Open University t207 specimen exam

7/26/2019 Open University t207 specimen exam

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T207/SEP

Specimen Examination Paper

ENGINEERING: MECHANICS,

MATERIALS, DESIGN

Time allowed: 3 hours

This examination is divided into TWOparts. You are advised tospend about 90 minuteson each part.

Part A is worth 50 per cent of the overall marks for theexamination. You should attempt ALL questions in this part.These questions require short responses across a wide range oftopics.

Part Bis also worth 50 per cent of the overall marks for theexamination. You should answer any TWOquestions from thispart. These questions probe more deeply your understanding of anarrower theme.

Various data and formulae are printed at the end of the paper.

Graph paper is available from the invigilators, should you requireit.

At the end of the examination

Check that you have written your personal identifier andexamination number on each answer book used. Failure to do sowill mean that your work cannot be identified.

Put all your used answer books together with your signed deskrecord on top. Fasten them in the top left corner with the roundpaper fastener. Attach this question paper to the back of theanswer books with the flat paper clip.

Copyright 2011 The Open University SUP 01375 5 Printed in the United Kingdom 4.1


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PART A Attempt ALLquestions in Part A. Your answers to these questions willtogether account for 50 per cent of your final exam mark. You shouldspend about half the examination time on this part.

Question 1 (a) Thebackofacertainseatinarailwaycarriageis100mmthick.Explainwhy

itwouldbeunreasonabletoinstall12rowsofseatsinacompartmentwithafloorlengthof7m.Suggest,withabriefjustification,amorereasonable

numberofrows.Youmayrefertodatasuppliedattheendofthepaper.

(4 marks)

(b) Theexternaldoorsofarailwaycarriageareoperatedelectro-pneumatically

byapush-button.Themeanforcerequiredtooperatethebuttonsuppliedby

onemanufacturerisspecifiedas14Nwithastandarddeviationof2N.

Explainwhythisproductisnotlikelytobeselected.Youmayrefertodata

suppliedattheendofthepaper.

(4 marks)

Question 2 (a) Sketchabeamthatissimplysupportedanduseittoshowwhereapointloadshouldbeplaced:

(i) tomaximizetheshearforceinthebeam

(ii) tomaximizethebendingmoment.

(2 marks)

(b) Auniformlydistributedloadonasimplebeamgivesrisetodistributionsof

shearforceandbendingmomentasshowninFigure1.Inafewwords,

interpretthesedistributionsandtheirconsequencesforbeamdesign.

(4 marks)

wL

L L

2

2

L

wL wL

2

2

S

0

_

wL

2

wL

2

L

0

M

wL

8

2

L

Figure 1 Reproduced from Block 2 of T207 (for Question 2)

T207/SEP2


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Question 3 Explaininwhatwaysacompositeformedfromfibres(of,say,carbonorglass)embeddedinapolymermatrix(sayepoxyresin)haspropertiesthataresuperiorto

thoseofeitherconstituentalone.

(5 marks)

Question 4 Determinethesteadythrustthatwouldenablea200-tonneairlinertoreachits

take-offspeed(75ms1

),fromrest,in30s.Explaininafewwordswhyinpracticethethrustrequiredwilldifferfromthatcalculatedbythissimplemodel.

(4 marks)

Question 5 Apermanentmagnetmotorinasmallmechanicaldevicehasstalltorque3 =2.610 Nmandno-loadspeed = 860 rads1whenconnectedtoas n

battery.

(a) Determinethegearratiothatwillenabletheoutputdriveshafttospinat

about120rpm(choosefrom4:1,16:1,64:1or256:1).

(b) Whendrivingaload,themotorshaftspinsatthree-quartersofitsno-load

speed.Calculatethemechanicalpowerthatisgeneratedbythemotorunderthesecircumstances.

(6 marks)

T207/SEP TURN OVER 3

Question 6 Describebrieflythedifferencebetweenboundarylubricationandfull-filmlubrication.Giveoneeverydayexampleofeach.

(6 marks)

Question 7 Identify:

(a) whyalowvalueofyieldstressisadesirablepropertyinametalthatistobe

usedtocreateusefulshapes

(b) whythatsamepropertymaybeadisadvantageforacomponentinitsfinal

form.

(4 marks)

Question 8 Explain,innomorethan100words,ageneralorsocialneedtowhichthebicycleoffersapossiblesolutiontoday.

