TWI Industrial Member Report Summary 516/1995
The elevation of fracture toughness in shallow-cracked fracture toughness specimens as compared with the conventional deeply-notched geometry is by now well-known. Similarly, the differences in fracture toughness which are observed when a specimen is loaded under tension instead of bending are well-documented. Since defects in real engineering structures tend to be shallow, and stress fields are often tensile, there is a strong technological need to quantify how small-scale fracture toughness data can be transferred to full-scale structures without excessive conservatism.
One approach to the problem is to express the crack tip stress field in terms of two parameters, stress intensity (K) and T-stress (T); hitherto, it has often been assumed that the single parameter K will suffice. T-stress can be considered as the elastic stress component acting parallel to the crack after the removal of the singular K-component. This report presents a review of assessment and application of the T- stress and other constraint parameters, emphasising the way in which fracture mechanics toughness parameters such as Jc can in principle be 'converted' from shallow-notch to deep-notch values and vice-versa, and from one geometry to another.