PSI - Issue 57

Felix-Christian Reissner et al. / Procedia Structural Integrity 57 (2024) 411–419 F.-C. Reissner et al. / Structural Integrity Procedia 00 (2023) 000–000

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1. Introduction In engineering applications shafts are normally used to transmit torque and rotation. Therefore, a shaft has at least two bearings to allow the shaft to rotate. When these bearings require special lubrication, such as the bearings in a car’s power train, lubrication is often provided by cross bores. However, these cross bores act as a notch and therefore the cross bore is critical to the failure of the whole component. In addition to this special application, shot peening is widely used to improve the fatigue strength of components. There are various studies on shot peening. Xie et al. (2023) introduced a state of the art overview of the shot peening process. While Wang et al. (2017) investigated the effect of shot peening on open-hole steel plates and Takahashi et al. (2012) the effect of shot peening on the torsional fatigue limit of high-strength steel containing artificial notches such as cross bores. The focus of this study is to investigate the effect of shot peening on the fatigue of shafts with cross bores made of EN-GJS-700-2 (cast iron) and 34CrNiMo6+QT (steel). The objectives are (1) to determine if shot peening can effectively improve the fatigue performance of these components, (2) if the resulting residual stresses can be simulated and (3) how the simulated residual stresses can be used to improve the estimation of design S-N curves. To evaluate the fatigue strength, cyclic fatigue tests are conducted on the shot-peened, thermally stress relieved and untreated specimens. The resulting fatigue data is analyzed to assess the effectiveness of shot peening in improving the fatigue strength of the specimens. Furthermore, a finite element analysis is employed to simulate the shot peening process and the cyclic loading of the specimens to investigate the residual stresses. Finally, the results of the simulation are used as input parameters for the estimation of a design S-N curves and the design S-N curves are compared to the experimental data. By investigating the relationship between shot peening, the change in residual stresses with load and fatigue strength, this research aims to contribute to the understanding of how surface treatments can influence the fatigue strength of components. The knowledge gained from this research will help to understand the change in residual stresses due to loading. In addition, a method to predict design S-N curves which considers the change in residual stresses is demonstrated. Nomenclature FKM Forschungskuratorium Maschinenbau engl.: Mechanical Engineering Research Board UT Test series with untreated specimens SL Surface layer SP Test series with shot-peened specimens SR Test series with thermal stress relieved specimens

TP Transition point XDR X-ray diffraction

2. Experiments 2.1. Experimental Procedure

To evaluate the effect of shot peening on the fatigue strength of shafts with cross bores, cyclic fatigue tests are conducted. For the fatigue tests a specimen geometry is chosen, which satisfies the requirements to evaluate the effect of the shot peening of the cross bore regarding the the fatigue strength, but is also as simple as possible, Figure 1. The specimens are made of EN-GJS-700-2 and 34CrNiMo6+QT. Some of the specimens are shot peened several times. Whereas, each shot peening has different process parameters in order to investigate the effects of the different process parameters, Table 1.