随机载荷下船海结构疲劳裂纹扩展寿命数值计算方法研究  

Numerical calculation method of fatigue crack propagation life of marine structures under random loads

作　　者：张永矿 黄小平[1] 余宏淦 ZHANG Yong-kuang;HUANG Xiao-ping;YU Hong-gan(State Key Lab of Ocean Engineering,Shanghai Jiao Tong University,Shanghai 200240,China)

机构地区：[1]上海交通大学海洋工程国家重点实验室,上海200240

出　　处：《船舶力学》2020年第7期942-950,共9页Journal of Ship Mechanics

基　　金：中国船级社项目和高新船舶项目资助。

摘　　要：采用有限元方法计算裂纹应力强度因子来预报船海结构的疲劳裂纹扩展是一种普遍认可的方法。由于需要根据裂纹尺寸不断更新有限元模型进行大量的计算,相当耗时,在某种程度上阻碍了该方法的广泛应用。本文针对变幅随机载荷,结合单一曲线模型提出了Cycle-by-Cycle(CBC)和数值计算方法(欧拉法、改进欧拉法、3阶龙格库塔法)相结合的计算格式。并分别应用在表面裂纹的疲劳裂纹扩展计算中,通过和常规CBC计算结果对比发现:随着步数增加,三种数值计算方法都可以达到较高精度;相比欧拉法,高阶计算方法的步长可以取得更大,而计算精度还可以更高。将该方法应用在一些需要有限元程序计算应力强度因子的复杂结构疲劳裂纹扩展中,可以有效减少裂纹更新次数,进而减少计算时间,提高计算效率。Fatigue crack propagation numerically simulated by Finite Element Method(FEM)has become a widely-recognized approach in assessing the fatigue life of complex structural details.Due to the Stress Intensity Factor(SIF)calculation of cracked structural details by FEM is time-consuming,and numerous calculations of the details with different crack sizes are required in the fatigue life calculation procedure,this problem hinders the wide application of the FCP theory.In the present study,methods which combine cycle-bycycle(CBC)with three numerical integration methods(Euler method,improved Euler method,three-order Runge Kutta method)respectively to predict the fatigue crack growth based on the unique crack growth rate curve model under random load have been proposed.By comparing these calculated results by each of the three methods with that of the conventional CBC,it is shown that all the three kinds of numerical integration methods can achieve a high accuracy when the number of steps is large enough,and that the step size of high order numerical calculation method can be set larger than that of Euler method while the calculation accuracy could be higher.The method can be applied to the fatigue crack growth prediction of the complex structure,in which the stress intensity factor needs to be calculated by finite element method.It can effectively reduce crack size update frequency,and thus reduce the computing time.

关 键 词：裂纹扩展 高阶数值积分 快速计算 随机载荷 风暴模型 

分 类 号：U661.4[交通运输工程—船舶及航道工程]