考虑载荷流泄时盾构机T形焊接结构疲劳可靠性分析

FATIGUE RELIABILITY STUDY ON T-WELDED COMPONENT OF SHIELD MACHINE CONSIDERING LOAD SHEDDING

T形焊接结构是盾构机刀盘的关键结构之一,焊接处裂纹在亚临界的扩展是其疲劳失效的关键因素.文章在考虑载荷流泄情况下,基于概率断裂力学的一次二阶矩方法提出了一种新的结构疲劳可靠性分析方法.将该方法应用到某盾构机T形焊接结构,给出了考虑与不考虑载荷流泄两种情况下结构疲劳可靠性计算结果,并用Monte Carlo方法验证了文章方法的有效性;利用最小二乘法拟合出了载荷流泄系数对该T形焊接结构疲劳可靠性的影响曲线,将该曲线划分了三个区域:高、中、低疲劳失效区,实际工程在盾构机T形焊接结构疲劳可靠性设计时,将T形焊接结构的厚度作为一个设计变量,而低失效区可以作为一个可靠度约束条件.结果表明在考虑和不考虑载荷流泄时,T形焊接结构的疲劳失效概率分别是8.2644×10-5和3.4314×10-4,即载荷流泄提高了结构的疲劳可靠度;研究成果对实际工程上盾构机刀盘的维修、检验计划和设计都有一定的理论指导意义.

T welded component is one of the key structures of the shield machine cutter-head,and sub- critical crack in the weld extensions is a key factor in its fatigue failure. By using probabilistic fracture me chanics based on the first order second moment method,a new structural fatigue reliability analysis method considering load shedding was applied to a T-welded shield structure in this contribution. The results of structural fatigue reliability were obtained in the cases of with and without considering load shedding. The accuracy of this method was verified using Monte Carlo method. Then a curve that describes the load shed- ding impacts on the T-welded structure fatigue reliability was fitted via least square method. Based on the fitted curve, three zones including high, medium and low were divided. The thickness of T-welded structure was adopted as a design variable in the practical project design of fatigue reliability,in which low fatigue failure zone may be used as a reliahility constraint. The results showed that the fatigue failure probabilities were 8.2644×10^-5 and 3.4314×10^-4,respectively,which indicated that load shedding could improve the structure fatigue reliability. These results can offer a theoretical guidance for the maintenance,inspection plan and design of shield machine cutter-head.