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 A SINGLE ENGINE

M Senthil Kumar1*, S Ragunathan2 and M Suresh3

*Corresponding Author: M Senthil kumar  [email protected]

A survey has been taken on used in two wheeler made from C45 (EN 8/AISI 1042) steel. It was reported that abnormal sound was heard in while in operation and identified as failure of crankshaft. Severe wear has been seen at crankpin location where the oil hole is provided. Crankpin is found as tempered. Mechanical and metallurgical properties of the crankshaft including chemical composition, micro-hardness, microstructure and tensile properties were studied and compared with the specified properties of the crankshaft material. As a result of the analysis, the main reason of failure was determined as lower surface hardness followed by rapid wear due to the contact of crankpin and bearing surface. The contact was resulted due to absence of oil and improper lubrication.

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

INTRODUCTION ments, improper journal bearings or improper Crankshaft is the heart of an Internal clearance between journals and bearings, Combustion Engine (Xue-qin Hou et al., vibration, high stress concentrations, 2010). The reciprocating motion of is improper grinding, high surface roughness, converted into rotary motion by crankshaft. and straightening operations. The crankshaft Crankshafts are generally subjected to faults caused high cost of maintenance in torsional stress and bending stress due to automotive industry (Ali Keskin et al., 2010). self-weight or weights of components or Reasons for failure of crankshaft assembly possible misalignment between journal and crankpin may be A) Shaft misalignment bearings. Crankshaft failures may be resulted B) Vibration cause by bearings application from by several causes which are oil C) Incorrect geometry (stress concentration) absence, defective lubrication on journals, D) Improper lubrication E) High engine high operating oil temperature, misalign- temperature F) Overloading G) Crankpin

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.

260 Int. J. Mech. Eng. & Rob. Res. 2014 M Senthil Kumar et al., 2014 material & its chemical composition H) Pep crankshaft assembly. Three-dimension Pressure acting on piston B.Kareem models of crankshaft and crankpin forces (KareemB, 2007) has studied mechanical were created using Pro/ENGINEER software crankshaft failure for automobile. This was and software ANSYS was used to analyze done using data gathered by oral interviews the stress status on the crankpin. The and questionnaire on mechanical failure of maximum deformation, maximum stress crankshafts. He has done research using point and dangerous areas are found by the Nissan, Datsun and other Japanese . stress analysis. Finally he has concluded that the failure of R K Pandey (2003), inestigated the failure crankshaft in automobile came as a result of of crankshaft used in tractor oil leakages in engines, overloading, made from C45 steel. Premature failure was misalignment, poor surface finishing, reported in the web region of the crankshaft. misassembling, poor reconditioning of thrust The crankshafts were forged, normalized and bearing and adultered engine oil. And the partly induction hardened. The investigation failure can be reduced by production of included determination of chemical crankshafts with locally sourced materials, composition, microstructural examination, improvement on the local roads, right evaluation of tensile properties and charpy mechanical maintenance practice and toughness as well as hardness educating the users. (Jian Meng et al., 2011) determination. The fracture toughness was have done stress analysis and model estimated from the charpy energy data. The analysis of four cylinder engine crankshaft failure zones in various crankshafts were using FEM .The three dimensional model of diesel engine crankshaft was created by pro- examined using the scanning electron e and also they analysed the vibration model, microscope (SEM) and the micro mechanism the distortion and stress status of throw of failure in the crankshafts was studied. and they found the dangerous areas by stress Fractographic studies indicated fatigue as the analysis. The relationship between the dominant mechanism of failure of crank- frequency and the vibration modal was shafts. Attempts were made to estimate the examined by the modal and harmonic stress level required for fatigue initiation from analysis of crankshaft using ANSYS. They the crankpin-web fillet region. Further, concluded that the maximum deformation fractographic methods were used to estimate appeared at the centre of crankpin neck the stress required for fatigue propagation. surface. The maximum stress appeared at Subsequently, the failure time was estimated the fillets between the crankshaft journal and and this was correlated with the observed crank cheeks, and near the central point failure times in different crankshafts. The journal. The edge of main journal was high studies indicated that fatigue initiation from stress area. The failure was due to bending the crankpin-web fillet region necessitated a fatigue. (S M Sorte et al., 2013) have stress level of about 175 MPa. To avoid analysed the stress and design optimization recurrence of failure, machining and final of a single cylinder crankpin of TVS Scooty grinding has to be done carefully to prevent

