PSI - Issue 68

J.A. Ziman et al. / Procedia Structural Integrity 68 (2025) 1159–1165 J.A. Ziman et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 1. Schematic representation of the LPM StressLife. (a) Cyclic deformation curve of a load increase test (LIT); (b) Morrow-equivalent plot containing the stress amplitudes as a function of the material response resulting from the LIT; (c) Cyclic deformation curves of the constant amplitude tests (CAT); (d) Calculated StressLife-curve including conventionally determined data for validation. 2.2. Experimental setup A resonance testing rig type MIKROTRON by Russenberger Prüfmaschinen AG was used to carry out CATs and LITs with a stress ratio of R = -1 and test frequencies of 80 and 260 Hz at ambient temperature. Based on Weber et al. (2023), the change in surface temperature of the specimens is recorded in three sections using an IR-camera, type thermoIMAGER TIM QVGA-HD by Micro-Epsilon Messtechnik GmbH. The change in electrical resistance was recorded using a four-point measuring method consisting of a current feed (3A DC) through the clamping tools, two wires attached to the edges of the gauge length of the specimens, one shunt resistant (0.02 Ω), an isolation plate on the lower clamping to prevent the flow of current through the machine, one DC power supply (type TOE 8851, Toellner Electronic Instrumente GmbH) and a data acquisition card, type NI-9238 by National Instruments. In addition, the residual stress values σ ES at different number of cycles was quantified through the sin 2 (ψ) method by means of X-ray diffraction (XRD) measurements. These were carried out using a Seifert Space XRD TS-4 research edition X-ray diffractometer modified by the company XRD Eigenmann GmbH with CrK α -radiation to investigate the diffraction peak corresponding to alpha-iron (α-Fe), Eigenmann and Macherauch (1996). Therefore, measurements at the Bragg angle of 2 Θ = 156.084 ° matching the {211} plane in α-Fe were performed. For the scans, the 2 Θ angle range was set from 148 to 161 °. To account angular variations and enhance peak resolution across different lattice orientations, an y angle range from -45 to 45 ° in 99 steps was used. Measurements were taken in axial (0 °) and tangential (90 °) direction of the specimens using the Center of Gravity method (COG) at three measuring points around the centre of the specimen, from which an average value is calculated. The fatigue setup as well as the X-ray system is shown in Figure 2.