Issue34

T. Itoh et alii, Frattura ed Integrità Strutturale, 34 (2015) 487-497; DOI: 10.3221/IGF-ESIS.34.54 487 Focussed on Crack Paths Crack mode and life of Ti-6Al-4V under multiaxial low cycle fatigue Takamoto Itoh, Masao Sakane Department of Mechanical Engineering, College of Science & Engineering, Ritsumeikan University, Japan itohtaka@fc.ritsumei.ac.jp, sakanem@se.ritsumei.ac.jp Takahiro Morishita Graduate School of Science & Engineering, Ritsumeikan University, Japan gr0202xp@ed.ritsumei.ac.jp Hiroshi Nakamura Engine Technology Department, Aero-Engine & Space Operation, IHI Corporation, Japan hiroshi_nakamura_2@ihi.co.jp Masahiro Takanashi Structural Strength Department, Research Laboratory, IHI Corporation, Japan masahiro_takanashi@ihi.co.jp A BSTRACT . This paper studies multiaxial low cycle fatigue crack mode and failure life of Ti-6Al-4V. Stress controlled fatigue tests were carried out using a hollow cylinder specimen under multiaxial loadings of λ=0, 0.4, 0.5 and 1 of which stress ratio R =0 at room temperature. λ is a principal stress ratio and is defined as λ=  II /  I , where  I and  II are principal stresses of which absolute values take the largest and middle ones, respectively. Here, the test at λ=0 is a uniaxial loading test and that at λ=1 an equi-biaxial loading test. A testing machine employed is a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loadings with inner pressure onto the hollow cylinder specimen. Based on the obtained results, this study discusses evaluation of the biaxial low cycle fatigue life and crack mode. Failure life is reduced with increasing λ induced by cyclic ratcheting. The crack mode is affected by the surface condition of cut-machining and the failure life depends on the crack mode in the multiaxial loading largely. K EYWORDS . Ti-6Al-4V; Low cycle fatigue; Multiaxial loading; Crack mode; Hollow cylinder specimen; Inner pressure I NTRODUCTION i-6Al-4V is frequently used as a material in rotating aero engines because it has the properties of high strength, light weight, and excellent corrosion resistance. A rotating aero engine receives cyclic loading under thermal and mechanical stresses which cause multiaxial low cycle fatigue. Under non-proportional loading in which the T