A project seminar onFINITE ELEMENT ANALYSIS OF A GEAR TOOTH
USING ANSYS AND STRESS REDUCTION BY STRESS RELIEF
HOLEByP.BRAHMESHWAR RAO G.SURYA MOHAN REDDY M.HEMANTH K.V.ANURAG
REDDY (08145A0310) (07141A0309) (07141A0305) (07141A0310)
Under the guidance ofMr. Y.NAVEEN (Asst.Proffessor)
ABSTRACT
The main aim of this project is to model a spur gear by PRO-E.
The model is then imported to ANSYS.
To reduce the stress in a gear tooth, with the help of a
stressrelief hole, to the minimum value, without affecting the
quality.
PROJECT OVERVIEW
A plane area element (plane stress with thickness) was chosen
and the model for the gear tooth whose stress was to be studied,
was created and the Von Misses stress was calculated. Then various
case studies were conducted using a stress relief hole at different
positions and the Von Misses stress value in each case was compared
with the Von Misses stress value without hole.
After a number of case studies, we were able to optimize the
position of the hole, because of which, stress in the gear tooth
was the minimum.
INTRODUCTION ABOUT GEARS
Gears are used to transmit motion from one shaft to another or
between a shaft and slide, this can be accomplished by successively
engaging teeth. Gears use no intermediate link or connector &
transmit the motion by direct contact. The two bodies have either a
rolling or a sliding motion along the tangent at point of contact
and no motion is possible along the common normal. Gear design has
evolved to such a level that throughout the motion of each
contacting pair of teeth the velocity ratio of the gears is
maintained fixed and the velocity ratio is still fixed as each
subsequent pair of teeth come into contact.
GEAR TERMINOLOGY:
Addendum circle Dedendum circle Addendum Dedendum Clearance Face
of tooth Flank of tooth Circular pitch Pitch point Base circle
CLASSIFICATION OF GEARS 1)
2.
3)
Gears are classified according to the relative position of their
shaft axes as follows. Parallel shaft Spur gears Helical gears
Herringbone gear Intersecting shaft Straight bevel gears Spiral
gears Zerol bevel gears Skew shaft Crossed helical gears Worm
gears
SPUR GEAR
Spur gears have straight teeth parallel to the axis and thus,
are not subjected to axial thrust due to tooth load.
At the time of engagement of the two gears, the contact extends
across the entire width on a line parallel to the axis of rotation.
This results in sudden application of load, high impact stress and
excessive noise at high speeds.
HELICAL GEAR
In helical gear, the teeth are curved, each being helical in
shape.
At the beginning of engagement, contact occurs only at the point
of leading edge of the curved teeth. As the gear rotates, the
contact extends along the diagonal line across the teeth. Thus the
load application is gradual which results in low impact stresses
and reduction in noise . Therefore helical gears can be used at
high velocities than spur gears and have greater load carrying
capacity
BEVEL GEARS
STRAIGHT BEVEL GEARS : The teeth are straight , radial to the
point of intersection of the shaft axes and vary in cross section
through out their length.
SPIRAL BEVEL GEAR: When the teeth of the bevel are inclined at
an angle to the face of the bevel , they are known as Spiral or
helical bevels.
ZEROL BEVEL GEARS: Spiral bevel gears with curved teeth but with
a zero degree spiral angle are known as Zerol bevel gears
WORM GEAR
Worm gear is a special case of a spiral gear
In which the larger wheel, usually, has a hallow or concave
shape such that a portion of the pitch diameter of the other gear
is enveloped on it.
The smaller of the two wheel is called the worm which also has a
large spiral angle
ADVANTAGES:
Provide Positive Drive without slip. Suitable for high speed ,
high torque & high power transmission. Properly designed &
properly maintained gear system can run over decades. Very high
transmission ratio is practicable.
Compact machine train in limited space.
DISADVANTAGES:
Needs Proper Lubrication System. which involve high cost.Needs
Proper alignment- misaligned gear train will damage within very
short time. Misaligned gear mesh or lack of lubrication will make
noise & vibration. Spare gear is costly and proper replacement
gear is difficult to procure in many cases it is available only
from OEM source. Require skilled technician to maintain.
TYPES OF FAILURES IN GEARS
Moderate wear
Pitting
Rippling
Ridging
Materials
NotesFerrous
Applications
Cast Iron
Low cost easy to machine with high damping
Large moderate power, commercial gears
Cast Steels
Low cost reasonable strength
Power gears with medium rating to commercial qualityPower gears
with medium rating to commercial/medium quality
Plain carbon steels
Good machining can be heat treated
Alloy Steels
Heat Treatable to provide highest strength and durability
Highest power requirement. For precision and high precision
Stainless Steels (Aust)
Good corrosion resistance. Non magnetic.
