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7/26/2019 Open University t207 specimen exam
1/12
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)
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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]
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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
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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
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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
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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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