Numerical Simulation of Limit Load Behaviour for Welded Aluminium Structures Based on Materials Knowledge

目前最重要的轻量化材料是铝及其合金，并得到了越来越多的成功应用。重要的是要确保开发的结构在使用期间安全完成其任务。在考虑事故的情况下，因此，例如造成结构破坏必须考虑在内。与焊接钢结构一样，即使使用铝合金，极限荷载行为也是由接缝和邻近区域的破坏所主导的。拟议的研究项目旨在从材料和生产技术原理出发，开发新的铝焊缝损伤模型，并在全球结构模型中进行测试。为此，首次通过量热法和膨胀法创建了焊接时间-温度-沉淀和溶解图，例如钢的焊接TTT图。淬火变形膨胀仪的热-力学分析能够描述所检测到的相变对力学性能的影响。所得结果为建立基于有限元法的焊接过程计算模型，确定结构性能、变形和残余应力提供了基础。通过对材料和焊接小试样的拉伸试验进行有限元模拟，确定基体、熔合区和热影响区真实的应力-应变关系，以确定韧性断裂破坏的判据。断裂应变与应力状态的依赖关系是通过使用不同的尖锐缺口试样来确定的。接下来，焊接x截面的结构行为将在轴向压缩载荷下进行详细的实验和数值研究。除了记录载荷-位移曲线和检测局部变形外，还需要以裂纹萌生和裂纹扩展的形式直观地捕捉断裂行为。有限元分析的最终目的是将焊接过程的过程模拟与极限载荷计算相结合，以充分准确地确定焊接结构的吸能能力，除考虑材料性能分布外，还考虑残余应力和变形。该研究项目为焊接铝结构的破坏机理及其数值模拟提供了基础性的见解，这在设计中变得越来越重要。

The currently most important lightweight material is aluminium and its alloys and is used successfully with increasing tendency. It is important to ensure that the developed structures fulfil their task safely over the period of use. In this consideration accident cases and thus, for example caused structural failure must be taken into account. As with welded steel constructions, the limit load behaviour is dominated by the failure of joints and adjacent areas even with the use of aluminium alloys. The proposed research project aims at the development of new damage models for aluminium welds under consideration from material- and production-technical principles and their testing in global structural models. For this purpose, welding time-temperature-precipitation and dissolution diagrams are created by calorimetry and dilatometry for the first time, as they are known, for example as welding TTT diagram for steels. The thermo-mechanical analysis in the quenching and deformation dilatometer enables the description of the influence of the detected phase changes on the mechanical properties. The results obtained therefrom are the basis for a calculation model of the welding process to determine structural properties, distortion and residual stresses based on the finite element method. With the aim to calibrate a criterion for the ductile fracture failure, the true stress-strain relations for the base material, the fusion zone and the HAZ should be determined by means of FE simulations of tensile tests on materials- and welded small samples. The dependence of the fracture strain from the stress state is determined by the use of different sharply notched test specimens. Following, the structural behaviour of welded X-sections will be investigated in detail both experimentally and numerically under axial compressive load. In addition to the recording of load-displacement curves and the detection of local deformations is desired to visually capture the fracture behaviour in the form of crack initiation and crack growth. The aim of the FE analyses is finally the coupling of the process simulation of the welding process with the limit load calculation for a sufficiently accurate determination of the energy absorption capacity of the welded structure, which considers in addition to the material properties distribution also the residual stress and distortion. The research project provides fundamental insights into the failure mechanism of welded aluminium structures and its numerical modelling, which are becoming increasingly important in the design.