The Tensile-Impact Resistance of Carbon-Molybdenum Welds at Elevated Temperatures

Citation preview

T ensile-2>npact R e s is ta n c e o f Carbon-Molybdenum Welds At E le v a te d T em peratures

THESIS

S ubm itted i n p a r t i a l f u lf ilm e n t o f th e re q u ire m e n ts f o r th e d eg ree o f MASTER OF MECHANICAL ENCINEERING a t th e POLYTECHNIC INSTITDTE OF BROOKLYN M arcel A* C ordovi June

1942

Approved: T h e sis A & fiser

H ead o f Peparrm ent

ProQuest Number: 27591418

All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted. In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscript and there are missing pages, these will be noted. Also, if m aterial had to be rem oved, a n o te will ind ica te the deletion.

uest ProQuest 27591418 Published by ProQuest LLO (2019). C opyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLO. ProQuest LLO. 789 East Eisenhower Parkway P.Q. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346

AÇSNOWLKBO£MKNT

The a u th o r w ish es t o e x p re ss h is a p p r e c ia tio n t o P r o f e s s o r O tto H. H enry, t h e s i s a d v is e r , f o r h i s v a lu a b le a d v ic e and f r i e n d l y c ritic is s a g *

Thanks a r e due t o ISr* H .S.Blum berg o f t h e

M. W.

K e llo g g Company f o r s u p p ly in g th e n e c e s s a ry m ate­ r i a l t o produce t h e sp ecim en s.

S p e c ia l th a n k s a r e due t o M rs. Renee M. C ordovi f o r h e r h e lp in th e c o u rse o f th e w ork.

C ONTENTS

In tro d u c tio n .

........................

1

T e n s ile -Im p a c t T e s t i n g .

3 ....................

A . G en eral D ie c u s s io n . B . At P o ly te c h n ic I n s t i t u t e ............... A p p a ratu s and M ethod.

3 6

..............................................

7

A. C a lib r a tio n o f M achine. . . . . . . . . . . . . . . . . . .

10

B . C a lib r a tio n o f S c a l e . . . . . ..............

13

C. Tem perature C o n t r o l . . . . . . . . .....................

17

D. T em perature M easurement................

23

E . C a lib r a tio n of Therm ocouple...................

27

M a te r ia ls T e s te d

...............................................................

A . Molybdenum in S t e e l

30

.....................

B. W elding Iblybdenum S t e e l s

..............

H o n -D e stru c tiv e T e s ts ...............

32 33 34

A. M acroscopic E x a m in a tio n ......................................

34

B • R ockw ell S u rv e y .

34

..........

C . M icroscop ic E x a m in a tio n . R e s u lts and C o n c lu s io n s .

.............

......................................

A. T a b u la tio n o f R e s u l t s .

...........

B . R e s u lts P l o t t e d . . . . . . . . . . . . . . . . ......................... S u g g e stio n s B ib lio g r a p h y ....

37

........................ ..................................................

43 44 45 53 54

I N T R O D U C T I O N

The s e r v ic e re q u ire m e n ts o f p o w e r-p la n t p ip in g in 1915 w ere seldom h i g h e r th a n 200 I h s . , 500 d e g re e s F a h re n h e it; by 1930, a p e rio d o f 15 y e a r s , th e s e re q u ire m e n ts w ere r a i s e d t o 1300 l b s . , 750 d e g re e s F ah ren ­ h e i t ; to d a y modern p o w e r-p la n ts a r e b e in g d e sig n e d f o r o p e ra tin g tem pe­ r a t u r e s o f 950 d e g re e s F a h re n h e it , 1800 l b s . w orking p r e s s u r e and p o s s i b l y h ig h e r .

T his f a c t makes th e s p e c i f i c a t i o n s , f a b r i c a t i o n and

r i g i d t e s t i n g o f p o w e r-p la n t m a te r ia ls and j o i n t s a n e c e s s i t y . The b a s ic c o n s id e r a tio n in p erfo rm in g t e s t s on a m a te r ia l f o r a g iv e n s e r v i c e , i s t h a t th e m a te r ia l sh o u ld s im u la te th e a c t u a l s e r v ic e a s c lo s e ly a s p o s s i b l e . T hus, in d e sig n in g an a p p a ra tu s t o be used a t ab­ n o rm al te m p e ra tu re s , i t i s e s s e n t i a l t h a t th e d e s ig n e r have p r e c is e know­ le d g e o f th e p h y s ic a l p r o p e r tie s o f th e m e ta ls t o be used and a ls o o f t h e c h a r a c t e r i s t i c s of th e d i f f e r e n t j o i n t s s p e c if ie d a t th e te m p e ra tu re s t o w hich th e y a re t o be s u b je c te d in s e r v i c e . D uring th e p a s t few y e a r s , w eld in g and w eld in g d e sig n have made a g i g a n t i c s te p fo rw a rd . Today w eld in g i s n o t c o n sid e re d as j u s t a n o th e r way o f jo in in g m e ta llic p a r t s b u t r a t h e r th e way o f doing th e jo b q u ic k ­ l y , p r e c i s e l y and e f f i c i e n t l y . I t i s , t h e r e f o r e , v e ry im p o rta n t

th a t a l l

p h a s e s and p o s s i b i l i t i e s of w elding be th o ro u g h ly surveyed and f u l l y u n d e rs to o d . In a d d i t i o n , i t i s e q u a lly im p o rta n t t h a t th e d i f f e r e n t phy­ s i c a l p r o p e r tie s and c h a r a c t e r i s t i c s o f w elds under d i f f e r e n t perform ance c o n d itio n s sh o u ld a ls o lie s tu d ie d . A good d e a l h as a lre a d y been done in t e s t i n g w elds i n t e n s i o n , c o m p ressio n , s h e a r , bending and to r q u e . S ince w e ld s , l i k e any o th e r s t r u c t u r a l e le m e n ts , o fte n must w ith s ta n d suddenly

