Some applications of aeronautical engineering in the construction of yachts

1

-SOME APPLICATIONS OF AERONAUTICAL ENGINEERING IN THE CONSTRUCTION OF YACHTS

by F.A. J a c o b s ( N a t i o n a l A e r o s p a c e L a b o r a t o r y , t h e N e t h e r l a n d s )

SUMMARY

Some r e c e n t d e v e l o p m e n t s o f t h e m a s t s and s t a n d i n g r i g g i n g o f r a c i n g - y a c h t s and, on t h e o t h e r hand, t h e f a i l u r e s o f a number o f m a s t s and r u d d e r s t o c k s l e d t o t h e a p p l i c a t i o n o f a e r o n a u t i c a l e n g i n e e r i n g . L o a d s p e c t r a o f t h e s t a n d i n g r i g g i n g o f a 10.OOm. r a c i n g y a c h t a r e g i v e n and t h e a p p l i c a t i o n o f them i n a l u g . Some i n f o r m a t i o n i s g i v e n on s t r e s s r a i s e r s and on m a t e r i a l s . F a n a l l y some t e s t a p p l i -c a t i o n s a r e m e n t i o n e d .

CONTENTS

1. INTRODUCTION

2 . ASSESSMENT OF LOADS

3. STRESSES AND STRESS RAISERS

4. MATERIALS AND HEAT-TREATMENTS

5. MISCELANEOUS

24 F i g u r e s , 6 t a b l e s , 10 r e f e r e n c e s .

Motto, by W i l l i a m Thompson, L o r d K e l v i n :

"When y o u c a n measure what y o u a r e t a l k i n g a b o u t , and e x p r e s s i t i n numbers, y o u know s o m e t h i n g about i t " .

1. INTRODUCTION One o f t h e i m p o r t a n t g o a l s o f a e r o n a u t i c a l e n g i n e e r i n g i s t o a c h i e v e s t r o n g and r e l i a b l e c o n s t r u c t i o n s w i t h a low w e i g h t . S i n c e t h e l a t t e r r e q u i r e m e n t i s i m p e r a -t i v e ^ -t h e s -t r e n g -t h - w e i g h -t r a -t i o o f a i r b o r n e c o n s -t r u c -t i o n s i s v e r y h i g h a s compared w i t h o t h e r v e h i c l e s ( c a r s , t r a i n s ) o r w i t h o t h e r p r o d u c t s o f m e c h a n i c a l e n g i n e e r -i n g . T h -i s c e r t a -i n l y -i s n e c e s s a r y t o keep a -i r t r a n s p o r t a t -i o n e c o n o m -i c a l l y f e a s -i b l e , w h i c h means t h a t t h e r e i s a n o n - l e s s e n i n g p r e s s u r e t o s a v e w e i g h t w h e r e - and when-e v when-e r p o s s i b l when-e . F o r example: s a v i n g 1kg, c o n s t r u c t i o n w e i g h t i n a B o e i n g 747 ( t a k e - o f f w e i g h t ~ 350.000kg, ) o r i n a DC-10 ( t a k e - o f f weight'v 250.000kg.) r e s u l t s i n s a v i n g $ 100 n e t t p e r y e a r . So, i n g e n e r a l i t a p p e a r s t o be w o r t h w h i l e t o s a v e w e i g h t by a l l r e a s o n a b l e means. Weight r e d u c t i o n c a n be a c h i e v e d by d e t a i l e d s t r e s s r e s e a r c h , by t h e a p p l i c a t i o n o f a d v a n c e d m a t e r i a l s and by e x t e n s i v e t e s t i n g . The l a t t e r v a r i e s from s m a l l p a r t s o r s p e c i m e n s t o f u l l - s c a l e e n v i r o n m e n t a l t e s t i n g ( l i k e t h e C o n c o r d e ) . A c o n s i d e r a b l e p a r t o f t h e knowledge g a t h e r e d i n a e r o n a u t i c a l e n g i n e e r i n g i s a v a i l a b l e f o r t h e a p p l i c a t i o n i n o t h e r e n g i n e e r i n g b r a n c h e s w i t h a demand f o r c o n -s t r u c t i o n -s w i t h a h i g h -s t r e n g t h - w e i g h t r a t i o , f o r i n -s t a n c e -s a i l i n g y a c h t -s ! T h i -s w i l l be e s p e c i a l l y u s e f u l l i f t h e c o n c e p t o f s u c h a y a c h t r e s e m b l e s an a i r p l a n e : b u i l t from a l u m i n i u m a l l o y s . B u t a l s o i n y a c h t s made o f o t h e r m a t e r i a l s , t h e r e a r e many p a r t s w h i c h c a n be t r e a t e d i n a a e r o n a u t i c a l way, a s f o r i n s t a n c e t h e s t a n -d i n g r i g g i n g an-d s p a r s o r t h e r u -d -d e r s h a f t . P a y i n g a t t e n t i o n t o r e a l i s t i c l o a d s , s t r e s s r a i s e r s and new m a t e r i a l s , w e i g h t c a n be s a v e d on one hand w h i l e on t h e o t h e r hand u n e x p e c t e d f a i l u r e s , l i k e t h e many mast and r u d d e r s h a f t f a i l u r e s o f t o d a y ' s ( b i g ) r a c i n g y a c h t s , c a n be p r e v e n t e d .

2. ASSESSMENT OF LOADS

The l o a d s a c t i n g on a i r p l a n e f l y i n g i n s t i l l a i r a t 1 g c a n be c a l c u l a t e d r a t h e r e a s i l y . B u t t h e n i m m e d i a t e l y t h e q u e s t i o n r i s e s how t h e s e l o a d s a r e i n f l u e n c e d by g u s t s and/or manoeuvres. To answer t h i s q u e s t i o n numerous r e c o r d i n g s from c o u n t i n g a c c e l e r o m e t e r s and from s t r a i n gauges, bonded i n c r i t i c a l a r e a s had t o be a n a -l y s e d t o a r r i v e a t -l o a d s p e c t r a , m o s t -l y f o r t h e w i n g , and a -l w a y s r e -l a t e d t o a s p e c i f i c t y p e o f a i r p l a n e . B a s e d on t h e s e d a t a , r e a s o n a b l e o v e r l o a d f a c t o r s h a v e been e s t a b l i s h e d t o make p o s s i b l e r e a l i s t i c s t r e s s c a l c u l a t i o n s . The t e s t i n g o f p a r t s and f i n a l l y a s t a t i c and dynamic f u l l s c a l e t e s t h a s t o p r o v e t h e i n t e g r i t y o f t h e c o n s t r u c t i o n .

A s i m i l a r development t o a s s e s s t h e dynamic l o a d s i n t h e r i g g i n g and o t h e r c r i t i c -a l -a r e -a s o f r -a c i n g y -a c h t s h -a s , t o my b e s t knowledge, n e v e r t -a k e n p l -a c e . C o n t r -a r y : t o c a l c u l a t e t h e d i m e n s i o n s o f t h e p a r t s o f t h e s t a n d i n g r i g g i n g t h e a p p r o a c h i s f u l l y s t a t i c ; i . e . t h e y a c h t i s assumed t o be h e e l e d by a e r o d y n a m i c f o r c e s u n t i l t h e maximum r i g h t i n g moment i s r e a c h e d . T h e s e f o r c e s a r e s p r e a d i n a r a t h e r p e c u -l i a r way o v e r t h e m a s t -l e n g t h , I n d u c i n g t h e -l o a d s i n t h e r i g g i n g w i r e s ( R e f , 1 ) .

