Fatigue Damage Assessment of Materials Under Uniaxial Variable Amplitude Loading Conditions
This thesis intends to further apply an earlier developed energy based-critical fatigue damage parameter to assess the fatigue damage of different materials subjected to repeated random block histories. In fatigue damage assessment under variable loading conditions, further phenomenological factors of: (i) sequence loading effect, (ii) memory effect, and (iii) the effect of small amplitude cycles below the material endurance limit have been introduced.The effect due to sequence loading is studied for variable amplitude loading conditions. It is found that the loading sequence has a great influence on the cyclic stress-strain hysteresis loops and therefore on fatigue damage of materials. Memory effect concept has been carefully monitored and programmed to correspond to the closed hysteresis loops in each block loading history. The small cycles exceeding 50% of the fatigue endurance limit contributed to the accumulated damage.A comparison of the predicted fatigue life results based on energy based-critical parameter including the phenomenological factors with the experimental live data reported in the literature has shown a good agreement.