Evaluation of the accident accumulation hypotheses of Manson and Haibach

The mathematical estimation of duration of operating stress always requires the application of a hypothesis of damage accumulation for which the Miner rule is used in most cases. The comparisons between predictions and rest results, however, show a very large scattering concerning accuracy caused by effects of sequence which cannot be prevented by the Miner rule. In order to consider these effects of sequence Manson and Haibach suggest various lines of proceeding. Manson derived the 'Double Linear Damage Rule (DLDR)' from comparisons made with a variety of test results. Based on considerations on the opening behaviour of short cracks during elastoplastic stress Haibach suggests an intrinsic damaging parameter. He introduces a method which considers the decrease of the fatigue strength due to the increase in damage incidence, on the basis of nominal stresses, however. Both suggestions can be combined. These hypotheses of damage accumulation by Manson (DLDR) and Haibach (the combination of the methods introduced) were evaluated with regard to their accuracy, the volume of computation required and their applicability in special load sequences. Experimental results from fatigue tests carried out under load with variable amplitudes are available. The results show that both conceptions improve the accuracy of the linear damage calculation. (orig./HP)