Mechanics and fracture of crack tip deformable bi-material interface Pizhong Qiao * , Jialai Wang Department of Civil Engineering, The University of Akron, 244 Sumner Street, Akron, OH 44325-3905, USA Received 4 December 2003; received in revised form 2 June 2004 Available online 20 July 2004 Abstract Novel interface deformable bi-layer beam theory is developed to account for local effects at crack tip of bi-material interface by modeling a bi-layer composite beam as two separate shear deformable sub-layers with consideration of crack tip deformation. Unlike the sub-layer model in the literature in which the crack tip deformations under the interface peel and shear stresses are ignored and thus a ‘‘rigid’’ joint is used, the present study introduces two interface compliances to account for the effect of interface stresses on the crack tip deformation which is referred to as the elastic foundation effect; thus a flexible condition along the interface is considered. Closed-form solutions of resultant forces, deformations, and interface stresses are obtained for each sub-layer in the bi-layer beam, of which the local effects at the crack tip are demonstrated. In this study, an elastic deformable crack tip model is presented for the first time which can improve the split beam solution. The present model is in excellent agreements with analytical 2-D continuum solutions and finite element analyses. The resulting crack tip rotation is then used to calculate the energy release rate (ERR) and stress intensity factor (SIF) of interface fracture in bi-layer materials. Explicit closed-form solutions for ERR and SIF are obtained for which both the transverse shear and crack tip deformation effects are accounted. Compared to the full continuum elasticity analysis, such as finite element analysis, the present solutions are much explicit, more applicable, while comparable in accuracy. Further, the concept of deformable crack tip model can be applied to other bi-layer beam analyses (e.g., delamination buckling and vibration, etc.). Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Bi-material layers; Crack tip element; Crack tip deformation; Interface fracture; Interface joint; Interface deformable bi-layer beam theory 1. Background A bi-material or bi-layer system is a common configuration in structural applications, and it is usually manufactured by either monolithically forming the two parts together or adhesively bonding the two substrate layers. Interface fracture or interlaminar delamination is one of most common failure modes in * Corresponding author. Tel.: +1-330-972-5226; fax: +1-330-972-6020. E-mail address: qiao@uakron.edu (P. Qiao). 0020-7683/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijsolstr.2004.06.006 International Journal of Solids and Structures 41 (2004) 7423–7444 www.elsevier.com/locate/ijsolstr