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 Crack Fatigue Life Fatigue Limit Fatigue Crack Propagation Load Cycle
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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## Copyright information

© Springer 2007