3

-I n t h e a p p l i e d , more o r l e s s e m p i r i c a l f o r m u l a e , o v e r l o a d - and/or s a f e t y f a c t o r s a r e i n c l u d e d , p r o b a b l y c o m p r i s i n g dynamic l o a d e f f e c t s a s w e l l . As G a r y M u l l i n h i s 1981 HISWA l e c t u r e mentioned ( R e f . 2 ) t h e r e h a s been and s t i l l goes on a t r i a l and e r r o r t y p e o f a p p r o a c h , w h i c h , i f t h e c a u s e s o f t h e e r r o r s a r e n o t i n v e s t i g a t e d and u n d e r s t o o d , w i l l n e v e r end. T h e r e f o r e , t o o b t a i n w e i g h t r e d u c t i o n w i t h o u t t h e p e n a l t y o f f a i l u r e s , t h e t r u e l o a d s and t h e number o f o c c u r e n -c e s i n t h e -c r i t i -c a l a r e a s o f t h e y a -c h t s h a v e t o be a s s e s s e d .

As a f i r s t s t e p t o o b t a i n some i n s i g h t i n t h i s m a t t e r , i n t h e S p r i n g o f 1982 measurements have been c a r r i e d o u t on a 3 0 f t . r a c i n g y a c h t , t h e d a t a o f w h i c h a r e g i v e n i n f i g u r e 1. T h e s e a c t i v i t i e s h a v e been e x e c u t e d i n c l o s e c o o p e r a t i o n between t h e S h i p - H y d r o m e c h a n i c s L a b o r a t o r y o f t h e T e c h n o l o g i c a l U n i v e r s i t y D e l f t , one o f i t s s c i e n t i s t s who made a v a i l a b l e t h e r a c i n g y a c h t , INTECHMY w h i c h made a v a i l a b l e an i n s t r u m e n t a t i o n r e c o r d e r and t h e S t r u c t u r e s and M a t e r i a l s D i v i s i o n o f t h e NLR.

S i n c e i n t h i s c a s e t h e s t a n d i n g r i g g i n g was o f p r i m a r y i n t e r e s t , s t r a i n g a u g e s were a p p l i e d on t h e r i g g i n g s c r e w s o f t h e p o r t s h r o u d s and o f f o r e - and b a c k s t a y . I n t h e b a r r e l b f t h e r i g g i n g s c r e w two a c t i v e s t r a i n g a u g e s w e r e g l u e d , w i r e d and s e a l e d . Then, w i t h a c a l i b r a t i o n i n a t e n s i l e t e s t i n g m a c h i n e , t h e l o a d f a c t o r , i . e . t h e t e n s i l e l o a d v e r s u s t h e e l e c t r i c a l o u t p u t , had been a s s e s s e d ( T a b l e 1 ) . The r i g g i n g s c r e w s were mounted and t h e w i r e s f o r t h e s u p p l y and o u t p u t c o n n e c t e d

to t h e i n s t r u m e n t s a c c o r d i n g t o t h e b l o c k - s c h e m e g i v e n i n f i g u r e 2. The 7 t r a c k (one t r a c k b e i n g a v o i c e c h a n n e l ) SE 3500 r e c o r d e r made p o s s i b l e t h e s i m u l t a n e o u s r e c o r d i n g o f 6 t r a n s d u c e r s . The pen r e c o r d e r p r o v i d e d a q u i c k l o o k ( F i g . 3 ) and a back-up f o r m a l f u n c t i o n i n g o f t h e SE 3500. A f t e r p r e l o a d i n g t h e r i g g i n g s c r e w s a c c o r d i n g t o common p r a c t i c e , t h e t e s t s e t - u p was r e a d y .

As i s shown i n t h e t a b l e s 2 and 3, v a r i o u s c o n d i t i o n s were e n c o u n t e r e d d u r i n g t h e 11 r u n s made, e a c h r u n l a s t i n g f o r about 20 m i n u t e s . U n f o r t u n a t e l y o n l y r u n s 8, 9, 11 and 12 a p p e a r e d t o have u s e f u l l r e s u l t s f o r a l l c h a n n e l s . S i n c e r u n 8 and 9 were c o m p a r a b l e : same w e a t h e r - and s e a c o n d i t i o n b u t g o i n g w i n d w a r d ( r u n 8 ) and r e a c h i n g w i t h s p i n n a k e r ( r u n 9 ) , i t was d e c i d e d t o p r o c e s s t h e d a t a o f t h e s e r u n s . The a n a l o g u e ( f r e q u e n c y m o d u l a t e d ) o u t p u t o f t h e S E 3500 was r e c o r d e d on a s t r i p c h a r t r e c o r d e r ( F i g . 4 - 9 ) . V i a an a n a l o g u e / d i g i t a l c o n v e r t e r t h e same s i g n a l was p a s s e d t o a p e a k - v a l l e y d e t e c t o r p r e s e n t i n g i t s d i g i t i z e d r e s u l t s a s a s e q u e n c e o f numbers r e p r e s e n t i n g t h e m i l l i - v o l t a g e o f t h e p e a k s , r e s p e c t i v e l y v a l l e y s . L o a d d i r e c t i o n changes s m a l l e r t h e n 40 mV ( r e p r e s e n t i n g 6 0 k g f a s an a v e r a g e f o r a l l c h a n n e l s ) were o m i t t e d . T h i s s e q u e n c e o f numbers was compared w i t h t h e s t r o p - c h a r t r e c o r d i n g t o c h e c k f o r EMI - and s w i t c h i n g e r r o r s . The now c o r r e c t e d s e q u e n c e was t h e n h a n d l e d by c o m p u t e r t o p r o d u c e t a b l e s 4 and 5 and • f i g u r e s 10 13 r e p r e s e n t i n g l e v e l c r o s s i n g s and r a n g e c o u n t i n g s (NLR r a n g e p a i r -r a n g e o -r -r a i n f l o w c o u n t i n g ; R e f . 3 and 4 ) .

A r e v i e w o f t h e i m p o r t a n t d a t a a r e r e p r e s e n t e d i n t a b l e 6. A l l d e s i g n e r s a r e i n -v i t e d t o a p p l y t h e i r f a -v o u r i t e f o r m u l a e on t h e s a i l p l a n o f f i g u r e 1 t o c h e c k w h e t h e r o r n o t t h e r e s u l t s o f t h e s e do a g r e e w i t h t h e m e a s u r e d l o a d s .

From t h e f i g u r e s w i t h l e v e l c r o s s i n g s and r a n g e c o u n t i n g s a d a n g e r looms up: t h e a p p a r e n t dynamic c h a r a c t e r o f t h e l o a d s i n s h r o u d s and s t a y s i m p l i e s m e t a l f a t i g u e . With t h i s a s p e c t a c o m p l e t e l y new a p p r o a c h i n c o n s t r u c t i o n i s n e c e s s a r y i f an

opt i m a l c o n s opt r u c opt i o n i s p u r s u e d . An example may i l l u s opt r a opt e opt h a opt opt h i s i s n o opt u n r e a s o n -a b l e . I f i t i s -assumed t h -a t :

- The y a c h t l i f e i s 16 y e a r s .

