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

铝及其合金是目前最重要的轻质材料，其应用越来越广泛。重要的是要确保已开发的结构在使用期间安全地完成其任务。在这种考虑中，必须考虑到事故案例和由此而导致的结构失效。与焊接钢结构一样，极限载荷行为以节点和邻近区域的破坏为主，即使使用铝合金也是如此。拟议的研究项目旨在开发从材料和生产技术原理考虑的铝焊缝的新损伤模型，并在全球结构模型中进行测试。为此目的，首次用量热法和膨胀法绘制了焊接时间-温度-析出物和溶解度图，例如钢的焊接TTT图。淬火和变形膨胀仪中的热机械分析能够描述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方法的焊接过程计算模型以确定结构性能、变形和残余应力提供了依据。为了标定韧性断裂失效判据，应通过材料拉伸试验和焊接小试件的有限元模拟来确定母材、熔合区和热影响区的真实应力-应变关系。断裂应变与应力状态的相关性是通过使用不同的尖锐缺口试件来确定的。接下来，将从试验和数值两个方面详细研究焊接X形截面在轴压荷载作用下的结构性能。除了记录载荷-位移曲线和检测局部变形外，还需要直观地捕捉裂纹萌生和扩展形式的断裂行为。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能量吸收能力，除了考虑材料性能分布外，还考虑残余应力和变形。这项研究项目为铝焊接结构的失效机理及其数值模拟提供了基本的见解，这些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.