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Fatigue Resistance of Metals

MORRIS E. FINE

A f t e r a b r i e f r e v i e w of t h e h i s t o r y of r e s e a r c h on t h e f a t i g u e of m e t a l s , t h e a u t h o r ' s p r e s e n t u n d e r s t a n d i n g of t h e p r o c e s s e s b y w h i c h f a t i g u e f a i l u r e s o c c u r i s c o v e r e d . The subjects discussed are: 1. 2. 3. 4.

P r o p e r t y and m i c r o s t r u c t u r a l c h a n g e s due to c y c l i c p l a s t i c d e f o r m a t i o n I n i t i a t i o n of m i c r o c r a c k s G r o w t h of m i c r o c r a c k s t o f o r m a m a c r o c r a c k P r o p a g a t i o n of m a c r o c r a c k s f r o m t h r e s h o l d t o n e a r f i n a l f a i l u r e

S p e c i a l e m p h a s i s i s g i v e n t o t h e r o l e of p l a s t i c w o r k in d e t e r m i n i n g t h e r a t e of f a tigue crack propagation. WHEN I f i r s t b e c a m e i n t e r e s t e d in m e t a l l u r g y in the m i d d l e t h i r t i e s , the ASM C a m p b e l l L e c t u r e w a s the h i g h l i g h t of t h e i m p o r t a n t F a l l N a t i o n a l M e t a l s C o n gress, which, unfortunately, has been discontinued. The early lecturers often began with personal refere n c e s t o E d w a r d d e M i l l e C a m p b e l l . I, of c o u r s e , c a n ' t do t h i s but I will b e g i n by giving c r e d i t to my teacher and thesis advisor, Ralph L. Dowdell, for the t i t l e of m y t a l k . P r o f e s s o r D o w d e l l t a u g h t a c o u r s e in m e t a l l o g r a p h y w h i c h I t o o k in 1 9 3 9 - 4 0 a t t h e U n i The Edward DeMdle Campbell Memorial Lecture was established m 1926 as an annual lecture in memory of and in recogmtton o f the outstanding scientific contnbutions to the metallurgical profess~o~l by a distinguished educator who was bhnd for all but two years o f his professional hfe. It recogmzes demonstrated abditv m metallurgical science and engineering

MORRIS E. FINE is WalterP. MurhpyProfessorof MaterialsScienceat The TechnologicalInstitute of NorthwesternUniversitywhere he has been active m major academiccapacitiessince 1954. He helped to organize the first Materials Science Department in the United States. His formaleducation was at the Universityof Minnesotawhere he was awarded the B. Met. Eng. with distinctionin 1940 and a PhD m 1943. He was on the Manhattan Project at both the Chicago and Los METALLURGICAL TRANSACTIONS A

v e r s i t y of M i n n e s o t a . H e a l w a y s e m p h a s i z e d t h e p o s i tive; thus subjects covered included corrosion resistance, fatigue resistance and so forth. I would also like to a c k n o w l e d g e my m e n t o r at B e l l T e l e p h o n e L a b o r a t o r i e s , W i l l i a m C. E l l i s , and "my s t u d e n t s " over the years. Without them, I would never have been invited to give a Campbell Lecture. In t h i s l e c t u r e I p l a n to b r i e f l y s a y s o m e t h i n g a b o u t t h e h i s t o r y of f a t i g u e a n d w h a t w e l e a r n e d w h e n I w a s a n u n d e r g r a d u a t e s t