Grant: Discovery Grants Program - Individual

Real materials are complex, inhomogeneous collections of highly anisotropic crystallites. Their mean response may approach the isotropic behaviour often assumed in practical applications.  However, many responses cannot be understood without accounting for the inherently inhomogeneous behaviour. Texture development, earring, intergranular failure, stress corrosion cracking and many other effects are dependent not on average stress, but rather on the local behaviour and the distribution of stresses around the average. When such materials are subjected to cyclic loading, they undergo irreversible microstructural change. After a number of fatigue cycles, cracks initiate and propagate through the specimen until failure occurs - this is the topic of the research program. As well as conventional techniques (microscopy) a range of diffraction techniques will be used to study, e.g. energy storage / dissipation as a function of local microstructure and the influence of microstructure on relaxation / deformation mechanisms. Diffraction can reveal many microstructural changes which are likely to have an influence on fatigue behaviour: the stress both between and within grains, and deformation-induced phase transformations or grain rotation/reorientation. Micromechanical models of plasticity have been highly successful in predicting the response of materials under simple loading conditions. Diffraction monitoring of grain populations is a powerful tool in exploring model limits, as well as tuning / validating them. We will combine experimental diffraction data with polycrystalline models to explore the contributions of local properties to the way that cracks form and grow. While temperature and stress provide two key variables for investigation, we will also investigate irradiation. Materials behave differently in a radiation environment than in conventional applications due to the presence of high energy particles. These cause atomic displacements by elastic collision with atoms, resulting in significant changes in material properties. We will use accelerator technology to simulate the conditions which can be found inside a nuclear reactor or in the hostile environment of space. The information from the combined experimental and modeling studies will highlight the influence of local response and atomic scale damage on accumulated deformation and energy storage as well as crack propagation and stress relief. It will provide an understanding of the influence of microscopic mechanisms on macroscale behaviour of engineering relevant alloys, and will have an impact on a range of industries including power generation, aerospace and automotive. This proposal will provide information that is simply not available through post-mortem analysis or conventional experiments, opening up new avenues of science. It will train HQP in state of the art experimental and modelling techniques.