261 Int. J. Mech. Eng. & Rob. Res. 2014 M Senthil Kumar et al., 2014 formation of discontinuities or crack-like within the specified values. The reason defects in the fillet region and induction identified for the failure was the thermal hardening of the fillet is desirable. Also, the fatigue because of contact of journal and fillet radius needs to be increased. (Changli bearing surface. This condition led to the Wang et al., 2005) have conducted a test run formation and growth of fatigue cracks. The for only 20 min and a crankshaft cracked in a contact was resulted from defective strange manner. The crankshaft is made of lubrication or high operating oil temperature. 40CrMnMo alloy steel. Four cracks were In the present study, a failed crankshaft used found on the edge of the oil hole. Using in 4 two wheeler has been examined mechanical analysis, microstructure and for the cause of failure. It was reported that metallurgy the reason of this event has been an abnormal sound was produced by the revealed. Force of friction caused by engine during the running time. When the improper crankshaft repair and assembling engine was disassembled, it was found that is main factor of the failure. Why friction crank pin was worn out severely and looked occurs, how the crack initiates and expands like material has been scraped at the centre and what the process of failure were studied. of the crankpin. They concluded that the crankshaft cracked by shearing stresses, caused by unusual EXPERIMENTAL METHODS friction between surface of shaft and the main General Specifications of the Engine bush, due to improper repairing and Item Specification assembling and Friction can cause slip on Number of Cylinder Single the surface of friction boundary, especially Cycle 4 stroke when the temperature goes up to a critical Stroke(mm) 49.5 level. To 40CrMnMo 300–500°C is a special (mm) 50 temperature which may lead to temper Displacement(cc) 97.2 brittleness. Finally they stated that it is 9.1 possible that molten copper from the bearing Maximum power 5.5 kW at 8000rpm shell caused liquid metal embrittlement in the Maximum Torque 7.95 Nm at 8000rpm crankshaft journal. (Ali Keskin et al., 2010) have gone for failure analysis of nodular A. Chemical Analysis graphite cast iron crankshaft used in petrol Figure 1: Crankshaft Assembly engine. They tested mechanical and metallurgical properties of the crankshaft including chemical composition, micro- hardness, tensile properties and roughness and were compared with the specified properties of the crankshaft materials. In the comparison, there were no metallurgical defects apart from slightly higher carbon content. All other measured values were

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

Table 1 and 2 gives the specified chemical Table 2: Chemical Composition of composition of crankshaft and crankpin Crankshaft Material material. In the same table the chemical Wt.% as Wt.% based Composition composition of the material from the failed Specified on analysis shaft and crankpin is reported by using Carbon 0.35-0.45 0.35 Optical Emission Spectroscope (OES) Manganese 0.6-0.10 0.75 analyser. The analysis showed that the Silicon 0.05-0.35 0.26 crankpin material is SCM 420 and crankshaft Sulphur Max 0.06 0.034 Phosphorus Max 0.06 0.009 material is EN 8 of BS 970 (C45 steel). It is observed that the chemical composition of both the shaft and crankpin are within the Table 3: Material Properties of Crankshaft and Crankpin specified range. Properties Crankshaft Crankpin Figure 2: Failed Crankpin Young’s modulus 200-210GPa 190-210GPa Density 7.83^3 kg/m3 7.9^3 kg/m3 Poisson ratio 0.27 0.3 Yield stress 465MPa 434MPa Tensile stress 780MPa 715MPa Elongation 16% 15%

B. Hardness Analysis Hardness of crankpin was tested using Vickers micro hardness tester-Wolpert group. The test load was 1kg and three locations in cross section were tested (Bayrakceken H et al., 2007). Hardness of the failed crank pin and a new crank pin was tested at both side and centre of the crankpin by using Vickers micro hardness tester – Wolpert group. The test result is listed in Table 4 and

Table 1: Chemical Composition of Table 5. Crankpin Material Table 4: Vickers Micro Hardness Results Wt.% as Wt.% based Composition (HV1) of Failed Crankpin Specified on analysis Carbon 0.18-0.23 0.18 Positions 1 2 3 Manganese 0.6-0.85 0.79 Results 718 715 700 Silicon 0.15-0.35 0.31 Sulphur Max 0.03 0.006 Table 5: Vickers Micro Hardness Results Phosphorus Max 0.03 0.005 (HV1) of New Crankpin Chromium 0.9-1.2 0.958 Positions 1 2 3 Molybdenum 0.15-0.3 0.15 Results 720 715 705

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

Hardness result shows that the failed Figure 4: Microsructure of the Crankpin region(centre of crankpin) has lower value Cross Section with 500X of hardness than cross section sides and hence the wear was initiated earlier due to friction and it propogated due to improper lubrication.

C. Microsturcture Analysis The crankpin was examined using METSCOPE (Metallurgical microscope).The image of 200X and 500X magnification shows that fine tempered martensite structure is throughout the matrix (Osam Asi, 2006). And the failure region shows the same structure too. Hence the microstructure is not the cause for the failure.

