Lecture30-Notes

# Lecture30-Notes - ME 382 Lecture 30 1 C OMBINED MODELING OF...

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Unformatted text preview: ME 382 Lecture 30 1 C OMBINED MODELING OF CREEP , ELASTIC AND PLASTIC DEFORMATION • Total strain consists of elastic + plastic +creep component ε total = ε elastic + ε plastic + ε creep • For uniaxial case: ε elastic = σ / E ; ε plastic = A σ n ; d ε creep dt = ˙ ε o σ σ o Λ Ν Μ Ξ Π Ο n • Represented by a spring, dash-pot and friction element Example: Assume that an alloy with a modulus of 100 GPa exhibits steady-state power-law creep of the form ˙ ˜ ε H = 7.4 × 10 − 10 ˜ σ H 5 exp − Q / RT ( ) s-1 , where Q = 160 kJ/mole, R = 8.31 J/mol.K, and ˜ σ H is in MPa. An applied uniaxial stress of 30 MPa is applied. What is the strain after 10,000 hours at 600 ° C? Creep rate with σ = 30 MPa at 600 ° C: ˙ ε = 4.75 × 10 − 1 2 s − 1 ε o = ε elastic + ε creep ∴ d ε o dt = d ε elastic dt + d ε creep dt ∴ d ε o dt = d σ / E ( ) dt + 7.4 × 10 − 10 σ 5 exp − Q / RT ( ) s-1 ( σ in MPa) But if σ = 30 MPa & independent of time: d ε o dt = 4.75 × 10 − 12 ∴ ε o = 4.75 × 10 − 12 t + ε ( ) ε (0) = 3 x10 6 /100x10 9 = 3.00x10-4 ∴ After 10,000 hours(3.6x10 7 s) ε o = 3.00 x 10-4 + 1.71 x 10-4 = 4.7 x 10-4 If stress removed, then permanent strain = 1.7 x 10-4 ....
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Lecture30-Notes - ME 382 Lecture 30 1 C OMBINED MODELING OF...

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