复杂载荷作用下潜艇结构疲劳裂纹扩展预报方法

Procedure to predict fatigue crack growth of submarine structures under complex loading conditions

统一疲劳裂纹扩展模型是课题组在McEvily模型基础上提出来的,它将疲劳裂纹扩展的3个扩展区域统一起来,并能解释更多的疲劳试验现象。本文介绍了统一疲劳裂纹扩展模型的基本表达式。将此模型与焊缝焊趾表面裂纹应力强度因子的计算方法结合起来,探讨复杂载荷作用下潜艇结构疲劳裂纹扩展预报方法。将服从Weibull分布的随机载荷系列编排为升序、降序载荷谱及随机载荷谱,预报潜艇锥柱结合壳焊缝焊趾处表面裂纹在3种载荷谱下的疲劳裂纹扩展情况,并分析随机载荷谱下载荷次序效应及初始裂纹尺寸对疲劳裂纹扩展行为的影响。结果表明,载荷次序效应对潜艇结构疲劳寿命的影响很明显,且合理的确定初始裂纹尺寸对潜艇结构的疲劳寿命预报是非常重要的。

The unified fatigue crack growth model proposed by our group is based on McEvily model, and it can unify three regions of crack growth rate curve and explain more fatigue phenomena observed in tests. The paper introduces the basic equations of the model. The model is combined with SIF calculation equations for surface crack in the weld toe, and the way to predict the fatigue crack growth behaviour of submarine structures under complex loading conditions is discussed. Random loading which obeys the Weibull distribution is arranged into ascending, descending and random loading spectrums respectively. Fatigue crack growth of submarine structural welded toe joints under the above three loading spectrums is predicted, and the effect of loading sequence interaction and initial crack size on fatigue life of submarine structures under random loading spectrum is analyzed. It is concluded that loading sequence interaction has great effect on fatigue life of submarine structures, and reasonable initial crack size is very important for fatigue life prediction of submarine structures.