PSI - Issue 5

Robert Hannemann et al. / Procedia Structural Integrity 5 (2017) 861–868 Hannemann et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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Jacoby (1965). In contrast to the specimens with transition radius (specimen type 1) the crack fronts tilts already at lower stress concentration factors for specimens with a press-fit (specimen type 2). For a better visualization of the dependence between the tilting of the crack front, the stress concentration factor and the crack depth, a tilt-angle β K was defined, Figure 5. The development of β K is shown in Figure 5 for all used specimens in the constant amplitude tests. It can be observed that the influence of the small stress concentrations factors is less than for a stress concentration factor of 1.32. However, a large scattering is noticeable for α K = 1.32. Moreover, the influence of the press-fit becomes obvious, too.

Fig. 5. Definition of β K and development of β K depending on crack depth a and stress concentration factor α K

Furthermore, the influence of the transition radii on the residual lifetime has been investigated, Figure 6. For comparison reasons in Figure 6 analytical simulations with NASGRO are additionally shown. The simulations have been performed using numerically determined stress intensity factors (SIF) of the appropriate shouldered solid shafts with elliptical surface cracks (Hannemann and Sander (2016)). In these calculations the FORMAN/METTU parameters of Table 2 are used. In contrast to the experimental results the analytical data show a clear trend. With increasing stress concentration factor the residual lifetime decreases. The analytically calculated remaining lifetime is 4% and 13% smaller for the stress concentration factor 1.18 and 1.32 in comparison to the specimen with α K = 1.10, respectively.

Fig. 6. Crack propagation behavior for rotating bending with constant amplitudes for different α K in comparison to analytical simulation results