PSI - Issue 39

Daniele Amato et al. / Procedia Structural Integrity 39 (2022) 582–598 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Experimental Tension-Torsion Tests The experimental campaign was carried out with Single-edge Notched-Tension-Compression specimens (SEN TC) made of the high-strength steel 34CrNiMo6 (cfr. Table 1). The corresponding experimental data were obtained by Köster, Sander et al. [24]; for further information about the experimental test rig, the specimen manufacturing and all the experimental conditions, the reader can refer to [25-26]. In this section, only the relevant information related to the loading conditions is emphasized. To remain in the material elasticity domain, the maximum load amplitude of the axial force was set to = 27.5 . Three different mode-mixity configurations were selected, as described by the quotient of the maximum nominal torsional ( ) and axial ( ) stresses in the undisturbed cross-section: / = 0.76 , 1 , and 1.31 . The axial load level remained constant in all tests whereas the maximum torsional moments were modified in each test in order to obtain the prescribed to ratios. Therefore, the torsional load = 60.5 , 80 , and 104.75 . Each axial and torsional loading ratio was tested with three different phase shifts, = 0° , 40° and 90° . Furthermore, the influence of the stress ratio of the axial load on the crack propagation behaviour under mixed-mode conditions was investigated. For this reason, tests were carried out both at = 0 (i.e., pulsating cycle from the origin) and = − 1 (i.e., fully reversed cycle). The stress ratio of cyclic alternating torsion was = − 1 in all experiments [24]. By combining all the loading conditions, eighteen different load cases were obtained, as reported schematically in Figure 1, creating both proportional and non-proportional loading conditions, see Figure 2.

Figure 1 Load-time curves used for the experimental investigation.

Figure 2 Loading paths for test case = − 1 , = − 1 and three different phase shifts.