Experimental Study on K-Dominance of Static Crack Tip in Functionally Gradient Materials

Abstract

In this paper, coherent gradient sensing (CGS) and digital speckle correlation method (DSCM) are introduced to study the K-dominance of static crack tip in functionally gradient materials (FGMs) with a crack oriented along the direction of the elastic gradient. And the numerical simulation is analyzed through finite element method (FEM). Firstly, the CGS and DSCM equations at the mode-I static crack tip of FGMs are developed, which can be used to calculate the stress intensity factors of FGMs. Secondly, three kinds of FGMs specimens with different variation of the modulus are prepared to observe the influences of the property variation on the K-dominance. Then three-point-bending experiments are carried out. The interference fringe pictures of CGS and the speckle patterns for DSCM on the specimens are shot through the camera. Thirdly, based on the results of the experiments, the stress intensity factors of three kinds of FGMs specimens are calculated by CGS and DSCM. Meanwhile, the stress intensity factors are obtained by FEM. Finally, comparing the results from CGS, DSCM and FEM, the K-dominance of mode-I static crack tip in FGMs is discussed in detail. It is found that the K-dominance of FGMs and homogenous material is almost same when the gradient index in FGMs is relatively small.