PSI - Issue 25

A. Gryguć et al. / Procedia Structural Integrity 25 (2020) 486– 495 Andrew Grygu ć / Structural Integrity Procedia 00 (2019) 000–000

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it is below, despite the total SED being very similar between both specimens. The synergistic effects of the multiaxial loading is related to the proportion of axial to shear SED and the level of each individual contribution being above or below their kink/transition thresholds for each uniaxial strain path. If the shear SED contribution is low, especially if it is below the threshold of 0.6 [MJ/m 3 ] the resulting early cracking behaviour will be purely transverse (i.e. 0 ° orientation), illustrating the suppression of the helical cracking shear mode contribution towards the combined cracking behaviour which is axial dominated. Conversely, when the shear SED contribution is high, i.e. above the threshold of 0.6 [MJ/m 3 ], the resulting early cracking behaviour is mixed with presence of branching and/or secondary cracks, as the longitudinal cracking shear mode contribution is more significant. These observations agree well with findings from Jiang et al. who detected the presence of secondary cracks in multiaxial low-cycle fatigue loading of extruded AZ31B Mg [34]. Furthermore, a similar phenomenon was observed by both Renzo et al. in additively manufactured Ti-6Al-4V [43] and Bemfica et al. in 304L stainless steel [36].

Figure 6 – Strain Energy Density (SED) vs. number of cycles to failure for various strain paths (a) pure axial, (b) pure shear, (c) multi-axial. Typical macroscopic fracture paths are show highlighting the plane of fracture for various specimens.