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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For the rotating bending experiments, two specimen types were designed with respect to the standard for design methods of railway applications, Figure 3. At specimen type 1 the transition radius has been varied, i.e. different stress concentration factors are realized, Table 3. While for specimen type 2 the preassigned transition radii were unchanged, but a press-fit has been realized with a shrink fitted ring. In the section planes with maximum bending stresses a notch has been inserted with a crack depth a of 0.5 mm using a pico-second laser, Table 3.

Fig. 3. Design of the scaled specimen with design details of a wheelset axle

Table 3. Variation of the specimens

Crack depth [mm]

Stress concentration factor α K

a / c

Design detail

transition radius

1.10; 1.18; 1.32 1.13; 1.21; 1.37

0.5

0.8

press-fit

3.2. Investigation on the crack shape and residual lifetime

To estimate the influence of the stress concentration factor on the development of the crack shape, rotating bending tests with constant amplitudes were carried out. In the constant amplitude loading, overloads are introduced in order to produce arrest marks on the fracture surfaces. These investigations were also used for the calibration of the potential drop test technique on the different specimen types. Figure 4 shows the semi-elliptical crack shape development for two specimens with different transition radii (specimen type 1) and one specimen with a press-fit design detail (specimen type 2).

α K = 1.10 (transition radius)

α K = 1.32 (transition radius)

α K = 1.13 (press-fit)

Fig. 4. Crack shape development for specimen with transition radius ( α K = 1,10 and 1,32) and for specimen with press-fit ( α K = 1,13)

It can be observed that the crack becomes flatter during the crack growth under rotating bending. This fact can be observed for all examined specimens regardless of the stress concentration factor. This phenomenon is confirmed by the rotating bending test results of Carpinteri, Brighenti and Spagnoli (1998). Furthermore, there is a stress concentration factor effect visible on the crack shape development in form of a tilting of the crack front. At higher stress concentration factors in specimens with a transition radius the crack front begin to tilt in higher crack depth regions. The tilting of the crack during rotating bending at high stress concentration factors was also observed by