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