Ew33895899

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Ew33895899

  1. 1. Dhavale A.S., Abhay Utpat / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.895-899895 | P a g e“Study of Stress Relief Features at Root of Teeth of Spur Gear”Dhavale A.S.*, Abhay Utpat***,** (Department of Mechanical, S.V.E.R.I. COE Pandharpur, India)ABSTRACT:Spur gear is cylindrical shaped gear inwhich the teeth are parallel to the axis. It is easy tomanufacture and it is mostly used in transmittingpower from one shaft to another shaft up to certaindistance & also used to vary the speed & Torque.The cost of replacement of spur gear is very highand also the system down time is one of the effectin which these gears are part of system. Failure ofgear causes breakdown of system which runs withhelp of gear. When gear is subjected to load, highstresses developed at the root of the teeth, Due tothese high stresses, possibility of fatigue failure atthe root of teeth of spur gear increases. There ishigher chance of fatigue failure at these locations.So to avoid fatigue failure of the gear, the stressesshould be minimized at maximum stressconcentrated area. Design of spur gear can beimproved by improving the quality of material,improving surface hardness by heat treatment,surface finishing methods. Apart from this stressalso occurs during its actual working.Hence it is important to minimize thestresses. These stresses can be minimized byintroducing stress relief features at stress zone.Many simulation packages are available forchecking the different values of stresses.Simulation is doesn’t give exact results but gives abrief idea where stresses are induced. Henceexperimental stress analysis method can also beadopted for studying stresses.Keywords: Spur gear, Stress, Simulation, Ansys1. INTRODUCTIONSpur gear is a cylindrical shaped gear inwhich the teeth are parallel to the axis. It is easy tomanufacture and it is mostly used in transmittingpower from one shaft to another shaft up to certaindistance & it is also used to vary the speed &Torque. e.g. Watches, gearbox etc.The cost of replacement of spur gear isvery high and also the system down time is one ofthe effect in which these gears are part of system.Failure of gear causes breakdown of system whichruns with help of gear. e.g. automobile vehicle.When gear is subjected to load, highstresses developed at the root of the teeth, Due tothese high Stresses, possibility of fatigue failure atthe root of teeth of spur gear increases. There ishigher chance of fatigue failure at these locations.So to avoid fatigue failure of the gear, the stressesshould be minimized at maximum stressconcentrated area. Design of spur gear can beimproved by improving the quality of material,improving surface hardness by heat treatment,surface finishing methods. Apart from this stressalso occurs during its actual working.Hence it is important to minimize thestresses. These stresses can be minimized byintroducing stress relief features at stress zone.Many simulation packages are available forchecking the different values of stresses.Simulation is doesn’t give exact results but gives abrief idea where stresses are induced. Henceexperimental stress analysis method can also beadopted for studying stresses:Gears have a wide variety of applications.Their applications vary from watches to very largemechanical units like the lifting devices andautomotives. Gears generally fail when the workingstress exceeds the maximum permissible stress.Number of studies has been done by variousauthors to analyse the gear for stresses. Gears havebeen analysed for different points of contact on thetooth profile and the corresponding points ofcontact on the pinion. In this studyThen the variation stress in root filletregion is found, which is then used for the study ofvariation of various parameters of stress reducingfeatures. The effect and use of stress relief featurein geometry of gear is studied as reported byresearchers. A study of the optimum size andlocation of the stress relief features for pinion andgear is proposed which help in reducing the fatiguefailure in gears.Gears are the most common means oftransmitting power in the modern mechanicalengineering world. They vary from a tiny size usedin watches to the large gears used in watches to thelarge gears used in lifting mechanisms and speedreducers. They form vital elements of main andancillary mechanisms in many machines such asautomobiles, tractors, metal cutting machine toolsetc. Toothed gears are used to change the speed andpower ratio as well as direction between input andoutput.Spur gear is a cylindrical shaped gear inwhich the teeth are parallel to the axis. It has thelargest applications and, also, it is the easiest tomanufacture. Spur gears are the most common typeused. Tooth contact is primarily rolling, withsliding occurring during engagement and
  2. 2. Dhavale A.S., Abhay Utpat / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.895-899896 | P a g edisengagement. Some noise is normal, but it maybecome objectionable at high speeds.2. LITRATURE REVIEWAndrews J.D, [1] investigated the finiteelement analysis of bending stresses in involutegears. This paper describes the use of the finiteelement method for predicting the fillet stressdistribution experienced by loaded spur gears. Thelocation of the finite element model boundary andthe element mesh density are investigated. Filletstresses predicted by the finite element model arecompared with the results of photoelasticexperiments. Both external and internal spur geartooth forms are considered.Costopoulos Th. [2] studied the reductionof gear fillet stresses by using one-sided involuteteeth. For increasing the load carrying capacity ofgeared power transmissions several tooth designsalternative to the standard involute have beenproposed. The use of non-involute teeth