2.

a p p lie d lo a d s , i t i s n o t u n n a tu ra l t h a t in p a c t t e s t s a r e f r e q u e n tly u s e d . F u rth e rm o re , i n o rd e r t o t e s t a l l zones o f a s in g le w elded J o i n t i n im p a c t, w hich i s v e ry d e s ir a b l e in numerous in s ta n c e s , i t seemed a d v is a b le t o s t a r t u s in g t e n s i l e in p a c t t e s t s f o r w e ld s. Up t o t h e p r e s e n t tim e , th e t e n s i l e in p a c t t e s t h as been a p p lie d t o w e ld s only a t r e l a t i v e l y low v e l o c i t i e s and a t room o r subnorm al tem pe­ r a t u r e s . % i l e c o n s id e ra b le a t t e n t i o n has been and s t i l l i s b ein g g iv en t o th e e f f e c t o f e le v a te d te m p e ra tu re s upon th e g e n e r a l p r o p e r ti e s o f m e ta ls , l i t t l e w ork, i f a n y , h as been done i n th e f i e l d o f t e n s i l e im p a c t t e s t i n g o f w elds a t h ig h e r th a n room te m p e ra tu re s . Much o f th e equipm ent in in d u s tr y i s s u b je c te d t o h ig h te m p e ra tu re s . T h e r e f o r e , th e e f f e c t o f e le v a te d te m p e ra tu re s on equipm ent i s o f p a ra ­ mount im p o rta n c e . A pre-know ledge o f th e e x a c t way in which a w eld i s g o in g t o behave w i l l f u r n is h th e p o s s i b i l i t y f o r a d eq u a te com pensation and p re c a u tio n in o rd e r t o a m e lio ra te th e s e c o n d itio n s in th e o r i g i n a l d e s ig n . T his w i l l u n d o u b ted ly and in v a r ia b ly r e s u l t in enormous sa v in g i n tim e , money and l a b o r - th e th r e e sy n ch ro n ize d f a c t o r s t h a t move th e w h e e ls o f in d u s tr y . The p re s e n t Emergency

h a s , more th a n e v e r b e f o r e ,

s e rv e d t o prove t o confirm ed s k e p ti c s th e g ig a n tic p o s s i b i l i t i e s and im p o rta n t r o l e t h a t w eld in g i s p la y in g to d a y and w i l l p la y in th e f u t u r e . The a u th o r , in u n d e rta k in g t o make an in v e s t i g a t i o n on th e e f f e c t o f e le v a te d te m p e ra tu re s on th e te n s i le - im p a c t r e s i s t a n c e of some w eld s, h a s f u l l y r e a l i z e d th e s ig n if ic a n c e o f h is ta s k and hopes t h a t t h i s in v e s ­ t i g a t i o n w i l l be a w o rth w h ile and tim e ly c o n tr ib u tio n t o an a r t whose im p o rta n c e in th e f i e l d of in d u s tr y in c re a s e s h o u rly . B rooklyn, New York June 1 , 1942 «%:

T E N S I L E - I M P A C T

T E S T I N G

3.

A* g e n e r a l D is c u s sio n

The te n s i le - im p a c t t e s t i s a sim p le t e s t t o d eterm in e com pleteness o f p ro c e s s in g and a f f o r d s th e d e sig n e n g in e e r in fo rm a tio n both as t o th e s a f e t y of th e m a te r ia l and i t s a b i l i t y t o w ith s ta n d im pact lo a d in g . In p a c t t e s t i n g as n o rm a lly perform ed w ith n o tch b a rs i s o b je c tio n ­ a b le because of la r g e e r r o r s in h e re n t in th e method o f t e s t i n g and e s p e c i a l l y th o s e due t o e r r o r s in m achining th e n o tc h .

Notch t e n s i l e

specim ens a r e more s a t i s f a c t o r y b e in g l e s s s e n s i t i v e t o e r r o r s o f oacM n in g o r t o a c c id e n ta l v a r i a t i o n s in th e s t r u c t u r e o f th e m a te r ia l. In te n s i le - im p a c t t e s t i n g th e energy v a lu e s a re s e n s i t i v e t o non h o m o g e n e itie s of th e t e s t specim en and e s p e c ia ll y of th o s e lo c a te d n e a r t h e s u r f a c e . By e x am in atio n of th e f r a c t u r e i t can be d eterm in ed w hether abnorm al v a lu e s a r e due t o u n u su al d e f e c ts such as e r r o r s in m ach in in g , i n t e r n a l c ra c k s , n o n -m e ta llic p a r t i c l e s , s la g o r o th e r d e f e c ts o f l o c a l n a t u r e o r i n s u f f i c i e n t h e a t- tr e a tm e n t. Abnormal v a lu e s o f a d is c o n tin u o u s n a t u r e n o t r e p r e s e n t a t i v e o f th e m a te r ia l may be re c o g n iz e d and d is c a rd e d . R e s u lts of t e s t s a re n o t h ig h ly s e n s i t i v e t o e r r o r s o r i r r e g u l a r i t i e s in m a c h in in g . By c a r e f u l e x am in atio n o f th e f r a c t u r e , r a t h e r r e l i a b l e o p in io n s a s t o i r r e g u l a r i t i e s and in c o m p le ten e ss o f p ro c e s s in g can be fo rm ed .*

* g .F .J e n k s , " A p p lic a tio n o f T en sio n -Im p act T e s ts " , T ra n s a c tio n s o f The American S o c ie ty o f M echanical E n g in eers,)% y 1937

4.

