mech-fea of crankshaft

7/29/2019 MECH-FEA of Crankshaft

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U.SURYAPAVANRAJU 07241A03B6

S.KARTHIK

07241A0337A.V.YESASVI 07241A0324


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ABSTRACTy Thecrankshaftexperiencesacomplexloadingduetothemotionoftheconnectingrod,whichtransformstwosourcesofloadingtothecrankshaft.

Themainobjectiveofthisstudywastheoptimizationoftheforgedsteel

crankshaftwhichrequiresaccuratemagnitudeoftheloadingonthis

componentthatconsistsofbendingandtorsion.

y Thesignificanceoftorsionduringacycleanditsmaximumcomparedto

thetotalmagnitudeofloadingisinvestigatedtoseeifitisessentialto

considertorsionduringloadingornot.

y Themain

objective

of

this

study

is

to

determine

the

magnitude

and

directionoftheloadsthatactonthebearingbetweenconnectingrodand

crankshaft,whichwasthenusedintheFEAoveranentirecycle.

y Inthisproject,structuralanalysiswasdoneatvariousspeedstostudythe

stressconcentrations

at

critical

locations

of

crankshaft.

Then

the

original

crankshaftisoptimizeforweightandgeometry

y Resultsfromthisstudyshowsthatoptimizedgeometrycanbeused

insteadoforiginalcrankshaftreducingitssize.Hencetheoptimized

crankshaftresults

in

increased

efficiency.


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y Crankshaftisalargecomponentwithacomplexgeometryintheengine,

motionwith

afour

link

mechanism.

y Sincethecrankshaftexperiencesalargenumberofloadcyclesduringits

,

consideredinthedesignprocess.

y Designdevelopments

have

always

been

an

important

issue

in

the

,

componentwiththeminimumweightpossibleandproperfatiguestrength

andotherfunctionalrequirements.

efficiencyandhigherpoweroutput.


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y Solidmodelingofthecrankshaftisdoneusingpro/ENGINEERasperthe

dimensionsandspecifications.

y Pro/ENGINEERisstandardin3Dproductdesign,featuringindustryleading

productivitytoolsthatpromotebestpracticesindesignwhileensuring

compliancewithindustryandcompanystandards.

y Integrated,parametric,3DCAD/CAM/CAEsolutionsallowyoutodesign

fasterthan

ever,

while

maximizing

innovation

and

quality,

to

ultimately

createexceptionalproducts.

y Acrankshaftcontainstwoormorecentrallylocatedcoaxialcylindrical

("main")journalsandoneormoreoffsetcylindricalcrankpin("rod")

journals.

y Thecrankshaftmainjournalsrotateinasetofsupportingbearings("main

bearings"),causingtheoffsetrodjournalstorotateinacircularpath

aroundthemainjournalcenters.


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y Structuralanalysisisaprocesstoanalyzeastructuralsysteminorderto

loadingand

external

environment

during

the

service

life

of

the

structure.

Thepurposeofastructuralanalysisistoensuretheadequacyofthedesign

y Thefollowingtypesofstructuralanalysiscanbeperformed:

yStatic

analysis

o a ana ys s

y Harmonicanalysis

y Transientdynamicanalysis

y Spectrumanalysis

y Bucklinganalysis.


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y Inaelasticbodythatissubjectedtoasystemofloadsin3dimensions,a

complex3dimensionalsystemofstressesisdeveloped.Thatis,atanypo n w n e o y ereares ressesac ng n eren rec ons,an

thedirections

and

magnitude

of

stresses

changes

from

point

to

point.

y TheVonmises criterionisaformulaforcalculatingwhetherthestresscombinationatagivenpointwillcausefailure.

y Therearethreeprinciplestressesthatcanbecalculatedatanypoint,actinginx,yandzdirections.

y VonMises found

that,

even

though

none

of

the

principal

stresses

exceed

,combinationofstresses.

y TheVonMises criterionisaformulaforcombiningthese3stressesintoanequivalentstress,whichisthencomparedtotheyieldstressofthe

.y TheequivalentstressisoftencalledtheVonMises Stressasashorthand

description.Itisnotreallyastress,butanumberthatisusedasanindex.IftheVonMises Stressexceedstheyieldstress,thematerialisconsideredtobeatthefailurecondition.


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DYNAMICANALYSISOFCRANKSHAFTy Themainobjectiveofthisstudywastheoptimizationoftheforgedsteelcrankshaftwhichrequiresaccuratemagnitudeoftheloadingonthe

componentthatconsistsofbendingandtorsion.

y Figure showsthevariationoftheforceatthejournalbearingbetween

crankshaftandconnectingroddefined.Ascanbeseeninthisfigure,the

maximumloadinghappensattheangleof355 wherethecombustion

takesplace.

y Asthedynamicloadingonthecomponentisafunctionofenginespeed,

thesame

analysis

was

performed

for

different

engine

speeds

which

were

intherangeofoperatingspeedforthisengine(i.e.2000rpmwhichisthe

minimumenginespeedand2800rpm).

y Thereasonforthissituationcouldbeexplainedasfollows.Asmentioned

previously,there

are

two

load

sources

in

the

engine;

combustion

and

inertiaload.

y Itwaspointedoutthatthemaximumpressureinthecylinderdoesnot

changeastheenginespeedchanges,thereforetheloadappliedtothe

crankshaftat

the

moment

of

maximum

pressure

due

to

combustion

does

notchange.