- I n 25 weekends p e r y e a r t h e y a c h t i s s a i l i n g f o r 10 h o u r s . - 50% o f t h a t s a i l i n g time i s a c c o r d i n g t o c o n d i t i o n s of r u n 8, - The e l a p s e d time o f r u n 8 was 20min.

Then t h e a c c u m u l a t e d l o a d h i s t o r y i s : 16 X 25 X 10 X 0,5 X = 6000 t i m e s t h e c o n t e n t of r u n 8. F o r t h e l o w e r s h r o u d t h e number o f l o a d s i n c l a s s 13, w h i c h i s A / 50% of t h e h i g h e s t measured l o a d , i s 1 3 0 . So d u r i n g i t s l i f e t h e y a c h t w i l l be e x p o s e d t o 130 x 6000 = 780.000 l o a c y c l e s o f t h a t m g n l t u d e . The number o f l o a d s i n c l a s s 19 ( 7 5 % of h i g h e s t m e a s u r e d l o a d i s 10, w h i c h jneans t h a t t h e y a c h t w i l l e x p e r i e n c e i n i t s l i f e t i m e 60.000 o f t h e s e l o a d -c y -c l e s .

P r o b a b l y a number o f mast f a i l u r e s i n t h e p a s t c a n be e x p l a i n e d by t h i s enemy i n ( e s p e c i a l l y a e r o n a u t i c a l ) c o n s t i u c t i o n s . I t i s even more p r o b a b l e t h a t , a l l t h o u g h some p a r t s o f t h e r i g g i n g have been c o n s t r u c t e d too l i g h t o t h e r s were too h e a v y , by s i m p l y a p p l y i n g a s a f e t y f a c t o r o f 4 o r 4,5 ( R e f . 1 ) .

The same r e a s o n i n g w i t h r e s p e c t t o t h e l o a d s i n t h e r i g g i n g a p p l i e s t o o t h e r c r i t i -c a l p a r t s ; r u d d e r s t o -c k ( F i g . 1 4 ) , l u g s , s t e e r i n g -c a b l e s and l a s t b u t not l e a s t t h e mast s e c t i o n i t s e l f . Thus an e x t e n s i v e f i e l d h a s p r e s e n t e d i t s e l f t o be e x p l o r e d .

I t seems w o r t h w h i l e t o s t a r t i t s e x p l o r a t i o n .

Some f i n a l r e m a r k s on t h e d i s c u s s e d s t r i p c h a r t r e c o r d i n g s and r a n g e c o v m t i n g s may be u s e f u l :

The s i m i l a r i t y o f upper, l o w e r and i n t e r m e d i a t e s h r o u d i s a p p a r e n t . A l t h o u g h d i f -f e r e n t i n magnitude, t h e p e a k s and v a l l e y s -f o l l o w t h e same p a t t e r n ,

- A marked d i f f e r e n c e between r u n 8 and r u n 9 i s shown i n f i g u r e 10. W h i l e i n r u n 8 t h e l o w e r s h r o u d i s s u b j e c t e d t o l o a d s w h i c h dominate i n number and m a g n i t u d e , t h e l o a d s on t h e back s t a y a r e c o n t r a r y to t h i s . I n r u n 9, however, t h e e f f e c t o f t h e empty s p i n n a k e r w h i c h s u d d e n l y f i l l s , r e s u l t i n g i n a s h o c k l o a d , c a n be s e e n c l e a r l y . I n r u n 9 t h e d i f f e r e n c e s between t h e l o a d s i n s h r o u d s and b a c k s t a y a r e r e l a t i v e -l y s m a -l -l as compared w i t h r u n 8, The a f f e c t o f t h e s p i n n a k e r - t o p -l o a d c a n be r e c o g n i z e d ,

3. STRESSES AND STRESS-RAISERS

I t i s s u p p o s e d t h a t t h e d i m e n s i o n i n g o f i m p o r t a n t s t r u c t u r a l p a r t s i s not b a s e d on r u l e s o f thumb but on s t r e s s c a l c u l a t i o n s . I t means t h a t , a f t e r h a v i n g a s s e s s e d the l o a d s , t h e s e have t o be t r a n s l a t e d t o s t r e s s e s i n t h e m a t e r i a l o f t h e p a r t s i n v o l v e d .

I t may be t h a t t h e c o n s t r u c t i o n h a s t o be r e s i s t a n t t o p l a s t i c d e f o r m a t i o n . Then t h e maximum l o c a l s t r e s s s h a l l n o t p a s s t h e y i e l d l i m i t o f t h e m a t e r i a l . I f p l a s -t i c d e f o r m a -t i o n i s a c c e p -t e d , -t h e u l -t i m a -t e s -t r e s s c a n be a p p l i e d . N e v e r -t h e l e s s , -t o cope f o r d e f i c i e n c i e s i n t h e s t r e s s c a l c u l a t i o n and/or i n t h e m a t e r i a l s a p p l i e d , a s a f e t y f a c t o r h a s t o be i n t r o d u c e d . I t i s p l a u s i b l e t h a t t h i s f a c t o r w h i c h c o -v e r s u n c e r t a i n t i e s , c a n be s m a l l e r when r e l i a b l e d a t a a r e a -v a i l a b l e w i t h r e s p e c t to l o a d s , s t r e s s e s and m a t e r i a l s .

B a s e d on a good u n d e r s t a n d i n g o f l o a d s and s t r e s s e s and on t i g h t m a t e r i a l r e q u i r e -ments, i n a e r o n a u t i c s a s a f e t y f a c t o r o f o n l y 1,5 i s an a c c e p t e d s t a n d a r d . Compare t h i s w i t h t h e f a c t o r 4 w h i c h i s o f t e n u s e d i n y a c h t b u i l d i n g .

As l o n g a s a s t r e s s c a n be c a l c u l a t e d , f o r i n s t a n c e i n t e n s i o n , a s : l o a d d i v i d e d by c r o s s s c t i o n a l a r e a , u n c e r t a i n t i e s a r e s m a l l . U n f o r t u n a t e l y t h i s i s s e l d o m t h e c a s e . S t r e s s r a i s e r s t e n d t o be e v e r y w h e r e , even when n o t e x p e c t e d ; f o r i n s t a n c e t h e damage i n d u c e d by f r e t t i n g c o r r o s i o n . An example o f t h i s danger c a n be t h e l i g h t a l l o y l u g o f f i g u r e 15 ( R e f . 4 ) . I t i s made o f t h e A l - C u - M g - a l l o y 2024-T3

