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 total = elastic + plastic + creep For uniaxial case: elastic = / E ; plastic = A n ; d creep dt = o o 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 H = 7.4 10 10 H 5 exp Q / RT ( ) s-1 , where Q = 160 kJ/mole, R = 8.31 J/mol.K, and 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 = 30 MPa at 600 C: = 4.75 10 1 2 s 1 o = elastic + creep d o dt = d elastic dt + d creep dt d o dt = d / E ( ) dt + 7.4 10 10 5 exp Q / RT ( ) s-1 ( in MPa) But if = 30 MPa & independent of time: d o dt = 4.75 10 12 o = 4.75 10 12 t + ( ) (0) = 3 x10 6 /100x10 9 = 3.00x10-4 After 10,000 hours(3.6x10 7 s) 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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