EFFECTS OF STRAIN RATE AND TEMPERATURE ON DUCTILE DAMAGE OF METALS

Ductile damage appears in ductile metallic materials when these undergo sufficient plastic deformation, and it is caused by voids and microcracks that are formed within the material due to those severe conditions. The main interest of the present research is to experimentally characterise ductile damage in different conditions of strain rate (from quasi-static to 103s-1) and temperature (from-80 C to 180 C). Estimations of damage accumulation along the plastic regime have been taken by measuring the stiffness reduction of the material. The effects of strain localisation and necking have been accounted for by monitoring the changes in the geometry of the specimens during the test. At high speed these experiments have required the use of an in-situ shadowgraph method to monitor the sample silhouette and accurately calculate stress-strain behaviour throughout the test. The design of a novel experimental rig to perform high speed interrupted tensile tests has also been needed, in order to measure the damage accumulation in those conditions. The low and high temperature tests have been carried out inside an environmental chamber maintaining the rest of the technique unchanged. These experiments at varying strain rate and temperature have allowed to better understand the effect these conditions have on damage properties.