Experimental investigation and FE simulation of ductile fracture of aluminium alloy laser welded butt joints

本研究以Al6061铝合金激光焊接头为研究对象，采用了裂纹扩展的Bracselier模型。基于焊接接头的硬度测试，定义了三个不同的焊接区域，即母材（BM）、熔合区（FZ）和热影响区（HAZ）。局部力学性能来自拉伸试验结果的平面试样提取这些焊缝区域。分别对BM、FZ和HAZ进行金相分析，获得非金属夹杂物的尺寸、形状和频率分布。对象分级技术（ARAMIS）是用来捕捉在平面试样的表面与焊缝位于中心的变形。数值计算工作分为三个部分：第一个活动是校准的金相调查和缺口圆棒的拉伸试验结果的基础上的Bullselier参数。第二个活动是预测韧性裂纹扩展在紧凑的拉伸（C（T））试样，并得出相应的应力和应变水平的平面试样在拉伸过程中，通过应用相同的的Ausselier参数中获得的第一部分。第三项活动是预测横向平板试样的最终断裂，包括Lüders带的扩展。其目的是应用考虑Lüders带传播的Müsselier模型来描述韧性断裂，可靠地预测激光焊接接头的力学行为，并改进激光焊接件的设计。

In this project, the Rousselier model is adopted to study the crack growth of an Al6061 laser welded butt joint. Based on hardness tests across the welded joint, three different weld regions are defined, i.e. the base material (BM), the fusion zone (FZ) and the heat affected zone (HAZ). Local mechanical properties are derived from tensile test results of flat specimens extracted from these weld regions. Metallographic investigations are performed on BM, FZ and HAZ, respectively, to obtain size, shape and frequency distribution of non-metallic inclusions. The object grading technique (ARAMIS) is used to capture the deformations at the surface of flat specimens with the weld seam located in the centre. The numerical work is divided into three parts: The first activity is to calibrate the Rousselier parameters based on metallographic investigations and tensile test results of notched round bars. The second activity is to predict ductile crack growth in compact tension (C(T)) specimens and to derive the corresponding stress and strain levels of flat specimens during the tensile process by applying the same Rousselier parameters obtained in the first part. The third activity is to predict the final fracture of transverse flat specimens including Lüders band propagation. The aim is to apply the Rousselier model taking Lüders band propagation into account to describe ductile fracture, to predict the mechanical behaviour of laser welded joints reliably and to improve the design of laser weldments.