Q

w i t h i t s t y p i c a l m e c h a n i c a l p r o p e r t i e s : u l t i m a t e t e n s i l e s t r e s s S^ = 49,5 kg/mm and y i e l d l i m i t ^ = 35,2 kg/mm^. W i t h a s a f e t y f a c t o r o f 1,5 a n e t t s t r e s s l e -v e l o f 33,0 kg/mm^ seems t o be a p p l i c a b l e . The f a t i g u e l i f e howe-ver o f t h i s l u g f o r a s t r e s s v a r y i n g between z e r o and 33,0 kg/mm i s o n l y v 2000 l o a d c y c l e s . T h i s i s f a r l e s s t h a n t h e e x p e c t e d 6000 max-load c y c l e s f o r a 1 6 - y e a r l i f e t i m e , b a s e d on t h e r a n g e c o u n t i n g d i s c u s s e d e a r l i e r . The r e a s o n f o r t h i s u n e x p e c t e d low f a t i g u e l i f e i s t w o f o l d : a s t r e s s c o n c e n t r a t i o n f a c t o r ( d e f i n e d by l o c a l peak s t r e s s „ „ = n o m i n a l s t r e s s ^ ° ' ^^^^^^ 'the l o c a l s t r e s s i n t h e w a l l m a t e r i a l n e x t t o t h e h o l e , t o t h e same e x t e n d and, on t o p o f t h i s , f r e t t i n g c o r r o s i o n i s i n t r o d u c e d by t h e m o t i o n o f p i n and w a l l m a t e r i a l d u r i n g t h e l o a d c y c l e ( F i g . 1 6 ) . S h o u l d a s a f e t y f a c t o r o f 4 h a v e been a p p l i e d on S^^, w h i c h y i e l d s a maximum n e t t s t r e s s o f 12 kgf/mm^, t h e n t h e f a t i g u e l i f e s h o u l d be about 100.000 l o a d c y c l e s . B a s e d on t h e d a t a g i v e n i n f i g u r e 10 t h i s i s c o m p a r a b l e w i t h t h e number o f l o a d c y c l e s a t l e v e l 18 ( l o w e r s h r o u d ) . 18 t i m e s t h e e a r l i e r m e n t i o n e d f a c t o r 6000. S i n c e l e v e l 18 i s 6 7 % o f t h e maximum l o a d t h i s i s d i s c o u r a g i n g b e c a u s e t h e l u g l i f e i s consumed c o m p l e t e l y by t h i s l o a d l e v e l . F o r t u n a t e l y t h e a c t u a l l o a d h i s -t o r y h a s -t h e s -t o c h a s -t i c c h a r a c -t e r a s shown b e f o r e : few h i g h l o a d s mixed w i -t h many low l o a d s . I t seems n e v e r t h e l e s s w o r t h w h i l e t o e l e m i n a t e d o u b t s by e x e c u t i n g s i m u -l a t i o n - o r a t -l e a s t programme t e s t s ( a s i m p -l e r f a t i g u e t e s t w i t h few -l o a d -l e v e -l s and t h e l o a d c y c l e s grouped) on l u g s . B e c a u s e t h e d i m e n s i o n o f l u g s i n v a r i o u s a p p l i c a t i o n s w i l l d i f f e r s t r o n g l y , f i g u r e 17 i s g i v e n , from w h i c h t h e s t r e s s c o n c e n t r a t i o n f a c t o r f o r o t h e r l u g s c a n be d e -d u c e -d . I t i s e v i -d e n t t h a t t h e s t r e s s e s n e x t t o t h e h o l e c a n r e a c h u n e x p e c t e -d h i g h l e v e l s . A n o t h e r i n t e r e s t i n g a p p r o a c h o f t h e d i m e n s i o n i n g o f l u g s i s i n r e f e r e n c e 5. U n f o r t u n a t e l y , u n e x p e c t e d s t r e s s r a i s e r s c a n be found i n many c o n s t r u c t i o n s .

i n t h e f o g u r e s 18a, b and c t a k e n from r e f e r e n c e 6. T h i s handbook c o n t a i n s an ex-, t e n s i v e d a t a - b a n k o f s t r e s s c o n c e n t r a t i o n c a s e s , p r e s e n t e d i n g r a p h i c a l from a s shown i n t h e f i g u r e s 18a., 18b and 18c. S i m i l a r d a t a a r e g i v e n f o r p l a t e s w i t h a v a r i e t y o f h o l e s , s h a p e s and p a t t e r n s , f o r s h a f t s w i t h and w i t h o u t h o l e s o r s t e p s , e t c e t e r a .

A p a r t from t h e p r o b l e m to a s s e s s t h e c o n c e n t r a t i o n o f s t r e s s e s i s how t o cope w i t h t h e s c r a c k s t a r t e r s . I t w i l l be c l e a r t h a t t h e p r e v e n t i o n o f g r o o v e s and w o r k i n g s c r a t c h e s p e r p e n d i c u l a r to 1he l o a d d i r e c t i o n ; o f i n c l u s i o n s and i d e n t a t i o n s w i l l s a f e a l r e a d y much t r o u b l e . A l s o , t h e b u i l d i n g - i n o f i n t e r n a l s t r e s s e s i s w o r t h w h i l e i n many c a s e s . T h i s i s p o s s i b l e by s h o t - p e e n i n g o r o t h e r forms o f c o l d d e f o r m a t i o n i n c l u d i n g t h e e x p a n s i o n o f h o l e s i n l u g - p i n c o m b i n a t i o o n s , A good example o f t h e e f f e c t o f h o l e e x p a n s i o n i s g i v e n i n f i g u r e 19 ( R e f . 7) w h i l e t h e e f f e c t o f s h o t -p e e n i n g i s shown i n f i g u r e 20 ( r e f . 8 ) ,

The m e n t i o n e d methods have been a p p l i e d f o r many y e a r s i n a e r o n a u t i c s . Why s h o u l d y a c h t d e s i g n e r s and - y a r d s n e g l e c t them w h i l e t h e y a r e g e n e r a l l y a v a i l a b l e ?

4. MATERIALS AND HEAT TREATMENTS

A r u l e o f thumb f o r m e t a l a l l o y s w h i c h a d e s i g n e r o f t e n h a s t o cope w i t h i s what can be c o n s i d e r e d a s t h e r e t a i n i n g t o t a l o f t h e p r o p e r t i e s o f an a l l o y . The m e a n i n g o f t h i s r u l e i s : I f b o o s t i n g one p r o p e r t y o f an a l l o y , w h e t h e r i t be a s t e e l o r an a l u m i n i u m a l l o y , t h i s n e a r l y a l w a y s r e s u l t s i n one o r o t h e r p r o p e r t y g e t t i n g w o r s e . Now t h e p r o p e r t i e s o f i n t e r e s t f o r t h e y a c h t d e s i g n e r a r e : u l t i m a t e t e n s i l e s t r e n g t h ( S ^ ) , y i e l d s t r e n g t h

(80^2)

>

e l o n g a t i o n ( ^ ) , c o r r o s i o n r e s i s t a n c e , w e l d a b i l i t y , s u s c e p t i b i l i t y f o t f a t i g u e and f o r s t r e s s - c o r r o s i o n c r a c k i n g . F o r e x a m p l e : b o o s t i n g Su and, c o n s e q u e n t l y SQ,2 . by c o l d w o r k i n g , t h i s w i l l r e d u c e 5 . The p e n a l t y f o r t h e l a t t e r v e r y o f t e n w i l l be an i n c r e a s e d s e n s i t i v i t y f o r f a t i g u e and/or f o r s t r e s s c o r r o s i o n c r a c k i n g . T h e r e f o r e a p a r t s u b j e c t e d t o a f a t i g u e l o a d h a s t o be made f r o m a m a t e r i a l w i t h an e l o n g r a t i o n o f a t l e a s t 12%, i f p o s s i b l e 15%. On t h e o t h e r hand, i n t h e a r e a o f a c o n s t r u c t i o n , not t h r e a t e n e d by f a t i g u e , an a l l o y c a n be a p p l i e d w i t h a temper, w h i c h shows a much h i g h e r Sy and SQ 2=

