Threshold crack growth behavior of shear and tensile cracks

• Published in: International journal of fatigue Vol. 42; pp. 122 - 130
• Main Authors: Bonnen, J.J.F., Topper, T.H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2012
• Subjects: Crack closure; Crack face interference; Multiaxial fatigue; Shear crack growth; Tensile crack growth; Crack face interference; Multiaxial fatigue; Tensile crack growth; Crack closure; Shear crack growth
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2011.08.002

► Shear/tensile plane cracking studied in SAE 1045 smooth specimen biaxial fatigue. ► Short/long crack models predicted specimen fatigue lives and endurance limits. ► Shear/tensile crack growth models qualitatively predicted max shear crack lengths. ► Computed threshold fatigue diagrams compare shear/tensile cracking at fatigue limit.
Crack-face interference-free mode I and mode II crack-growth data was combined with smooth axial (λ=εxy/εxx=0) and torsional (λ=∞) endurance limit data to develop unified crack growth models that incorporate both shear and tensile cracking. The crack growth models incorporated growth from a slip band (including short crack behavior) size crack until the final failure of a long crack, and the ability to switch between crack growth on shear planes to growth on tensile planes. The models successfully predicted smooth specimen crack-face interference-free fatigue lives and gave reasonable estimates of the smooth specimen endurance limits of crack-face interference free tubular tests run at intermediate strain ratios (λ=3/4, 3/2, and 3). The series of Kitigawa–Takahashi (threshold fatigue) diagrams developed from the models help illustrate the competition between shear and tensile cracking at the fatigue limit under crack-face interference-free crack growth.