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

RESIDUAL STRESS ANALYSIS OF NITRIDE STEELCRANKSHAFT FOR MULTICYLINDER ENGINE

M Manickam1*, S Prathiban1, P Renuka Devi1 and P Vijaya Kumar2

*Corresponding Author: M Manickam,manickam.mpm@gmail.com

Crankshaft is a most critical component in Multi cylinder Engine. The residual stresses inducedby the fillet rolling process of ductile cast iron crankshaft. The stress concentration near the filletof the crankshaft section under bending without concentrations of residual stresses areinvestigated by a two-dimensional elastic finite element analysis. Effective Residual stressintensity factor ranges are approximately estimated and compared to an assumed thresholdstress intensity factor range which determine cracks can continue to propagate for a givencrack length. The conventional material such as ductile cast-iron is replaced by Nitride steel forminimizing the residual stress of Multi cylinder crankshaft. The results indicate that the four-bubble failure criterion only determines the crack initiation life for small cracks initiated on thesurfaces of fillets. The four-bubble failure criterion does not indicate whether a fatigue crackinitiated on the fillet surface can propagate through or arrest in the compressive residual stresszone induced by the rolling process. The remodelled crank shaft shows that the residual stressis less when compared with conventional crankshaft.

Keywords: Engine, Crankshaft, Residual stress, Nitrite steel, Analysis

INTRODUCTIONThe crankshaft in an internal combustionengine converts the linear motion of the pistoninto a rotary motion. This rotary motion is usedto drive the automobile or other device thatmeans by the crankshaft. A crankshaft has avery wide range of applications from small onecylinder lawnmower engines to very large multicylinder marine engines. Crankshaft is a

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Int. J. Mech. Eng. & Rob. Res. 2014

1 Department of Mechanical Engineering, Ponnaiyah Ramajayam College of Engineering and Technology, Thanjavur 613403, India.2 Department of Mechanical Engineering, PRIST University, Thanjavur 613403, India.

component that is intended to last the lifetimeof the engine and/or vehicle. Being a highspeed, rotating component, its service lifecontains many millions, or even billions ofcycles of repetitive loading. Since thecrankshaft experiences a large number of loadcycles during its service life, fatigueperformance and durability of this componenthas to be considered in the design process.

Research Paper

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

Design developments have always been animportant issue in the crankshaft productionindustry, in order to manufacture a lessexpensive component with the minimum weightpossible and proper fatigue strength and otherfunctional requirements. Fatigue crack growthanalysis of a diesel engine forged steelcrankshaft was investigated by Guaglianoet al. (1993) and Guagliano et al. (1994). Theyexperimentally showed that with geometry likethe crankshaft, the crack grows faster on thefree surface while the central part of the crackfront becomes straighter. Based on thisobservation, two methods were compared; thefirst considers a three dimensional model witha crack modeled over its profile from theinternal depth to the external surface. In orderto determine the stress intensity factorsconcerning modes I and II a very fine meshnear the crack tip is required which involves alarge number of nodes and elements, and alarge computational time. The secondapproach uses two dimensional models witha straight crack front and with the depth of thereal crack, offering simpler models and lesscomputational time. Osman Asi (2006)performed failure analysis of a diesel enginecrankshaft used in a truck, which is made fromductile cast iron. At present nitriding forincreasing fatigue strength of structural metallicmaterials more widely is used (Prakash et al.,1998; Zoroufi, 2005; Shenoy, 2006; Farzinet al., 2007; Jonathan Williams et al., 2007;and Xiaorong Zhou, 2009) which it results innegative effect (for example, nitriding of highstrength bearing steel SUJ2 resulted indecrease of fatigue strength. The results ofexperimental data on the influence of nitridingon fatigue strength will be considered belowLow cycle fatigue.

Nitride SteelNitriding is a process of case hardening aspecial alloy steel (nitralloy) in an atmosphereof ammonia or in contact with nitrogenousmaterial at a temperature below thetransformation range. The surface hardnessis produced by the absorption of nitrogenwithout quenching. Single stage nitriding isbeing done at 500-510 ºC with 30%dissociation of ammonia. Ammoniadissociates according to the following reaction2NH3 ↔ 3H2 + N2 Nitriding steel arehardened and tempered at 560-650 ºC tominimize distortion and to have a uniform highsurface hardness. Hence the process is veryideal for components having complex shapes/critical section to control distortion.

Area Affected due to residual stresses inCrank shaft.

1. Gudgeon pin.

2. Connecting rod.

3. Crank shaft.

4. Engine block.

5. Cylinder.

6. Piston.

STRUCTURAL ANALYSIS OFCRANKSHAFTANSYS is a general-purpose finite-elementmodelling package for numerically solving awide variety of mechanical problems. Theseproblems include static/Dynamic; structuralanalysis (both linear and nonlinear), heattransfer, and fluid Problems, as well asacoustic and electromagnetic problems maybe analyzed with finite element methods.Structural analysis is probably the most

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

common application of the finite elementmethod. The term structural implies crank shaftresidual stress and fatigue analysis. Thecrankshaft bears the constraints of mainjournals and longitudinal thrust bearing.Because of the effect of load, crankshaft mainjournals appear bend deformation between thelower main-bearing half and upper main-bearing half. And the longitudinal thrust bearingcan prevent effectively the crankshaft axialmovement and ensure the piston andconnecting rod assembly normally works. Fivesurface radial symmetry constrains wereexerted on the five main journals surfacerespectively, axial displacement constrainswere exerted on the two end face of crankshaft.Then the modal analysis was carried out usingthe ANSYS software. In this experimental workcrank shaft model was created by PRO-Emodelling and Imported to ANSYS software.The figure represents the bending stress andtwisting moment is influenced in crank pin andthen spread the crank web surface, howeverthe yield point of von misses is less than forgedsteel crankshaft. So it is best suitable formanufacturing crankshaft for multi cylinder ICEngine.

Figure 1: X-Component of Stress

Figure 2: Y-Component of Stress

Stress Analysis of ExistingCrankshaft (Ductile Cast Iron)

Figure 3: Z-Component of Stress and Von-Mises Stress

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

Stress Analysis in the RedesignCrankshaft (Using Nitride Steel)

Figure 4: X-Component Stress

Figure 5: Y-Component Stress

Figure 6: Z-Component Stress and VonMises Stress

X-component 0.0079230 0.001898

Y-component 0.007915 0.938E-03

Z-component 0.00805 0.002080

Von Mises Stress 0.640E-03 0.640E-03

Table 1: Comparison BetweenCrankshaft Stresses

Stresses inDirection

BeforeModeling theCrankshaft

AfterModeling theCrankshaft

CONCLUSIONIn the conventional crankshaft the residualstress is maximum at the crank pin journal areaand the possibility of occurrence of crack ishigh. This residual stress is minimized bychanging material as nitride steel and formingthe fillet between the edges of crank pin journal.The remodelled crank shaft shows that theresidual stress is less when compared withconventional crankshaft. Thus the remodelleddesign can be adopted in manufacturing ofcrank shaft and may avoid the crack beingproduced in crankshaft journal.

ACKNOWLEDGMENTWe express sincere thanks to our BelovedPrincipal Prof M Abdul Ghani Khan, PonnaiyahRamajayam College of Engineering andTechnology, Thanjaur for given valuablesuggestions and Motivate this Efforts.

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