Crack Growth Behavior of Al Alloy 7075-T6 under Ultrasonic Fatigue

• CHEN Qiang

  Kochi National College of Technology

• KAWAGOISHI Norio

  Faculty of Engineering, Kagoshima University

• OKI Masahiro

  Kochi National College of Technology

• GOTO Masahiro

  Faculty of Engineering, Oita Univeraity

• WANG Qingyuan

  College of Architecture and Environment, Sichuan University

Abstract

In order to investigate the effect of loading frequency on crack growth behavior, ultrasonic fatigue and rotating bending fatigue tests were carried out for an extruded age-hardened Al alloy 7075-T6 in ambient air and in N₂ gas. Fatigue strength increased in ultrasonic fatigue due to the retardation of crack initiation and its early propagation. In ultrasonic fatigue, however, crack growth transition took place from tensile mode to shear mode when cracks grew faster than ∼3x10^-9m/cycle. As a result, macroscopic crack paths changed from nearly vertical to stress axis to oblique ∼35 degrees against the axis. Fracture mechanism involved in ultrasonic fatigue also changed from striations featured to transgranular facets characterized with microscopic voids. The relation between the applied stress, σ_a, and the crack depth at the crack growth transition, b_T, can be expressed as σ_aⁿb_T = constant. The results were discussed from the viewpoints of time dependent environmental effect and the texture of the alloy.

Journal

• Journal of Solid Mechanics and Materials Engineering

  Journal of Solid Mechanics and Materials Engineering 2 (11), 1399-1409, 2008

  The Japan Society of Mechanical Engineers

Keywords

• Fatigue
• Ultrasonic
• Age-Hardened Al-Alloy
• Crack Growth
• Fracture Mechanism
• Environmental Effect
• Texture

Details

• CRID: 1390001205264583040
• NII Article ID: 130000079042
• DOI: 10.1299/jmmp.2.1399
• ISSN: 18809871
• Web Site: http://www.jstage.jst.go.jp/article/jmmp/2/11/2_11_1399/_pdf
• Text Lang: en
• Data Source:
  • JaLC
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed