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Dual boundary element method in modelling of fatigue crack propagation

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$UAL"OUNDARY%LEMENT-ETHODIN-ODELINGOF&ATIGUE#RACK0ROPAGATION

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#RACKBEHAVIOURISPREDICTEDBASEDONSTRESS INTENSITY FACTOR4HIS ANALYSIS ALSO CALL DAMAGE TOLERANCEANALYSISISDEVELOPEDBASEDONLINEAR ELASTICFRACTUREMECHANICSTHEORY

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(4)

Fatigue crack grwth rate, da/dN

Stress intensity range, ∆K Stage I

Region

Stage II Region

Failure

Stage III Region

m Kth

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(6)

Cycle of propagation, Np

Cycle of initiation, Ni

×103

Monte Carlo-Beasy Test (Kebir H. et al., 2001) Deterministic

100 80 60 40 20 0

0 100 200 300 400

&)'52%&ATIGUEPREDICTIONLIFE PATCHINTHEMODEL4HENUMERICALRESULTSHAVEA

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&)'52%,IFECYCLEOFFATIGUECRACKPROPAGATIONBYITERATIONS Cycle Crack propagation at notch 1 to notch 24

Notch number

1 24

0.29 × 105 0.50 × 105 0.73 × 105 1.25 × 105 1.38 × 105 1.51 × 105 1.72 × 105 1.98 × 105

PROCESS)NALONGDURATIONTIMETHESMALLCRACKS SIZEMAYHAVETHEMOSTDOMINANTEFFECTONTHE FAILUREPROBABILITY

4ABLESHOWSAMAXIMUMCRACKLENGTH MM BEFORE THE COMPONENT IS FAILURE !T THIS

MOMENTTHELIFECYCLEONLYXCYCLESAS PRESENTSINTHITERATION4HISHAPPENEDBECAUSEA CRACKNOTCHHADENOUGHENERGYTOPROPAGATE ANINITIALCRACK4HECRACKGROWTHVERYFASTAND VERIlESTHEHIGHPROPAGATIONRATE(OWEVERTHE FAILUREOFTHESAMPLEHASBEENNOTHAPPENEDYET UNTILTHELIFECYCLEREACHEDATXCYCLES 4HE NOTCH IS RANDOMLY PROPAGATED THE INITIAL CRACK APPROPRIATE WITH THE INCREASE OF STRESS INTENSITYFACTORVALUE4HESTRESSINTENSITYFACTOR

(7)

VALUEISCONSTANTLYINCREASEDFORAFEWITERATIONS UNTILITISSLOWLYTRENDEDTOACHIEVEAMAXIMUM VALUE&ORTHEFOURTEENHOLESPLATENOTCHES ANDHAVEBEENCHOSENFORPROPAGATESAN INITIALCRACKASSHOWNIN&IGURE4HEINCREASING WASCONTINUINGFORCERTAINITERATIONS!FTERTHAT THECRACKHASBEENRANDOMLYPROPAGATEDATOTHER NOTCH WHICH HAD LOWER STRESS INTENSITY FACTOR )NTHISSCENARIOTHENOTCHHAVE BEENRANDOMLYPROPAGATEDTHECRACK4HECRACK HAS BEEN CONTINUING PROPAGATE FOR A CERTAIN ITERATIONSTOGETCLOSEWITHTHEMAXIMUMSTRESS INTENSITYFACTORATTHATTIME4HEINCREASEDOFTHE LIFECYCLEWASCONTINUINGTHECRACKPROPAGATION AT HIGH PROBABILITY LOCATION RANDOMLY !T THIS

MOMENT THE CRACK PROPAGATION CAN MAKE THE SAMPLEFAIL.OTCHWASHAVINGACATASTROPHIC FAILUREWHENITSEFFECTIVESTRESSINTENSITYFACTOR REACHED THE VALUE OF -0A M4HE HIGHPOTENTIALENERGYHASBEENASSEMBLESATA LOWSTRESSINTENSITYFACTORNOTCHANDCATASTROPHIC FAILUREWASOCCURREDBECAUSEOFTHEHIGHGROW CRACKPROPAGATIONRATE