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y

This

is

a

bending

load

since

it

passes

thought

the

center

of

the

crank

radius.Ontheotherhand,theloadcausedbyinertiavariesasafunctionofenginespeed.

y Astheenginespeedincreasesthisforceincreasestoo.Theloadproducedb combustion is reater than the load caused b inertia and is in theoppositedirection,whichmeansthesumofthesetwoforcesresultsinthebending

force

at

the

time

of

combustion.

y Soastheenginespeedincreasesthemagnitudeoftheinertiaforce

causedbycombustion,resultinginadecreaseintotalloadmagnitude.However,factorssuchaswearandlubricationareimportantathigher

enginespeeds.

ence eana ys s orspee o rpm ssu c en o n ou efatiguenatureofcrankshaft.

y Furtherdiscussionoftheseissuesisavoidedsincetheyarenotofconcerninthisstudyandfatiguefailureisthemainfocus.Inthisspecificengine

withits

dynamic

loading.

The

torsional load

has

no

effect

on

the

range

of

vonMises stressatthecriticallocation.

y Themainreasonfortorsional loadnothavingmucheffectonthestressran eisthatthemaximumsofbendin andtorsional loadin ha enatdifferenttimesduringtheenginecycle.Inaddition,whenthemainpeakof

the

bending

takes

place

the

magnitude

of

torsional


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variationofforceovercrankshaftan leataspeedof2000rpm


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Def.+undef.shapeoforiginalmodel


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Disp.vectorsumoforiginalmodel


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Vonmises strainoforiginalmodel


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Vonmises stressoforiginalmodel


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Ycomp.ofdisp.Oforiginalmodel


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Def+ undef. sha e of o timized model


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Vonmises stressofoptimizedmodel


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Vonmises strainofoptimizedmodel


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Ycomp.ofdisp.ofoptimizedmodel


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THEORITICALCALCULATIONSy ThetheoreticalworkingstressesoftheCrankshaftarecalculatedbyusingthe

formula:

y MaximumAllowable

Stress

= Ultimate

Tensile

Strength

/factor

of

Safety.

y Thefactorofsafetyforthismodelisintherangeof46.

687n/mm2.

y Fromtheanalysisitwasobservedthatmax.stressoccursat2000rpmsince

maxloading

occurs

at

that

rpm.

Hence

the

stresses

due

to

other

loadings

are

.

y Therefore,byapplyingtheaboveformulaforthetwomodelsofcrankshaft,thetheoreticalcalculationisdoneinthefollowingmanner.

y Originalmodel:Maximum

allowable

stress=687/4=171.7

N/mm^2.

y Optimizedmodel:Maximumallowablestress=687/5=137.4N/mm^2


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UNOPTIMIZEDMODELy TheDeformedandUndeformedcontourshapeoftheunoptimizedmodel

hasbeen

plotted

y Fromfigure,themaximumvalueofVonMises stressis104.261N/mm2 and

theminimumvalueis11.85N/mm2.Themaximumstressisobtainedat

thepointofapplicationoftheload.

y Themaximum

value

of

Von

Mises Strain

is

.938e

10

and

the

minimum

valueis.595e04

y ThemaximumvalueoftheYcomponentofdisplacementofthe

unoptimized modelis.511e3mm.Theminimumvaluewillbe.01191mm.

Vonm ses stress N/mm^2 Vonm ses stra n11.85 .0595e3

34.756 .178e

3

57.927 .297e3

. . e

104.269 .535e3


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OPTIMIZEDMODEL

plotted

Fromfigure,themaximumvalueofVonMises is116.497N/mm2 andthe2

application oftheload.

ThemaximumvalueofVonMises Strainis.597e3andtheminimumvalueis

682e9

ThemaximumvalueoftheYcomponentofdisplacementoftheoptimizedmodel

is595e3.Theminimumvaluewillbe .013mm

Vonmises stress(N/mm^2) Vonmises strain12.94 .664e4

..199e

3

64.72 .332e3

. . e

116.49 .597e3


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CONCLUSIONy Thefollowingconclusionscanbedrawnfromtheanalysis:y Dynamicloadinganalysisofthecrankshaftresultsinmorerealistic

.

stresses

are

critical

input

to

fatigue

analysis

and

optimization

of

the

crankshaft.

effectonvonMises stressatthecriticallystressedlocation.Theeffectof

torsiononthestressrangeisalsorelativelysmallatotherlocations

under oin

torsional load.Therefore

the

crankshaft

anal sis

could

be

simplifiedtoapplyingonlybendingload.

y Critical(i.e.failure)locationsonthecrankshaftgeometryarealllocatedon

thefilletareasbecauseofhi hstress radientsintheselocations which

resultin

high

stress

concentration

factors.

y Geometryoptimizationresultedin18%weightreductionoftheforged

steelcrankshaft whichwasachievedb chan in thedimensionsand

geometryofthecrankwebswhilemaintainingdynamicbalanceofthe

crankshaft.

mech-fea of crankshaft

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