Many f a c t s in th e te n s i le - im p a c t t e s t rem ain t o be e lu c i d a te d . A form ula o f lim ite d a p p lic a tio n r e l a t i n g s iz e b f specim en

to te n ­

s ile - im p a c t v a lu e has been evolved by g a r c ia * . U sing a Charpy pendu­ lum , Duwez** found t h a t p l o t s of te n s ile - im p a c t en erg y and e lo n g a tio n t o f r a c t u r e v s . le n g th of p a r a l l e l s e c tio n (specim en o.59 in ch d ia m e te r 0 .3 9 t o 4 .3 in c h e s p a r a l l e l s e c t i o n , m d e o f c o p p e r, aluminum o r s t e e l s w ith t e n s i l e s tr e n g th e q u a l from 57,000 t o 120,000 l b s . p e r sq u are in c h ) w e re s t r a i g h t l i n e s . E x tra p o la te d t o zero le n g th o f p a r a l l e l s e c tio n t h e l i n e s r e s u l t e d in th e d e te rm in a tio n o f a " s p e c i f i c ” e lo n g a tio n and " s p e c i f i c " energy w hich w ere in d ep en d en t o f le n g th and c h a r a c t e r i s t i c o f each m a t e r i a l . The e f f e c t of v e lo c i t y was n o t s tu d ie d . The k i n e t i c energy o r v e l o c i ty o f th e blow , how ever, i s an im p o rta n t f a c t o r in t e n s i l e - im pact t e s t i n g . In s tu d y in g te n s io n -im p a c t sp ecim ens, Jen k s* * * found t h a t m t e r i a l s r e q u ir e d a c o n s ta n t en erg y t o r u p tu r e in d e p e n d e n t of th e v e lo c i ty o f lo a d in g p ro v id ed c e r t a i n c r i t i c a l v e l o c i t i e s w e re n o t ex ceed ed . T his c r i t i c a l o r " t r a n s i t i o n " v e l o c i t y a p p e a rs t o be a fundam ental p ro p e rty of a m a t e r i a l . T e n s ile -im p a c t t e s t s p e rm it th e s e p a r a tio n o f t h i s fundam ental p ro p e rty from th e re c o rd o f im pact s tr e n g th s a nd th e d e te rm in a tio n o f th e optimum v a lu e s . * g a r c ia , V .L ., " I n t e r n a t i o n a l A s s o c ia tio n f o r T e s tin g l b . t e r i a l s C ongress" London, group A, 32-33 (1937) * * D uw ez,P.,

" A rc o s", 15 (83) 1772-1779, Jan u a ry 1938.

* * * J e n k s ,g .F .

" T ra n s . A .S .M .E .", 59, 313-318 (1937)

ô.

The in tr o d u c tio n o f t h i s concept o f " t r a n s i t i o n ” v e l o c i t y in to im p a c t t e s t i n g g iv e s th e d e sig n e n g in e e r a n o th e r f a c t o r t o c o n s id e r i n s e le c tio n of m a te ria ls .

Study o f th e v e l o c i ty f a c t o r by Jen k s*

h a s shown th e f a l s i t y of th e b e l i e f t h a t b r i t t l e f r a c t u r e i s fa v o re d by in c re a s e d v e l o c i t y o f lo a d in g . I t was b e lie v e d t h a t s in c e c r y s t a l l i n e s l i p o c cu p ie s a d e f i n i t e tim e , and s in c e th e s t r e s s a t w hich flo w s t a r t s a p p e a rs t o be r a i s e d a s th e v e l o c i t y of s t r a i n in c r e a s e s , th e r e w ould be no tim e f o r s l i p a t h ig h v e l o c i t i e s o f s t r a i n . E xperim ents p erfo rm ed by I n g li s * * and Jen k s* showed th e c o n tra ry t o be t r u e . Namely, t h a t as th e v e lo c i ty of lo a d in g in te n s ile - im p a c t in c re a s e d beyond th e c r i t i c a l v e lo c i ty up t o 310 f e e t p e r second (maximum in v e s tig a te d ) th e specim en f r a c tu r e d w ith in c r e a s in g e lo n g a tio n and r e d u c tio n o f a r e a , a l b e i t th e energy t o f r a c t u r e d e c re a s e d . As i t was a lre a d y s t a t e d , th e in tr o d u c tio n o f th e n o tio n o f c r i t i c a l o r t r a n s i t i o n v e l o c i t y in to im p a c t- te s tin g i s an im p o rta n t f a c t o r to b e c o n sid e re d in th e s e l e c t i o n o f m a t e r i a l s . M a te ria ls of g iv e n p h y s ic a l p r o p e r t i e s as e x p re sse d in s tr e n g th and d u c t i l i t y , a r e n o t in te rc h a n g e a b le a s t o u s e . I f th e v e l o c i t y o f a p p li c a ti o n o f lo a d in g i s a f a c t o r , th e t r a n s i t i o n v e lo c i ty o f th e m t e r i a l becomes one o f th e most i s p o r t a n t e le m e n ts in th e s e l e c t i o n o f chem ical c o m p o sitio n o f th e m s-te ria l and i t s h e a t-tre a tm e n t.

* J e n k s , G .F .

" T ra n s . A .S .M .S .", 59, 313-318 (1937)

* * I n g l i s ,N .P .

" T ra n s a c tio n N .E . C oast I n s t n . E n g in ee rs and S h ip ­ b u i l d e r s " , 53, 101-136 (1936/1937)

6.

I f th e te n s i le - im p a c t t e s t i s t o be used a s an in s p e c tio n t o o l to d e te rm in e th e com pleteness o f p ro c e s s in g , th e v e l o c i ty o f t e s t sh o u ld b e j u s t under th e t r a n s i t i o n v e lo c i ty in h e re n t in w e ll-p ro c e s s e d m e ta l o f th e c o n p o s itio n and s t r u c t u r e s p e c i f i e d .

B . T e s tin g a t P o ly te c h n ic I n s t i t u t e

T e n s ile -im p a c t t e s t i n g had i t s o r ig i n a t th e P o ly te c h n ic In s jb itu te i n 1934 when Mr. Em il Imbembo u n d erto o k t o i n v e s t i g a t e th e e f f e c t o f lo w te m p e ra tu re on th e r e s i s t a n c e o f some w elded j o i n t s , là*. Imbembo made th e n e c e s s a ry equipm ent and s ta n d a rd iz e d a specim en t o be used f o r t e n s i l e - i m p a c t t e s t s . * He perform ed t e s t s on s t e e l and N aval b ro n z e . I n 1936, P r o fe s s o r O tto H. Henry c o n tin u e d th e s e low te m p e ra tu re t e s t s and o b ta in e d some v e ry i n t e r e s t i n g r e s u l t s .