Corrosion resistance with low power ratings. Up to precision
quality Low to medium power ratings Up to high precision levels of
quality
Stainless Steels (Mart)
Hardenable , reasonable, corrosion resistance , magnetic
Non-ferrous metals Aluminium alloys Light weight ,non corrosive
and good mach inability Light duty instrument gears up to high
precision quality
Brass alloysBronze alloys Magnesium alloys Nickel alloys
Titanium alloys Di-cast alloys Sintered powder alloys
Low cost, non-corrosive, excellent machinabilityExcellent
machinability low friction and good compatibility with steel Light
weight with poor corrosion resistance. Low coefficient of thermal
expansion. poor machinability High strength, for low weight, good
corrosion resistance Low cost with low precision and strength Low
cost low quality, moderate strength
low cost commercial quality gears. Quality up to medium
precisionFor use with steel power gears. Quality up to high
precision Light weight low load gears. Quality up to medium
precision Special gears for thermal applications to commercial
quality Special light weight high strength gears to medium
precision High production, low quality gears to commercial quality
High production, low quality to moderate commercial quality
Gear has been developed by using PRO-E
COMMANDS USED
Curve id(by using program) Sketch 1 Extrude 1 Extrude cut 2
Pattern of Extrude 2 Round 1 Round 2
PROGRAM TO GENERATE CURVE ID
/* For cylindrical coordinate system, enter parametric equation
/* in terms of t (which will vary from 0 to 1) for r, theta and z
/* For example: for a circle in x-y plane, centered at origin /*
and radius = 4, the parametric equations will be: /* r=4 /* theta =
t * 360 /* z=0
/*------------------------------------------------------------------N
o t=17 P angle=20 M =8 x=.15 O d=128 R d=92
P cd=not*m
B cd=p cd*cos(p angle)R base=b cd/2
T t=(((3.141592654)*m)/2)+(2*m*x*tan ( pangle ))K =b cd*((tt/
pcd)+((tan(pangle)-((pangle*(3.141592654)))/180)))
Gamma
=(((bcd*(3.141592654))-(not*k))/(not*2))*(360/(bcd*(3.141592654)))R
=r base/(cos(t*40))
Inv =tan(t*40)-(((t*40)*(3.141592654))/180)Theta
=(((inv*180)/3.141592654)+gamma) Z =0
Spline is generated by using program
STRESS CONCENTRATION
The fracture of a material is dependent upon the forces that
exist between the atoms. Because of the forces that exist between
the atoms, there is a theoretical strength that is typically
estimated to be one-tenth of the elastic modulus of the material.
The stress is concentrated around the crack tip or flaw developing
the concept of stress concentration.
METHODS TO REDUCE STRESS CONCENTRATIONA number of methods are
available to reduce stress concentration in machine parts. Some of
them are as follows: 1. Provide a fillet radius so that the
cross-section may change gradually. 2. Sometimes an elliptical
fillet is also used. 3. If a notch is unavoidable it is better to
provide a number of small notches rather than a long one. This
reduces the stress concentration to a large extent. 4. If a
projection is unavoidable from design considerations it is
preferable to provide a narrow notch than a wide notch.
SURFACE WHICH IS TO BE ANALYSED1VOLUMES TYPE NUM MAR 16 2011
13:20:36
Y Z X
1NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) DMX =.075412 SMN
=.211E-04 SMX =136.713 MAR 16 2011 13:18:11MN
YMX
Z
X
.211E-04
15.19
30.381
45.571
60.761
75.952
91.142
106.332
121.523
136.713
Without hole von misses stress = 136.716N/mm2
1
MN
NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics
EFACET=1 AVRES=Mat DMX =.075724 SMN =.204E-04 SMX =133.361 YMX
Z
X
XV =1 YV =2 ZV =3 DIST=100.909 XF =-.366964 YF =.183072 ZF
=-.001143 Z-BUFFER .204E-04 14.818 29.636 44.454 59.271 74.089
88.907 103.725 118.543 133.361
Position of the hole :x=30,y=60,dia=3 Von misses stress
value=133.36 N/mm2
1
MN
NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics
EFACET=1 AVRES=Mat DMX =.075491 SMN =.170E-04 SMX =136.212 XV =1 YV
=2 ZV =3 DIST=100.909 XF =-.365144 YF =.185921 ZF =-.001269
Z-BUFFER .170E-04 15.135 30.269 45.404 60.539 75.673 90.808 105.943
121.077 136.212
YMX
Z
X
Position of the hole : x=30,y63,dia=1mm Von misses stress value
= 136.212N/mm2
1
MN
NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics
EFACET=1 AVRES=Mat DMX =.075717 SMN =.289E-04 SMX =135.663 XV =1 YV
=2 ZV =3 DIST=100.91 XF =-.367417 YF =.182698 ZF =-.001001 Z-BUFFER
.289E-04 15.074 30.147 45.221 60.295 75.368 90.442 105.516 120.589
135.663
YMX
Z
X
Position of the hole :x=28,y=58,dia=3 Von misses stress value =
135.663N/mm2
1
MN
NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics
EFACET=1 AVRES=Mat DMX =.075632 SMN =.221E-04 SMX =135.639 XV =1 YV
=2 ZV =3 DIST=100.909 XF =-.367262 YF =.18355 ZF =.357E-03 Z-BUFFER
.221E-04 15.071 30.142 45.213 60.284 75.355 90.426 105.497 120.568
135.639
YMX
Z
X
Position of the hole :x=35, y=60,dia=2mm Von misses stress =
135.639N/mm2
CONCLUSION:By creating hole in the gear, we can alter stress in
the gear. Stress reduction is neither directly nor inversely
proportional to the Stress Relief
Hole Diameter. Stress Reduction is neither directly nor
inverselyproportional to the position of the stress relief hole.
Horizontal shift of the hole position has larger effect on the
stress value then the vertical shift.
Better results on stress reduction, were observed on the
negative side of theload point, for each tooth By optimizing the
diameter and position of the stress relief hole, we can reduce the
stress value in a gear tooth by a considerable amount, without
affecting the functioning of the gear (In this problem, we could
reduce stress from 136.731N/mmA2 to 133.36 N/mmA2 at x=30,y=20 with
hole dia 3)
QUERIES ?
THANK YOU