Compositionally graded materials with cracks normal to the elastic gradient

Mixed-mode crack tip deformations and fracture parameters in glass-filled e poxy beams with cracks normal to the elastic gradient are studied. Crack ti p fields are optically measured for different crack locations in the elasti c gradient when subjected to symmetric pure bending. A companion finite ele ment model is developed and validated by the measurements. The numerical mo del is then used to examine the influence of the elastic gradient on crack location by evaluating stress intensity factor, mode-mixity and energy rele ase rate. For certain crack locations, computed stress intensity factors an d 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 composition al gradients are examined and are successfully compared with the vanishing K-II criterion based on a locally homogeneous material behavior. (C) 2000 A cta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserve d.