The Effect of Specimen and Testing Variables on the Fracture of some Fibre Reinforced Epoxy Resins

Abstract

The work of fracture of composite materials has often been measured without sufficient attention, for example, to specimen geometry and test conditions. In this work a range of testing techniques has been used to investigate how the measured work of fracture of unidirectionally- reinforced carbon fibre/epoxy composites, containing fibres of types 1 and 2, changes with various specimen and test variables. The measured work of fracture is seen to be independent of specimen width, and shows but slight dependence on notch root radius and test rate. More significant variations occur with orientation, specimen height and notch depth, however. Attempts are described to measure other fracture parameters which, for this class of materials, might prove to be of more value than the total work of fracture. In particular, an effort has been made to adapt the methods of Linear Elastic Fracture Mechanics, and some degree of success has been achieved in relating K _{1 c} , the critical stress intensity factor, measured by double edge notched plate techniques, and G _{1 c} , the critical strain energy release rate, with those measurements discussed previously.