An example i s t h e s t a i n l e s s s t e e l swaged t e r m i n a l f o r i x 19 r i g g i n g w i r e . The mate-r i a l a p p l i e d h a s t o be s t mate-r o n g enough t o p mate-r e v e n t f a i l u mate-r e a t t h e l u g o mate-r a t t h e end o f t h e b o r e i n t h e s h a f t . Commonly A I S I 316 m a t e r i a l , 1/4 o r 1/2 h a r d i s u s e d . By t h e s w a g i n g p r o c e s s ( c o l d d e f o r m a t i o n ) t h e e l o n g a t i o n & i s r e d u c e d a g a i n and t h e r e f o r e t h e s u s c e p t i b i l i t y f o r s t r e s s - c o r r o s i o n c r a c k i n g i s i n c r e a s e d . P l a c e d i n a s a l i n e (= c o r r o s i v e ) e n v i r o n m e n t , as s t r o n g a s f o r i n s t a n c e i n t h e G u l f o f M e x i c o , t h e n , c r a c k s w i l l s t a r t i n t h e s h a f t , i n d u c e d by t h e r e s i d u a l t a n g e n t i a l s t r e s s e s a f t e r t h e s w a g i n g p r o c e s s . F o r a l u m i n i u m a l l o y s t h e r e t a i n i n g t o t a l o f p r o p e r t i e s ( a g a i n a t one p r o p e r t y means a l o s s a t a n o t h e r ) i s shown i n f i g u r e 21 w h i c h was d e r i v e d from r e f e r e n c e 9.

7

-The e f f e c t o f c o l d w o r k i n g on S ^ , SQ g and B i s e v i d e n t . B a s e d on t h e above men-t i o n e d minimum e l o n g a men-t i o n l e v e l o f 1 2 % i men-t i s a d v i s a b l e men-t o a p p l y men-t h e men-t e m p e r s -H12 o f -H32 ( i . e . 1/4 h a r d ) . S h o u l d f a t i g u e l o a d s b e a b s e n t , t h e n t h e t e m p e r s -H14 and -H34 may be a c c e p t a b l e . F i g u r e 22 ( R e f . 1 0 ) shows t h e r e l a t i o n s h i p o f t h e m e n t i o n e d p r o p e r t i e s f o r t h e e x i s t i n g s e r i e s o f a l u m i n i u m a l l o y s . I t a p p e a r s t h a t f o r s h e e t and p l a t e t h e A l -Mg ( 5 0 0 0 ) s e r i e s o f f e r s an a t t r a c t i v e compromise, e s p e c i a l l y t h e a l l o y AA 5083 i n t h e temper -H321 and a l s o AA 5086 i n t h e temper -H116. R e s i s t a n c e t o c o r r o s i o n and s t r e s s c o r r o s i o n c r a c k i n g i s v e r y good. W e l d a b i l i t y i s good. S t r e n g t h i s mo-d e r a t e t o goomo-d. F a t i g u e s t r e n g t h i s m o mo-d e r a t e . E l o n g a t i o n i s s u f f i c i e n t , even i f some c o l d d e f o r m a t i o n i s n e c e s s a r y .

I t seems a t t r a c t i v e t o a p p l y a l l o y s from t h e 2000 o r 7000 s e r i e s , d e v e l o p e d f o r t h e a e r o s p a c e I n d u s t r i e , b e c a u s e o f t h e i r f a v o u r a b l e t e n s i l e s t r e n g t h ( F i g , 2 3 ) , O t h e r I m p o r t a n t p r o p e r t i e s , however, a low r e s i s t a n c e t o c o r r o s i o n and s t r e s s

c o r r o s i o n c r a c k i n g and bad w e l d a b i l i t y , p r e v e n t a s i m p l e a p p l i c a t i o n u n l e s s s p e -c i a l m a n u f a -c t u r i n g methods ( f o r i n s t a n -c e b o n d i n g and p r e s e r v a t i o n by -c o a t i n g ) -c a n be u s e d ,

S p e c i a l a t t e n t i o n i s n e c e s s a r y f o r h e a t t r e a t a b l e a l u m i n i u m a l l o y s l i k e t h e A l -Mg-Si ( 6 0 0 0 ) s e r i e s . An AA6061 mast s e c t i o n i n t h e -T6 temper ( a r t i f i c i a l l y aged) w i l l l o o s e l o c a l l y i t s -T6 p r o p e r t i e s a f t e r h a v i n g been w e l d e d . The m a t e r i a l h a s a r r i v e d t h e n i n t h e - 0 ( a n n e a l e d ) o r , a f t e r a s h o r t - t i m e , i n t h e - T l temper w h i c h show s u b s t a n t i a l l y l o w e r s t r e n g t h l e v e l s . To a r r i v e a t an optimum s t r e n g t h l e v e l , a f t e r t h e e x t r u s i o n t h e m a t e r i a l h a s t o be t r e a t e d i n t o t h e -T4 o r -T5 temper. Then t h e w e l d i n g c a n be e x e c u t e d f o l l o w e d by f u l l a r t i f i c i a l a g e i n g t o t h e -T6 temper o f t h e c o m p l e t e d m a s t . I t i s a r a t h e r e x p e n s i v e way t o p r e v e n t l o c a l w e a k n e s s by a ^0.2 mast s e c t i o n by t h e w e l d i n g ( w h i c h u n f o r t u n a t e l y o f t e n i s combined w i t h a s t r e s s c o n c e n t r a t i o n ) . However, i f t h i s i s a method t o p r e v e n t l o c a l b u c k -l i m g and c o n s e q u e n t -l y mast f a i -l u r e , i t seems t o be w o r t h w h i -l e .

W i t h r e s p e c t t o s t e e l s : a h e a t t r e a t a b l e s t e e l l i k e t h e ARMCO 17-4 p r c i p i t a t i o n h a r d e n i n g s t e e l a p p a r e n t l y i s a p e r f e c t r e p l a c e m e n t f o r A I S I 316 w h e r e h i g h s t r e n g t h i s r e q u i r e d . S i n c e t h e s t r e n g t h o f i t c a n be v a r i e d b e t w e e n 80 and 150 Kgf/mm by v a r y i n g t h e a g e i n g t e m p e r a t u r e i t i s p o s s i b l e t o o b t a i n e x a c t l y t h e c o m b i n a t i o n o f p r o p e r t i e s a s r e q u i r e d . O t h e r w i s e i t s h o u l d be n o t e d t h a t t h e n o t c h - s e n s i t i v i t y o f s t e e l s i s s l i g h t l y w o r s e t h a n o f a l u m i n i u m a l l o y s , e s p e c i a l l y i n t h e c a s e o f s m a l l r a d i i . F i n a l l y , a t i t a n i u m a l l o y s h o u l d be m e n t i o n e d ( T i 6 A 1 4 V ) a s a m a t e r i a l f o r s p e c i a l p u r p o s e s , l i k e r u d d e r s t o c k s . B e i n g l i g h t ( s p e c i f i c g r a v i t y o f 4,43) and s t r o n g (Su =0. 112 kg/mia2) b u t v e r y e x p e n s i v e ( ƒ. 80,-/kg.) i t c a n s o l v e a c o n s t r u c t i o n a l p r o b l e m when no o t h e r m a t e r i a l i s a b l e t o do t h i s . A l t h o u g h a number o f T i a l l o y s i s a v a i l a b l e , o n l y t h e above m e n t i o n e d a l l o y i s a p p l i c a b l e f o r i t s good c o r r o s i o n r e s i s t a n t c a p a b i l i t y .

