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Int. J. Mech. Eng. & Rob. Res. 2014 M Senthil Kumar et al., 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 4, October, 2014

© 2014 IJMERR. All Rights Reserved

Research Paper

ANALYSIS OF CRANKPIN FAILURE IN ASINGLE CYLINDER ENGINE

M Senthil Kumar1*, S Ragunathan2 and M Suresh3

*Corresponding Author: M Senthil kumar � msksona@gmail.com

A survey has been taken on petrol engine crankshafts used in two wheeler made from C45 (EN8/AISI 1042) steel. It was reported that abnormal sound was heard in crankshaft while in operationand identified as failure of crankshaft. Severe wear has been seen at crankpin bearing locationwhere the oil hole is provided. Crankpin is found as tempered. Mechanical and metallurgicalproperties of the crankshaft including chemical composition, micro-hardness, microstructureand tensile properties were studied and compared with the specified properties of the crankshaftmaterial. As a result of the analysis, the main reason of failure was determined as lower surfacehardness followed by rapid wear due to the contact of crankpin and bearing surface. The contactwas resulted due to absence of oil and improper lubrication.

Keywords: Crankshaft, Failure analysis, Surface hardness, Finite element analysis

1 Asst.Professor, Dept. of Mechanical Engineering, Sona College of Technology, Salem, India.2 Principal, Jayalakshmi Institute of Technology, Thoppur, India.3 PG Student, Engineering Design, Sona College of Technology, Salem, India.

INTRODUCTION

Crankshaft is the heart of an InternalCombustion Engine (Xue-qin Hou et al.,2010). The reciprocating motion of Piston isconverted into rotary motion by crankshaft.Crankshafts are generally subjected totorsional stress and bending stress due toself-weight or weights of components orpossible misalignment between journalbearings. Crankshaft failures may be resultedfrom by several causes which are oilabsence, defective lubrication on journals,high operating oil temperature, misalign-

ments, improper journal bearings or improperclearance between journals and bearings,vibration, high stress concentrations,improper grinding, high surface roughness,and straightening operations. The crankshaftfaults caused high cost of maintenance inautomotive industry (Ali Keskin et al., 2010).Reasons for failure of crankshaft assemblyand crankpin may be A) Shaft misalignmentB) Vibration cause by bearings applicationC) Incorrect geometry (stress concentration)D) Improper lubrication E) High enginetemperature F) Overloading G) Crankpin

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material & its chemical composition H)Pressure acting on piston B.Kareem(KareemB, 2007) has studied mechanicalcrankshaft failure for automobile. This wasdone using data gathered by oral interviewsand questionnaire on mechanical failure ofcrankshafts. He has done research usingNissan, Datsun and other Japanese cars.Finally he has concluded that the failure ofcrankshaft in automobile came as a result ofoil leakages in engines, overloading,misalignment, poor surface finishing,misassembling, poor reconditioning of thrustbearing and adultered engine oil. And thefailure can be reduced by production ofcrankshafts with locally sourced materials,improvement on the local roads, rightmechanical maintenance practice andeducating the users. (Jian Meng et al., 2011)have done stress analysis and modelanalysis of four cylinder engine crankshaftusing FEM .The three dimensional model ofdiesel engine crankshaft was created by pro-e and also they analysed the vibration model,the distortion and stress status of crank throwand they found the dangerous areas by stressanalysis. The relationship between thefrequency and the vibration modal wasexamined by the modal and harmonicanalysis of crankshaft using ANSYS. Theyconcluded that the maximum deformationappeared at the centre of crankpin necksurface. The maximum stress appeared atthe fillets between the crankshaft journal andcrank cheeks, and near the central pointjournal. The edge of main journal was highstress area. The failure was due to bendingfatigue. (S M Sorte et al., 2013) haveanalysed the stress and design optimizationof a single cylinder crankpin of TVS Scooty

Pep crankshaft assembly. Three-dimensionmodels of crankshaft and crankpin forceswere created using Pro/ENGINEER softwareand software ANSYS was used to analyzethe stress status on the crankpin. Themaximum deformation, maximum stresspoint and dangerous areas are found by thestress analysis.

