INFLUENCE OF RESIDUAL WELDING STRESS ON FATIGUE CRACK GROWTH RATE
INFLUENCE OF RESIDUAL WELDING STRESS ON FATIGUE CRACK GROWTH RATE
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残余焊接应力对疲劳裂纹扩展速率的影响
DOI：
10.2208/jscej1969.1983.330_161
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发表时间：
1983
期刊：
影响因子：
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通讯作者：
K. Takena
中科院分区：
文献类型：
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作者：
C. Miki;F. Nishino;Y. Hirabayashi;K. Takena
结构构件的疲劳寿命可细分为疲劳裂纹萌生前的寿命(裂纹萌生寿命：NC)和疲劳裂纹扩展到构件失效前的寿命(裂纹扩展寿命：NP)。在焊接接头中，人们认为疲劳裂纹是在寿命的早期阶段产生的，最近的研究在实际焊接件中得到了实验证实。因此，准确评估净现值对于避免在役结构的疲劳失效和进行新结构的疲劳设计具有重要意义。利用应力强度因子范围(4K)和疲劳裂纹扩展速率(da/dN)之间的关系，应用疲劳裂纹扩展的断裂力学概念来评价Np是有效的。但疲劳裂纹扩展速率受多种因素的影响，如钢的力学性能和显微组织。此外，在焊接接头中，还必须考虑焊缝金属、母材和热影响区等成分的差异，特别是焊接残余应力的影响。Horikawa et A1.9)指出，拉伸残余应力加速了疲劳裂纹扩展速率，并用疲劳裂纹闭合行为解释了这一现象。Ohta等人。10)研究了对接焊接头疲劳裂纹的扩展情况，结果表明，由于焊接残余拉应力的作用，对接焊接头的疲劳裂纹扩展速率高于母材。作者等3)、11)、12)阐明，在部分熔透的纵向焊缝中，残余焊接应力导致的疲劳强度降低是显著的。本文的主要目的是阐明焊接残余应力对疲劳裂纹扩展速率的影响。对于实际的结构，有许多情况下，大部分寿命是在一个较小的区域内进行传播时度过的。为此，在包括门槛应力强度因子范围(AKH)在内的较宽的AK区进行了疲劳裂纹扩展试验。研究了残余应力随疲劳裂纹扩展的变化规律。
Fatigue life in structural members can be subdivided into the life until fatigue cracks initiate (crack initiation life: Nc) and life until these fatigue cracks propagate to the failure of member (crack propagation life: Np). In welded joints, it was said that fatigue cracks initiated at the early period of the life, and that has been confirmed experimentally in actual weldments by recent studies1),2),3). Accordingly, accurate evaluation of Np is very important in avoiding the fatigue failure of existing structures and in performing fatigue design for new structures. For the evaluation of Np, it is valid to apply the fracture mechanics concepts of fatigue crack propagation using the relation between stress intensity factor range (4K) and fatigue crack propagation rate (da/dN). But fatigue crack propagation rate is affected by many factors such as mechanical properties and microstructure of steel5)-8). Further, in welded joints, it is also necessary to consider the difference in composition such as weld metal, base metal and heat affected zone, and particularly the influence of residual welding stress. Horikawa et a1.9) indicated that fatigue crack propagation rate is accelerated by tensile residual stress and explained this phenomenon by using the behavior of fatigue crack closure. Ohta et al. 10) examined the propagation of fatigue cracks in butt weld joints and showed that due to the tensile residual stress by welding, propagation rate in butt weld joints is higher than in base metal. The authors et al.3),11),12) clarified that the reduction in fatigue strength due to residual welding stress is substantial in partially penetrated longitudinal welds. The main objective of this paper is to clarify the influence of residual welding stress on the fatigue crack propagation rate. With actual structures, there are many cases that most of the life is spent while propagation occurred in a region of small 4K3),11)19). Therefore, fatigue crack propagation tests are carried out in the wide region of AK including threshold stress intensity factor range (AKh). The change of residual stress with fatigue crack propagation is also examined.