Crack closure and fatigue striations in 2024-T3 aluminum alloy
- PDF / 315,550 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 27 Downloads / 252 Views
a l l o y s a s w e l l a s p o l y m e r i c m a t e r i a l s , d i f f e r on l o g - l o g plots of growth r a t e v s AK, the r e s p o n s e of m e t a l s , at l e a s t , m a y be n o r m a l i z e d by dividing the s t r e s s intensity f a c t o r by the m a t e r i a l s ' r e s p e c t i v e moduli of e l a s t i c i t y . ~ In a s i m i l a r fashion, B a t e s and C l a r k ~ r e c e n t l y showed that the s i z e of the fatigue s t r i a t i o n in s e v e r a l e n g i n e e r i n g m e t a l a l l o y s could be r e l a t e d to the s t r e s s i n t e n s i t y f a c t o r r a n g e when n o r m a l i z e d by the m o d u l u s of e l a s t i c i t y as shown in Eq. [2] (English units). striation spacing ~ 6
Such an equation is useful in f a i l u r e a n a l y s e s w h e r e fatigue s t r i a t i o n m e a s u r e m e n t s can be obtained f r o m the f r a c t u r e s u r f a c e . Knowing the s i z e of the fatigue s t r i a t i o n s and the m o d u l u s of e l a s t i c i t y of the m a t e r i a l it is p o s s i b l e to e s t i m a t e the s t r e s s i n t e n s i t y r a n g e a c c o r d i n g to Eq. [2]. U n f o r t u n a t e l y , the s c a t t e r band of the s t r i a t i o n s i z e vs A K / E plot is r a t h e r l a r g e , t h e r e b y r e s t r i c t i n g the d e t e r m i n a t i o n of AK only to within =E30 to 40 pet of the e s t i m a t e d v a l u e . While Eq. [2] does o f f er the potential for a rough e s t i m a t i o n of the s t r e s s i n t e n s i t y r a n g e v al u e d u r i n g an a c t u a l fatigue condition, the r e s u l t s a r e l i m i t e d to the extent that Eq. [2] does not account for mean s t r e s s e f f e c t s . S p e c i f i c a l l y , the data used by B a t e s and C l a r k w e r e obtained f r o m s p e c i m e n s s u b j e c t e d to loading conditions a s s o c i a t e d with R = 0 (R = m i n i m u m l o a d / m a x i m u m load). While mean s t r e s s v a r i a t i o n s do not a f f e c t fatigue c r a c k p r o p a g a t i o n (FCP) as much a s s t r e s s r a n g e c h a n g e s , it is n o n e t h e l e s s i m p o r t a n t that m e a n s t r e s s c o n s i d e r a t i o n s be f a c t o r e d into Eq. [2J; this m a y be done through a p p l i c a t i o n of the c r a c k c l o s u r e concept. E l b e r 6 has r e c e n t l y shown that r e s i d u a l t e n s i l e d i s p l a c e -
AKapp(MN/m 3x2)
Crack Closure and Fatigue Striations in 2024-T3 Aluminum Alloy RICHARD W. H E R T Z B E R G AND ERIC F . J .
[2]
,d 4
I0
30
I
'on/
~ /
VON EUW
~
u~ u/ %
/o
-
-4 I0
FORSYTHand
R y d e r ' showed a d i r e c t c o r r e l a t i o n b e tw e en fatigue s t r i a t i o n i n c i d e n c e on the f r a c t u r e s u r f a c e and n u m b e r of loading c y c l e s and r e l a t e d the s i z e of the s t r i a t i o n to the a m p l i t u d e of the load. Since this o b s e r v a tion, s e v e r a l i n v e s t i g a t o r s have shown a c l o s e c o r r e l a tion b et ween fatigue s t r i a t i o n s p a c i n g s
Data Loading...
