Welding Institute Research on the Fatigue Precracking of Fracture Toughness Specimens

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Abstract
Three techniques are described for growing uniform fatigue cracks in fracture toughness specimens originally containing welding residual stresses. These are local compression, reverse bending, and the use of a high R-ratio in the fatigue cycle. The possible effects of the techniques on the subsequent measurements of fracture toughness are assessed. The relative merits of the three techniques are summarized, and the main conclusion reached is that local compression is the best defined technique at present, and that reverse bending and high R-ratio, although probably more convenient, require further research and development.