TC4-DT焊接接头Ⅰ-Ⅱ复合型疲劳裂纹扩展实验及模拟研究

拉剪复合载荷作用下,构件中的裂纹呈现复杂的Ⅰ-Ⅱ复合型扩展模式,研究其扩展规律对准确评估构件疲劳寿命具有重要意义。针对TC4-DT钛合金电子束焊接头Ⅰ-Ⅱ复合型疲劳裂纹扩展规律开展研究,设计并加工紧凑拉伸剪切(CTS)试样,通过开展不同加载角度下接头试样的疲劳裂纹扩展实验,得到接头Ⅰ-Ⅱ复合型裂纹的a-N曲线及疲劳裂纹扩展路径。在上述基础上引入Ⅰ-Ⅱ复合型等效应力强度因子并结合Paris公式建立TC4-DT电子束焊接头Ⅰ-Ⅱ复合型疲劳裂纹扩展速率方程。采用扩展有限元法(XFEM)对复合型疲劳裂纹扩展过程进行数值模拟研究,得到不同加载角度下的扩展规律,并与实验结果进行比较。结果表明:不同加载角度下Ⅰ-Ⅱ复合型疲劳裂纹开裂角模拟值与实验结果误差均在10%以内,并且扩展路径均与实验结果吻合;XFEM能够有效预测复合型疲劳裂纹扩展路径。

Experimental and simulation study on Ⅰ-Ⅱ mixed-mode fatigue crack growth of TC4-DT welded joint

The crack growth in the structure shows the complex Ⅰ-Ⅱ mixed-mode under the combined tensile and shear fatigue loading. It is of great significance to understand its growth law for evaluating the fatigue life of structures accurately. In order to study the fatigue crack growth law of Ⅰ-Ⅱ mixed-mode welded joint of TC4-DT alloy, compact tension-shear(CTS) specimens were designed and machined, fatigue crack growth tests of welded joints under different loading angles were carried out, curves and fatigue crack growth paths of welded joints under Ⅰ-Ⅱ mixed-mode crack propagation were obtained. Based on the above situation,the equivalent stress intensity factor of Ⅰ-Ⅱ mixed-mode was introduced and the Paris law was employed to deduce the Ⅰ-Ⅱmixed-mode crack growth rate equation of TC4-DT welded joint. In addition, the extended finite element method(XFEM) was adopted to simulate the fatigue crack growth progress of Ⅰ-Ⅱ mixed-mode crack, and the growth law under different loading modes were obtained and compared with test results. The research shows that the error values of the cracking angle under different loading modes are less than 10% compared simulation with experiment. What’s more, the simulated growth paths are agree with the experimental results well. XFEM shows its advantages in simulating crack problems. XFEM can predict mixed-mode fatigue crack growth paths effectively.