IABEM 2002, International Association for Boundary Element Methods, UT Austin, TX, USA, May 28-30, 2002 A symmetric boundary integral formulation for cohesive interface problems. A. Salvadori 1 Dept. of Civil Engng., University of Brescia, via Branze 38, 25123 Brescia, ITALY Abstract An incremental symmetric boundary integral formulation for the problem of many domains connected by non-linear cohesive interfaces is here presented. The problem of domains with traction-free cracks and/or rigid connections are particular instances of the proposed cohesive formulation. The numerical approxima- tion of the considered problem is achieved by the symmetric Galerkin boundary element method. 1 Introduction The present work deals with isotropic linear elastic bodies linked to each other by interfaces. In particular, M non linear cohesive interfaces are considered to connect N domains made of different materials. Under the assumption of small displacements and strains, the response of such a system to quasi-static external actions is studied. The problem of N domains with M traction- free or pressurized cracks and/or rigid connections are particular instances of the proposed cohesive formulation. The subject of the present work is significant to predict the mechanical behavior and to assess the safety factor of structures. The interface between different materials is indeed one of the most important regions governing the strength and stability of structures (Chandra Kishen, 1996) and plays a major role in fracturing of quasi brittle materials (Salvadori, 1999), polymer (Lauke and Schueller, 2001), ceramics and composites (Smith and Teng, 2001), bioengineering materials, bi- ological solids and tissues (Middleton et al., 1996). Investigations over interface constitutive laws have been undergoing a great development in the last years. Starting from pioneering works, co- hesive interfaces are often modelled by a (holonomic) nonlinear elastic relation between cohesive tractions p and opening displacement w (Hillerborg et al., 1976). This approach is meaning- ful only when local unloading can be reasonably assumed as negligible. During the last decade, various authors proposed non-associated elastoplastic cohesive models to describe the interface be- havior under combined normal and shear stresses in the presence of local unloading. A literature review on the subject can be found in (Salvadori, 1999). For the problem of N domains connected by M cohesive non linear interfaces, a boundary integral incremental formulation is given (section 2), in terms of the displacement fields u, v, the traction field t and the displacements discontinuity field w along the interfaces. The integral operator that governs the problem, in presence of a holonomic interface law, is proved to be linear 1 email: alberto@ing.unibs.it 1