Metal Fatigue pp 15-33 | Cite as

# Constant Amplitude Fatigue

Chapter

## Abstract

A
The

*constant amplitude fatigue loading*(or*constant amplitude loading*) is a*fatigue loading*in which all the*load cycles*are identical. A load cycle is usually called either just a*cycle*or a*fatigue cycle*. The notation used is shown in Figure 3.1. A*cycle*is the smallest unit of the*stress history*which repeats exactly. Cycles are often, but not always, sinusoidal.*σ*_{a}(sometimes*σ*, as in the figure) is the*alternating stress*,*σ*_{m}is the*mean stress*,*σ*_{max}is the*maximum stress*in the load cycle, and*σ*_{min}is the*minimum stress*in the load cycle. Mathematically a load cycle (or*stress cycle*) is expressed as*σ*_{m}±*σ*_{a}. Compressive stresses are taken as negative. It follows that$$
\sigma _{max} = \sigma _m + \sigma _a ,
$$

(3.1)

$$
\sigma _{min} = \sigma _m - \sigma _a ,
$$

(3.2)

$$
\sigma _m = \frac{{\sigma _{max} + \sigma _{min} }}
{2}.
$$

(3.3)

*stress range*is*S*= 2*σ*_{a}=*σ*_{max}−*σ*_{min}, and the*stress ratio, R*=*σ*_{min}/*σ*_{max}. The term stress ratio and its symbol,*R*, are very well established, and both are often used in the metal fatigue literature without explanation.### Keywords

Fatigue Steam Brittle Shrinkage## Preview

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© Springer 2007