R K Pandey (2003), inestigated the failureof diesel engine crankshaft used in tractormade from C45 steel. Premature failure wasreported in the web region of the crankshaft.The crankshafts were forged, normalized andpartly induction hardened. The investigationincluded determination of chemicalcomposition, microstructural examination,evaluation of tensile properties and charpytoughness as well as hardnessdetermination. The fracture toughness wasestimated from the charpy energy data. Thefailure zones in various crankshafts wereexamined using the scanning electronmicroscope (SEM) and the micro mechanismof failure in the crankshafts was studied.Fractographic studies indicated fatigue as thedominant mechanism of failure of crank-shafts. Attempts were made to estimate thestress level required for fatigue initiation fromthe crankpin-web fillet region. Further,fractographic methods were used to estimatethe stress required for fatigue propagation.Subsequently, the failure time was estimatedand this was correlated with the observedfailure times in different crankshafts. Thestudies indicated that fatigue initiation fromthe crankpin-web fillet region necessitated astress level of about 175 MPa. To avoidrecurrence of failure, machining and finalgrinding has to be done carefully to prevent

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formation of discontinuities or crack-likedefects in the fillet region and inductionhardening of the fillet is desirable. Also, thefillet radius needs to be increased. (ChangliWang et al., 2005) have conducted a test runfor only 20 min and a crankshaft cracked in astrange manner. The crankshaft is made of40CrMnMo alloy steel. Four cracks werefound on the edge of the oil hole. Usingmechanical analysis, microstructure andmetallurgy the reason of this event has beenrevealed. Force of friction caused byimproper crankshaft repair and assemblingis main factor of the failure. Why frictionoccurs, how the crack initiates and expandsand what the process of failure were studied.They concluded that the crankshaft crackedby shearing stresses, caused by unusualfriction between surface of shaft and the mainbush, due to improper repairing andassembling and Friction can cause slip onthe surface of friction boundary, especiallywhen the temperature goes up to a criticallevel. To 40CrMnMo 300–500°C is a specialtemperature which may lead to temperbrittleness. Finally they stated that it ispossible that molten copper from the bearingshell caused liquid metal embrittlement in thecrankshaft journal. (Ali Keskin et al., 2010)have gone for failure analysis of nodulargraphite cast iron crankshaft used in petrolengine. They tested mechanical andmetallurgical properties of the crankshaftincluding chemical composition, micro-hardness, tensile properties and roughnessand were compared with the specifiedproperties of the crankshaft materials. In thecomparison, there were no metallurgicaldefects apart from slightly higher carboncontent. All other measured values were

within the specified values. The reasonidentified for the failure was the thermalfatigue because of contact of journal andbearing surface. This condition led to theformation and growth of fatigue cracks. Thecontact was resulted from defectivelubrication or high operating oil temperature.In the present study, a failed crankshaft usedin 4 stroke two wheeler has been examinedfor the cause of failure. It was reported thatan abnormal sound was produced by theengine during the running time. When theengine was disassembled, it was found thatcrank pin was worn out severely and lookedlike material has been scraped at the centreof the crankpin.

EXPERIMENTAL METHODS

General Specifications of the Engine

Item

Number of Cylinder

Cycle

Stroke(mm)

Bore(mm)

Displacement(cc)

Compression ratio

Maximum power

Maximum Torque

Specification

Single

4 stroke

49.5

50

97.2

9.1

5.5 kW at 8000rpm

7.95 Nm at 8000rpm

A. Chemical Analysis

Figure 1: Crankshaft Assembly

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Table 1 and 2 gives the specified chemicalcomposition of crankshaft and crankpinmaterial. In the same table the chemicalcomposition of the material from the failedshaft and crankpin is reported by usingOptical Emission Spectroscope (OES)analyser. The analysis showed that thecrankpin material is SCM 420 and crankshaftmaterial is EN 8 of BS 970 (C45 steel). It isobserved that the chemical composition ofboth the shaft and crankpin are within thespecified range.

