A unified equation for creep-fatigue

• Published in: International journal of fatigue Vol. 68; pp. 186 - 194
• Main Authors: Wong, E.H., Mai, Y.-W.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 2014; Elsevier
• Subjects: Applied sciences; Brazing. Soldering; Creep; Creep (materials); Creep-fatigue; Economic conditions; Exact sciences and technology; Fatigue; Fatigue (materials); Fatigue equation; Joining, thermal cutting: metallurgical aspects; Life prediction; Mathematical analysis; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Solder; Solder; Life prediction; Fatigue equation; Fatigue; Creep-fatigue; Lifetime; Creep; Prediction; Mechanical properties; Soldering
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2014.05.004

•Coffin–Manson equation Δεp=CoN-βo is a special case of a unified creep-fatigue equation, Δεp=Cos(σ)c(T,f)N-βob(T,f).•The stress function s(σ) incorporates the stress-characteristic of creep.•The creep functions c(T, f) and b(T, f) embody the time-temperature characteristic of creep.•At the reference condition when creep is dormant, s(σ)=c(T, f)=b(T, f)=1, the Coffin–Manson equation is recovered. “Pure fatigue” is a special case of creep-fatigue; and the Coffin–Manson equation, Δεp=CoN-βo, is a special case of the general creep-fatigue equation, which is proposed to take the form: Δεp=Cos(σ)c(T,f)N-βob(T,f). The functions, s(σ),c(T, f) and b(T, f), embody the stress–time–temperature characteristic of creep. At the reference condition when creep is dormant, s(σ)=c(T, f)=b(T, f)=1, the Coffin–Manson equation is recovered. At the extreme condition when c(T, f)=0, creep-rupture occurs without fatigue. In between these two extreme conditions whence 0⩽c(T, f)⩽1, creep-fatigue prevails.