Small punch testing of advanced metal matrix composites

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This Doctoral thesis investigates the use of the small punch test (SPT) as a means for assessing yield strength and fracture toughness from alloys and metal matrix composites (MMCs). Metal matrix composites have been implemented in many high performance applications due to their high strength to weight ratio, however, low fracture toughness and ductility remain a concern for these materials. Therefore, techniques for conventional mechanical tests including tensile and fracture toughness tests have been utilised to assess the mechanical performance for these materials, however, more often than not, situations will arise where there are limited volumes of material for testing, this is especially true in the case of MMCs. Thus, there is great demand for mechanical tests that are capable of assessing small samples. The small punch test (SPT) is proposed as a suitable small specimen mechanical test technique that is capable to meet this challenge. This research examines the SPT on MMCs and the effect of ceramic reinforcement content on yield strength and fracture toughness. To achieve this small punch, tensile and fracture toughness tests are performed on as-received 7A04-T6 aluminium and TC4 titanium alloy and related MMCs. In particular, small punch values such as the small punch elastic-plastic load, Py, equivalent fracture strain, eqF, and small punch energy, ESP, are correlated against conventional tensile yield strength, sYS, and plane-strain fracture toughness, J1c, values. Furthermore, empirical, analytical and numerical solutions are assessed. A polynomial relationship is found to correspond well with J1c-eqF relationship for both elastic and elastic-plastic materials. This research further investigates and develops the application of the SPT which may lead to an inexpensive straightforward multi-mechanical non-destructive test technique for advanced alloys and MMCs.
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