Initiation of fracture at the interface corner of bi-material joints

Within the context of linear elasticity, a stress singularity of the form Hr(lambda-1) may exist at the interface corner of a bi-material joint, where r is the radial distance from the corner, H is the stress intensity factor and lambda - 1 is the order of the singularity. Recent experimental results in the literature support the use of a critical value of the intensity factor H = H-c as a fracture initiation criterion at the interface corner. In this paper, we examine the validity and limitations of this criterion for predicting the onset of fracture in a butt joint consisting of a thin layer of an elastic-plastic adhesive layer sandwiched between two elastic adherends. The evolution of plastic deformation at the corner is determined theoretically and by the finite element method, and the solution is compared with the extent of the elastic singular field. It is shown that H, is a valid fracture parameter if h > B(H-c/sigma(Y))(1/(1-lambda)) where the non-dimensional constant B = 100 for beta = 0 and B = 13 for beta=alpha/4. Here, h is the thickness of the adhesive layer, sigma(Y) is the uniaxial yield stress of the bulk adhesive and (alpha, beta) are Dundurs' parameters (Dundurs, J., J. Appl. Mech. 36 (1969) 650). Experimental results for aluminium/epoxy/aluminium and brass/solder/brass sandwiched joints are used to assess the role of plastic deformation on the validity of the failure criterion. (C) 2002 Elsevier Science Ltd. All rights reserved.