The limiting strength of worn metal surfaces
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IN a study
of a b r a s i v e w e a r K r u s c h o v and Babichev ~ found that the w e a r of m e t a l s was v e r y little affected if they w e r e h a r d e n e d by p l a s t i c s t r a i n p r i o r to a b r a s i o n . They p r o p o s e d that this was b e c a u s e the m a t e r i a l s r e a c h e d a l i m i t i n g h a r d n e s s and flow s t r e s s d u r i n g a b r a s i o n , i r r e s p e c t i v e of any w o r k - h a r d e n i n g applied p r e v i o u s l y . S e v e r a l w o r k e r s have m e a s u r e d the h a r d n e s s e s of s u r f a c e s s u b j e c t e d to a b r a s i v e w e a r 2-5 and adhesive wear,6 and also of w e a r d e b r i s , 7 ' s but t h e r e is little a g r e e m e n t in the r e s u l t s or in r e l a ting them to w e a r p r o p e r t i e s of the m a t e r i a l s . L a r s e n - B a d s e 4 has shown that the a b r a s i o n r e s i s t a n c e of s o m e h a r d e n e d and t e m p e r e d s t e e l s is p r o p o r t i o n a l to both the bulk h a r d n e s s of the m a t e r i a l and the m i c r o h a r d n e s s of the w o r n s u r f a c e , and, also, can be r e l a t e d to the m a t e r i a l s t r e s s - s t r a i n r e l a t i o n , r e p r e s e n t e d by the power law: (7= C . E n
w h e r e C and n a r e c o n s t a n t s , F o r t e m p e r e d s t e e l s c o n t a i n i n g a d i s p e r s i o n of e e m e n t i t e in f e r r i t e , L a r s e n Badse has shown that w e a r r e s i s t a n c e can be r e l a t e d to the v o l u m e of c e m e n t i t e and the m e a n f r e e f e r r i t e path, and he c o n c l u d e s that the y i e l d i n g of these m a t e r i a l s , when they a r e a l r e a d y h e a v i l y d e f o r m e d , follows the Orowan c r i t e r i o n : "ry = 2 o t G b / ~ + r a
w h e r e G is the s h e a r m o d u l u s , b is the B u r g e r ' s v e c t o r of a glide d i s l o c a t i o n , r a is the flow s t r e s s of the m a t r i x , k is the m e a n f r e e path between p r e c i p i t a t e s and a is the d i s l o c a t i o n line t e n s i o n . R i c h a r d s o n has i n v e s t i g a t e d the h a r d n e s s of s u r f a c e s s t r a i n e d by shot p e e n i n g , a b r a s i v e w e a r in field s o i l s c o n t a i n i n g s t o n e s , and t r e p a n n i n g with M. A. MOORE is with the Engineering Research Department, National Institute of Agricultural Engineering,Wrest Park, Silsoe, Bedford, Great Britain. The late R. C. D. RICHARDSON was Head of the EngineeringResearch Department, National Institute of Agricultural Engineering.D. G. ATTWOOD,formerly with EngineeringResearch Department, National Institute of Agricultural Engineering, is now with Department of Metallurgy, Oxford University, Oxford, Great Britain. Manuscript submitted February 4, 1972. METALLURGICALTRANSACTIONS
a blunted tool, and he c l e a r l y d e m o n s t r a t e d the s i g n i f i c a n c e of s u r f a c e h a r d n e s s in r e l a t i o n to a b r a s i v e w e a r . It is g e n e r a l l y a g r e e d that the bulk h
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