Low-Temperature and High-Temperature Anomalies in Temperature Shift of Stress-Lifetime Fatigue Curves

Most families of S-N curves determined at various temperatures present certain general regularities on whose basis the Basquin equation describing finite-life S-N curves can be generalized for various temperatures. This equation can be represented by straight lines with common slope if log-log fit for stress vs. temperature dependence is used. Deviations from these straight lines (anomalies) are evidence that additional degradation mechanisms are effective besides fatigue, whose temperature dependences differ from the mentioned temperature dependence of fatigue strength. In high-temperature region it is most often cyclic creep, in low-temperature region athermal processes of plastic deformation can play significant role in fatigue failure.