Compositionally graded materials with cracks normal to the elastic gradient

Mixed-mode crack tip deformations and fracture parameters in glass-filled epoxy beams with cracks normal to the elastic gradient are studied. Crack tip fields are optically measured for different crack locations in the elastic gradient when subjected to symmetric pure bending. A companion finite element model is developed and validated by the measurements. The numerical model is then used to examine the influence of the elastic gradient on crack location by evaluating stress intensity factor, mode-mixity and energy release rate. For certain crack locations, computed stress intensity factors and energy release rates in the graded material exceed that of the bimaterial counterpart. However, when reconciled with measured critical values of the fracture parameters, graded beams show consistently better performance for all crack locations in the graded region. Crack kinking due to compositional gradients are examined and are successfully compared with the vanishing K-II criterion based on a locally homogeneous material behavior. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.