On some basic problems of fatigue research in engineering

Research on the basic fatigue formula, the criterion for omitting small loa ds, the rule for cumulative fatigue damage, and models for predicting the f atigue crack initiation (FCI) life and probability distribution under varia ble-amplitude loading are comprehensively studied and summarized in the pre sent paper. First, the formula for FCI life is given as a function of the e quivalent stress amplitude, and the procedures for investigating overload e ffects are introduced. Using the above formula to analyze test results of t he overload effect on FCI life yields the formula for FCI life containing t he overload effect factor, z, which can be adopted to characterize the load interaction effect when Miner's rule is used to compute the cumulative fat igue damage. Fatigue test results and analysis of the underload effect show that the FCI threshold in the FCI life formula can be taken as the criteri on for omitting small loads in life prediction and in compilation of the lo ad spectrum. Then, the fatigue damage function is defined, the cumulative f atigue damage can be computed and the FCI life of structure members under v ariable-amplitude loading can be obtained by using Miner's rule. Procedures for predicting the probability distribution of FCI life or fatigue life ar e described and examples are introduced. Furthermore, factors affecting the value of z and the applicability of Miner's rule are briefly discussed. Fi nally, further areas for fatigue research are tentatively proposed. Most in terest should be focused on research into generally applicable life predict ion models and the approach for fatigue reliability assessment of structure details made of the metals with continuous strain-hardening characteristic s, which have been widely adopted in aeronautical engineering, under servic e load and environments. (C) 2001 Elsevier Science Ltd. All rights reserved .