The Deformation of Gray Cast Irons under Combined Stresses

Abstract

One of the authors presented a fracture criterion of metals in a general form previously, explaining the fractures under polyaxial stresses and the notch brittleness of ductile metals. To ascertain the validity and applicability of this criterion to brittle metals, we carried out fracture tests on thin-walled-tubes of gray cast irons under various ratios of combined tension and torsion, measuring all strain components independently. In this paper, only the deformation behaviours before fracture are reported. First, the distinguishing characteristics under fundamental tension and compression, which have not been seen in ductile metals, are explained by taking account of the notch effect due to heterogeneous graphites in perlitic matrix. Then, a number of specularities in elastic and plastic behaviours under combined stresses can be well explained analytically. On the basis of the above mechanism, the fracture will be discussed in a following paper by applying the fracture criterion.