Figure 2: Failed Crankpin

Composition

Carbon

Manganese

Silicon

Sulphur

Phosphorus

Chromium

Molybdenum

Wt.% asSpecified

0.18-0.23

0.6-0.85

0.15-0.35

Max 0.03

Max 0.03

0.9-1.2

0.15-0.3

Wt.% basedon analysis

0.18

0.79

0.31

0.006

0.005

0.958

0.15

Table 1: Chemical Composition ofCrankpin Material

Composition

Carbon

Manganese

Silicon

Sulphur

Phosphorus

Wt.% asSpecified

0.35-0.45

0.6-0.10

0.05-0.35

Max 0.06

Max 0.06

Wt.% basedon analysis

0.35

0.75

0.26

0.034

0.009

Table 2: Chemical Composition ofCrankshaft Material

B. Hardness Analysis

Hardness of crankpin was tested usingVickers micro hardness tester-Wolpert group.The test load was 1kg and three locations incross section were tested (Bayrakceken Het al., 2007). Hardness of the failed crankpin and a new crank pin was tested at bothside and centre of the crankpin by usingVickers micro hardness tester – Wolpertgroup. The test result is listed in Table 4 andTable 5.

Positions

Results

Table 5: Vickers Micro Hardness Results(HV1) of New Crankpin

1

720

2

715

3

705

Properties

Young’s modulus

Density

Poisson ratio

Yield stress

Tensile stress

Elongation

Crankshaft

200-210GPa

7.83^3 kg/m3

0.27

465MPa

780MPa

16%

Crankpin

190-210GPa

7.9^3 kg/m3

0.3

434MPa

715MPa

15%

Table 3: Material Properties ofCrankshaft and Crankpin

Positions

Results

Table 4: Vickers Micro Hardness Results(HV1) of Failed Crankpin

1

718

2

715

3

700

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Hardness result shows that the failedregion(centre of crankpin) has lower valueof hardness than cross section sides andhence the wear was initiated earlier due tofriction and it propogated due to improperlubrication.

C. Microsturcture Analysis

The crankpin was examined usingMETSCOPE (Metallurgical microscope).Theimage of 200X and 500X magnification showsthat fine tempered martensite structure isthroughout the matrix (Osam Asi, 2006). Andthe failure region shows the same structuretoo. Hence the microstructure is not the causefor the failure.

Figure 3: Microsructure of the CrankpinCross Section with 200X

Figure 4: Microsructure of the CrankpinCross Section with 500X

The macro etched crank pin doesn’t showany crack. Hence, the failure is only due tofriction occurred due improper lubrication.

D Hardnening A new pin is taken andanalysed its hardness value again and thetest result gives the hardness value tabulatedin Table 4. Then the crankpin central portionwas subjected to selective inductionhardening to the depth of 3mm followed bysalt bath quenching (Paswan M K and GoelA K, 2008). The hardness measured afterhardening is listed in Table 6.

Figure 5: Macro Etched Image of Crank pin

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Positions

Results

Table 6: Vickers Micro Hardness Results(HV1) of New Crankpin After Induction

Hardening

1

720.8

2

720.7

3

728.4

The measured value shows that there isincrease in Hardness value after inductionhardening of the crankpin. By this increasein hardness value at the centre of crankpin,wecan able to increase the life of the pin.

Figure 6: After Induction Hardening

FINITE ELEMENT ANALYSIS

The stress level of the failed crankshaft isanalysed by finite element method. Figure 7-11 gives the Pro-E model and finite elementmodel of crankshaft and shows us the stressresults at the crankpin location. Crankshaftassembly and crank pin are analysed sepa-rately.

