Synergistic Effect of Stress Relief Holes and Composite Patches on Fatigue Life Extension of Notched Steel Structures

In the case of notched specimens, the introduction of additional stress relief holes (SRHs), or a local increase in the cross-section stiffness by means of composite overlays, decreases the stress level in the zone of the notch. The synchronous use of SRHs and composite patches has not been extensively investigated so far. Therefore, the main objective of the proposed research is to analyse the synergistic effect resulting from the simultaneous application of SRHs and structural reinforcement in the form of composite patches bonded to the bare steel element. The influence of this approach is investigated with the use of the finite element solution and experimental fatigue tests. As a result, a reduction in the stress concentration by almost 28% with respect to the bare plate with a hole was received. The use of composite overlays increases fatigue life by over 700% at the same cyclic tensile load in comparison with specimens without reinforcement and SRHs (base configuration). The use of reinforcement overlays or the synergetic application of overlays and SRHs guaranteed higher fatigue life (five and 10 times, respectively) at a higher load (by approximately 11%) compared to the base configuration. This confirmed the synergetic and positive influence of both modifications used in parallel.