Biaxial cyclic high-strain fatigue of aluminum alloy RR58

Abstract

In the régime of biaxial high-strain fatigue there is a scarcity of data and consequently of information regarding methods of predicting such behaviour from simpler uniaxial tests. An investigation was carried out on the aluminum alloy RR58 in the form of cylindrical specimens subjected to axial tensile/compressive load and internal/external pressures at room temperature and 140°C. Additional tests were also conducted in separate cyclic torsion and uniaxial machines. The results in the range 100–5000 c indicated that the biaxial strain ratio 1/1 was the most severe case, the effect being less severe as the ratio changed to 1/-1. Of the correlation techniques examined the most successful was a von Mises strain function using the concept of a equivalent Poisson's ratio; the method of maximum shear strain showed promise. Comparative tests on the different cyclic test rigs on the same batch of material indicated the need for care when such aspects as specimen shape and definition of failure are considered, as well as the more obvious effects of material variation and anisotropy.