Some Tests to Assess the Effect of Crack Stoppers on the Fatigue Life of Center-Notched Specimens

摘要

Crack stoppers were evaluated in crack propagation tests on Alclad 2024-T3 sheet specimens (thickness 2 mm) provided with a central crack to assess the usefulness of very simple crack stopping elements which can be applied to macrocracks in sheet metal structures accessible from one side only. Results show that a stop hole at the crack tip should be filled to obtain a good propping of the hole. Self tapping screws and tapered pins give large crack growth retardation lives. Large retardations are obtained with hard driven rivets and with heavily tightened bolts in the stop holes, but they require accessibility from two sides. Flight-simulation loading on specimens with tightened bolts indicates a significant retardation, but quantitatively the effects under flight-simulation loading and under constant-amplitude loading are highly different.