Fraunhofer Institute for Mechanics of Materials IWM
Internal stresses in large jacket pipes play a crucial role in the structural integrity of offshore wind turbines. Due to their complex geometry, internal stresses are difficult to determine; however, given the long service life required and the climatic stresses involved, understanding these stresses is of great importance for the safe design of components. The stresses arise from manufacturing processes such as welding, as well as from continuous external loads such as wind and ocean current forces. To reliably predict fatigue strength, it is necessary to accurately measure the residual stresses — which vary significantly locally — at critical component locations.
Only by understanding the complex interplay of residual stresses, materials strength, structural integrity, and external loads can the full potential of the material be exploited. Knowledge of the influence of residual stresses is of great importance for calculating the fatigue strength of welds. On-site measurements are taken at critical locations such as the weld transition. The data is then supplemented by numerical models that simulate stress distributions along the structure to identify and specifically monitor the critical areas prone to fatigue failure.