Studies of and modelling of the fracture behaviour of composite materials

Griffin, David (1998) Studies of and modelling of the fracture behaviour of composite materials. Doctoral thesis, University of Northumbria at Newcastle.

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Abstract

The programme of work involved creating a new method of modelling to realistically predict failure in a unidirectional fibre-reinforced material and some experimental studies of the fatigue behaviour of A1203/CPA1 and A120J6061A1* composites.
For the modelling, a traditional linear elastic fracture mechanics stress intensity factor approach was initially used, in conjunction with finite element analysis, to predict crack growth. The limitations of conventional micromechanical models to single mode type failure was demonstrated and a more novel approach was used whereby a model which incorporated bonded surface algorithms was constructed; this model was capable of simulating multimode failure mechanisms.
The investigation was carried out using three different finite element analysis programmes: Display 3, Applied Structure and ABAQUS.
On running the simulation it was found that the fibre/matrix bond strength played a key role in determining the dominant failure mechanisms in the composite: a low bond strength resulted in debonding/fibre bridging as the dominant mode of failure, whereas a high bond strength indicated that catastrophic fracture in mode 1 failure was the more dominant mechanism.
The fatigue behaviour of the Al based MMCs was conducted at ambient temperatures. It was found that the A1203/6061 had the better fatigue properties and further work was carried out on this material in air and a simulated sea water environment. The sea water environmental tests showed that a reduction of approximately 4% in fatigue life compared to the results for fatiguing in air could be expected.

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