Influence of stress ratio on the threshold level for fatigue crack propagation in high strength steels

✍ Scribed by Ohta Akihiko; Sasaki Etsuo

• Publisher: Elsevier Science
• Year: 1977
• Tongue: English
• Weight: 722 KB
• Volume: 9
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(77)90024-8

✦ Synopsis

Centrally cracked specimens of JIS SM58Q and I-IT80 steels were fatigued. The fatigue crack growth rates, da/dn, and the stress intensity threshold levels, AK,, were measured over the range of stress ratio, R, from -1 to 0.8 by the use of an automatic method of continuously decreasing stress intensity factor with crack extension. The measured AK, was well represented as (AK,,,& = (1 -R)71AK,/21n_o; and the propagation rate, as do/dn = A(1 -R)-m [(AK/Z)" -{(l -R)'IAKfh/21R_0}m] for -I$ R SO.33 or da/dn = A(1 I -0.33)-lm [(AK/2)" ((1 -R)'IAK,J21n_o}m] for 0.33 <R S0.8. A i K mu R ; AK/2 A&l2 AK,,, AK,,,, API2 daldn d(AK)/da a cr. Vd Y NOTATION material constant, coefficient of crack propagation rate half-crack length, mm thickness of plate, mm maximum stress intensity factor during fatigue loading, kg/mn?'* ratio of minimum to maximum applied stress, urn&,,,,: ratio of minimum to maximum stress intensity factor, K,,IK,.. material constant, exponent of crack propagation rate width of plate, mm amplitude of stress intensity factor, wmm"* amplitude of stress intensity factor before suddenly decreasing stress, kg/mm"* stress intensity threshold level of materials below which fatigue crack propagation becomes insignificant, kdrnrn"l stress intensity threshold level just after suddenly decreasing stress, kg/mm"* amplitude of alternating load, kg cyclic crack propagation rate, mmlcycle decreasing rate of stress intensity range with crack extension, kg/mm"* material constant which characterizes the effect of stress history amplitude of alternating stress, kglmm2 amplitude of alternating stress before suddenly decreasing stress, kg/mm* material constant which characterizes the effect of stress ratio