抄録
A waveform based methodology for prediction of variable loading fatigue life of composites is developed. The variable R-ratio fatigue tests in which the stress ratio of fatigue loading alternates between two specified values with different stress levels that correspond to the same number of cycles to failure are first reviewed. It is confirmed that the prediction of fatigue life using the Miner rule is excessively optimistic for alternating R-ratios loading, while it is satisfactory in the case of alternation of fatigue stresses of different magnitudes under a constant stress ratio. On the basis of these observations, it is assumed that a variable maximum stress loading at a constant stress ratio which is equivalent to a given alternating R-ratios loading can be identified. This assumption allows us to predict fatigue life for any given alternating R-ratios loading by applying the Miner rule to the constant stress ratio waveform identified. In order to test this idea, fatigue tests are performed for the variable maximum stress loading waveforms at a constant stress ratio that are equivalent to the alternating R-ratios loading waveforms examined in the previous study. A good correlation between the predicted and experimental fatigue lives suggests that the use of the concept of a single R-ratio waveform in conjunction with the anisomorphic constant fatigue life diagram approach provides a potentially useful tool for prediction of variable loading fatigue life of composites.
