临界距离理论评定焊接接头疲劳寿命的研究

研究局部法应用于焊接接头疲劳评定的有效性和适应性.基于Taylor的临界距离理论,引入开裂部位的当量应力,它由有限元计算得到.针对钢质与铝质十字接头的疲劳数据进行分析,承载型十字接头的疲劳裂纹源于焊趾或焊根,由当量应力的大小所预测的开裂部位与实验结果相符.对疲劳裂纹源于焊趾部位的承载与非承载型十字接头,以焊趾部位的当量应力作为控制应力,此时疲劳数据的离散程度低,可望将焊趾开裂十字接头的疲劳强度以及S-N曲线统一表示.对疲劳裂纹产生于焊根的承载型十字接头,将焊根部位的当量应力作为控制应力,疲劳数据的分散度较大,与名义应力法相当,此时,局部法的有效性值得进一步考察.

Study of Critic Distance Theory on the Fatigue Assessment of Welded Joints

This paper was concerned with the validity and applicability of local approaches used for the fatigue assessment of welded joints.The equivalent stress was introduced according to Taylor’s critic distance theory classified as local approaches,and determined in the finite element method.The fatigue data of both steel and aluminium cruciform joints were analyzed.The fatigue failure might originate from weld toes and roots in load-carrying cruciform joints.The analysis results have shown that the equivalent stress can be used to predict the position where fatigue failures occur.The data of fatigue strength and stress-life were examined in terms of equivalent stress.It has been shown that the data scattering is remarkably reduced for cruciform joints with fatigue failure originating from weld toes.Then,the unified strength and S-N curve can be expected to be determined,but it is not the same for cruciform joints with fatigue failure originating from weld roots.The data scattering is high and comparable with the case where fatigue strength is expressed in terms of nominal stress.The latter indicates that the validity of local approaches is absent and its applicability needs further studies.