焊接接头焊趾部位的疲劳裂纹多呈现为多裂纹形式.针对十字焊接接头，开展变幅载荷谱块下的拉伸疲劳试验，获得了表征裂纹瞬时前沿迹线的海滩条带的演变过程，验证了多裂纹的存在性，并且发现焊接接头焊趾处的多裂纹具有明显的不同步特性.采用有限元仿真技术，在焊趾部位分步插入多个半椭圆形初始裂纹，模拟了多裂纹的演变过程，获得了与试验断口一致的仿真结果.结果表明，裂纹融合导致裂纹前沿形状不断发生变化，最终有向半椭圆形状演变的趋势；焊接结构裂纹萌生和小裂纹扩展阶段在疲劳全过程中的寿命占比较大，具有不可忽略的影响.
The fatigue cracks at weld toes of welded joints mostly take the form of multiple cracks.Carrying out the tensile fatigue tests based on spectrum with variable amplitude loading of cruciform joints. The evolution process of beach marks characterizing the instantaneous front track of cracks is obtained, the existence of multiple cracks is verified. It was found that the multiple cracks at weld toes of welded joints had obvious asynchronous characteristics. By means of finite element simulation technology, several semi-elliptical initial cracks were inserted into the weld toe step by step, and the evolution process of multiple cracks was simulated. The simulation results were consistent with the experimental fracture. The results show that the shape of crack front changes continuously due to crack fusion, but eventually it tends to evolve towards semi-elliptical shape;The life of crack initiation and small crack propagation in welded structures accounts for a large proportion in the whole fatigue process and has an important influence.
[1] 魏国前, 岳旭东, 党章, 等. 结合S-N曲线和断裂力学的焊接结构疲劳寿命分析[J]. 焊接学报, 2017, 38(2):23-27 Wei Guoqian, Yue Xudong, Dang Zhang, et al. S-N and IEFM combined fatigue life analysis for welded structures[J]. Transactions of the China Welding Institution, 2017, 38(2):23-27
[2] 王桂阳, 王海斗, 张玉波, 等. 超声冲击法提高焊接接头疲劳特性研究进展[J]. 材料导报, 2016, 30(9):87-94 Wang Guiyang, Wang Haidou, Zhang Yubo, et al. Development of research in improving fatigue properties of welded joints by ultrasonic impact treatment[J]. Materials Review, 2016, 30(9):87-94
[3] Ngoula D T, Beier H T, Vormwald M. Fatigue crack growth in cruciform welded joints:influence of residual stresses and of the weld toe geometry[J]. International Journal of Fatigue, 2016, 101:253-262.
[4] Hou C Y. Fatigue analysis of welded joints with the aid of real three-dimensional weld toe geometry[J]. International Journal of Fatigue, 2007, 29(4):772-785.
[5] Pang J H L, Hoh H J, Tsang K S, et al. Fatigue crack propagation analysis for multiple weld toe cracks in cut-out fatigue test specimens from a girth welded pipe[J]. International Journal of Fatigue, 2017, 94:158-165.
[6] Branco R, Antunes F V, Costa J D. A review on 3D-FE adaptive remeshing techniques for crack growth modelling[J]. Engineering Fracture Mechanics, 2015, 141:170-195.
[7] Ma K, Xie H. Mixed-mode fracture investigation of PMMA with initial single/double crack(s) interference using phase-shifted coherent gradient sensing method[J]. Polymer Testing, 2017, 59:296-307.
[8] 占勇, 温建锋, 涂善东, 等. 基于疲劳寿命的共面多裂纹合并准则研究[J]. 压力容器, 2016, 33(2):1-9 Zhan Yong, Wen Jianfeng, Tu Shandong, et al. Study on coplanar multi-crack combination criteria based on fatigue life[J]. Pressure Vessel Technology, 2016, 33(2):1-9
[9] 刘新灵, 张峥, 陶春虎. 疲劳断口定量分析[M]. 国防工业出版社, 2010.
[10] Lin X B, Smith R A. Shape growth simulation of surface cracks in tension fatigued round bars[J]. International Journal of Fatigue, 1997, 19(6):461-469.
[11] Forman, R G, Mettu, et al. Behavior of surface and corner cracks subjected to tensile and bending loads in Ti-6Al-4V alloy[J]. Fracture Mechanics Twenfy-second Symposium, 1992, ASTM STP, 1131, 1:519-540.