5. MISCELANEOUS

T h e r e i s no doubt t h a t t h e a e r o s p a c e i n s t i t u t e s c a n a s s i s t y a c h t d e s i g n e r s i n many more c a s e s t h a n i n t h e above m e n t i o n e d : L o a d s - S t r e s s e s - M a t e r i a l s . Some e x a m p l e s may be g i v e n . - F o r t h e e v a l u a t i o n o f k e v l a r r o p e f o r s h e e t s , b e n d i n g f a t i g u e t e s t s w i t h p u l l e y s a c c o r d i n g t o s h e a v e s i n p r a c t i c e c a n be e x e c u t e d ( F i g . 2 4 ) , I t h a s b e e n done w i t h i n t e r e s t i n g r e s u l t s . - F o r t h e a s s e s s m e n t o f t h e c o n s t r u c t i o n w e i g h t o f a y a c h t , an a i r c r a f t w e i g h i n g k i t c a n be a p p l i e d . T h i s w e i g h t a s s e s s m e n t c a n be c a r r i e d o u t w i t h and w i t h o u t k e e l ( b a l l a s t ) and/or w i t h o u t g e a r inventory., A b e t t e r u n d e r s t a n d i n g o f t h e com-p o s i t i o n o f t h e t o t a l d i s com-p l a c e m e n t i s com-p o s s i b l e t h e n ,

- The t e n s i l e t e s t i n g o f w e l d s , e i t h e r f o r t h e e v a l u a t i o n o f new w e l d i n g t e c h n i q u e s o r t o c h e c k t h e q u a l i t y o f w e l d i n g equipment and/or t h e w e l d e r . MIG and T I G w e l -d i n g s y s t e m s a r e r o u t i n e l y u s e -d f o r w e l -d i n g a l u m i n i u m a l l o y s an-d r e g u l a r c h e c k - u p i s v e r y u s e f u l l . - The t e n s i l e t e s t i n g o f newly d e v e l o p e d c o n n e c t i o n s o f s t a n d i n g r i g g i n g w i r e s t o t h e mast s e c t i o n , - B o n d i n g t e c h n i q u e s f o r s e c o n d a r y l o a d e d c o n n e c t i o n s i n p a r t s l i k e booms. I t h a s n o t b e e n t h e g o a l o f t h i s p a p e r t o d e s c r i b e i n d e t a i l t h e r e s u l t s o f t h e a¬ bove m e n t i o n e d t e s t s . T h e s e h a v e been e x c e c u t e d f o r a w e l l known y a c h t y a r d i n H o l -l a n d and c a n be r e p e a t e d f o r anybody i n t e r e s t e d i n f a c t s and f i g u r e s .

F i n a l l y , i t i s i n t e r e s t i n g t o q u o t e , a p o s t u l a t i o n o f t h e famous s c i e n t i s t who's e x p r e s s i o n was l e n t a s a motto on t h e f i r s t page o f t h i s p a p e r , namely:

" F l y i n g m a c h i n e s a r e i m p o s s i b l e ; t h e y a l w a y s ; t h e y a l w a y s w i l l a p p e a r t o be t o o h e a v y " .

By m e a s u r i n g , c a l c u l a t i n g and t e s t i n g , h i s t o r y h a s d n i e d t h i s . Y a c h t d e s i g n e r s c a n make u s e o f i t , t o c o m p l e t e f u t u r e m i s s i o n s t h a t may now be c o n s i d e r e d i m p o s s i b l e .

6. REFERENCES

1. K i n n e y , F . S . - S k e n e ' s e l e m e n t s o f y a c h t d e s i g n . A. and C. B l a c k , London ( e d i t i o n 1 9 7 3 )

2. M u l l , G.W. - A r a t i o n a l a p p r o a c h t o t h e s t r u c t u r a l d e s i g n o f s a i l i n g y a c h t s . HISWA Symposium 1981; S u p p l e m e n t .

3. J o n g e , J . B . de The a n a l y s i s o f l o a d time h i s t o r i e s by means o f c o u n t -i n g methods, NLR MP 83039 U ( 1 9 8 2 ) .

4. S c h i j v e , J . and J a c o b s , r.A, 5, H o b b i t , F.M. 6. P e t e r s o n , R.E. 7. S c h i j v e , J . , B r o e k , D and J a c o b s , F.A. The f a t i g u e s t r e n g t h o f a l u m i n i u m a l l o y l u g s . NLR-TN M.2024 ( 1 9 5 7 ) .

A n a l y s i s o f l u g s and s h e a r - p i n s . Aluminium and s t e e l a l l o y s . L o c k h e e d A i r c r a f t C o r p o r a t i o n r e p e r t LAC-R-8025 ( 1 9 5 2 ) . S t r e s s C o n c e n t r a t i o n F a c t o r s . John W i l e y and S o n s , New York ( 1 9 7 3 ) , F a t i g u e t e s t s on a l u m i n i u m a l l o y l u g s w i t h s p e c i a l r e f e r e n c e t o f r e t t i n g , NLR r e p o r t M 2103 ( 1 9 6 2 ) , 8. G r a a f , E.A.B. de, J a c o b s , F.A. and N a s e t t e , J.H. 9. Anonymous: 10. W a n h i l l , R.J.H. I n f l u e n c e o f r e s i d u a l c o m p r e s s i v e s t r e s s e s upon t h e f a t i g u e s t r e n g t h o f n o t c h e d and u n n o t c h e d 7079 s p e c i m e n s . NLR TR 71105 ( 1 9 7 1 ) .

Aluminium s t a n d a r d s and D a t a . The Aluminium A s s o -c i a t i o n I n -c . , W a s h i n g t o n ( 1 9 7 8 ) .

F a t i g u e and f r a c t u r e - t o u g h n e s s i n Aluminium. NLR MP 82058 ( 1 9 8 2 ) . ( I n D u t c h ) .

TABLE 1 D a t a o f l o a d t r a n s d u c e r s and p r e - l o a d s C H A N N E L No. L O C A T I O N O F L O A D T R A N S D U C E R S L O A D F A C T O R kHN P R E - L O A D I N G O F T R A N S D U C E R S k N C H A N N E L No. L O C A T I O N O F L O A D T R A N S D U C E R S L O A D F A C T O R kHN before after C H A N N E L No. L O C A T I O N O F L O A D T R A N S D U C E R S L O A D F A C T O R kHN P R E S S U R I Z I N G T H E BACK S T A Y A C T U A T O R

