A study of the stability of sharp notches in the orthotropic heterogeneous media T. Profant 1 , J. Klusák 2 and M. Kotoul 3 1,3 Brno University of Technology, Technická 2, 616 69, Brno, Czech Republic, profant@fme.vutbr.cz , kotoul@fme.vutbr.cz 2 Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62, Brno, Czech Republic, klusak@ipm.cz ABSTRACT. The bi-material notch composed of two orthotropic parts is considered. The radial and tangential stresses and strain energy density are expressed using the Stroh-Eshelby-Lekhnitskii formalism for the plane elasticity. The stress singular exponents and corresponding eigenvectors are the solution of the eigenvalue problem leading from the prescribed notch boundary and compatibility conditions. In generally, there is more than one solution of this eigenvalue problem and consequently the generalized stress intensity factors. The potential direction of the crack initiation is determined from the maximum mean value of the tangential stresses and local minimum of the mean value of the generalized strain energy density factor in both materials. Following the assumption of the same mechanism of the rupture in the case of the crack and the notch, an expression can be obtained for the critical values of the generalized stress intensity factor. INTRODUCTION In practical engineering structures or in parts of electronic devices joints of different materials occur (e.g. layered composite materials, constructions with protective surface layers, thermal barriers). They enable achievement of properties which could not be attained by means of homogeneous materials. In the case of composite materials, parts of the joints often exhibit orthotropic material properties. The stress field in closed vicinity of such material joints has singular character and complicated form. In comparison to a crack in homogeneous media, in the case of bi-material joints, the stress singularity exponent is different from 1/2 and can generally be complex. The stress is mostly characterized by more singular terms and at the same time each singular term covers combination of both normal and shear modes of loading. Such stress concentrators preclude any application of the fracture mechanics approaches originally developed for a crack in isotropic homogeneous materials, so the assessment of such singular stress concentrators becomes topical [1-3]. 733