The Significance of Crack Depth (a) and Crack Depth-to-Width Ratio (a/W) With Respect to the Behavior of Very Large Specimens

Abstract

Previous studies have shown that there is an increase in cleavage fracture toughness of laboratory specimens with shallow flaws compared with those laboratory specimens having deep flaws. Typical crack depths in real structures generally are very small relative to the member width. Therefore, the crack depth to structural member width (a/W ) ratios are very small (less than 0.1). Accordingly, the effect of this observation on the behavior of larger structures that actually represent typical engineering applications could be significant. Using experimental and analytical results from previous studies on A533-B steel specimens, the effect of the shallow flaw behavior with respect to very large specimens was examined. Using the Dodds and Anderson constraint correction, predictions of the cleavage fracture toughness of large-scale wide-plate tests and full thickness clad beams from an actual reactor pressure vessel were shown to compare favorably with actual test results. The results of these studies suggest the possibility of predicting the increase in fracture toughness for low constraint structural geometries using high-constraint laboratory test specimen results. The ability to take advantage of this increase in toughness in analysis of actual structures could be very useful in estimating the actual safety and reliability of existing structures with service cracks.