A Method for Determining Conservative Fatigue Threshold While Avoiding Crack Closure

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Abstract
The low-rate fatigue properties of a mild steel are obtained on small compact-type (CT) specimens while avoiding crack closure. These properties are similar to those of butt-welded joints obtained at a much lower stress ratio in the range −1 to 0.5. This is a result of the existence of tensile residual stress at the crack tip of the welded joint which prevents crack closure even at low stress ratios. It is concluded that the most conservative fatigue crack propagation properties, including fatigue threshold values, can be easily obtained by confirming that the results are the same for CT specimens tested at different terminal stress ratios using a ΔK decreasing method which avoids crack closure.