Critical Examination of the Use of Coherent Gradient Sensing in Measuring Fracture Parameters in Functionally Graded Materials

Abstract

Specific relations for out-of-plane deformation near crack tips of linearly graded materials are introduced and used with the optical method of coherent gradient sensing (CGS) to interpret experimentally obtained fringes. Stress intensity factors are thus derived and used to reconstruct synthetic fringes that are then compared to experimental ones. An error function is used with sets of 2-6 terms in the asymptotic solution to gage the incremental accuracy contributed by using these additional terms with the experimental results. The study reveals the necessity of using up to the sixth higher-order term to obtain a precise agreement between the analytical solution and the experimental interferograms. Specimen configurations with cracks consecutively positioned at the stiffer, and then at the more compliant end of the gradient are used. Distinct features of the interferograms indicate the benefits of having the crack on the compliant side of the elastic modulus variation.