= a/y, k = cos 7t0'/2/and = (the yield strain). The origin of

Initial experimental results, on sheet aluminium alloy at fairly small overall strain, confirmed the curve of Fig. 2.8 for the relevant gauge length, but more extensive tests [13] using steel, the first of which was carried out on steel plates roughly 1 m square by 75 mm thick with a variety of gauge lengths and notch depths, showed no general trend [13]. As is evident from Fig. 2.9, all the experimental results scattered around one part of the

diagram, and did not follow the predictions of the Dugdale model. The results in Fig. 2.9 are the basis of the COD design curve discussed in Chapter 5.