinforced composite materials. The bi-axial test bench uses four independent servo hydraulic actuators to introduce in-plane loads in a cruciform shaped test coupon. Carbon and glass epoxy material systems are tested under quasi-static bi-axial loading conditions. A full field optical measurement technique (Digital Image Correlation) is employed to capture the strain field of zones of interest and to evaluate the accuracy of the test. Experimental data are compared with numerical simulations and analytical predictions. As a result interesting information is obtained about the damage initiation and progression of commonly used cruciform specimens. Finally a numerical optimisation technique is coupled with a finite element model to come up with modifications of the cruciform geometry and to provide more accurate experimental data.