During years 2005–2006, a series of semi-large scale experiments on specimens containing underclad (embedded) crack were performed in NRI Rez. The experiments were performed in the frame of EU PHARE project EUROPAID/116529/D/SV/CZ, in cooperation with VTT, FNS, TVONS (Finland) and Tecnatom (Spain). The aim of the project was to investigate fracture mechanics properties of cladding, in particular, to establish the role of cladding in the fracture/failure process of the specimens, and to exploit the obtained knowledge in the procedure for evaluation of integrity of WWER reactor pressure vessels. Experimental results of the project are described in details in parallel paper [1]. In the present paper, brief summary of experimental results is provided, and FE evaluation of the experiments is described, with focus on constraint evaluation. FE evaluation covers, among others, evaluation of J-integral in the moment of cleavage fracture initiation (1st pop-in or sudden fracture through) for both upper and lower crack fronts, and evaluation of some type of constraint parameter. Three types of constraint parameter were calculated: T-stress based on elastic calculation, T-stress based on elastic-plastic calculation and Q-parameter. In the paper, detailed development of elastic-plastic T-stress as well as Q-parameter with loading is presented for one specimen that sustained the highest load. Besides of that, the approach of effective stress intensity factor KIeff is examined in the paper, and results of sensitivity analysis with respect to uncertainty concerning the way in which the effect of constraint is included into the KIeff approach are presented.

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