©

U P P E R S H R O U D 1 4 . 9 5 4 . 2 0 4 . 2 0 L O W E R S H R O U D 1 3 . 8 9 3 5 6 3 . 1 6

©

I N T E R M E D I A T E 1 0 . 6 9 1.64 1.64

®

B A C K S T A Y 1 8 . 9 2 3 . 2 4 6 . 9 0

©

F O R E S T A Y 1 4 . 1 5 2 . 8 9 3 . 7 0 T A B L E 2 C o n d i t i o n s d u r i n g the measurement r u n s R U N 1 2 3 3 ' 4 8 9 10 11 1 2 D A T E ( 1 9 8 2 ) 2 3 / 4 2 3 / 4 2 4 / 4 2 4 / 4 2 5 / 4 2 7 / 4 2 7 / 4 2 7 / 4 3 0 / 4 3 0 / 4 C O U R S E W I N D W W I N D W W I N D W R E A C H W I N D W W I N D W R E A C H * W I N D W W I N D W W I N D ( B f ) 4 - 5 5 6 - 7 6 - 7 4 5 5 4 5 - 6 S A I L S M -t-G4 M - ) - G 4 M 2 r + G 4 M +G2 M - h G 4 M -hS M + G2 M - t - G 4 W A V E S (m) 0.5 - 1 0.7 - 1 0.5 1.0 1.0 1.0 1.0 S P E E D ( k t s ) 5.5 - 6 5.5 - 6 5.5 - 6 5.5 - 6 5 6 6.5 5 - 6 5 H E E L A N G L E ( ° ) 3 0 3 0 - 3 5 > 3 0 3 0 3 0 15 3 0 3 0 • Z E R O - C H E C K O F A L L C H A N N E L S I N H A R B O U R M = M A I N G 4 = G E N O A # 4 M 2 r = M A I N W I T H T W O R E E F S S = S P I N N A K E R G E N E R A L R E M A R K S ; - D U R I N G R U N S 1 , 2 , P R O B A B L Y 3, 4 , 8 A N D 9 T H E L E E S H R O U D S S H O W E D S L A C K - W I N D , W A V E S A N D H E E L A N G L E E S T I M A T E D T A B L E 3 S u r v e y of u s e f u l tape r e c o r d i n g s ( i n d i c a t e d w i t h x ) R E C O R D E R C H A N N E L L O C A T I O N R U N R E C O R D E R C H A N N E L L O C A T I O N 1 2 3 3 ' 4 5 6 7 8 9 10 1 1 12 1 U P P E R S H R O U D

-

-

-1

-

-

-

-

X X X X X 2 L O W E R S H R O U D X X X

-

-

-

X X X X X 3 I N T E R M E D I A T E X X X

-

-

-

X X X X X 4 B A C K S T A Y X X X

-

-

-

X X X X X 6 F O R E S T A Y X X X

-

-

-

X X X X X 7 M A S T

-

-

—

* R E C O R D E R D A M A G E D B Y S A L T W A T E R . P E N R E C O R D I N G S A V A I L A B L E

TABLE 4 Range c o u n t i n g s a c c o r d i n g to r a n g e - p a i r - r a n g e method ( r a i n f l o w - m e t h o d ) TABLE 5 L e v e l c r o s s i n g s R U N 8 C H A N N E L 1 2 3 4 R A N G E 1 1209 1435 1501 1169 2 1121 1339 1235 1155 3 897 1087 991 983 4 681 947 8 1 3 785 5 499 807 627 600 6 336 7 0 1 502 428 7 191 584 374 308 8 112 481 240 182 9 46 395 157 138 10 22 307 99 77 n 8 226 62 43 12 6 169 36 25 13 0 129 20 19 14 0 71 10 18 15 0 53 6 16 16 0 32 3 8 17 0 26 1

_'

18 0 14 0 6 19 0 10 0 6 20 0 5 0 4 21 0 3 0 3 22 0 2 0 2 23 0 1 0 1 2 4 0 0 0 1 25 0 0 0 0 2 6 0 0 0 0 27 0 0 0 0 28 0 0 0 0 29 0 0 0 0 30 0 0 0 0 31 0 0 0 0 32 0 0 0 0 9 1 2 3 4 1099 1581 1281 1021 969 1279 898 979 5 7 2 673 4 9 0 617 330 355 293 349 203 207 163 223 130 129 106 134 78 8 6 66 8 6 54 64 49 63 31 47 32 59 23 31 2 0 49 21 25 17 39 16 18 10 29 13 10 6 19 6 10 5 11 4 4 3 7 4 4 1 5 2 1 0 3 0 0 0 3 0 0 0 2 0 0 0 2 0 0 0 2 0 0 0 2 0 0 0 2 0 0 0 2 0 0 0 2 0 0 0 2 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 R U N 8 C H A N N E L 1 2 3 4 L E V E L 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0 4 0 0 0 0 5 0 0 0 1 6 0 0 0 1 7 0 0 0 3 8 0 0 0 5 9 0 1 4 6 10 0 5 12 8 11 0 17 39 10 12 7 41 89 13 13 8 4 91 194 31 14 2 8 3 177 329 87 15 453 2 6 6 430 213 16 501 349 5 1 6 344 17 462 428 501 463 18 355 499 444 513 19 2 2 6 5 2 6 340 4 7 3 20 125 490 219 363 21 48 4 3 4 128 235 22 18 351 61 123 23 4 277 27 58 24 0 203 8 29 25 0 128 1 6 2 6 0 75 0 3 27 0 31 0 2 28 0 18 0 1 29 0 6 0 0 30 0 1 0 0 31 0 1 0 0 32 0 0 0 0 9 1 2 3 4 0 0 0 1 0 0 0 1 0 0 0 1 0 4 1 1 0 13 A 1 0 49 18 1 0 111 78 2 0 205 155 5 0 322 2 3 0 9 1 418 2 9 6 15 8 416 298 17 48 320 2 6 6 24 134 191 183 41 2 5 4 102 99 75 328 47 51 101 332 32 25 108 273 16 11 150 167 10 6 2 0 3 100 6 1 238 55 1 0 2 3 6 34 0 0 239 19 0 0 174 11 0 0 116 8 0 0 63 4 0 0 27 3 0 0 7 0 0 0 2 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

TABLE 6

I m p o r t a n t r e s u l t s from the r u n s 8 and 9

R U N 8 C H A N N E L * 1 2 3 4 E L A P S E D T I M E O F R U N ( m in/sec) 2 0 7 " 2 0 - 2 " 1 9 ' 4 7 " 20" 6 " N U M B E R O F L O A D -C Y -C L E S (-C) 6 0 5 7 1 8 7 4 3 5 8 5 A V E R A G E F R E Q U E N C Y ( H z ) 0 . 5 0 0 . 6 0 0 . 6 3 0 . 4 9 M A X I M U M L O A D ( k g f ) 1 1 0 2 1 4 5 0 1 1 6 9 1 2 9 2 M I N I M U M L O A D ( k g f ) 5 3 1 4 0 2 3 9 5 2 0 6 L O A D R A N G E ( m a x - m i n ) (kgf) 5 7 1 1 0 4 8 7 7 4 1 0 8 6 R U N 9 1 2 3 4 1 8 ' 1 " 1 8 ' 4 2 " 1 9 ' 3 " 1 8 ' 2 6 " 5 5 0 7 9 1 6 4 3 5 1 1 0 . 5 1 0 . 7 0 0 . 5 6 0 . 4 6 1 2 4 3 9 6 0 9 1 0 1 2 9 2 4 6 8 1 8 1 197 6 1 7 7 5 7 7 9 7 1 3 1 2 3 1 C H A N N E L 1 = U P P E R S H R O U D C H A N N E L 3 = I N T E R M E D I A T E S H R Q U D C H A N N E L 2 = L O W E R S H R O U D C H A N N E L 4 = B A C K S T A Y

O 0.4 0.8 1.2 1.6 2.0 m K A L I K 3 3 . D E S I G N J . H . D E R I D D E R L O A B E A M D I S P L A C E M E N T I J P E 10.00 m 3.35 m 4 . 8 0 0 kg 1 3 . 1 5 m 4 . 2 0 m 11.11 m 3 . 4 5 m L O A D T R A N S D U C E R S B U I L T I N . C H A N N E L 1 : U P P E R S H R O U D C H A N N E L 2 : L O W E R S H R O U D C H A N N E L S : I N T E R M E D I A T E S H R O U D C H A N N E L 4 : B A C K S T A Y C H A N N E L 5 : F O R E S T A Y C H A N N E L S : M A S T C H A N N E L ? : V O I C E S T R A I N G A U G E S