Figure 3: Microsructure of the Crankpin Cross Section with 200X Figure 5: Macro Etched Image of Crank pin

The macro etched crank pin doesn’t show any crack. Hence, the failure is only due to friction occurred due improper lubrication. D Hardnening A new pin is taken and analysed its hardness value again and the test result gives the hardness value tabulated in Table 4. Then the crankpin central portion was subjected to selective induction hardening to the depth of 3mm followed by salt bath quenching (Paswan M K and Goel A K, 2008). The hardness measured after hardening is listed in Table 6.

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

Table 6: Vickers Micro Hardness Results Figure 7: Pro-e Model of the Crankshaft (HV1) of New Crankpin After Induction Hardening

Positions 1 2 3 Results 720.8 720.7 728.4

The measured value shows that there is increase in Hardness value after induction hardening of the crankpin. By this increase in hardness value at the centre of crankpin,we can able to increase the life of the pin. Figure 8: Meshing Figure 6: After Induction Hardening

Figure 9: Boundary Conditions

Figure 10: Finite Element Stress FINITE ELEMENT ANALYSIS Analysis of the Crankshaft The stress level of the failed crankshaft is analysed by finite element method. Figure 7- 11 gives the Pro-E model and finite element model of crankshaft and shows us the stress results at the crankpin location. Crankshaft assembly and crank pin are analysed sepa- rately.

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

the rapid wear of the crankpin at the contact Figure 11: Finite Element Stress Analysis of the Carankpin region. This initiation of failure is consequently propogated by absence of oil due to improper lubrication. Hence the stress and wear at this region becomes more.

CONCLUSION 1. By visual examination it is seen that the crankpin wears at the centre and caused failure. 2. The lower value of hardness at that region increases the wear between contacts. 3. Finite Element Analysis result confirms The model was imported to ANSYS. The that the highly stressed regions are the finite element mesh is generated with SOLID contact region with the web and centre 185 element and meshed using tetrahedra of crank pin where oil hole is provided. freemesh. The node numbers are 19329 and number of Elements are 94584. 4. The absence of oil and improper lubrication increases the wear rapidly Bearings are assumed as boundary and hence the undesirable sound is conditions and their displacement is assumed heard. zero. Force is applied from the crankpin 5. Now-a-days most of the youngsters bearing location for 120°angle of contact only ride the two wheelers with high (Jonathan Williams et al., 2007). Vonmises speed and without proper maintenance. stress in the failure location and fillet radius Hence, the life of crankshaft becomes are higher and hence they are considered shorter. as critical location for the analysis. REFERENCES RESULTS AND DISCUSSION 1. Ali KESKIN et al., (2010), “Crack Analysis It is found that the chemical composition of of a Gasoline Engine Crankshaft”, Gazi the crankshaft material and crankpin are in University Journal of Science, Vol. 23, No. general within the range of the technical 4, pp. 487-492. specifications and no obvious manufacturing and machining defects were found. The 2. Bayrakceken H et al., (2007), “Failure of crankpin was not case hardened except Single Cylinder Diesel Engine tempering followed by general hardening. Crankshafts”, Elsevier, Engineering Failure Analysis, Vol. 14, pp. 725-730. However the hardness value at the failure region was lower (705 HV1) than other 3. Changli Wang et al., (2005), “Analysis of locations (720 HV1) and it is the cause for an Unusual Crankshaft Failure”, Elsevier,

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Engineering Failure Analysis, Vol. 12, pp. 8. Pandey P K (2003), “Failure of Diesel- 465-473. Engine Crankshafts”, Pregamon 4. Jian meng et al., (2011), “Finite Element Engineering Failure Analysis, Vol. 10, pp. Analysis of 4- Cylinder Diesel 165-175. Crankshaft”, I.J. Image, Graphics and 9. Paswan M K and Goel A K (2008), Signal Processing, Vol. 5, pp. 22-29. “Fatigue Testing Procedure of 6 Cylinder 5. Jonathan Williams et al., (2007), “Fatigue Diesel Engine Crankshaft”, ARISER, Vol. Performance Comparison and Life 4, No. 3, pp. 144-151. Predictions of Forged Steel and Ductile 10. Silva F S (2003), “Analysis of a Vehicle Cast Iron Crankshafts”, Final Project Crankshaft Failure”, Pergamon, report. Engineering Failure Analysis, Vol. 10, 6. Kareem B (2007), “A Survey of Failure in 605-616. Mechanical Crankshafts of Automobile”, 11. Sorte S M et al., (2013), “Stress Analysis Journal of Engineering and Applied and Design Optimization of Crankpin”, Sciences, Vol. 2, No. 7, pp. 1165-1168. International Journal of science and Modern Engineering, Vol 1, No. 4. 7. Osam Asi (2006), “Failure Analysis of a Crankshaft from Ductile cast iron”, 12. Xue-qin Hou et al., (2010), “Fracture Elsevier, Engineering Failure Analysis, Failure Analysis of Ductile Cast Iron Vol. 13, pp. 1260-1267. Crankshaft in a Vehicle Engine”, ASM International.

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