Lecture10-Notes - ME 382 Lecture 10 YIELD CRITERIA Yield is...

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ME 382 Lecture 10 1 Y IELD C RITERIA Yield is a shear driven process Tresca yield criterion Yield occurs when shear stress on any plane equals k (shear yield strength) Loading parameter: τ max(1-2) or τ max(2-3) or τ max(1-3) Material parameter: k Tresca yield criterion: τ max(1 2) or max( 2 3 ) or max(1 3) k Example: Uniaxial test ( σ xx = σ ο ) From Mohr’s circle: τ max = σ o /2 yield when σ o /2 k Uniaxial yield stress: σ Y = 2 k (by Tresca) Tresca yield criterion can also be stated by defining an effective normal stress : σ S = max 1 2 , 2 3 , 1 3 ( ) Loading parameter: S Material property: σ Y Tresca yield criterion: S Y For uniaxial loading this reduces to the special case of σ o σ Y Example Torsion of a cylinder (assume material property for yield is σ Y ): Maximum shear stress on surface of cylinder θ z = o = TR / J
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ME 382 Lecture 10 2 τ r θ = rz = σ θθ = rr = zz = 0 11 = ο , 22 = - , 33 = 0 Loading parameter: s = 2 o Yield if Y /2 (or if τ ο k ) Example: σ 1 = 150 MPa, σ 2 = 50 MPa, σ 3 = 0 MPa. Does yield occur if σ Y = 200 MPa?
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This note was uploaded on 09/08/2011 for the course MECHENG 382 taught by Professor Thouless during the Fall '08 term at University of Michigan.

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Lecture10-Notes - ME 382 Lecture 10 YIELD CRITERIA Yield is...

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