Fracture in thin sheets due to biaxial loading

Abstract

Although actual structural members are subjected to multi-axial loads, material properties are derived from expurim ntal works in a single-direotion load application. Thus analysis of materials under multi-axial loads helps to understand the actual situation prevailing in structural members in operation. In this thesis the Griffith's fracture criterion and linear elastic fracture mechanics are used to predict the stress needed to rupture a biaxially loaded specimen containing a central crack. The analytical results suggest dependence of the critical strocc on oombLna Ll.on n 01' I'ol nson 's rat i.o, biaxiality, crack inclination and. on whether the state of plane stress or plane strain prevails. Experimental work performed on mild steel specimens for the horizontal crack (a=90o) indicate increased critical stress with increasing biaxiality whereas the effect on PVC specimens with the same crack inclination was the revere and this agreed ~ith the predictions of the analytical results.

, The experimental work also included fatigue tests on the steel specimens while different horizontal loads were applied. The fatigue crack propagation data indicated dependence of the FCG rate on the applied horizontal load such that there is a higher crack growth rate with higher horizontal loads.