Observations of stress corrosion crack-front bowing in high-strength aluminum alloy double cantilever beam specimens

  • PDF / 627,233 Bytes
  • 3 Pages / 612 x 792 pts (letter) Page_size
  • 109 Downloads / 196 Views

DOWNLOAD

REPORT


longest i n t e r n a l c r a c k length o c c u r r e d at the c e n t e r of the s p e c i m e n . T a b l e I l i s t s the data used i n p l o t ting Fig. 2. Optical " S i d e 1 " d a t a was plotted on the left of the f i g u r e , " S i d e 2 " data was piotted on the right, and the a v e r a g e of the two u l t r a s o n i c v a l u e s was plotted in the c e n t e r . A b e s t n a k e d - e y e fit was d r a w n in each case, It should be noted that the c r a c k p o s i t i o n

P E T E R J. BLAU The b o l t - l o a d e d double c a n t i l e v e r b e a m s p e c i m e n , DCB (Fig. 1) has b e e n used in the p a s t for m e a s u r i n g the growth r a t e s of s t r e s s c o r r o s i o n c r a c k s in high s t r e n g t h a l u m i n u m a l l o y s (e.g., Refs. 1 to 4). In a n u m b e r of p r e v i o u s s t u d i e s , the c r a c k p r o g r e s s was o p t i c a l l y m o n i t o r e d on the s i d e s of the s p e c i m e n s . T h e s e c r a c k l e n g t h s were used to c a l c u l a t e the d e p e n d e n c e of c r a c k growth r a t e on the applied s t r e s s i n t e n s i t y at the c r a c k tip. E x a m i n a t i o n of b r o k e n open high s t r e n g t h a l u m i n u m alloy DCB s t r e s s c o r r o s i o n s p e c i m e n s has r e v e a l e d t h e i r i n n a t e p r o p e n s i t y toward c r a c k f r o n t bow-out, o r tunneling. This p h e n o m e n o n m a y b e due in p a r t to the change in the s t a t e of s t r e s s with depth in the s a m p l e and to the p r e s e n c e of s u r f a c e r e s i d u a l s t r e s s e s i n the wrought p r o d u c t f r o m which the DCB was machined, l'z W h a t e v e r the cause, the d e v e l o p m e n t of c r a c k front bowing d u r i n g the s t r e s s c o r r o s i o n t e s t would lead to e r r o r s in the c r a c k growth r a t e (da/dt) d e t e r m i n a t i o n , e s p e c i a l l y if the bow out i n c r e a s e d at a g r e a t e r r a t e than did the e x t e r n a l c r a c k length. The p u r p o s e of this c o m m u n i c a t i o n , then, is to d i s p l a y an e x a m p l e of how the c r a c k f r o n t m a y develop i n t e r n a l l y d u r i n g the t e s t i n g of a l u m i n u m alloy DCB s p e c i m e n s . The s p e c i m e n used h e r e i n was p a r t of a study being conducted i n - h o u s e at the A i r F o r c e M a t e r i a l s L a b o r a tory on the r e l i a b i l i t y of high s t r e n g t h a l u m i n u m a l loys. ~ Its c o m p o s i t i o n is A1, 5.68 Zn, 2.13 Mg, 1.51 Cu, 0.04 F e , 0.02 Si, 0.12 Z r , 0.005 Ti, and

Data Loading...