4HERESULTOFTHECRACKPROPAGATIONBASEON THE COMPONENT LIFE CYCLE WAS SHOWN THAT THE CRACKPROPAGATESINTHREEPHASES4HElRSTPHASE STARTEDATCYCLESANDlNISHEDAT CYCLES!TTHISPHASEEACHOFTHEITERATIONCAUSES OFCMCRACKLENGTHWHICHISCONSIDEREDAS AMINORCRACK

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7 th Iteration 13th Iteration

0 5 10 15 20 25 1000000

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Notch number Effective stress intensity factors, Keff (MPa m1/2)

(8)

Number of sample, n

Standard deviation of life cycle, Ó

0 100 200 300 400 500

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Mean of life cycle, NTotal

(9)

4HE SECOND PHASE WAS STARTED AT CYCLES"ETWEENANDCYCLESA MAJORCRACKWASPROPAGATED4HESIZEISCM FOREACHLIFECYCLESITERATION

&ORTHETHIRDPHASEMINORCRACKPROPAGATION ISOCCURREDASINlRSTPHASE(OWEVERTHETHIRD PHASEWASTOOSHORTWHICHONLYCYCLES 4HE COMPONENT TOTALLY FAILED AFTER CYCLES

&IGUREAND&IGURESHOWAMEANLIFEANDA STANDARDDEVIATIONPREDICTIONFORATHITERATION BYTHEEFFECTOFNUMBEROFSAMPLES)TISSEENTHAT THENUMBEROFSAMPLESINmUENCESTHEFATIGUELIFE CYCLE4HERESULTSARECONSTANTWHENTHENUMBER

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OF SAMPLES IS OVER 3O THE -ONTE #ARLO

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4HEBOUNDARYELEMENTMETHODHASBEENAPPLIED TOACENTREMEMBERBAR&OURHOLESWITHNOTCHES HAVEBEENMODELLEDASSHOWNIN&IGUREAND 4HELOCATIONOFTHENOTCHESBASEDONTHEHIGH FORCECONCENTRATIONANDHIGHPROBABILITYOFTHE

(10)

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4HE ELEMENTS HAVE BEEN GENERATED ONLY AT THE BOUNDARY AS SHOWN IN &IGURE 7ITH THE LOADGIVENTHEELEMENTSOFTHECOMPONENTHAVE DISPLACEDASSHOWNIN&IGURE4HECRACKSHAVE

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!NOVERALLASSESSMENTMETHODPROPOSEDINTHIS PAPER WAS DEVELOPED IN ORDER TO VALIDATE THE FATIGUECRACKPROPAGATIONWITHTHEPROBABILISTIC

(11)

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THAT THE COMPUTER SIMULATION CAN BE USED TO PREDICTFATIGUECRACKPROPAGATION4HEPROPOSED ALGORITHMCANBEUSEDFORAGUIDELINETOHAVEA RISK AND RELIABILITY ANALYSIS AND LIFE EXPECTANCY OFTHESTRUCTURE

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Other researchers developed their own two-dimensional source code program to predict the fatigue crack growth and crack propagation under static loading as well as the prediction

In the present study, efforts were made to prove that fatigue degradation and entropy generation are correlated, thereby ensuring that their relationship would

To investigate the effect of initial crack size, crack aspect ratio, and tension- torsion load ratio on the SIFs, crack growth direction and fatigue life of a surface

Keywords: Fracture Mechanics, ANSYS, Crack, Displacement Extrapolation Method (DEM), J-integral, Interaction Integral Method (IIM), Virtual Crack Closure Method (VCCM),

Conclusions This paper presents finite element simulations of mixed-mode fatigue crack propagation in 2D problems based on linear elastic fracture mechanics by adopting the

For the main findings of this research objective, there are total of six types of cracks commonly occur on double-storey houses have been identified which included plaster

Pada tahun 1999, Kementerian Pelajaran telah menetapkan Komponen Sastera dalam Bahasa Inggeris sebagai satu keperluan untuk diajar kepada semua pelajar sekolah

Jika keseluruhan gandaan diset kepada 0.25, berapakah masa diperlulcan untuk sistem tersebut mengenap ke dalam lingkungan 2% nilai akhirnya bagi satu masukan rangkap