Vol.11, No3, 2011, pp. 157-171
UDC 539.43.012

Spectrum loading, i.e. load-time histories with variable amplitudes, occurs in almost all engineering structures during their service life. The behaviour of such structures and components cannot be assessed properly on the basis of constant amplitude data. Their safe design, in the context of weight reduction requirements, demands detailed and deep knowledge about the effects of spectrum shape, blocked or random sequences, material response, cumulative damage, residual stresses, environment and corrosion on lifetime in interaction with variable load amplitudes. Especially, the reliability of assumptions must be assured when test time reduction procedures are applied. Also, the substitution of variable amplitude loading by constant amplitudes is not generally possible because of the aforementioned influencing parameters and changed damage mechanisms. The proper consideration of effects of spectrum loading on structural durability requires a hybrid design procedure consisting of experiences in laboratory testing, knowledge of service behaviour, both implemented in numerical assessment procedures.

Keywords: load spectrum shape, blocked and random sequence, cumulative damage, residual stresses, corrosion