Figure 7: Pro-e Model of the Crankshaft

Figure 8: Meshing

Figure 9: Boundary Conditions

Figure 10: Finite Element StressAnalysis of the Crankshaft

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Figure 11: Finite Element StressAnalysis of the Carankpin

The model was imported to ANSYS. Thefinite element mesh is generated with SOLID185 element and meshed using tetrahedrafreemesh. The node numbers are 19329 andnumber of Elements are 94584.

Bearings are assumed as boundaryconditions and their displacement is assumedzero. Force is applied from the crankpinbearing location for 120°angle of contact(Jonathan Williams et al., 2007). Vonmisesstress in the failure location and fillet radiusare higher and hence they are consideredas critical location for the analysis.

RESULTS AND DISCUSSION

It is found that the chemical composition ofthe crankshaft material and crankpin are ingeneral within the range of the technicalspecifications and no obvious manufacturingand machining defects were found. Thecrankpin was not case hardened excepttempering followed by general hardening.

However the hardness value at the failureregion was lower (705 HV1) than otherlocations (720 HV1) and it is the cause for

the rapid wear of the crankpin at the contactregion. This initiation of failure isconsequently propogated by absence of oildue to improper lubrication. Hence the stressand wear at this region becomes more.

CONCLUSION

1. By visual examination it is seen that thecrankpin wears at the centre andcaused failure.

2. The lower value of hardness at thatregion increases the wear betweencontacts.

3. Finite Element Analysis result confirmsthat the highly stressed regions are thecontact region with the web and centreof crank pin where oil hole is provided.

4. The absence of oil and improperlubrication increases the wear rapidlyand hence the undesirable sound isheard.

5. Now-a-days most of the youngstersonly ride the two wheelers with highspeed and without proper maintenance.Hence, the life of crankshaft becomesshorter.

REFERENCES

1. Ali KESKIN et al., (2010), “Crack Analysisof a Gasoline Engine Crankshaft”, GaziUniversity Journal of Science, Vol. 23, No.4, pp. 487-492.

2. Bayrakceken H et al., (2007), “Failure ofSingle Cylinder Diesel EngineCrankshafts”, Elsevier, EngineeringFailure Analysis, Vol. 14, pp. 725-730.

3. Changli Wang et al., (2005), “Analysis ofan Unusual Crankshaft Failure”, Elsevier,

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Engineering Failure Analysis, Vol. 12, pp.465-473.

4. Jian meng et al., (2011), “Finite ElementAnalysis of 4- Cylinder DieselCrankshaft”, I.J. Image, Graphics andSignal Processing, Vol. 5, pp. 22-29.

5. Jonathan Williams et al., (2007), “FatiguePerformance Comparison and LifePredictions of Forged Steel and DuctileCast Iron Crankshafts”, Final Projectreport.

6. Kareem B (2007), “A Survey of Failure inMechanical Crankshafts of Automobile”,Journal of Engineering and AppliedSciences, Vol. 2, No. 7, pp. 1165-1168.

7. Osam Asi (2006), “Failure Analysis of aCrankshaft from Ductile cast iron”,Elsevier, Engineering Failure Analysis,Vol. 13, pp. 1260-1267.

8. Pandey P K (2003), “Failure of Diesel-Engine Crankshafts”, PregamonEngineering Failure Analysis, Vol. 10, pp.165-175.

9. Paswan M K and Goel A K (2008),“Fatigue Testing Procedure of 6 CylinderDiesel Engine Crankshaft”, ARISER, Vol.4, No. 3, pp. 144-151.

10. Silva F S (2003), “Analysis of a VehicleCrankshaft Failure”, Pergamon,Engineering Failure Analysis, Vol. 10,605-616.

11. Sorte S M et al., (2013), “Stress Analysisand Design Optimization of Crankpin”,International Journal of science andModern Engineering, Vol 1, No. 4.

12. Xue-qin Hou et al., (2010), “FractureFailure Analysis of Ductile Cast IronCrankshaft in a Vehicle Engine”, ASMInternational.