Fatigue crack propagation through weld heat affected zones
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c r a c k - l i k e d e f e c t in a l a r g e s t r u c t u r e s u b j e c t e d to c y c l i c s t r e s s i n g m a y g r o w by f a t i g u e c r a c k p r o p a g a tion to such an e x t e n t that u n s t a b l e f a s t f r a c t u r e can o c c u r . In p a r t i c u l a r , m a t e r i a l in the v i c i n i t y of w e l d m e n t s is l i a b l e to contain such d e f e c t s and h e n ce the b e h a v i o r of fat i g u e c r a c k s in o r a d j a c e n t to a w e l d is of g r e a t p r a c t i c a l i m p o r t a n c e . Only a l i m i t e d amount of w o r k has b e e n u n d e r t a k e n to study fatigue c r a c k p r o p a g a t i o n in weld m e t a l l-a and the s i t u at i o n in r e a l s t r u c t u r e s is c o m p l i c a t e d by the p r e s e n c e of a heat a f f e c t e d zone ( r e f e r r e d to as H.A.Z.) in the p a r e n t m e t a l a d j a c e n t to the weld. T h i s zone d i f f e r s m e c h a n i c a l l y and s t r u c t u r a l l y f r o m the bulk p a r e n t m a t e r i a l ; h e n c e , any c o n s i d e r a t i o n of fatigue f a i l u r e at a weld should include a c o m p r e h e n s i v e study of fatigue c r a c k p r o p a g a t i o n in the a s s o c i a t e d H.A.Z. T h i s r e p o r t p r e s e n t s the r e s u l t s of an i n v e s t i g a t i o n into the e f f e c t s of a H.A.Z. on f a t i g u e c r a c k p r o p a g a tion in and a r o u n d welds. S i n c e the fatigue t e s t s w e r e done on a c t u a l H . A . Z . ' s u n d e r known s t r e s s c o n d i t i o n s , the c o n c l u s i o n s can be applied to the b e h a v i o r of f a tigue c r a c k s in a c t u a l s t r u c t u r e s u n d e r o p e r a t i n g c o n ditions.
f u r n a c e c o o l e d to r e l i e v e the i n t e r n a l s t r e s s e s and t e m p e r the D u co l H.A.Z. The c o m p o s i t i o n s of the m i l d s t e e l , D u co l W30, and H1 weld m e t a l a r e shown in T a b l e I. 1.2) S p e c i m e n P r e p a r a t i o n Single e d g e - n o t c h e d t e s t p i e c e s 300 by 76 by 5 m m w e r e m a c h i n e d f r o m the w e l d e d b l o c k in two o r i e n t a t i o n s as shown s c h e m a t i c a l l y in Fig. l ( a ) . T h i s r e s u l t e d in the H.A.Z.~s lying at 90 and 75 deg to the s t r e s s a x i s , e n a b l i n g f at i g u e c r a c k s to be p r o p a g a t e d both p a r a l l e l to and at an angle to the H . A . Z . ' s , Fig. l(b). S p e c i m e n s to be u s e d f o r t e s t i n g the m i l d s t e e l H . A . Z . ' s w e r e m i l l e d to a t h i c k n e s s of 1.5 m m . The r e a s o n f o r this is that the m i l d s t e e l H . A . Z . ' s w e r e
WELDING DIRECTION I
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DUCOLW30~
1) E X P E R I M E N T A L P R O C E D U R E 1.1) P r e p a r a t i o n and C o m p o s i t i o n of Weld Two 76 m m t h i c k s l a b s , one of m i l d s t e e l , the o t h e r of Ducol W30 (a low alloy s t e e l ) , w e r e w e l d e d t o g e t h e r u s i n g a K - p r e p a r a t i o n as shown in Fig. 1. A m a n u a l
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