The aim of this work is to study the behaviour of a crack with its tip at the interface between two polymer materials. A numerical model of a cracked bi-material tension specimen is investigated and different stability criteria are tested. The stability criterion of a general stress concentrator usually needs a relation between the critical value of the generalized stress intensity factor (HIC) and critical value of the stress intensity factor KIC (fracture toughness). This relation is a function of the elastic mismatch of particular mterials; the fracture toughness of the main material and the critical distance d ahead of the stress concentrator, where the criterion is applied. Estimation of distance d is usually not straightforward and different authors use different approaches for its determination. Therefore the main aim of this study is the mutual comparison of published approaches for d estimaton and to quantify the influence of d choice on the critical load value. The results obtained can lead to a better residual lifetime prediction and safer design of layered structures. and Obsahuje seznam literatury