Temperature dependence of mechanical properties of zinc and Zircaloy measured using miniaturised disc tests

A miniaturised, small punch disc test method has been used to measure the load-displacement curves for a pure polycrystalline zinc and a Zircaloy 4 zirconium based alloy. The latter has a more complex microstructure than the zinc, comprising α-phase (hcp) precipitates in a β-phase (bcc) matrix. The load-displacement curves have been measured over a range of temperature that spans the ductile to brittle transition, with both yield stress and fracture energy measured from these data. The temperature dependence of the yield strength for each material has been compared with the corresponding bulk value. The temperature dependence of the total fracture energy obtained from the disc specimens provides a measure of the ductile to brittle transition temperature. Values obtained using Charpy impact test energies have been compared with these data on an empirical basis. The results demonstrate the benefits of undertaking tests on small specimens to evaluate yield strength, fracture energy, the ductile to brittle transition temperature and to characterise the variation of fracture mode with temperature.