The aim of this research project is to holistically investigate the fatigue behaviour for large diameter bolts under the influence of mean stress, coating and surface layer condition.
Up to now, these influencing factors have been considered very inconsistently in the design principles, depending on the regulations applied. In the past, the experimental basis for evaluating various influences for large diameter bolts was limited, although these large-diameter bolts are used in large quantities in wind turbines. For SMEs, such as engineering firms, this often results in very conservative dimensioning or cost-intensive certification processes with time-consuming individual examinations.
The planned fatigue strength tests in the HCF range as well as the VHCF range are intended to counteract this. This is supplemented by an accompanying in-situ sonic emission measurement to monitor crack initiation and crack growth in combination with non-destructive µ-computer tomography. In addition, X-ray diffraction and measurements of the µmagnetic properties provide information about the residual stress behaviour in the thread root before and after cyclic loads. The state of the art on the fatigue behaviour of bolts in the VHCF range under consideration of the manufacturing influences is to be expanded due to the low data basis. The research project represents a contribution to the expansion and adaptation of the EC3 catalogue of detail categories and secures the competitiveness of SMEs.