SEDL / STP / STP857-EB / STP32747S

Effect of Low Temperature on Apparent Fatigue Threshold Stress Intensity Factors

Esaklul, KA
professorassistant professorpostdoctoral associate, University of MinnesotaFaculty of Engineering, Al-Fateh UniversityUniversity of California, MinneapolisTripoliBerkeley, MNCA

Yu, W
professorassistant professorpostdoctoral associate, University of MinnesotaFaculty of Engineering, Al-Fateh UniversityUniversity of California, MinneapolisTripoliBerkeley, MNCA

Gerberich, WW
professorassistant professorpostdoctoral associate, University of MinnesotaFaculty of Engineering, Al-Fateh UniversityUniversity of California, MinneapolisTripoliBerkeley, MNCA

Pages: 21    Published: Jan 1985

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Abstract

Near-threshold fatigue crack growth in high-strength low-alloy (HSLA) steel, Fe, and Fe-Si alloys was found to depend on test temperature from room temperature down to 123 K. Near-threshold crack growth rates were lowered and threshold stress intensity factors increased with decreasing temperature. A “prominent” closure was observed for all test temperatures and materials and was further confirmed by the examination of fracture surfaces. The magnitude of closure increased with decreasing temperature, suggesting a dependence on yield strength and fracture morphology. The effects of R ratio were found to be closure-related for the same fracture processes. However, a change in the fracture process, (e.g., to cyclic cleavage) may lead to a ΔK^th(eff) dependence on load ratio even at very high R values. Hence mean stress may affect threshold independently of any closure-related phenomena. A reasonable correlation was obtained with a theoretical model for closure that could account for both geometrical and reversed plasticity phenomena.