Influence of strain rate and temperature on the failure criterion of aluminium AA7075

The damage and failure behaviour of the precipitation hardenable aluminium wrought alloy AA7075 is studied in tension tests under quasi-static and dyn amic loading conditions up to strain rates of (epsilon) over dot less than or equal to 5500 s(-1). The results determined at room temperature are comp ared with that received at an elevated temperature of 150 degreesC. Using d ifferent heat treatment conditions the influence of size, volume fraction a nd distribution of particles on the fracture strain can be determined. Expe riments with unnotched tensile specimens allow the investigation of the mat erial behaviour, which can be described by a constitutive model in case of high speed deformation. In addition to the increased strain rate sensitivit y and the adiabatic character of the deformation process with high strain r ates, successive structural damage has to be taken into account for a formu lation of the material law under tensile loading. Using differently notched tension bars the state of stress is varied and the influence of multiaxial ity on the elongation at fracture can be investigated. Combining experiment s and finite element simulation the failure criterion for ductile fracture will be formulated and the influence of an increased strain rate and temper ature on the local plastic deformation at fracture as a function of degree of multiaxiality can be determined. Applying the failure criterion the loca tion of crack initiation in notched bars resulting in ductile fracture can be determined.