不完善概率疲劳S-N曲线的Monte Carlo修正

Monte Carlo Modification of Imperfect Probabilistic Fatigue S-N Curves

提出不完善概率疲劳S-N曲线情形之一,在高应力幅范围对数疲劳寿命方均差预测值为负时的Monte Carlo修正法。方法包含利用'混合乘同余法'的随机数发生器,按符合生产实际的相同应力水平每组试样模拟样本5～15个的策略,以可接受的精度重构试验S-N数据和疲劳极限数据。重构后概率曲线以极大似然法确定,并采用'概率协同法'拓展到超长寿命范围。历史不完善Q235钢概率曲线的研究表明,存在负对数疲劳方均差预测时曲线在高应力幅范围具有交叉点,不符合疲劳物理统计规律,并给出偏于危险的分析结果;而重构曲线克服了上述缺点,并把分析范围拓展到了超长寿命范围。

Monte Carlo modification is carried out in one of imperfect cases,the negative prediction of standard deviation of the logarithm of fatigue lives in high stress amplitude range,for historic probabilistic fatigue S-N curves.An adjustable random numerical generator which utilizes mixed multiplicative congruential method is applied in the random simulation process.Sample size for the simulation is controlled in a range of 5 to 15 for each group of specimens on the same stress level to address real possible fatigue tests.Reconstructions are made successively on the curves in mid-long life regime and the fatigue limits.Modification is then performed by an improved maximum likelihood method to estimate the curves.And the curves are extended into super long life regime by a so-called concurrent probability approach.Reasonability and feasibility of the present method are verified by a modification of Q235 steel historic curves.Results show that,for the case of negative prediction of standard deviation,the historic curves have cross points in high stress amplitude range and tend to give a non-conservative prediction.After modification,the above deficiencies are overcome and the curves are reasonably extended into super long life regime.