The edge delamination test (EDT) is being developed to measure the critical energy required to cause a thin film, under biaxial tensile stress, to debond from a rigid substrate[1]. The test uses circular features etched through biaxially stressed films adhered to a rigid substrate. If the stress is large enough, a stable debond ring grows radially about the feature. We use a finite element analysis to model the test, solving for the applied strain energy release rate as a function of crack length, feature hole radius and other geometrical parameters. The model identifies both mode I and mode II components of the strain energy release rate, and agrees with previous analytical solutions for the total debond energy. However, the model predicts, with a very refined mesh at the crack tip, the fracture process is pure mode I. To explore this result, critical strain energy release rates from the EDT and the island blister test (IBT) are compared. This agreement supports the model prediction that the failure process in the EDT is modeI peeling.

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The thermosetting polyimide, PMR-15, is the leading contender for use in polymer matrix composites intended for high temperature applications. Although the properties of PMR-15 are generally good, its widespread use in aircraft and aeroengines has been hampered by a number of drawbacks. Among these are microcracking due to thermal cycling, irreproducibility of processing and the toxicity of the methylene diamine comonomer. The aim of the work reported here was to develop a PMR-type polyimide with properties equivalent to conventional PMR-15 but with none of the drawbacks. A key target of the work was to reduce the hazards associated with the use of methylene dianiline (MDA). Consequently, much of the work involved screening formulations in which MDA was replaced by a diamine of reduced toxicity. One formulation, coded B1, has been identified of which initial results look extremely promising. This formulation uses a partially fluorinated, four-ring diamine of low toxicity. This material was synthesized in-house and subsequently scaled-up in a semi-commercial process. Prepreg was manufactured on commercial equipment. Cure cycles were developed using mechanical spectrometry (RDS). Laminates were made by autoclave molding, and mechanical properties before and after high temperature ageing were determined. Preliminary results show that the B1 formulation compares favorably with conventional PMR-15.

A review on the requirement of the mechanical behaviour of composite materials under high strain rate and impact loading conditions is given. A technique for the determination of the mechanical behaviour is described and some data and experimental results are presented