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LEE A. JAMES is Senior Research Engineer, WADCOCorp., Richland, Wash. EARL B. SCHWENK,JR. is Research Engineer, Battelle-Northwest, Richland, Wash. Manuscript submitted August 10, 1970 MI!TALLURGICALFRANSACTIONS

j e w e l e r s ' saw was used to p r o d u c e a c r a c k - s t a r t e r notch approxxmately ~- in. long in the SEN s p e c i m e n s and the fatigue c r a c k was allowed to i n i t i a t e f r o m the notch and grow a p p r o x i m a t e l y 0.05 in. before c r a c k length m e a s u r e m e n t s were c o m m e n c e d . All s p e c i m e n s were cycled in u n i a x i a l t e n s i o n at s t r e s s r a t i o s b e t w e e n z e r o and 0.05, see T a b l e III f o r t e s t p a r a m e t e r s . Two types of fatigue t e s t i n g m a c h i n e s w e r e e m p l o y e d : an e l e c t r o h y d r a u l i c s e r v o c o n t r o l l e d MTS fatigue m a c h i n e , and a B a l d w i n - T a t e - E m e r y u n i v e r s a l t e s t i n g m a c h i n e (BTE) equipped with a loadc y c l i n g a t t a c h m e n t . T w o ' c y c l i c load w a v e f o r m s were u t i l i z e d with the MTS m a c h i n e , (a sawtooth r a m p for s p e c i m e n s n o s . 1, 4, 5, and a s i n u s o i d a l w a v e f o r m f o r s p e c i m e n no. 3), while the BTE m a c h i n e produced a w a v e f o r m that a p p r o x i m a t e d a sawtooth r a m p , see F i g . 2. Cyclic f r e q u e n c i e s w e r e kept low (4 cpm) for the e l e v a t e d t e m p e r a t u r e t e s t s s i n c e m a n y of the r e a c t o r s t r u c t u r a l l o a d i n g s of i n t e r e s t do not o c c u r at the highe r f r e q u e n c i e s . It was found that e v e n at 4 cpm, the loads indicated by the l o a d i n g d i a l on the BTE c o n t r o l console w e r e u n r e l i a b l e due to the i n e r t i a of the loading s y s t e m and the r e s p o n s e c h a r a c t e r i s t i c s of the b o u r d o n tube and a s s o c i a t e d m e c h a n i c a l l i n k a g e s that c o m p r i s e the load i n d i c a t o r s y s t e m . T h e r e f o r e , a load cell was i n s e r t e d in the loading t r a i n , in s e r i e s with the s p e c i m e n and the output of the load c e l l was used in s e t t i n g up the cyclic load l i m i t s . C r a c k l e n g t h s w e r e r e a d at a p p r o x i m a t e l y 65X with a G a e r t n e r t r a v e l l i n g m i c r o s c o p e (least dial d i v i s i o n 0.0001 in.), and c r a c k length v s c y c l e s data were taken throughout each t e s t . In the case of the e l e v a t e d t e m p e r a t u r e s p e c i m e n s , c r a c k length r e a d i n g s were always taken a f t e r the s p e c i m e n s had c o m p l e t e l y cooled to room t e m p e r a t u r e . C r a c k length r e a d i n g s were made on each side of the s p e c i m e n and then a v e r a g e d . The c r a c k l e n g t h s were not c o r r e c t e d f o r p l a s t i c i t y e f f e c t s . In g e n e r a l , the i n c r e m e n t of c r a c k e x t e n s i o n b e t w e e n r e a d i n g s was l i m i t e d to 1 p