Hint:aspiderdiagrammayhelpyouplanyouranswer.

(5 marks)

Question 9 (a) Sketchatypicalcreepcurveforametal,labellingtheaxesandthethree

regionsofcreep.

(4 marks)

(b) Analloysteelhasameltingtemperatureof1650C.Determinethe

maximumoperatingtemperaturethatthissteelcantolerateifitisnotto

creep.

(2 marks)


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PART B Attempt TWOquestions from Part B. Your answers to two questions willaccount for 50 per cent of your final exam mark. You should spend abouthalf the examination time on this part.

Question 10 (a) Listthethreecategoriesofsolutionstoengineeringproblems,andforeach

onegiveapracticalexamplethattypifiesthecategory.(6 marks)

(b) Bimetallicstripsareusedtomonitorandcontroltemperature.Explainthe

principlebywhichthesestripsfunction.Whenmakingabimetallicstrip

whatmaterials,withrespecttotheirproperties,wouldbechosentomakethe

stripmostsensitivetoachangeintemperature?

(5 marks)

(c) (i) Materialsexpandwhenheated;brieflydescribewhy,attheatomiclevel,

thishappens.

(ii) Ahollowcylinderofaluminium1mlongwitha40mmoutsidediameterisatatemperatureof20C.Whatisthechangeinlengthand

circumferenceofthecylinderwhenitiscooledto25C?

(Note:thethermalco-efficientofexpansionofaluminiumis

24106K1.)

(iii) Assumingthatthecylinderisfixedatbothendsandthatitswall

thicknessis7.5mm,whatforcewouldbeexertedbythecylinderduring

thischangeintemperature?

(Note:theYoungsmodulusforaluminiumis70GPa.)

(3 + 6 + 5 = 14 marks)

(Total 25 marks)

T207/SEP4


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Question 11 Table1showssometypicalvaluesofthecoefficientofstaticfriction,s,forhard

steelonitself.

Table 1

Contact condition s

Unlubricated 0.6

Lubricated, mineral oil 0.2

Lubricated, molybdenum disulphide 0.1

(a) Asimpleslidingbearingwithhardsteelsurfacessupportsamassof575kg.

Assumingyourmassis75kgandyoucanexertahorizontalforceequivalent

to80%ofyourweight,determinewhetheryouwouldbecapableofmoving

themassunderanyofthesefrictionalconditions.(Takeg=9.8ms2.)

(7 marks)

(b) Describethemicroscopicprocessesbetweentwosurfacesduringfrictional

contact.

(4 marks)

(c) Brieflyoutlinetwomechanismsofwearwhentwosurfacesareincontact.

(6 marks)

(d) Thecombinedmassofageneratingrotoranditshollowshaftis450tonnes,

therotorsdiameteris4.5m,andtheshaftshollowinnerdiameteris0.75m.

(i) Treatingtherotorandshaftasonecombinedunit,calculatetheirsecond

momentofmass.

(ii) Calculatethekineticenergyoftherotorwhenitisspinningat

300revolutionsperminute.

(iii) Usingthekineticenergycalculatedin(ii),whatdistanceinkilometres

couldtheunlubricatedmassfrompart(a)bemoved?Assumethatin

thisinstancestaticfrictionisequaltodynamicfriction.

(2 + 3 + 3 = 8 marks)

(Total 25 marks)



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Question 12 (a) Table2showsthemeasuredelectrodepotentials,relativetomildsteel,formetalsinseawater.Calculatethecellpotentialandstatewhichmetalwill

corrodeforthefollowingcombinations:

(i) copperdeckplatesheldtogetherwithmildsteelrivets

(ii) atitaniumpropellershaftrunninginagraphitebearing

(iii) aleadweathershieldincontactwithabrassporthole.

(2 + 2 + 2 = 6 marks)

Table 2

Metal Potential in sea water/volts

Aluminium 0.59

Brass 0.12

Copper 0.20

Graphite 0.42Lead 0.22

Magnesium 1.40

Mild steel 0

Stainless steel 0.11

Titanium 0.30

Zinc 0.66

(b) Describethedifferenceinmechanismsofcreepinmetalsandpolymers,and

howtemperatureinfluencestherateofcreepinbothofthesematerials.

