Final Exam MD2016 Final

8/20/2019 Final Exam MD2016 Final

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Faculty Of Engineering 3rd Year Time : 3 hours

Mechanical Engineering Department 5/2/2016 2nd Term

Design of Machine Elements I FINAL EXAM

Questions: Answer only tree !uestions Poin

ts

Q Figure P! sho"s a portion of a high#pressure $oiler accumulator ha%ing&at head' The end plates are a()ed using a num$er of $olts of

M 16×2−UNC ! grade *'+! "ith rolled threads' ,i%en: Se=100 Mpa

!

e)ternal load P varies¿0¿12

kips

bolts -andk p=5k b "here the connection is

permanent' Determine:

I' The factor of safety n of the $olt against fatigue failure "ith and

"ithout preload'

II' The load factor ns against .oint separation'

/0

Q/ a1 2 ri%eted .oint is under an inclined eccentric load P! as indicated in

Fig'P/#a' alculate the ma)imum shear stress in the #in diameter

ri%ets'

0

$1 2 steel side plate is to $e "elded to a %ertical steel column

according to the speci4cations in Fig'P/#$' 5eglecting stress

concentrations e6ects! calculate the magnitude and clearly

indicate the direction of the resultant shearing stress at the critical

point' In selecting the critical point is sure to consider e6ects of

$oth torsion#li7e shear and direct shear'

0

Q3 2 helical#coil spring "ith plain ends and ground is to $e used as a return

spring on the cam#dri%en %al%e mechanism sho"n in Fig'P3' The '*0#in

diameter rod must pass freely through the spring' The cam eccentricity is

0'8* inch 9the total stro7e is '*0 inches1' The height of the compressed

spring "hen the cam is at the head#end#dead#center 9ED1 position is

;'8* in as sho"n' The spring must e)ert a force of 300 l$ "hen at the

ED position sho"n in the s7etch! and must e)ert a force of *0 l$ "hen

the cran7#end#dead#center 9ED1 at the $ottom of the stro7e' That is!

the spring is preloaded into the machine' The spring is to $e made of a

patented spring steel "ire that has a /00!000#psi ultimate tensile

strength! <0!000#psi tension yield strength! and <0!000#psi fatigue

endurance limit' =ased on in4nite life design a safety factor of '/* and

Springindex ,C =8 are desired' Determine the follo"ing:

' Mean coil radius! > !/' ?ire diameter! d!

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3' 5um$er of acti%e coils! 5!@' Apring rate! 7! and*' Free length of the spring! Bf'

Q@ 2 /0#mm po"er scre" for a hand#cran7ed ar$or press is to ha%e a single#

start sCuare thread "ith a pitch of @#mm' The scre" is to $e su$.ected to

an a)ial load of * 75' The coe(cient of friction for $oth threads and

collar is estimated to $e a$out 0'0<' The mean friction diameter for the

collar is to $e 30#mm' Find :

' The nominal thread "idth! thread height! mean thread diameter!

and the lead'/' Estimate the torCue reCuired to raise the load'3' Estimate the torCue reCuired to lo"er the load'@' Estimate the e(ciency of this po"er scre" system'

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Final Exam MD2016 Final