Experimental observations of tensile fracture in unidirectional boron filament reinforced aluminum sheet
- PDF / 4,290,789 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 55 Downloads / 175 Views
D
.IDASED on c o n s i d e r a t i o n s of d e n s i t y , s t i f f n e s s , and c o m p r e s s i v e s t r e n g t h over a r e l a t i v e l y wide t e m p e r a ture range, unidirectional boron filament reinforced a l u m i n u m (B-A1) c o m p o s i t e is r e g a r d e d as a p o t e n t i ally u s e f u l m a t e r i a l for advanced a e r o s p a c e a p p l i c a t i o n s . The t e n s i l e s t r e n g t h of the m a t e r i a l , however, has been s o m e w h a t d i s a p p o i n t i n g , with t e n s i l e f a i l u r e s f r e q u e n t l y being o b s e r v e d at an a v e r a g e f i l a m e n t s t r e s s l e s s than half the s t r e n g t h of the v i r g i n f i l a m e n t used in f a b r i c a t i o n of the c o m p o s i t e . A r e c e n t i n v e s t i g a t i o n at the Langley R e s e a r c h C e n t e r of NASA ~ has shown that one c o m m e r c i a l l y a v a i l a b l e B-A1 c o m p o s i t e , used in a s t r u c t u r a l e l e m e n t with s u f f i c i e n t s u p p o r t to p r e v e n t buckling, could r o u t i n e l y withstand c o m p r e s s i v e s t r e s s e s on the o r d e r of 225 ksi without f a i l u r e . The t e n s i l e s t r e n g t h of the v e r y s a m e m a t e r i a l b a r e l y e x ceeded 100 ksi. The p r o b l e m of t e n s i l e f r a c t u r e in c o m p o s i t e s c o n t a i n i n g p a r a l l e l , b r i t t l e f i l a m e n t s was a n a l y z e d by Zweben and R o s e n 2-5 in a s e r i e s of r e c e n t p a p e r s . Zweben,2 in p a r t i c u l a r , d e s c r i b e d two f u n d a m e n t a l f r a c t u r e m o d e s . One of t h e m , the c u m u l a t i v e mode, was c h a r a c t e r i z e d by the g r a d u a l a c c u m u l a t i o n of a c o n s i d e r a b l e n u m b e r of f i l a m e n t b r e a k s in a d v a n c e of total composite f r a c t u r e . The c u m u l a t i v e mode o c c u r r e d when f i l a m e n t s broke u n d e r the influence of s t r e s s c o n c e n t r a t i o n s r e s u l t i n g f r o m b r e a k s in n e i g h b o r i n g f i l a m e n t s , or when f i l a m e n t s broke in s c a t t e r e d l o c a tions a c c o r d i n g to t h e i r i n d i v i d u a l l o a d - b e a r i n g c a p a b i l i t i e s . F r a c t u r e of the c o m p o s i t e u l t i m a t e l y o c c u r r e d when the c r o s s - s e c t i o n a l a r e a of u n b r o k e n f i l a m e n t s b e c a m e too s m a l l to withstand the applied load. The second f r a c t u r e mode, r e f e r r e d to as the n o n c u m u l a t i v e mode, did not involve a s i g n i f i c a n t n u m b e r of i n d i v i d u a l f i l a m e n t b r e a k s p r i o r to c o m p o s i t e f a i l u r e . H. W. HERRING is Materials Engineer, NASA-LangleyResearch Center, Hampton, Va. 23365. J. L. LYTTON and J. H. STEELE, JR. are Professor and Chairman of MetallurgicalEngineeringand Assistant Professor of Metallurgical Engineering,respectively, VirginiaPolytechnic Institute and State University, Blacksburg, Va. Manuscript submitted April 14, 1
Data Loading...