has anumber of disadvantages and for this reasonasymmetric involute-type teeth have been studiedas a promising alternative. In this paper the idea ofone-sided involute asymmetric spur gear teeth isintroduced to increase load carrying capacity andcombine the good meshing properties of the drivinginvolute and the increased strength of non involutecurves. These novel teeth are intended for constantdirection of rotation although they can be used in alimited way for reverse rotation. Both flanks arefully generated by a hob, the design of which isalso investigated. The increase in load carryingcapacity can reach up to 28% compared to thestandard 200involute teeth.Hebbal M.S, [3] explains the reduction inroot fillet stress in spur gear using internal stressrelieving features. Gear teeth failure due to fatigueis a common phenomenon observed. Even a slightreduction in the root tensile stress results in greatincrease in the fatigue life of a gear. If gear fails intensile fatigue, the results are catastrophic andoccur with little or no warnings. Therefore for allthe reasons mentioned above, this work is of morepractical importance. For many years, gear designhas been improved by using improved material,hardening surfaces with heat treatment andcarburization, and shot penning to improve surfacefinish etc. Few more efforts have been made toimprove the durability and strength by altering thepressure angle, using the asymmetric teeth, alteringthe geometry of root fillet curve and so on. Most ofthe above methods do not guarantee theinterchangeability of the existing gear systems.This work presents the possibilities of using thestress redistribution techniques by introducing thestress relieving features in the stressed zone to theadvantage of reduction of root fillet stress in spurgear. It also ensures interchangeability of theexisting gear systems. In this work, combination ofcircular and elliptical stress relieving features areused and better results are obtained than usingcircular stress relieving features alone which wereused by earlier researchers. A finite element modelwith a segment of three teeth is considered foranalysis and stress relieving features of varioussizes are introduced on gear teeth at variouslocations. Analysis revealed that, combination ofelliptical and circular stress relieving features atspecific, locations are beneficial than singlecircular, single elliptical, two circular or twoelliptical stress reliving features.Senthil Kumar V. [4] focused theoptimization of asymmetric spur gear drives toimprove the bending load capacity. In a given sizeof symmetric involute gear designed throughconventional approach, as the load carryingcapacity is restricted at the higher pressure angledue to tipping formation, the use of the asymmetrictoothed gear to improve the fillet capacity inbending is examined in this study. Non-standardasymmetric rack cutters with required pressureangles and module are developed to generate therequired pinion and gear of a drive withasymmetric involute surfaces and trochoidal filletprofiles. The respective profiles thus generated areoptimized for balanced fillet stresses that are equaland possibly the lowest also. For this study ofoptimization, several non-standard asymmetric rackcutters are designed to accommodate differentcombinations in the values of pressure angle, topland thickness ratio, profile shift, speed ratio andthe asymmetric factors. However for any drive witha given center distance and a speed ratio, only twonon-standard asymmetric rack cutters, one for thepinion and other for the gear are used to generate arequired numbers of pinion and gear with differentcutter shift values for the purpose of optimization.The influence of these parameters on the maximumfillet stress has been analyzed to suggest theoptimum values of these parameters that improvethe fillet capacity in bending. The optimization ofthe asymmetric spur gear drive is carried out usingan iterative procedure on the calculated maximumfillet stresses through FEM for different rack cuttershifts and finally the optimum values of rack cuttershifts are suggested for the given center distanceand the speed ratio of an asymmetric gear drive.Comparisons have also been made successfullywith the results of the AGMA and the ISO codesfor symmetric gears to justify the results of thefinite element method pertaining to this study.Ulrich T.W.[5] explains the auxiliaryholes for stress reduction. Stress concentrationreduction in a plate is accomplished by introducingoptimum size holes and regularly placed. Thispaper presents a method based on boundaryelements and mathematical programming todetermine these auxiliary holes. The mathematicalprogramming method consists of a modified
  3. 3. Dhavale A.S., Abhay Utpat / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.895-899897 | P a g eNewtons method and subsequent parallel tangentsmethod (PARTAN). A solution is presented for anelliptical hole in a tension strip.3. ANALYSISA finite element model with segment offive teeth is considered for analysis. A point load of300N is applied at the teeth are meshed with twodimensional nodes. The boundary conditions used,program is developed in ansys to automate theprocess of geometry creation, meshing, applyingboundary conditions and displaying the results.Gear teq software is used for geometry of gearteeth, the location and size of the stress relievingfeatures A spur gear with module 20 mm, numberof teeth 20, pressure angle 20 degrees is consideredfor analysis. The FEA results of root fillet stresswithout holes are compared with the stresscalculated using the gear root fillet stress withholes. The maximum principal stress is obtainedwithout any stress relieving features. Used forstress reliving feature.Configurations of stress reliving featureused, for the various analyses are as follows:• Circular stress reliving feature of different sizesand at same location (Varying dia.2 holes).