438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1964 



The fact that fractures propagate less easily in materials in which 

 some plastic work occurs as the fracture advances may prove useful. 

 Indications are that reinforced solids can be devised which, while 

 retaining many of the good properties that brittle solids have, will 

 inhibit fracture growth of catastrophic nature. Certainly a large 

 amount of information about the strength properties of solids has 

 been assembled in the comparatively short time since the original paper 

 by Griffith. In the last few years understanding of the cause of frac- 

 ture and the mechanism of its propagation has advanced considerably. 

 It is reasonable to expect that in the near future new and exciting 

 materials will be developed. 



