The paper deals with crack propagation through an interface between two elastic materials. The basic idea of developing stability criteria of general singular stress concentrators introduced in the first part is applied to the case of a crack with its tip at the interface between two different materials. Three different stability criteria based on different physical principles are presented and a numerical example with their mutual comparison is carried out. A procedure based on a generalized strain energy density factor is shown which makes it possible to estimate the further direction of crack propagation after the crack has passed the interface. The procedure presented is applied in the numerical examples. and Obsahuje seznam literatury
The influence of through crack in the protective surface layer on damage of coated structure is investigated. The coated structure is modeled as a particular case of a bi-material body consisting of thin surface layer on the substrate. The problem is studied under the assumptions corresponding to small scale yielding conditions and calculations are performed by the finite element method. Specific attention is devoted to the case of a through coating crack with its tip at the interface between coating and the substrate. To estimate how the coating crack with its tip at the interface influences the substrate failure the general approach described in [1, 2, 3] (Part I, II, III of this contribution) is applied. An aproximate approach based on calculations of crack mouth opening displacement for thin protective layers is suggested and developed. It is concluded that in the case of a stiffer coating on a more compliant substrate, the through coating cracks represent dangerous stress concentrators and as a consequence of elastic mismatch of both materials, the critical applied stress for substrate failure decreases. Traditional approaches may have underestimated this effect and estimations of the service life of coated structures neglecting this phenomenon could lead to non-conservative values, with unexpected failures. and Obsahuje seznam literatury
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