role of shot peening in fatigue life improvement of metals · some common fields of shot peening...
TRANSCRIPT
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Role Of Shot Peening In Fatigue
Life Improvement Of Metals
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Overview
Ø Introduction
Ø Mechanical causes of fatigue failure
Ø Shot peening equipment
Ø Shot peening control
Ø Shot peening applications
Ø conclusion
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IntroductionØ Cold working process.
Ø Used to produce a compressive residual stress layer.
Ø Modifies mechanical properties of metal like increasing strength & hardness.
Ø Done by bombarding shots.
Ø Prevents formation of cracks, thus increasing the fatigue life of component.
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Mechanical causes of fatigue failure
Ø Residual Stresses from Surface
Finishing
Highly finished surfaces & fillets may lead to a false sense of security if the parts have highly residual stresses as the result of machining or straightening operations.
Ø Residual Stresses from Thermal Gradient
Internal stresses may occur in components where instantaneous temperature in a thin top surface layer is so great that its stressed by thermal expansion.
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Ø Residual Stresses from Processing
Many parts such as crankshafts, camshafts require straightening. This is usually done at room temperatures & the parts are rarely stress relieved.
Ø Size & Distribution of Internal Defects
Ø Environment
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Shot peening equipmentAirless Peening
MachinePneumatic Peening
MachineHigh cost of plants but low
cleaning costLow cost of plants
High maintenanceSimple to operate & negligible
maintenance
Lack of flexibility Extremely flexible
High production ratesLow & medium production
rates
Use of limited size of media Fine to very fine sizes of media can be used
Limitations: Distortion of material, Immobile
Unlimited scope
Mostly suitable for in-house operations
Suitable for in-house & outdoor operations
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Shot peening controlØ Shot Material & Its
Hardness
Shots used are usually of
cast steel with hardness of
40-50 on Rockwell C scale.
Ø Shape & Size of Shots
The shots or beads should
be free from sharp edges
& deformed shapes.
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Ø Shot Velocity & Impact Angle
Higher the shot velocity more will be the work done, & more will be the effect of shot peening process.
Ø Shot Peening Intensity
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Shot peening applications
Some common fields of shot peening application are:
Ø Vehicles & agricultural machinery.
Ø Power drive & transmission system.
Ø Internal combustion engines.
Ø Steam & gas turbines.
Ø Aviation equipment.
Ø Chemical equipment.
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Shot peening of gearsØ Excellent means of increasing beam strength of gears
with high load carrying capacity.
Ø Highest concentration of stress is in the tooth fillets at the gear roots.
Ø Subjected to bending fatigue failure.
Ø Shot peening treatment is generally applied to tooth fillets only.
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Shot peening of welds
Ø Regular welds fail after 250,000 cycles.
Ø Shot peened welds fail after 2.5 million cycles, that too outside the weld area.
Ø Popular operation with aerospace equipment parts.
Ø Improves property performance by cancelling residual tensile stresses that develop in surfaces as welds cool.
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Ø Fatigue tests on springs showed peened springs to have longer life than unpeened ones.
Ø Shot peening of springs is performed in batch type equipment where a centrifugal wheel is used to propel the shots.
Shot peening of springs
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Ø Excellent corrosion resistance, austenitic 316L SS is used in wide range of environments.
Ø Presents relatively low strength & poor wear resistance.
Ø Thus its treated with shot peening process to increase its strength & wear resistance, without any loss of corrosion resistance & ductility.
Shot peening of Stainless steel
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conclusion
Thus its concluded that shot peening results in increasing the fatigue life of components by inducing a layer of compressive stress on the surface of the metal.
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Thank You