B-A1 Composite Failure Under Combined Torsion and Tension Loading

An essentially experimental investigation was made regarding the effect of combined torsion and tension loading on the fracture characteristics of an aluminium matrix, unidirectional boron fiber reinforced composite. Three types of loading path were considered. The experiments were performed on notched specimens thereby allowing the fracture behaviour to be tentatively interpreted in terms of linear elastic fracture mechanics. The combined mode fracture loads did not appear to obey a constant energy of fracture criterion. This conclusion is supported by a substantial difference in fracture surface morphology for pure tension and pure torsion loading. However, the lack of agreement between theory and experiment may be due to data reduction errors caused by the tendency for stable crack growth and plastic shear between the fiber and matrix to increase as the ratio of torsion to tension loading is increased. The fracture loads were found also to be loading path dependant with radial loading being the most severe.