Mr. G. L. M cFarland,

i n 1938 là*. G.de Rosa and in 1939 Mr. M. üm anoff conducted a s e r i e s o f t e s t s a t low te m p e ra tu re s * The p r e s e n t in v e s t i g a t i o n b e a rs no r e l a t i o n t o any o f th e work on T e n s ile - I n p a c t t e s t i n g p re v io u s ly done a t th e P o ly te c h n ic I n s t i t u t e . To th e a u t h o r 's knowledge no te n s i le - im p a c t t e s t s a t e le v a te d te m p e ra tu re s h a v e e v e r been conducted-any w h ere.

T his f a c t makes th e p r e s e n t i n v e s t i ­

g a t i o n an o r i g i n a l t r e a t i s e and i t i s th e hope o f th e a u th o r t h a t f u r t h e r t e s t s a lo n g t h a t l i n e w i l l be u n d e rta k en by o th e r in v e s t i g a t o r s s h o r t l y . T h is w i l l

p ro v id e a b a s is f o r c o n p a riso n , and a c o m p ila tio n o f s e v e r a l

s e t s o f r e s u l t s m ight prove t o be v e ry u s e f u l d a ta f o r many an i n d u s t r i a l c oncem .

* See F ig . 7

APP ARATUS

and

METHOD

The p h y s ic a l t e s t i n g conducted in t h i s in v e s t i g a t i o n

was perform ed

on th e T in iu s O lsen Im pact Machine ( § 6785 ) o f t h e pendulum ty p e , which i s lo c a te d in th e M a te ria ls T e s tin g L a b o ra to ry a t th e P o ly te c h n ic I n s t i ­ t u t e o f B rooklyn. T his m achine, shown in F ig . 1 , i s o r d i n a r i l y used f o r m aking t h e O lsen n o tc h e d -b a r t e s t in which th e specim en i s t e s t e d as a c a n t i l e v e r . However, w ith th e a d d itio n o f s e v e r a l p a r t s and f i x t u r e s , t h e machine was ad ap ted t o te n s ile - im p a c t t e s t i n g . The a d d itio n o f a gas fu r n a c e makes h ig h te m p e ra tu re t e s t i n g p o s s ib le . The c o u rse o f e v e n ts c a n be fo llo w e d by r e f e r r i n g t o f ig u r e s 2 , 3 , 8 , 9 and 1 0 . When r e le a s e d from i t s h ig h e s t p o s itio n by means o f a t r i g g e r * t h e pendulum s t r i k e s and r u p tu r e s th e specim en and th e n r i s e s t o some p o s i t i o n on th e l e f t o f th e m achine. The specim en i s s tr u c k as th e h a ­ mmer re a c h e s th e lo w e st p o s i t i o n o f i t s sw ing, t h a t i s , w here th e k i n e t i c e n e rg y i s maximum and th e p o t e n t i a l en erg y i s z e r o . The hammer i s so c o n s tr u c te d t h a t i t s c e n te r of p e rc u s s io n i s a t th e p o in t o f in p a c t w ith t h e specim en. The h e ig h t t o which th e pendulum r i s e s a f t e r r u p tu r in g th e specim en i s a m easure o f th e energy rem ain in g in th e pendulum . T h e re fo re , t h e amount o f work r e q u ir e d t o r u p tu r e th e specim en i s th e d if f e r e n c e b etw een th e i n i t i a l and f i n a l en ergy o f th e pendulum. T h is v a lu e i s r e ­ c o rd e d by a p o in te r ( F ig . 1 ) in a s e m i - c ir c u la r s c a le c a l i b r a t e d in f o o t- p o u n d s . The p o s i t i o n t o which th e pendulum ( o r hammer) r i s e s i s re c o rd e d by th e p o in te r which i s pushed alo n g in f r o n t o f th e pendulum on i t s upward s t r o k e , b u t does n o t fo llo w th e r e t u r n sw ing.

* F ig . 1

r F ig . 1

/

Method f o r making O lsen 1

N otched Bar T e s t.

F ig . 2 C lo se up o f J i g and Cross-Arm

r

y

F ig . 3

Showing T e n s ile - I n p a c t J i g in V ise o f O lsen

l b chine

10 .

The m a n u fa c tu re r s t a t e s t h a t th e pendulum of th e machine w eighs

33 - I / 3 Ih s# and t h a t th e v e r t i c a l drop o f th e hammer i s 3 f t . T his w ould g iv e th e pendulum 3 3 -1 /3 x 3 ■ 100 f t . - l b s . o f p o t e n t i a l en erg y when r a i s e d t o i t s h ig h e s t p o s i t i o n . The in s ta n te n e o u s v e l o c i t y , t h a t i s , th e pendulum v e l o c i t y a t th e i n s t a n t of s t r i k i n g th e specim en i s T * i n w hich:

2gh a

2 (3 2 .2 ) 3

* 1 3 .9 f t . - s e c s .

g . . . . a c c e le r a ti o n due t o g r a v i t y » 32.2 f t . / s e c . / s e c . h . . . . v e r t i c a l drop » 3 f t .

CALIBRATION OF MACHINE

The c a p a c ity o f th e s c a le o f th e m achine was checked by c a l i b r a t i n g t h e t e s t i n g m achine. As our case i s t h a t o f a sim p le pendulum , i t was n e c e s s a r y t o f in d f i r s t an e x p re ss io n c o r r e l a t i n g th e tim e o f o s c i l l a t i o n , and th e le n g th of th e e q u iv a le n t sim ple pendulum . The f i r s t o f th e s e can be d eterm in ed

b y t e s t , w h ile th e second -b y computat i o n .

