5. Temperature

Numerous test results show that the endurance ratio ( σ _D / R _m ) generally remains constant as temperature varies. The endurance limit therefore varies in the same direction as the mechanical properties of steels when they are subjected to fatigue loading at a temperature other than ambient. The endurance limit can therefore be predicted from the curves of variation in tensile strength as a function of temperature.

However, a number of precautions need to be taken if the part is likely to be working in borderline conditions, i.e. at low and high temperatures.

• Low-temperature fatigue [3]

  Fracture strength increases with decreasing temperature, as does...