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

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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.