ANALYSIS OF A WAVY CRACK IN SANDWICH SPECIMENS

A crack in a brittle adhesive layer joining two substrates can grow in a variety of ways. The crack can grow along one of the interfaces, within the adhesive or alternate between the two interfaces. In this paper, we consider a crack that grows along an alternating path between the two interfaces. A quantitative analysis of this elastic problem is carried out using the finite element method to predict the wavelength of the alternating crack. The joint is loaded remotely by the singular stress field for a cracked homogeneous solid, parameterised by K(I)infinity and K(II)infinity, and by an in-plane tensile residual stress delta-0 in the layer, parallel to the interface. The induced interfacial stress intensity factor and its phase angle-psi are evaluated and used to predict the onset of kinking out of the interface. The wavelength of the alternating crack is found to depend on the elastic mismatch parameters, alpha and beta, and on the level of residual stress in the layer. parameterised zeta=sigma-0 square-root h/square-root EBAR*GAMMA(I), where h is the adhesive layer thickness, EBAR* is a modulus quantity and GAMMA(I), is the toughness of the interface,