By r e f e r r i n g t o f i g . 5, a n g le 6 i s th e d is p la c e m e n t and 1 i s th e le n g th . The fo r c e

1r rp

L

a lo n g th e ta n g e n t t o th e c i r c l e d e s c rib e d b y P i s m g .sin 9 o r mg9

i f G i s s z m ll,

s i n c e th e f o r c e i s on ly th e n p r o p o r tio n a l t o th e d is p la c e m e n t.*

P J » f mgsinG

^ mg

P ig . 5

*B.L.W orsnop and H .T .F lin t, "Advanced P r a c t i c a l P h y sic s f o r S tu d e n ts " , M ethuen,London, 1939

n,

The a c c e le r a ti o n in t h i s d i r e c t i o n i s ; o r s in c e S* L9, i t i s

d^S / dt^ w here S« a rc (OP)

& (d^0 / d t ^ ) ;

• ml (^© / dt?) . -

• #

• { ^ 9 / d f ) ♦ ( g /l) 9 - 0 • •

whence* or

TV Z 't l ' / / g / l 1 - ( f g / 4 ir ^ )

• Z 'S' / l / g

...............................( l )

................................................... (2)

To d e term in e T, th e pendulum was allow ed t o swing th ro u g h a sm all a r c and th e tim e f o r f i f t y o s c i l l a t i o n s was m easu red . The av erag e o f f i v e re a d in g s gave th e tim e f o r f i f t y o s c i l l a t i o n s as 7 3 .2 sec o n d s, e q u iv a le n t t o 1 .4 6 4 seconds p e r o s c i l l a t i o n . Then from fo rm u la (2)

1 - ( T ^ g /tir ^ ) . (1.4642% 3 2 .2 ) / 4 (3 .1 4 )^ - 1 .7 5 5 f t . t h e r e f o r e : 1 » 21*06 in c h e s .

The pendulum was th e n su p p o rte d by a s t i c k and w eighed in i t s v e r t i ­ c a l p o s itio n ( f ig * 6 ) . The n e t w eig h t was found t o be 142*74 l b s .

The

d is ta n c e A from th e a x is o f r o t a t i o n a t which th e pendulum was weighed w as m easured a t 1 .5 8 f t . found t o be 35,31 in c h e s .

The e v r t i c a l drop o f th e pendulum h e a d , was Thus th e c a p a c ity o f th e machine i s e q u a l to

( 3 5 .3 1 /1 2 ) X 4 2 .7 4

« 125.62 f t .

la.

A X I S OF PENDU LUM

RO TATIO N

STIC K \ - T A B L E O F PLATFORM SCALE

FIG. 6

The r a t e d c a p a c ity o f th e O lsen Ija c h in e , as a lre a d y s t a t e d i s 100 f t . l b s . H ow ever, t h i s c a p a c ity vms found i n s u f f i c i e n t t o r u p tu r e some o f th e to u g h ­ e r specim ens i n p re v io u s t e s t s by Iv5*. Em il Imbembo. T h e re fo re , he in c re a s e d t h e c a p a c ity o f th e m achine t o ab o u t 125 l b s . by f a s te n in g -J in c h th ic k p l a t e s on each s id e o f th e pendulum . They w ere p la c e d i n such a v%y t h a t t h e c e n te r o f p e rc u s s io n * rem ained e s s e n t i a l l y th e same i . e . 2 1 .0 6 in c h e s

* I f a body i s f r e e t o r o t a t e ab o u t a fix e d a x is and i f an im p u lsiv e f o r c e can be a p p lie d t o th e body so t h a t th e r e i s no im p u lsiv e r e a c tio n a t th e a x i s , any p o in t on t h e l i n e o f a c tio n o f t h e im p u lsiv e fo r c e i s c a l l e d a c e n te r o f p e r c u s s io n .

13 .

fro m th e a x is o f r o t a t i o n . The v a lu e o f 125.62 f t . - l b s . o b ta in e d in c a l i b r a t i n g th e m achine f o r t h i s s e t o f t e s t s i s , t h e r e f o r e , ta k e n t o be c o rre c t. The s e m i- c ir c u la r s c a le of th e O lsen Im pact îfe.chine i s d iv id e d in t o 100 d i v i s i o n s . The com plete s c a le o f th e machine im s checked and th e f i g u r e s d eterm in ed ap p ear in th e fo llo w in g t a b l e . The c a l i b r a t i o n curve i s shown p l o t t e d in f i g . 4 , page 1 4 .

CALIBRATION OF THE SCALE

S c a le R eading

V e r tic a l Drop o f h e a d ,in c h e s

P t - l b s . A v a ila b le

F t-lb s * used

0

36.29

1 2 5 .5

0 .0

10

32.67

1 1 2 .9

1 2 .6

20

2 9 .5 3

101.0

2 4 .5

30

2 5 .4 3

8 7 .9

3 7 .6

40

2 1 .8 0

7 5 .3

50.2

50

1 8 .2 0

6 2 .7

6 2 .8

60

1 4 .6 0

5 0 .3

75.2

70

1 0 .9 0

3 7 .8

8 7 .7

80

7 .3 0

2 5 .4

1 0 0 .1

90

3 .7 0

1 2 .8

1 1 2 .7

100

0 .0 0

0 .0

1 2 5 .5

14 *

m

m

15 *

F ORM AHD DIMENSIONS OF TENSILE-BŒ^ACT SPECIMEN

The form and dim ensions o f th e specim ens used i n t h i s i n v e s t i g a t i o n a r e shown in fig * 7 , page 16*

!Di m achining th e s e specim ens i t h a s been

fo u n d a d v is a b le t o th r e è d th e ends f i r s t a n d 't l o n machine th e t e s t s e c ­ t i o n . Because o f th e sm a ll d ia m e te r (o*200 in c h e s ) o f th e t e s t s e c t i o n , s p e c i a l c a re must be ta k e n in m achining i t in o rd e r t o p re v e n t bending d u r in g t e s t i n g . j

