Q460C钢缺口板的疲劳裂纹萌生寿命计算模型和总疲劳寿命计算

Calculation Model of Fatigue Crack Initiation Life and Total Fatigue Life Calculation of Q460C Steel Notched Plates

基于位错随循环加载次数的增加加速移动、聚合形成疲劳裂纹的试验事实,假设疲劳裂纹萌生速率是循环加载次数的单调递增幂函数,通过积分推导出疲劳裂纹萌生寿命计算模型。Q460C钢缺口板的疲劳试验结果显示,疲劳裂纹萌生寿命、扩展寿命和总疲劳寿命均随应力幅和名义最大应力的降低而增加,疲劳裂纹形成寿命与总疲劳寿命的比值为0.82~0.90。我国《钢结构设计标准》建议的总疲劳寿命计算式的计算误差为-17.0%~+84.9%。以椭球面断裂模型作为裂尖开裂判据,对Q460C钢缺口板的疲劳裂纹扩展进行了理论计算和数值模拟。以疲劳裂纹萌生处应变溢出时裂纹长度0.05 mm作为疲劳裂纹萌生临界尺寸,标定的Q460C钢缺口板的疲劳裂纹萌生寿命计算式、扩展寿命计算式和总疲劳寿命计算式的计算误差分别为-15.0%~-1.2%、-12.4%~+2.8%和-12.1%~-1.4%。

Based on the experimental fact that the rate of dislocation movement and polymerization to form fatigue crack accelerates with the number of cyclic loads,it is assumed that the fatigue crack initiation rate is a monotonically increasing power function of the number of cyclic loads.The calculation model of fatigue crack initiation life is derived by integrating the power function between the fatigue crack initiation rate and the number of cyclic loads.The fatigue test results of Q460C steel notched plates show that the fatigue crack initiation life,propagation life and total fatigue life increase with the decrease of stress amplitude and nominal maximum stress,and the ratio of fatigue crack initiation life to total fatigue life ranges from 0.82 to 0.90.The calculated error of the fatigue life calculation formula recommended in China’s code‘Standard for design of steel structures’is-17.0%—+84.9%.Considering an ellipsoidal fracture model of structural steel originally proposed by the author as the instability propagation(fracture)criterion of fatigue crack,a set of theoretical calculation and numerical simulation were established to investigate the fatigue cracking of the notched plates.Taking a crack length of 0.05 mm at which the strain over flows at the site of fatigue crack initiation as the critical size of fatigue crack initiation,the calculated errors of the calibrated fatigue crack initiation life formula,propagation life formula and total fatigue life formula of the Q460C steel notched plates are-15.0%—-1.2%,-12.4%—+2.8%and-12.1%—-1.4%,respectively.