Y. Nadot | Searcharxiv

arXiv2014

Multiaxial Fatigue Behaviour of A356-T6

Aluminum alloy A356-T6 was subjected to fully reversed cyclic loading under tension, torsion and combined loading. Results indicate that endurance limits are governed by maximum principal stress. Fractography demonstrates long shear mode III propagation with multiple initiation sites under torsion. Under other loadings, fracture surfaces show unique initiation sites coincidental to defects and mode I crack propagation. Using the replica technique, it has been shown that the initiation life is negligible for fatigue lives close to 1E6 cycles for combined loading. The natural crack growth rate has also been shown to be comparable to long cracks in similar materials.

cond-mat.mtrl-sci↗

arXiv2012

Multiaxial Kitagawa analysis of A356-T6

Experimental Kitagawa analysis has been performed on A356-T6 containing natural and artificial defects. Results are obtained with a load ratio of R = -1 for three different loadings: tension, torsion and combined tension-torsion. The critical defect size determined is 400 \pm 100 \mum in A356-T6 under multiaxial loading. Below this value, the microstructure governs the endurance limit mainly through Secondary Dendrite Arm Spacing (SDAS). Four theoretical approaches are used to simulate the endurance limit characterized by a Kitagawa relationship are compared: Murakami relationships [Y Murakami, Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions, Elsevier, 2002.], defect-crack equivalency via Linear Elastic Fracture Mechanics (LEFM), the Critical Distance Method (CDM) proposed by Susmel and Taylor [L. Susmel, D. Taylor. Eng. Fract. Mech. 75 (2008) 15.] and the gradient approach proposed by Nadot [Y. Nadot, T. ~Billaudeau. Eng. Fract. Mech. 73 (2006) 1.]. It is shown that the CDM and gradient methods are accurate; however fatigue data for three loading conditions is necessary to allow accurate identification of an endurance limit.

cond-mat.mtrl-sci↗