To d e term in e th e p e rc e n ta g e e lo n g a tio n o f th e a m te r ia l t e s t e d ,

a gage le n g th o f 0*80 in c h e s was used* T h is gave a gage le n g th t o d i a ­ m e te r r a t i o o f fo u r* Thus th e e lo n g a tio n r e s u l t s o b ta in e d a re com parable t o th o s e o b ta in e d w ith a s ta n d a rd 2 in c h e s te n s io n specim en in w hich th e d ia m e te r - to gage l e n g t h - r a t i o i s a ls o fo u r*

The gage p o in ts w ere marked

b y a s p e c ia l j i g c o n s is tin g e s s e n t i a l l y o f two h ard en ed s t e e l c o n ic a l p o i n t s s e t 0*80 in c h e s a p a r t i n a b ra s s block* In c o n s id e rin g w hat th e dim ensions o f th e specim en sh o u ld be i t was f e l t t h a t th e specim en should be m d e as la r g e a s p o s s ib le from a p r a c t i ­ c a l s ta n d p o in t b u t a t th e same tim e i t s s iz e was lim ite d b ecause o f th e a v a i l a b l e c a p a c ity o f th e machine*

Imbembo* h as d e s c rib e d in d e t a i l th e

m ethod used t o d eterm in e th e d im e n sio n s, so t h a t th e m a te r ia ls m ight be r u p tu r e d in a s in g le blow . The method c o n s is te d e s s e n t i a l l y o f assum ing a d ia m e te r ( s m a lle r th a n th e r o o t d ia m e te r o f th e th re a d e d ends) and d e te rm in in g th e approxim ate work t o r u p tu r e th e specim en when s u b je c te d t o a g r a d u a lly a p p lie d load* T his v a lu e , f o r 0.30% C S te e l was found to

* Imbembo,E.A*, " E f f e c t o f Low T em perature on th e T e n s ile Im pact R e s is ta n c e o f Some W e l d e d J o i n t s " ,T h e s i s , 1934

16

TmSILE-IMPACT SKCIM EN

GAGE - LE N G T H

W

• i

TW/CE SIZE

FIG. 7

.

17*

be

5 4 .1 f t . - l b s .

However, t h i s was th e amount o f work r e q u ir e d to

r u p t u r e th e specim en in a s t a t i c t e s t . S in ce th e en erg y n e c e s s a ry t o r u p tu r e a m a te r ia l in a dynamic t e s t i s g r e a t e r , th e v a lu e 5 4 .1 f t . - l b s , fo u n d , was m u ltip lie d by a f a c t o r o f 1 .4 8 * and th e ap p ro x im ate work to r u p t u r e a m a te r ia l in a dynamic t e s t was found t o be th e e q u a l t o 80 f t . l b s w hich r e p r e s e n ts o n ly 64 % o f th e c a p a c ity o f th e machine and t h e r e f o r e , a d ia m e te r o f 0 .2 0 in c h e s f o r th e t e s t s e c tio n was c o n sid e re d s a t i s f a c t o r y .

TEMPERATURE CONTROL

S in ce th e t e s t s w ere perform ed a t te m p e ra tu re s ra n g in g from Room te m p e ra tu re t o 1100 d e g re e s F a h r e n h e it, th e n e x t s te p was t o f in d some way o f h e a tin g th e specim ens so t h a t t h e i r r e s i s t a n c e a t e le v a te d tem pe­ r a t u r e s m ight be m easured. The e a s i e s t method was t o h e a t th e j i g t h e specim en a tta c h e d in a s a l t T^ath ( f o r te m p e ra tu re below 400 F , o i l w as u s e d . ) . The j i g i s a tta c h e d t o th e ends o f two th in - m e ta l s t r i p e s t h e o th e r ends o f w hich t u r n ab o u t a p iv o t on th e b ase o f th e m ach in e.* * I n t h i s way i t was p o s s ib le t o q u ic k ly t r a n s f e r th e specim en from th e h e a ti n g medium t o th e t e s t i n g machine w ith o u t an a p p re c ia b le change in t h e sp e c im e n 's te m p e ra tu re . F ig u re 2 shows th e specim en in " p o s itio n " * H onda, K o ta ro , "A Comparison o f S t a t i c and Dynamic T e n s ile and NCtKhed B ar T e s ts " , J o u rn a l o f th e I n s t , o f M e ta ls , 736,1926 * * F i g . 3 and 9

18*

f o r th e t e n s i l e - i n p a c t t e s t . The s a l t b a th ta n k was p la c e d in s id e a g a s fu rn a c e e s p e c i a l l y d e sig n e d and b u i l t by th e a u th o r f o r t h i s t e s t s . A s k e tc h showing th e e x a c t dim ensions

set of

and c o n s tr u c tio n o f th e fu rn a c e

an d th e s a l t - b a t h ta n k i s on page 1 9 . A s a l t b a th was s e le c te d a s a h e a tin g medium b ecau se o f i t s many advan­ t a g e s o v er oven f u r n a c e s * . Some o f them a r e ;

1 . The b a th te n d s t o h e a t th e work more u n ifo rm ly th a n do most o v e n s . The work i s suspended in a b a th b u t i s u s u a lly l a i d on th e h e a r t h in an oven* The n a tu r e o f a b a th n a t u r a l l y e lim in a te s c o n ta c t o f c o ld a i r w ith th e w ork, w hereas many oven fu rn a c e s a r e n o t a i r - t i g h t . 2 . S a lt b a th s , i f p ro p e rly m ain ta in ed and o p e ra te d u s u a lly e le im in a te 8 c a lin g . 3 . S a lts h e a t th e work more q u ic k ly . The r a p id h e a ti n g , to g e th e r w ith th e p ro x im ity o f th e h e a tin g medium and th e a tm o sp h ere, makes s a l t s m ore d e s ir a b le f o r l o c a l h e a tin g . The te m p e ra tu re s s e le c te d f o r t h e s e t of t e s t s in c o n ju n c tio n w ith t h i s t h e s i s w ere;

