Standard Guide for In-Plane Biaxial Testing with Cruciform Type Specimens

Abstract

5.1 Deformation and damage under biaxial loading conditions can be significantly different from that typically observed under uniaxial loading conditions. In particular, cyclic hardening in fatigue tests depends upon biaxial loading ratio (λ(σ) or λ(ɛ)) and biaxial phase angle (φ). As a result, fatigue, crack growth, and fracture data generated under uniaxial conditions may not be appropriate for predicting material behavior under biaxial loading conditions. Biaxial deformation and fatigue behaviors of metallic materials are typically investigated with either tubular or planar cruciform-type specimens. ISO technical report (ISO TR/12112) contains a summary of principles and designs of different types of specimens and test equipment used in multiaxial fatigue testing. Practice E2207 provides details for performing strain-controlled axial-torsional fatigue testing with thin-walled tubular specimens. It is not possible to achieve all combinations of biaxial load or strain ratios under combined axial-torsional loading only without using internal and/or external pressurization of the tubular specimens. Moreover, material form available (bars or rods versus plates or sheets) and specific structural applications require evaluation of the material behavior under biaxial loading conditions with planar specimens. In particular, this guide provides relevant details on the following for testing planar cruciform-type specimens: 5.2 Evaluation of material’s deformation, fatigue and crack growth behavior under various biaxial loading conditions. 5.3 Generation of biaxial test data at ambient and elevated temperatures, which can be useful for designing engineering components subjected to similar loading conditions and for estimating fatigue crack initiation or crack growth lives of such components.