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In general structural components such as rails and bearings are subjected to complex combinations of Mode I, II and III loadings during service. Studies have shown that under monotonic loading a crack subjected to pure Mode II loading propagates into a certain direction and bifurcates under a distinctive angle, which can be described with certain criteria, for instance the maximum stress criterion. From the physical point of view that can be explained by a void initiation and coalescence process, which shows a maximum under a certain bifurcation angle. However in the case of cyclic loading the situation is more difficult to understand. Cracks subjected to cyclic Mode II loading show often again a crack deflection under a certain angle, however after some coplanar crack growth. The latter case is not clearly to understand regarding the cyclic deformation behind the crack tip. The aim of the study is to get better insight for the mechanical reasons for the final bifurcation on the fatigue fracture surface.