T em perature Room 5 50 F 820 F 920 F 1020 F * M.P. 480 F ; B .F. 1700 F

H e a tin g medium _ _ _ Tem pering s a l t s * - **- **• -

19

HEATING AHRANGEMENT

COVER 16

a&w b r ic k

ASBESTO S

BURNER AIR

FIG. 6

20,

r

F ig * 8~a A p p a ra tu s

f o r making te n s ile - im p a o t t o s t s a t e le v a te d

te m p e ra tu re s showing O lsen Im pact lîach in e (A ), h e a tin g a rra n g e m e n t(B ), and th erm o co u p le arrangem ent f o r tem pe­ r a t u r e m easurem ents.

84.

6 4 s FURNACE W IT H SPECIMEN. JIG & CROSS-ARM /MM£RSfD IH HEATING BATH

PIV O T

TO COLD JUNCTION r

SPECIME

GAS

I

FUPNACE

Two t e s t s w ere perform ed a t each o f th e te m p e ra tu re s d e s c rib e d on th e p r e v io u s p a g e. In p re p a rin g f o r a t e s t , th e p a r t i c u l a r h e a tin g medium was poured i n t o th e s t e e l ta n k o f th e gas fu rn a c e t o a h e ig h t w hich would co v er th e j i g and specim en ( f i g . 9) • The s lid i n g cover was th e n p la c e d o v er th e ta n k . A therm ocouple was in s e r te d in a whole d r i l l e d in a dummy t e s t sp e ­ cim en and packed w ith 1%. pow der. T his th erm o co u p le and dumny w ere p la c e d i n th e h e a tin g ta n k c lo s e t o th e t e s t b a r . An a d d i tio n a l therm ocouple i n d i c a t e d th e te m p e ra tu re o f th e h e a tin g medium. 'Waen th e two th erm o co u p les gave re a d in g s a s n e a r a l i k e as i t was found p o s s ib le t o o b ta in » t h e tem pe­ r a t u r e o f th e t e s t b a r was c o n sid e re d t o be v e ry c lo s e t o th e te m p e ra tu re o f th e dummy t e s t b a r as shown by th e in s e r te d th erm o co u p le r e a d in g . Ho d i f f i c u l t y was e x p e rie n c e d in h o ld in g th e d e s ir e d te m p e ra tu re f o r any le n g th o f tim e , p ro b a b ly due t o th e good i n s u l a t i o n o f th e fu rn a c e and s t e e l ta n k . # ie n th e specim en had been a t th e d e s ir e d te m p e ra tu re f o r about h a l f h o u r ( n o t l e s s th a n 20 m in u te s ), th e cover was rem oved, th e j i g q u ic k ly swung in to p o s itio n in th e m achine, th e v ic e tig h te n e d and th e pendulum r e l e a s e d . The tim e o f t r a n s f e r r i n g th e specim en from th e c o n v e n ie n tly l o ­ c a te d fu rn a c e t o th e m achine was observed by means o f a s to p wa.tch. Because o f th e s h o r t i n t e r v a l o f tim e ( about 2 seco n d s) e la p s in g in t r a n s f e r r i n g t h e specim en, th e te m p e ra tu re o f th e t e s t b a r a t th e moment o f th e t e n s i l e im p a c t c lo s e ly approxim ated th e d e s ir e d te m p e ra tu re , and i t i s b e lie v e d t h a t each specim en was t e s t e d w ith in 5 d e g re es F a h re n h e it above o r below t h e te m p e ra tu re re c o rd e d . * M etals Handbook, Page 317, 1939

23*

To a s c e r t a i n th e m agnitude o f a p ro b a b le n e c e s s a ry to compen­ s a t e f o r th e change in te m p e ra tu re , i f a n y , o f th e specim en in b ein g t r a n s f e r r e d t o th e m achine, a th erm o co u p le was s tra p p e d t o th e t e s t s e c t i o n o f a specimen* The specim en ( a tta c h e d t o th e j i g ) was th e n lo w e re d t o th e b a th a t 500 d e g re e s F a h re n h e it and k e p t a t t h i s tem pe­ r a t u r e f o r ab o u t h a l f h o u r. I t was fo u n d , a f t e r s e v e r a l t r i a l s , t h a t i n th e tim e i t ta k e s t o make a t e s t (ab o u t 2 seco n d s) th e r e ?,as no change in th e te m p e ra tu re o f th e specim en. T h e re fo re , th e b e l i e f t h a t n o a p p re c ia b le amount o f h e a t ( + o r - 5 d e g re es F a h re n h e it) i s l o s t w h ile th e specim en i s b e in g t r a n s f e r r e d from th e h e a tin g b a th t o th e O lsen Im pact Ifec h in e .

TEMPERATURE MEASUREMENT

Ih e a c c u ra c y o f th e te m p e ra tu re measurement i s a v e ry im p o rta n t f a c t o r in c o n d u ctin g t e s t s a t e le v a te d te m p e r a tu r e s . The a u th o r h a s , t h e r e f o r e , e x e r te d extrem e c a re in th e s e l e c t i o n and u se o f th e appa­ r a t u s f o r te n p e r a tu r e m easurem ent. The sm a lln e ss of th e th e r m o e le c tr ic s u b s ta n c e , th e r a p i d i t y o f i n ­ d i c a t i o n s as w e ll a s th e p o s s i b i l i t y o f p la c in g a t any d is ta n c e from th e m e asu rin g a p p a ra tu s make th erm o co u p les a most c o n v en ie n t means o f te m p e ra tu re m easurem ent. In th e s e l e c t i o n o f a c o u p le , acco u n t h a s t o be ta k e n o f t h e e le c tro m o tiv e f o r c e , t h e ab sen ce o f p a r a s i t e c u r r e n ts and th e i n a l t e r ­ a b i l i t y o f th e m e ta ls u s e d .

