| Summary: | The demand for materials with high strength- and stiffness-to-weight ratios has been driving the development of new metal matrix composites for the past few decades. Among the various possibilities, the 2124 aluminium alloy reinforced with silicon carbide particles is a good alternative in applications where quasi-isotropic properties are required. Although faster quench cooling rates generally result in improved mechanical properties in these composites, residual stress levels also become higher. High residual stress levels, although beneficial in some circumstances, may lead to distortions or even premature failure of the structure. This thesis presents the following original contributions to knowledge: (1) the characterisation of the mechanical properties of two novel composites reinforced with different volume fractions of sub-micrornetre-sized SiC particulates after a quench in either cold water or a 25%vol. polymer-glycol solution followed by annealing, where simultaneous improvement in tensile strength, ductility, hardness, fracture toughness and fatigue crack growth have been observed with the use of cold water as a quenchant; (2) the validation and first application of the contour method to measure residual stresses in such particulate reinforced composites, which showed that although better mechanical performance is obtained with the use of cold water as a quenchant, the residual stress levels introduced by this quench are also higher, which was undesired; (3) the first attempt to apply the fracture contour method to a pair of surfaces containing a fatigue crack and a new method to extend the fracture contour method to measure 2-D maps of shear-residual residual stresses in addition to the normal component, which was the first experimental proof of the entire theory of the contour method and possibly of Bueckner's superposition principle in 3-D.
|
|---|
