Creep Lecture1 0823

8/13/2019 Creep Lecture1 0823

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!"# !"#$%&""%&''( ') *+,-+../-+,

CREEP - AME 559

Fall 2011


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Latest edition

Elsevier, 2009

1st edition

Elsevier, 2004


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References: (i) M.E. Kassner and M.T. Perez-Prado, Prog. Mater. Sci. 45(2000), p.1.

(ii) !" $%&'(%)'* +Fundamentals of creep and creep rupture inmetals ,* -%./0))%1* 2345 67849"$:4

(iiI;


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AME 559 - Fall 2011

Class schedule:

Course Syllabus

Week Date Lecture Topics1 8/23 Introduction

8/25 Phenomenological approach2 8/30 Analysis of activation energy

9/1 Factors influencing activation energy I

3 9/6 Factors influencing activation energy II9/8 Factors influencing activation energy III4 9/13 Stress dependence of creep I

9/15 Stress dependence of creep II5 9/20 Stress dependence of secondary creep rate I

9/22 Stress dependence of secondary creep rate II6 9/27 Power-law creep I

9/297 10/4 Mid-term Exam

10/6


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AME 559 - Fall 2011

15 11/29 Creep fracture III12/1 ( )

12/8 (Th): Final Exam (2-4 p.m.)

Week Date Lecture Topics8 10/11

10/13

9 10/18 Power-law creep II10/20 Creep equation

10 10/25 Three-Power-law creep10/27 Structure dependence of Creep I

11 11/1 Structure dependence of Creep II

11/3 Structure dependence of Creep III12 11/8 Creep mechanism I

11/10 Creep mechanism II13 11/15 Superplasticity

11/17 Creep fracture I

14 11/22 Creep fracture II11/24 Thanksgiving recess


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0

2

4

6

8

10

12

-70 71-75 76-80 81-85 86-90 91-95 96-100

Number ofstudents

Total points

Final score (Fall 2009)

Homework: 10%Term paper: 20%1 Midterm Exam: 25%Final Exam: 45%

AME 559 - Fall 2011Course Syllabus

Grading:

Mid-term Exams:80 minutes, in class

Final Exam:120 minutes, December 8 (Th), 2-4 p.m.

0

1

2

3

4

5

-70 71-75 76-80 81-85 86-90 91-95 96-

100

Number ofstudents

Total points

Final score (Fall 2010)


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Choose a journal paper (not conferences or company reports,etc.) regarding to creep, write a short critical review paper.The target paper should be selected and approved no later than November 1 . The paper can be submitted until the lastclass ( November 29 ).

Format: Abstract (~200 words)Review (10)

Recommended journals:

Acta MaterialiaPhilosophical Magazine AMetallurgical and materials transactions AMaterials science & engineering AScripta Materialia

Journal of materials science

AME 559 - Fall 2011

Term paper:Course Syllabus


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Writing a critical review paper:Focus on the content (e.g. experimental materials, experimental

methods, experimental results & discussion).The contents you have to understand and evaluate include;

(1) The purpose of the paper

(2) The hypothesis of the experiments

(3) The experimental set-up(4) The experimental results (well-presented? Reliable? Sufficient?)

(5) Discussion (able to explain all the results? Anything make itoriginal? Well-demonstrated?)

(6) Conclusions (well-supported? Meet the original goal?)

Abstract (~200 words)Review (


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Finding Journal papers


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I. Introduction


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Definition:

H Creep occurs at all temperatures above 0 K.

H Creep is only important at temperatures I 0.5 T m.

Creep is +time-dependent , deformation of materialsoccurring at constant stress, ! , and temperature, T .

Lead (Pb) T m = 327 C = 600 K T RT = 0.5 T m


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1800 1900 2000

0

100

200

300

400

T e m p .

f o r o p e r a

t i n g p

l a n t

o n

i n d u s t r y

( e . g .

b o

i l e r )

C

year

use any steelNeedcreep-resistance

Why is creep important ?

Creep is important in all systems:

engines, turbines, piping, rockets, etc.(Also important in glaciers, ice flow,moment of rocks in earth.)

steam turbine used in apower plant
http://en.wikipedia.org/wiki/File:Dampfturbine_Laeufer01.jpg


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Need creep-resistant alloys


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Level A J .'1=01>B ?B&K0.B C>= /'10='& F%/%LB %= : DB%& 01=B&K%)?;MBKB) N J .'1=01>B ?B&K0.B C>= (0O 01?EB.=0'1 01=B&K%)? %= 2"5 DB%&?P

MBKB) Q J )0/0=BF ?B&K0.B 0? E'??0C)B >1=0) &BE%0&P

MBKB) R J &BE%0& 0//BF0%=B)D.


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Damage parameters are different for the same material used indifferent conditions.

HGas turbine blades:0.0001% per hour (1% in 10,000 hours)

HSteam turbines:0.00001% per hour (1% in 100,000 hours S 11.5 years)

HNuclear reactors:0.2% in 200,800 hours (~22 years)

Creep rate: % / hour

Example: Minimum creep rate interested to design engineers

Hot working of metalsEngineering creep

10 610 -6 1

Experimental creep tests


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10 -15 10 -12 10 -9 10 -6 10 -3 10 0 10 3 10 6

geologyNormal design

code

Creep testing

Standardtensile test

Industrialprocesses

(Forging, Rolling, Extrusion, Drawing)

Dynamic

testing

Explosive

testing

constant T

)(s -1 log !!

"log

Variation of ! with !!


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Comparison between creep & fatigue:

Fatigue

1. Cyclic stress (


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Important definitions and parameters:

1. Mechanical process

Applied stress Applied shear stressTrue strain (rate of change of instant length)Engineering strain (rate of change of initial length)Shear strain

Strain rate

Shear strain rate

1! e "#"#

o o

o

l l

l l l

$ %1!lnln! e ## 'o

l

l

l

l

l

dl o

!!

where l is instantaneous lengthand l o is initial length.

#!

"$!

e!#

t d

d !#

t d

d ##


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2. Diffusion process

D Diffusion coefficient

)/exp( RT Q D D o "#where D o is frequency factor, Q is activation energy fordiffusion in kJ/mol and R is gas constant (8.31 J/mol ! K) .

D gb Grain boundary diffusion coefficientD l Lattice diffusion coefficient

U Activation energy in eV

k Boltzmann V? .'1?=%1= W2":X4 Y10 -29 MPa ! m3/K )T m Melting temperature of a material

)/exp( k T U D D o "#

S Entropy

( Atomic volume [ ( " 0.7 b 3 ]

1 kcal/mol = 4.19 kJ/mol


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3. Elasticity

G Shear modulusE Z'>1LV? modulus! ['0??'1V? ratio

12

"#G E

)

4. Special symbols for creep structural terms

d Grain sizeS +\=&>.=>&B =B&/," Width of grain boundaryb Burgers vector of dislocation* density of dislocations


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H.J. Frost and M.F. Ashby, D e f or m a t ion-M ec hani s m Map s ; Th e Pla st i c i t yand Cr ee p o f M e t al s and C e ra m i c s , Pergamon Press, Oxford, UK, (1982)

For pure metals,

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Creep Lecture1 0823

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