Application of FEM Analyses and Neural Networks Approach in Multi-Stage Optimisation of Notched Steel Structures Subjected to Fatigue Loadings

The stress concentration, which appears in loaded structural elements with voids, holes or undercuts, is the main source of premature fatigue failure. So, an increase in fatigue life can be achieved by reducing stress concentrations around the notches. Different techniques can be used to reduce the stress concentration. One of them is the application of additional stress relief undercuts or holes, while a second one relies on the application of overlays glued in the vicinity of notches. The proposed study is focused on the optimisation of notched specimens using a multi-stage optimisation process, including the use of artificial neural networks (ANNs). On this basis, the comparison of the effectiveness of various modern finite element optimisation tools is made. Here, special attention is paid to samples with elliptical holes and the application of the ANN technique in determining the optimal solution for the configuration of stress relief holes. The proposed study is illustrated by the example of a steel specimen with an elliptical opening. Specimens without stress relief holes and with an optimal configuration of stress relief holes are subjected to fatigue tests to confirm the effectiveness of the proposed approach. The performed study revealed that the cutting of additional circular stress relief holes reduces the stress concentration around the elliptical opening by about 12% and leads to an increase in fatigue life by about 79% for the applied material. Moreover, the comparison of the possibilities of the reduction in SCF by the application of stress relief holes, composite overlays and the simultaneous application of composite overlays and stress relief holes for the investigated notched samples is performed. Following the numerical results, it is observed that the use of composite overlays additionally decreases the stress concentration factor in relation to specimens with stress relief holes by an additional 6%.