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ENGINEERING DESIGNbatch-3

Design of a component considering the axial stresses basedon the following theories of failurei)Maximum principal stress thoery.ii)Maximum shear stress theory.

PRESENTED BYM.AHILESH-10A201A.G.KIRANPRAKASH-10A219R.NIRMAL-10A228V.SAI PRASANTH-10A242S.UDAYAKUMAR-10A255

R.KALAISELVAN-10A436

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STRESSES:When an external force acts on a material,the internalresisting force developed per unit area of the material iscalled stress.

AXIAL STRESSS:The stresses acting along the axis of the component arecalled axial stresses.TENSILE AND COMPRESSIVE STRESSES:The axial stress is known as tensile if the componentelongates in length due to the external force .The axial stress is known as compressive if thecomponent reduces in length due to the external force.

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Tensile or compressive stress= load/area=P/A

Unit-N/mm 2

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PRINCIPAL STRESSES:Principal stresses are consideration of both axial and shear stress.

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THEORIES OF FAILURE:• Applicable to elastic failure of machine parts• Help to determine the dimensions of the components based on the

mechanical properties obtained from tension test in addition toconsideration of torsional and bending stress which it may undergo whileoperating.

• We are going to consider,

1.Maximum principal stress theory(R ankine’s theory) 2Maximum shear stress theory(Coulomb,Tresca and Guest’s theory) 1.MAXIMUM PRINCIPAL STRESS THEORY:• This theory states that the failure of the mechanical component subjected

to biaxial or triaxial stresses occurs when maximum principal stress reaches

the yield or ultimate strength of the material.i.e. σ1=Syt or Sut• Considers only the influence of maximum principal stress.• The dimensions of the component is designed using the relation,

σ1=Syt or Sut /fos

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• The maximum principal stress theory ignores the possibility of failure due

to shear stress and mostly not applied for ductile materials.

• For brittle materials which are relatively stronger to shear but weak

intension/compression , this theory is suited well.

2.MAXIMUM SHEAR STRESS THEORY:•

This theory states that the failure of a mechanical component subjected tobiaxial or triaxial stresses occur when the maximum shear stress at any

point in the component becomes equal to he maximum shear stress in the

standard specimen τof tension test, when yielding starts i.e. at yield point.

τmax= τyt/fos

τmax= σyt/2 x fos

τyt=0.5 σyt

•

This theory is most suitable for the designing of ductile material.

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