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In this paper the rather complex 3D fatigue crack growth behavior in3PB-specimens or in cantilever beam specimens undergoing respectively bending ortorsion loading, with inclined planes for the initial crack, is investigated by the aid of theBEM program BEASY. Mixed mode conditions along the crack edge are characterized.The stress intensity factors (SIFs) are determined using the crack opening displacementmethod (COD) and the crack growth direction is computed by the minimum strain energydensity criterion. It will be shown that the computationally simulated results of fatiguecrack growth in the Boundary Element (BE) model of the specimen are in goodagreement with experimental findings for the development of the spatially twisted ortwisted and warped crack faces in the real laboratory test-specimens. In particular, thecomparisons with experimental findings are related to the evolving crack shape. TheBEM results are also compared with FEM results, for which the SIFs are computed bythe virtual crack closure integral (VCCI)-method and strain energy release rates(SERRs) and for the evolving 3D crack shape the σ´1 criterion is adopted as fracturecriterion. Consequently, also for these cases with a rather complex 3D crack growthbehaviour, the functionality of the BEASY programme and the validity of the proposed3D fracture criterion can be stated.