Identification of a fracture mode: the tearing topography surface
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1. A. K. Ghosh and R. A. Ayres: Met. Trans. A, 1976, vol. 7A, pp. 1589-91. 2. J. W. Edington: Met. Technol., 1976, vol. 3, no. 3, pp. 138-50. 3. D. Lee and W. A. Backofen: Trans. TMS-AIME, 1967, vol. 239, pp. 1034-40. 4. D. A. Woodford: Trans. ASM, 1969, vol. 62, pp. 291-93. 5. C. H. Hamilton and G. W. Stacher: Met. Progr., 1976, vol. 109, no. 3, pp. 3437. 6. R. R. Royer and J. Magnuson: Unpublished research, The Boeing Company, Seattle, WA, 1977.
Identification of a Fracture Mode: The Tearing Topography Surface ANTHONY
W. THOMPSON
AND
JAMES
C. CHESNUTT
F r a c t u r e s u r f a c e s of m e t a l s have long been c h a r a c t e r i z e d as " b r i t t l e " or " d u c t i l e , " a c c o r d i n g to t h e i r v i s u a l a p p e a r a n c e ; the f o r m e r type has also been des c r i b e d as " c r y s t a l l i n e " or " f a c e t e d , " while the latt e r is often called " f i b r o u s . " With the use of higher m a g n i f i c a t i o n t e c h n i q u e s of f r a c t u r e e x a m i n a t i o n , p a r ticularly replica transmission electron microscopy (TEM) and s c a n n i n g e l e c t r o n m i c r o s c o p y (SEM), t h e r e have grown up a group of m i c r o s c o p i c a p p e a r a n c e types, often called f r a c t u r e " m o d e s . " A m o n g the e a r l y efforts to catalog these modes were those of B e a c h e m and P e l l o u x ~ and P h i l i p s et aL e c u r r e n t l y t h e r e a r e a v a i l a b l e two r a t h e r c o m p r e h e n s i v e catalogs of this type. T M All c l a s s i f y m i c r o s c o p i c f r a c t u r e d e t a i l s ( p a r *Ref. 3 is currently available version of Ref. 2.
t i c u l a r l y of t e n s i l e f r a c t u r e s ) into four c l a s s i c a l m o d e s : i n t e r g r a n u l a r , cleavage, q u a s i - c l e a v a g e , and m i c r o v o i d c o a l e s c e n c e (or dimpled) f r a c t u r e s . T h e r e is a consequent t e n d e n c y 4 to a s s i g n any p a r t i c u l a r f r a c t u r e topography to one of these four modes, although it is often the case that the m a j o r i t y of a f r a c t u r e s u r f a c e is " i l l d e f i n e d " in c l a s s i c a l t e r m s and one m u s t s e a r c h to find local a r e a s which a r e adequately " r e p r e s e n t a t i v e " of the mode a s s i g n e d . What we d e s c r i b e in this c o m m u n i c a t i o n is an addit i o n a l mode of f r a c t u r e , one with a c h a r a c t e r i s t i c a p p e a r a n c e ; such a d i s t i n c t i v e a p p e a r a n c e is the fundam e n t a l c r i t e r i o n for d i s t i n g u i s h i n g f r a c t u r e m o d e s . 1-3,S T h i s mode is often o b s e r v e d in s t e e l s and in a l p h a - b e t a t i t a n i u m a l l o y s , such as Ti-6A1-4V ( T i - 6 - 4 ) , but is ANTHONY W. THOMPSON is Professor, Department of Metallurgy and Materials Science, Carnegie-MellonUniversity, Pittsburgh, PA 15213. JAMES C. CHESNUTTis Member of Technical Staff, Science Center, Rockwell International, Thousand Oaks, CA 91360. Manuscript submitt
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