Multiaxial Kitagawa analysis of A356-T6

TL;DR

This study applies multiaxial Kitagawa analysis to A356-T6 alloy with defects, comparing theoretical models to determine the critical defect size and endurance limit under various loadings.

Contribution

It introduces a comprehensive comparison of four theoretical approaches to predict fatigue limits in A356-T6 under multiaxial loading conditions.

Findings

Critical defect size is approximately 400 micrometers.

CDM and gradient methods accurately predict endurance limits.

Fatigue data for multiple loadings improves model accuracy.

Abstract

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.