Table 2.

Sample values of the plot of strain against D/R given in figure 6b.

D/R	average strain
0.0000	0
0.0040	0.0237
0.0267	0.0732
0.0753	0.1280
0.1466	0.1825
0.2308	0.2356
0.3150	0.2823
0.3863	0.3198
0.4349	0.3441
0.4577	0.3555
0.4616	0.3574