The significance of variable amplitude fatigue testing

Experimental fatigue and durability assessment plays a prominent role in lightweight design. There is broad evidence, however, that the fatigue strength of materials and structures determined under constant amplitude loading may be not relevant - quantitatively or even qualitively - for variable amplitude or spectrum loading. Various phenomena both on a a microstructural and a macrostructural level constribute to this finding as discussed in the paper including consideration of the fatigue limit, the role of crack growth mechanisms and fracture surface topography, residual stresses, scatter, relative proportions of crack initiation and crack propagation phases, detection of fatigue-critical locations, and ranking of materials and design details. Some general aspects regarding the application of variable amplitude testing for design and clearance purposes such as the required experimental efforts are also considered.