Plastic Stress–Strain Relations and Yield Surfaces for Aluminium Alloys:

The theoretical study of the behaviour of materials in the ‘plastic’ state has progressed rapidly on the basis of a few assumptions, some of which are insufficiently well supported, and even occasionally contradicted, by available experimental evidence.In the present work three types of experiment are carried out. In the first several different materials are ‘overstrained’ into the plastic region, either by tensile or by shear stresses, and then subjected to additional stresses, shear or tensile respectively, the modulus of resistance to the additional stresses being measured. Similar experiments have been carried out previously but the results are not wholly concordant. The present work indicates that for initially stress-free material the ‘incremental’ type of theory is well founded. An explanation for the behaviour of material in other conditions is suggested which does not involve the existence of ‘corners’ on the ‘yield surface‘overstrained’ into the plastic region, either by tensile or by shear stre...