2 %.

E le c tro m o tiv e f o r c e »The ju n c tio n o f two m e ta ls h e a te d t o a g iv e n te m p e ra tu re i s th e s e a t o f an e le c tro m o tiv e f o r c e w hich i s a f u n c tio n o f te m p e ra tu re o n ly . T h is fo r c e v a r ie s enorm ously from one co u p le t o a n o th e r . The o n ly m e ta ls t o keep by re a s o n o f t h e i r h ig h e le c tro m o tiv e f o r c e a re th e a l lo y s o f p la tin u m w ith i r o n , n i c k e l , chromium, irid iu m and rhodium . The fo llo w in g t a b l e g iv e s in m ic ro v o lts th e e le c tro m o tiv e fo r c e o f th e t e n p e r c en t a llo y s o f th e s e f i v e m e ta ls up t o th e te m p e ra tu re o f 1500 d e g re e s C e n tig ra d e | * e n p e ra tu re

Fe

Hi

Cr

Ir

Rh

100

438

644

405

995

640

445

3962

4095

3583

6390

3690

920

9200

9100

——

14670

8660

1500

19900

20200

— —

26010

15550

A bsence o f p a r a s i t e c u r r e n ts The a l l o y w ith n ic k e l g iv e s p a r a s i t e c u r r e n ts o f g r e a t i n t e n s i t y , a s do a l l th e a llo y s o f t h i s m e ta l. Chromium does n o t seem t o p r e s e n t th e same in c o n v e n ie n c e j i t form s an a llo y d i f f i c u l t t o f u s e an d , f o r t h i s r e a ­ s o n , d i f f i c u l t t o p r e p a r e . W ith th e a llo y s o f ir r id iu m and o f rhodium th e r e i s no c o n s id e ra b le p ro d u c t o f p a r a s i t e c u r r e n ts i f th e m e ta ls a re p u re and *

B urges8 , O.K. and L e C h a te lie r,H .,

The Measurement o f High T e m p e ra tu re s", J#W iley and Sons, 1912

25.

th e a l l e y s homogeneous. T here re m a in , th e # , b u t t h r e e m e ta ls t o c o n s id e r : ir id iu m , rhodium , chromium and t h e i r a l l o y s .

C hem ical changes A ll th e a llo y s o f p la tin u m a r e s l i g h t l y a l t e r a b l e . Those o f n ic k e l and i r o n , a t 'h i g h te m p e r a tu r e s , assume a s l i g h t s u p e r f i c i a l brow nish t i n t cau se d by o x id a tio n o f th e m e ta l. No t e s t h a s been made t o see i f , a f t e r a long tim e t h i s a t t a c k w i l l re a c h even t o th e i n t e r i o r o f t h e w ire s* * A fte r c o n s id e r a tio n o f a l l o f th e above on th e n a t u r e , q u a li ty and s u i t a b i l i t y o f th e therm ocouple most d e s ir a b le and r e a d i l y a v a i l a b l e f o r t h e t e s t s in c o n ju n c tio n w ith t h i s t h e s i s th e Chromel C o n stan t a n , ty p e NC th e rm o c o u p le was s e le c te d # T h is n ick el-ch ro m iu m co u p le (80 N i-20 Cr) h a s an e le c tro m o tiv e fo rc e a b o u t fo u r tim e s t h a t o f o rd in a ry Pt-R h c o u p le s , and th e e le c tro m o tiv e f o r c e - te m p e r a tu r e r e l a t i o n i s n e a r ly l i n e a r t o 1400 d e g re e s c e n tig ra d e w ith o u t any re c a le s c e n c e d is tu rb a n c e s o f s u f f i c i e n t ma,gnitude t o s e r io u s ly a f f e c t th e te m p e ra tu re re a d in g s in te c h n i c a l work.-*** A f te r a n n e a lin g t h i s c o u p le r e t a i n s i t s re a d in g s s u f f i c i e n t l y f o r many com m ercial u s e s ,e v e n when h e a te d t o over 1300 d e g re e s c e n tig ra d e f o r s h o r t p e r io d s .

*

B u rg e s s , C Æ ., and L e C h a te lie r, H . , ”The Measurement o f High T e m p e ra tu re " , John W iley & Sons, 1912

26

ELECTRICAL CONNECTIONS , SPECIMEN TH E R M O C O U H E

/

BATH

THERMOCOUPIM

' COLD \ JUNCTIO N \ \ r

D. THROW-D. POLE SW TCH

STANDARD CELL

BA

S.C

BA

TYPE K PO TEN TIO M ETER

.

C a l i b r a t i o n o f Chromen C o n sta n ta n th e rm o c o u p le i For an a c c u ra c y of b e t t e r th a n te n d e g re e s , o r as in th e p re ­ s e n t c ase f i v e degree## i t i s n e c e s s a ry t o u se th e p o te n tio m e tric m ethod o f m easurem ent. As t h e chrom el - c o n s ta n ta n th erm o co u p les used by th e a u th o r h a v e been p re v io u s ly c a l i b r a t e d by th e Brown In stru m e n t Company*and by o th e r men a t th e P o ly te c h n ic I n s t i t u t e in c o n n e c tio n w ith t h e i r indi* v i d u a l r e s e a r c h p r o j e c t s , i t seemed u n n e c e ssa ry f o r th e a u th o r to co n cern h in æ e lf w ith t h i s m a tte r# However, two p o in ts w ere checked on t h e c a l i b r a t i o n curve as g iv e n by th e m a n u fa c tu re r.* F o llo w in g i s a t a b l e and c a l i b r a t i o n cu rv e o f th e Chrom elC o n sta n ta n , ty p e NC, th e rm o c o u p le .

* The Brown In s tru m e n t Company, P h ila d e lp h ia , Pa