ductile materials

brittle materials

equally serious in both cases

depends on other factors

dynamic loading

static loading

combined static and dynamic loading

completely reversed loading

cold working

shot peening

grinding and lapping surface

hot working

cold working

shot peening

surface decarburisation

under-stressing

metal strength by cycling

metal hardness by surface treatment

metal resistance to corrosion by coating

fatigue limit by overstressing the metal by successively increasing loadings