Cumulative Damage by Miner's Rule and by Energetic Analysis

According to Miner's rule, the fatigue life of a material (or a mechanical component) is not a function of the order of the application of load. Many authors have already observed that the model proposed by Palmgren/Miner leads to underestimation of the damage and one of the reasons could be the disregard of the sequence of loads. Referring to the energy loss related to irreversible damage of the material, it was observed that the Miner's rule gives exact results only if the damage caused by the fatiguing load is low compared to the limit energy of the material. Whereas, if the damage caused by the fatiguing load is high, Miner's rule is no longer valid. In this work, according to previous observations reported in other authors' works, tensile fatigue tests on AISI304 steel specimens were performed. The load stories consisted of loading ramps in subsequent blocks. For each group of specimens the same blocks were applied but with inverted sequence. The surface temperature, recorded during application of loads, has been chosen as a benchmark of the damage.