C.P. No. I306 PROCUREMENT EXECUTIVE, MINISTRY OF DEFENCE

Deformation and failure under multiaxial stresses-a survey of laboratory techniques and experimental-data-by-W, J. Evans National Gas Turbine Establishment SUMMARY A survey has been made of techniques for producing multiaxial stress conditions on a laboratory scale and it is concluded that one of the more suitable systems is combined tension-torsion of thin-walled tubes. Experimentally this technique, although complex, appears to offer several advantages. Furthermore, the shear/normal stress ratio can be conveniently controlled, thus enabling deformation and fracture mechanisms under multi-axial stresses to be studied. A review has also been presented of relevant experimental work, most of which has been concerned with assessment of the various deformation and failure criteria. Although there is some correlation for yield data, ductile or brittle fracture and creep behaviour, the situation is not nearly so well defined for fatigue. Work on the micro-structural effects of biaxial stresses is also considered. It would appear that although the mechanisms by which. dislocations operate remain unchanged from the uniaxial state, modifications can occur to the products of interactions between dislocations. In addition fracture behaviour can be altered by the ratio of tensile to shear stress. Generally, however, little work has been published on this aspect of deformation behaviour. It is concluded that it is important to study micro-structural effects particularly in relation to design criteria.