(8 marks)

(c) Acylindricalpressurevesselisusedforchemicalprocessingandisdesigned

towithstandamaximumpressureof30MNm2.Thevesselhasamean

diameterof5mandawallthicknessof250mm.Itisconstructedfrom

weldedplatesofmaterialwithanultimatetensilestrengthequalto

500MNm2,ayieldstrengthof300MNm2andatoughnessof

50MNm3/2.Assumethatthevesselisthinwalled.

(i) Calculatethehoopstressat75%ofitsdesignpressure.

(ii) State,withjustification,whetherornotthisserviceconditionrepresentsahighloadonthestructure.

(iii) Duringoperation,anedgecrackhasbeendiscoveredinthevesseland

measuredtobe10mmlong.Whatisthemarginofsafetywiththis

lengthofcrackwhenthevesselisoperatingatfullpressure?Take

Y=1.12forthisgeometry.

(4 + 3 + 4 = 11 marks)

(Total 25 marks)

[END OF QUESTIONS]

T207/SEP6


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Data

ThesetablesrelatetospecificquestionsinPartA.

Table 3 Anthropometric data for adult (aged 1965 years) British

population (Pheasant, 1986)

Body dimension Male Female

Mean/mm SD*/mm Mean/mm SD*/mm

Stature 1740 70 1610 62

Eye height 1630 69 1505 61

Shoulder height 1425 66 1310 58

Elbow height 1090 52 1005 46

Sitting height 910 36 850 35

Sitting eye height 790 35 740 33

Sitting shoulder height 595 32 555 31

Sitting elbow height 245 31 235 29

Thigh thickness 160 15 155 17

Buttock-to-knee length 595 31 570 30

Buttock-to-popliteal length 495 32 480 30

Knee height 545 32 500 27

Popliteal height 440 29 400 27

Shoulder breadth (bi-deltoid) 465 28 395 24

Hip breadth 360 29 370 38

Chest (bust) depth 250 22 250 27Shoulder-to-elbow length 365 20 330 70

Elbow-to-fingertip length 475 21 430 19

Forward grip reach (from the 780 34 705 31

back of the shoulder blade)

Upper limb length 780 36 705 32

* SD = standard deviation

Table 4 Ergonomic data: maximum finger pushing force

(Haaland et al., 1963)

Digit Thumb Index finger Middle finger Ring finger Little finger

Mean force/N 17 11 10 8 5

Range/N 1420 814 812 510 39



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Equations

Equationsarelistedundertheblockinwhichtheywerefirstintroduced.

Block 1

X

X X0 = X0 = T

L

=

L0(1

+

T

)

= exp( / Tr r E k )0 a

= exp( / TD D

E k )0 a

Ea 1lnr = + ln r0

k T

Block 2

I= y2dAAM E

= =

I y R

EI2P = E 2l

= = 3(n 1) 2jM F C

= = 6(n 1) 3jM F C

M = 3g n 62

E=

F =

A

l =

l

/ F A G = =

p pVK = =

/ VV V

E =E v +E v C m m f f

1 v vm f= +

E E Ec

m f

EGC

=

a

K

=

EG

=

aC C c

T207/SEP8


9/12

Block 3

= v r

t=

+ t= i

2

2

)(

i

=

2

1 2 t+ = ti 2

= + tv u a

1 2s u=

t+

at

2

2 2v =u +2as

2

2 v

a( =v) = r=

r

2

=

1 f = =

T 2

2a= y

F=ma

d(mv)F=

dt

=I

P=Fv

P=

d =I =I

dt

dva=

dt

d =

dt

2 2F=mv /r=mr

I = mr 2

12I= mr for shaft on axis

2

12 2I = m (R +r ) for hollow shaft on axis

2

F=R



10/12

F=B I l sin

= 1

s

n

P=IV

2P

=

I Rtherm

Pout=

Pin

=V E IR

1 2

FD

= v CDA2

1 2F v C AL

= L2

Block 4

1 12 2K = mv + Itotal

2 2

U =mgh grav

= c TQ m

T21=

T1

1p v2 + gh E = +v

2

v = 2gh jet 0

m =vA

= AQ v

QHk=

W

=

G

d =

dt

=

32r L =

Cr

T207/SEP10


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Block 5

TT =H

Tm

1/2 = +kdt 0

K

=

Y

a1

da m=C K( )

dN

Pr=hoop

t

[END OF EXAMINATION PAPER]

T207/SEP 11


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Open University t207 specimen exam

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