RIGGING SCREW PROVIDED WITH TWO ACTIVE STRAINGAUGES

L O A D T R A N S D U C E R S 5 R I G G I N G S C R E W S C O N D I T I O N E R j P E A K - D A T A A N D S E 3 5 0 0 j V A L L E Y A C Q U I S I T I O N C D C C Y B E R A M P L I F I E R R E C O R D E R I D E T E C T O R S Y S T E M C O M P U T E R M A S T

0

1

1 n —\—

1

P E N R E C O R D E R ( O U T P U T - C H E C K ) S E A - B O R N E I I I ^ L _{L A B O R A T O R Y} ( D A T A H A N D L I N G ) F i g . 2 E x p e r i m e n t a l s e t - u p f o r dynamic l o a d measurements T A B L E S F I G U R E S N O T E ! C O M P A R E T H E P E N R E C O R D I N G B E F O R E T H E S I G N W I T H T H E R E C O R D I N G O F F I G . 4 F i g . 3 P a r t o f p e n r e c o r d i n g to c h e c k o u t p u t ( c h a n n e l 1 )

C H A N N E L 4 C H A N N E L 2 M A X L O A D P R E L O A D M I N Z E R O h- 1 0 0 0 k g f ^ Z E R O M I N L O A D M A X T R Ë TOAD^'

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N O T E : P O L A R I T Y O F C H A N N E L 4 W A S R E V E R S E D I F C O M P A R E D W I T H O T H E R C H A N N E L S F i g . 6 Run 8; l e f t h a n d c h a n n e l 4 ( b a c k s t a y ) , r i g h t h a n d c h a n n e l 2 ( l o w e r s h r o u d )

M A X P R E L O A D M I N ^ E R O

• 1 0 0 0

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10^ 10 NUMBER OF LOADCYCLES — kgf 970 889 808 727 646 566 485 404 323 242 162 81 F i g . 10 Range c o u n t i n g of r u n 8, a c c o r d i n g t o r a n g e - p a i r - r a n g e ( = r a i n f l o w ) method c l a s s O l -a c (0 JS UJ

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DC Q < O 10' 10' NUMBER OF LOADCYCLES F i g . I I Range c o u n t i n g o f r u n 9, a c c o r d i n g t o r a n g e - p a i r - r a n g e ( = r a i n f l o w ) method

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485

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O B S E R V A T I O N S O F F R A C T U R E S U R F A C E O F F I G U R E 1 4 - M A N Y R A D I A L S T E P S I N D I C A T E N U M E R O U S C R A C K O R I G I N S P R O V O K E D B Y S H A R P T U R N I N G G R O O V E S I N R U D D E R S T O C K . ( K ^ f t i 2 . 6 A T L E A S T ) - B E N D I N G F O R C E S A R E M A I N L Y R E S P O N S A B L E F O R T H E S T A R T A N D T H E P R O P A G A T I O N O F T H E F R A C T U R E . T O R S I O N S E E M S T O BE LESS I M P O R T A N T . T H E R E S I D U A L F R A C T U R E S U R F A C E IS E X T R E M E L Y S M A L L A S C O M P A R E D W I T H T O T A L S U R F A C E A R E A . - F R O M T H E N U M B E R O F S T R I A T I O N S I T IS N E A R L Y P O S S I B L E T O E S T A B L I S H W H E N T H E C R A C K S S T A R T E D . A C O N S E R V A T I V E C O U N T S E E M S T O BE A T L E A S T 2 0 T R I P S . - R E M E D Y : P R E V E N T S H A R P N O T C H E S B Y T H E A P P I I C A T I O N O F A R A D I U S > 5 m m . P R E V E N T T U R N I N G G R O O V E S D E N T S A N D S C R A T C H E S . P O L I S H C R I T I C A L A R E A A N D , E V E N T U A L , A P P L Y S H O T P E E N I N G T O I N T R O D U C E I N T E R N A L C O M P R E S S I V E S T R E S S E S , 7 5 6 P A R T OF B R O K E N R U D D E R S T O C K W I T H F R A C T U R E F i g . 14 F a t i g u e L r a c L u r e o f i . s p . i c k v i r u d d f r - . s Loi-k J 4 5 rfim

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T T T I I T T T

T T i — 1 — n -S ^ j = 4 5 . 5 k g f / m m ' ' m a x m m 3 0 t = 5 m m T E S T S A T S ^ j ^ = 1 0 k g f / m m ^ I I l l l I I l l l I I l l l I L_U 10' 10' 10"" 10'' 10

FATIGUE LIFE (CYCLES)

F i g . 15 S t r e s s - f a t i g u e l i f e c u r v e f o r a l u g . E x t r a p o l a t e d to s t a t i c s t r e s s : ( R e f . 4) ^ 16 14 12

I

1 O) P 8 4 h 1 I I I I \ \ L U G . L O A D , P " ^ ' " ( k - d l t k^ = 3.5 b = 3 0 8 12 16 20 24 28 32 36 40 44 S ^ S^n (kg/mm2) — F i g . 15a F a t i g u e d i a g r a m f o r l u g ( R e f . 4 )

T i 1 I \ \ 1 1 r ( R O W O F H O L E S ) -J 1 1 1 L

0

0.2 0.4 0.6 0.8 1.0

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F i g . 17 T h e o r e t i c a l s t r e s s c o n c e n t r a t i o n f a c t o r f o r l u g s w i t h a s q u a r e head a c c o r d i n g to measurements o f F r o c b t and H i l l

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1 J y 2 0 C L A M P E D -H O L E E X P A N D E D 3% F R O M 9 . 7 0 T O 1 0 . 0 0 m m T H I C K N E S S 5 m m M A T E R I A L 7 0 7 5 K , = 3.5 S ^ = 1 2 . 5 k g / m m 2 O O P R E L O A D E D O N C E T O S = 3 3 7 k g / m m ^

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CO F i g . 19 The e f f e c t of h o l e e x p a n s i o n on the f a t i g u e l i f e ( R e f . 7) X - « C U R V E G I V E S R E S U L T S O F A S M A C H I N E D S P E C I M E N S O S H O T P E E N E D ( S T E E L , 10a) P O L I S H E D A E D G E S B E V E L E D S H O T P E E N E D ( S T E E L 10a) P O L I S H E D a E D G E S B E V E L E D ' ' ' ' ' S H O T P E E N E D ( S T E E L , 10a) G L A S S B E A D P E E N E D P O L I S H E D • E D G E S B E V E L E D G L A S S B E A D P E E N E D S P E C I M E N D I D N O T F A I L 1 \ 1 — I I I I I

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F i g . 20 E f f e c t of v a r i o u s s h o t - p e e n i n g t r e a t m e n t s on t h e f a t i g u e l i f e of a s h a r p - n o t c h e d s p e c i m e n ( R e f . 8)

5 0 0 5

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LO CO LD 4 CM O CD 1-S CD H 4 o CN U5 1000 3000 5 0 0 0 A N D 6 0 0 0 K2000-I I-7000H F i g . 2 3 T e n s i l e d a t a o f some w r o u g h t a l u m i n i u m a l l o y s ( R e f . 10) F i g . 24 S c h e m a t i c o f t e s t s e t up f o r e n d u r a n c e t e s t a c c o r d i n g t o MIL-W-83420 b

31

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