Classical fatigue analysis and load cycle mix-event damage accumulation in fibre reinforced laminates

A survey of Classical Fatigue Analysis predictions has been carried out for fibre reinforced composite laminate specimens subjected to spectrum loading. Results illustrate acceptable predictions for matrix dominated composites but unreliable and generally un-conservative predictions for fibre dominated composites. A need for cyclic damage event definition relating to composite behaviour has been identified. Load-cycle “Mix” damage events have been proposed based on block test results which show reduced fatigue life for increased load cycle mixing. A methodology has been proposed based on two-level block test base data to account for mix damage events. New counting methods have been investigated to account for possible mix damage events in addition to “Rainflow” hysteresis events. FALSTAFF, TWIST and variations of these spectra have been interrogated using mix counting algorithms to illustrate the level of load mixing that occurs in these standard spectra. Preliminary predictions have been made using simple multi-block tests to trial the proposed methodology accounting for mix-damage events. Results show improved predictions warranting further work on mix event definition and extrapolation methods.