Weld simulation for fatigue strength improvement
During recent years, the potentials of fatigue enhancement procedures have caught the attention of many industries, such as the off-shore industry, heavy lifting industry and the transportation industries. Improving the fatigue life by post-weld treatment is today a well-established and industrialized process in these branches and enables the utilization of high strength steel and light weight structures. Fatigue problem caused by a few details in a bridge is often a decisive design criterion and results in more use of material than otherwise necessary. This has caused the steel and composite bridges to lose competitiveness compared to other materials. Handling the fatigue problem at these limited details by post-weld treatment would with a low cost not only reduce the required material necessary for the fatigue design, but also enable the use of higher strength steels for more efficient designs in the ultimate limit state as well, leading to cheaper and lighter bridges. This can promote the choice of steel and composite bridges, which thanks to their relative light weights and high capacity-to-weight-ratio are superior during construction phase, enabling simpler erection methods, cheaper transportations to building sites and needing less costly sub-structure solutions. Together with the environmental and societal benefits that this leads to, it will be an important step towards sustainable development. The aim of this project is to gather existing knowledge regarding post-weld treatment, which mainly is valid for thin plates loaded with cyclic loading of constant amplitudes, and further develop it so it becomes applicable to the conditions for bridges. This, by means of laboratory testing of large-scale specimens with thick plates subjected to variable amplitude loading, thorough finite element modeling of all relevant phenomena for post-weld treated details to simulate fatigue strength, and parameter studies to investigate effects of plate thickness, welding size and sequence and different loading parameters. The final goal is to develop design rules and guidelines, consistent with current design codes, for resource-efficient calculation of the fatigue improvement gained by post-weld treatment of bridge details. Within the proposal to SNIC I aim to carry out below items. 1. Closed, multistage simulation loops including welding simulation, numerical computation of the HFMI-process, and numerical analysis for an estimation of the local fatigue behaviour. 2. Numerical simulations with parametric studies. These are performed with both spectrum loading (a simplified loading model which allows the production of a relatively large number of tests) and full variable amplitude loading.