Materials suffered from varying amplitude
cycle loads are
damaged along with the process of loading. With the purpose of appraising the stress
life behavior of damaged materials, a series of analysis and discussion based on the S-N curve of material are carried out, and a new formula to calculate the surplus strength of damaged materials is derived. Based on the recurrent method, the new formula can be used to show the decline process of the strength of materials and obtain S-N curve of damaged materials at any stage. Further analysis shows an important factor that cycle loads lower than the material's
fatigue limit can also
damage materials when they act at the later period of materials life, and should not always be ignored in fatigue design. New formula is compared with the Miner formula and shows that when the levels of all cycle loads are higher than the fatigue limit of the material, the new formula gives the same results to those from the Miner formula, but when the level of cycle loads lower than the material's fatigue limit, new formula is much superior: treating these kinds of loads, Miner formula can do nothing. New formula can be looked as an extension of the Miner formula. An example in fatigue design is provided and shows that the new formula is convenient to use and the result is reasonable.
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