PRINCIPAL STRAINS IN BUCKLED SURFACES 529 



In the example given, 



X. = 0.439, e, = -0.561 



Polyothyloiie sheaths of cabh^ specimens 3 feet long buckled severely 

 over their entire length when the cables were twisted 720° and showed 

 the strains given in Table I at steps up to the final twist . 



The ratio of maximum to minimum strain parallel to the surface is 

 about 2:1. Tests with a 1: 1 ratio , a more severe condition, have shown 

 that the principal strains at rupture will be of the order of 300 per cent. 

 Therefore it is evident that the strains incidental to the most severe 

 types of handling will not, of themselves, cause rupture of the sheaths. 



2 Unpublished memorandum by A. G. Hall. 



3 I. L. Hopkins, W. O. Baker and J. B. Howard, J. Appl. Phys., 21, No. 3, pp. 

 206-213, March, 1950. 