• Circular stress reliving feature of same size atdifferent locations (1 hole).• Circular stress reliving feature of same size atdifferent locations (fixing the dia. of 2 hole).3.1 Stress relief features of different sizes and atsame location (2Holes)Application of Stress relief features ofdifferent sizes and at same location (with 2 Holes)is shown in Fig. 1 Diameter of hole varies from1mm to 9 mm and at the same time locations ofholes is kept same. For first hole value for X axis=9.39 mm and for Y axis= 13.86 mm. For secondhole value for X axis =13.47 mm and for Y axis=9.87 mm. Stress value is minimum for diameter 8mm 6.353 N/mm2Fig. 1. Equivalent stress maximum for diameter8 mmTable 1 Stress relief features of different sizes andat same location (2Holes)3.2 Stress relief features of same size at differentlocations (1- hole)Application of Stress relief features ofsame sizes and at different location (with 1 Holes)is shown in Fig.2 Diameter of hole is same 8 mmand at the same time locations of holes are varies.For first hole value for X axis Varies in betweenfor x axis 9.39 mm to 15.39 mm and for Y axis inbetween 13.11 to 14.65 mm. varying location forgetting minimum value of stress at that location.Fig. 2 Equivalent stress maximum for locationX=9.39 mm and Y= 13.86 mmTable 2 Stress relief features of same size atdifferent locations (1- hole)
  4. 4. Dhavale A.S., Abhay Utpat / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.895-899898 | P a g e3.3 Stress relief features of same size at differentlocations (two holes)Application of Stress relief features ofsame sizes and at different location (with 2 Holes)is shown in Fig.3 Diameter of hole is same 8 mmand at the same time locations of holes are varies.For first hole value for X axis 9.39 mm and for Yaxis in between 13.9 mm. and at the same timevarying locations for another hole for X axis=13.23 mm to 13.79 mm, For Y axis = 9.46 mm to12.54 mm.Fig. 3. Equivalent stress maximum for diameter 8mm with 2 holesTable 3 Stress relief features of same size atdifferent locations (two holes)4. RESULT AND DISCUSSIONIt is seen that the maximum principalstress at root fillet is 7.5 N/mm2without any stressrelieving features Maximum principal stress v/sorientation of major axis of the circular stressreliving features at more beneficial locations andcombination of size, are plotted in Fig. 4.Principal stresses in the gear segment withcircular stress reliving features are as shown in Fig.3. Different cases are considered for analysischoosing different values of parameters viz. size ofhole, locations of holes and hole and varyingnumber of holes.Analysis shows that the case with twocircular holes having parameters for 1sthole, x=9.39 mm, y= 13.86 mm, and 2ndhole, x= 13.47mm, y= 9.87 mm. shows the greater benefit incomparison with other cases.As the location of stress relieving featureapproaches the high stress effective zone up to acertain value, the results are found to be beneficial.Later on the benefit reduces, it indicating that thebenefit becomes more sensitive as the location ofthe stress relieving features approaches the zone ofstress concentration to a certain value only.It is important to note that introduction ofmore than one stress relieving feature has addedadvantages In one of the most beneficial locationprincipal stresses in the gear segment with acombination of two circular stress reliving featuresare as shown in Fig. 3. A maximum of 15%reduction in maximum principal stress is obtained.Fig. 3 shows the stress pattern in gear with thecombination of two circular stress relieving featureobtained in the above analysis at the mostbeneficial location. Fig. 4 shows a diameter of holevs equivalent Stress
  5. 5. Dhavale A.S., Abhay Utpat / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.895-899899 | P a g eFig 4 Diameter of hole Vs Equivalent StressMaximumFig 5 Position of hole Vs Equivalent Stress Max6. CONCLUSIONSingle stress reliving features did notimprove gear stress. stress reduction by means ofintroducing of stress reliving feature is possible.Stress redistribution is highly sensitive to thechange in size, Location and Number so select size,Location and Number very carefully. Using twoholes as a stress reliving features gives more stressreduction. Small variation in size, location andnumber gives large difference in equivalent stress.Introduction of stress reliving feature at specificlocation of specific size and number givesmaximum reliving of stress otherwise strength ofgear reduces.REFERENCES1. Andrews J.D. (1991) – “A Finite ElementAnalysis of Bending Stresses induced inexternal and internal involute spurgears”, The Journal of Strain Analysis forEngineering Design, page no.153-163.2. Costopoulos Th. Spitas V. (2009) –“Reduction of gear fillet stresses by usingone-sided involute asymmetric teeth”,page no.1524 – 1534.3. Hebbal M. S., Math V. B., SheeparamattiB. G. (2009) – “A Study on Reducing theRoot Fillet Stress in Spur Gear UsingInternal Stress Relieving Feature ofDifferent Shapes”, International Journalof Recent Trends in Engineering, Vol. 1,No. 5, May 2009, page no.163 – 165.4. Senthil Kumar V., Muni D.V.,Muthuveerappan G. (2008) –“Optimization of asymmetric spur geardrives to improve the bending loadcapacity”, Mechanism and MachineTheory, page no. 829 – 858.5. Ulrich T.W., Moslehy F.A. (1995) – “Aboundary element method for stressreduction by optimal auxiliary holes”,Engg. Analysis with Boundary elements,page no. 219 – 223.0.002.004.006.008.0010.0012.00 135797.58.18.25EquivalentStressMaximumDiameter Of Holes (mm)Equivalent StressMaximum(N/mm2)0501001502002503003504004502 4 6 8 10 12 14 16EquivalentStress(Mpa)POSITION OF HOLES ( X,Y)Equivalent StressMaximum( Mpa)

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