Factors Affecting Fatigue Strength

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Fatigue strength is somewhat correlated with tensile strength. A "rule of thumb" often used is that fatigue strength equals one-third the tensile strength. But this approximation is not valid for many higher tempers of highly alloyed metals. The stronger tempers of some metals have lower fatigue strength than their weaker tempers.

Orientation affects the fatigue strength. Data typically compiled and published are for test specimens with a longitudinal orientation (their length is parallel to the rolling direction). But, fatigue strength can be measurably affected by the manner in which the part is positioned on the strip for stamping. The literature shows several instances where the transverse fatigue strength is 10% to 50% greater than that in the longitudinal orientation. In some cases, this is merely reflective of the higher strength that many alloys have in the transverse direction. The metallurgical basis for fatigue strength beyond that accountable to the greater transverse strength has not been extensively investigated and reported.