Fatigue stability of residual stress in shot peened alloys
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Table I. Composition of Alloys (Wt Pct)
Heat
Ni
Co
C
A1
Mg
59809 59810
Bal. 41.4
19.5 Bal.
0.004 0.016
0.08 0.08
0.01 l 0.011
Table II. Shot Peening Parameters for Almen Intensity 0.008N2
Parameter Shot Dmmeter AirPressure Coverage Timeper Piece NozzleSize Angleof Peening PeeningDistance
0.0032 to 0.0046cm 25 psi (172,700 N/m2) 200 pet two rain 0.95 cm 90 deg 10.16cm
by the I n t e r n a t i o n a l Nickel Company. To f a c i l i t a t e d i s c u s s i o n , heat n u m b e r 59809 will be r e f e r r e d to as the 20 pet Co a l l o y and heat n u m b e r 59810 will be r e f e r r e d to as the 60 pet Co alloy. C a n t i l e v e r fatigue s p e c i m e n s w e r e p r e p a r e d f r o m 0.203 c m thick sheet m a t e r i a l a c c o r d i n g to Sonntag Scientific C o r p o r a t i o n D r a w i n g N u m b e r 90881-S. After shaping the s p e c i m e n s , all s u r f a c e s w e r e f i n ished with 2/0 e m e r y p o l i s h i n g p a p e r and a n n e a l e d at 600~ for 1 h in an a r g o n a t m o s p h e r e . E l e c t r o p o l i s h i n g r e m o v e d any oxide s c a l e f o r m e d d u r i n g the s t r e s s - r e l i e f a n n e a l . Subsequently, both alloys were g l a s s - b e a d shot peened to an A l m e n i n t e n s i t y of 0.008N2. P a r a m e t e r s used to a t t a i n the 0.08N2 A l m e n i n t e n s i t y a r e l i s t e d in Table If. Using the r e c r y s t a l l i z a t i o n t e c h n i q u e s of V a l e n t i n e , *~ the r e s i d u a l s t r e s s l a y e r was m e a s u r e d and found to be 0.0064 c m deep for both a l l o y s . 1.2 X - R a y Diffraction Method Residual s t r e s s m e a s u r e m e n t s w e r e made u s i n g the t w o - e x p o s u r e X - r a y d i f f r a c t o m e t e r t e c h n i q u e , n In the c u r r e n t work c h r o m i u m K s r a d i a t i o n d i f f r a c t e d f r o m the {200} c r y s t ~ d l o g r a p h i c p l a n e s p r o v i d e d the b e s t r e s o l u t i o n and peak heights in the high 20 r e g i o n b e tween 133 and 134 deg 20. VOLUME 4, SEPTEMBER 1973-2153
T h e o r e t i c a l l y the s t r e s s c o n s t a n t , K, is a function only of Young's m o d u l u s , the B r a g g angle, P o i s s o n ' s r a t i o , and the angle of r o t a t i o n , ~b, d u r i n g m e a s u r e m e n t . H o w e v e r , t h i s r e l a t i o n d o e s not allow f o r a n i s o t r o p y in p o l y c r y s t a l l l n e m a t e r i a l s , hence, it is g e n e r a l l y p r e f e r a b l e to obtain K e x p e r i m e n t a l l y b y e l a s t i c a l l y s t r a i n i n g an a n n e a l e d m a t e r i a l b y known i n c r e m e n t s and m e a s u r i n g the c o r r e s p o n d i n g change in B r a g g a n g l e . Thus, s t r e s s a l w a y s will be p r o p o r t i o n a l to h20 f o r a given c r y s t a l l o g r a p h i c r e f l e c t i o n and ~b r o t a t i o n . A p p l i c a t i o n of only e l a s t i c s t r e s s is i m p o r tant s i n c e u n i a x i a l l y a p p l i e d p l a s t i c s t r e s s p r o d u c e
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