A method for assessing the ductile failure of thin structures containing arbitrarily oriented cracks is presented. The crack tip displacement vector δ_v is used as fracture parameter. Experiments carried out on 4- to 6-mm-thick steel StE 550 and aluminum alloy A12024-T3 sheets with various mixed-mode specimens demonstrate that δ_v is more appropriate to characterize ductile mixed Mode I/II crack initiation and stable crack growth than the J-integral. The Mode I crack resistance curves of standardized C(T)-type specimens give a conservative estimate of crack initiation and resistance to stable growth in the range of near Mode II loading to pure Mode I loading. The δ_v>-parameter of a cracked component is evaluated with Engineering Treatment Model (ETM). The analytical ETM method requires only the stress intensity factor and plastic limit load solutions of the considered structure as well as the material stress and strain power law as input parameters. Close agreement of ETM predictions to the experimental load versus δ_v relationships or load-displacement curves can be achieved, if the proper limit load solution of the cracked structure is available.