PSI - Issue 68

T. Korschinsky et al. / Procedia Structural Integrity 68 (2025) 1196–1202 Korschinsky et al./ Structural Integrity Procedia 00 (2025) 000–000

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various radii and is embossed to different degrees, which translates to different material behaviors within the component. The goal of this study is a fatigue life estimation to be as precise as possible. For this purpose, experimental investigations are performed to collect data on the cyclic transient material behavior. Based on the experimental results, a procedure for the simulation of the cyclic transient material behavior is developed. While the state-of-the art Chaboche model is not capable of describing the material behavior accurately, the newly introduced Damage dependent Modified Material Model (DD3M) improves the representation of the cyclic transient material behavior as a basis for the fatigue life evaluation. 2. Theory and Methodology 2.1. Experimental setup In Figure 1 the experimental setup used for the investigations on the cyclic transient material behavior of EN AW 1050A H24 is shown. The actuator of the so-called E-cylinder test system is a stepper motor that can move very precisely with relatively low frequency, which is the reason why this test system is specifically designed by Fraunhofer LBF for investigations in the LCF regime. For force measurement a load cell by Interfaceforce, model 1710DLL – 2,5kN, was used besides a clip-on extensometer, model Sander Messtechnik EX A 10-0.25 U with a maximum strain to be measured of 2.5 %. Additionally, an optical strain control for further investigations published in (Korschinsky, et al., 2024) is also part of the test system. Further details of the E-cylinder test system is described in (Kiel, et al., 2024). For the study a sinusoidal waveform of the strain-signal was the target setting for the controller. Due to alternating fatigue loading without mean strain (R ε =-1) the maximum and minimum strain equals the strain amplitude. A constant velocity instead of a frequency is defined by the E-cylinder test control. However, the test frequency never exceeds 1 Hz. This low frequency also precludes heating of the sample. Thus, the samples temperature remains at ambient temperature (t ≈ 21 °C).

Figure 1. Experimental test setup for the investigations on the cyclic transient material behavior

The experiments to characterize the cyclic transient material behavior use unnotched specimens of 80 mm length with a gauge length of 10 mm mandatory for the application of the clip-on extensometer. The area between the gauge length and the clamping area is elliptically rounded resulting in a notch factor close to ! =1 . The edges of the specimens