A l a r g e p r o p o r t i o n of f a i l u r e s of mach ine p a r t s is a s s o c i a t e d with the p ropaga t i on of fa t igue c r a c k s . In such c a s e s the " l i fe" of a p a r t counted f rom the ins tan t of c r a c k nuc lea t ion cons t i tu tes a c o n s i d e r a b l e p a r t of i t s total t i m e t o r u p t u r e . Fa t igue f r a c t u r e , which in the USA alone is be ing inves t iga ted in m o r e than 209 l a b o r a t o r i e s , has been s tud ied by many i n v e s t i g a t o r s both in the Soviet Union (N. N. Davidenkov, S. V. Se rensen , I. A. Oding, R. M. Schneide rov i ch , R. D. Vagapov) and e l s e w h e r e (Orowan, F r o s t , McClintock, P a r i s ) . However , insuf f ic ien t a t ten t ion has been paid to quant i ta t ive s tud ies of the growth of fat igue c r a c k s .