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Computational Solid Mechanics Computational Plasticity C. Agelet de Saracibar ETS Ingenieros de Caminos, Canales y Puertos, Universidad Politécnica de Cataluña (UPC), Barcelona, Spain International Center for Numerical Methods in Engineering (CIMNE), Barcelona, Spain Chapter 1. 1D Plasticity Models

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Computational Solid MechanicsComputational Plasticity1D Plasticity Models

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  • Computational Solid Mechanics Computational Plasticity

    C. Agelet de Saracibar ETS Ingenieros de Caminos, Canales y Puertos, Universidad Politcnica de Catalua (UPC), Barcelona, Spain

    International Center for Numerical Methods in Engineering (CIMNE), Barcelona, Spain

    Chapter 1. 1D Plasticity Models

  • Contents 1. 1D Rate independent plasticity models

    1. Motivation 2. Perfect plasticity model 3. Hardening plasticity model

    2. 1D Rate dependent plasticity models 1. Motivation 2. Perfect plasticity model 3. Hardening plasticity model

    1D Plasticity Models > Contents

    Contents

    April 1, 2015 Carlos Agelet de Saracibar 2

  • Contents 1. 1D Rate independent plasticity models

    1. Motivation 2. Perfect plasticity model 3. Hardening plasticity model

    2. 1D Rate dependent plasticity models 1. Motivation 2. Perfect plasticity model 3. Hardening plasticity model

    1D Plasticity Models > Contents

    Contents

    April 1, 2015 Carlos Agelet de Saracibar 3

  • Physical and rheological models: Linear elastic spring

    1D Plasticity Models > Rate Independent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 4

  • Physical model: Rigid block sliding on a rough surface. Coulombs frictional law

    1D Plasticity Models > Rate Independent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 5

    0

    0

    no equilibrium

    F N

    F N

    F N

    < =

    =

    >

  • Rheological model: Coulombs frictional device

    1D Plasticity Models > Rate Independent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 6

    0

    0

    not admissible

    e

    e

    e

    < =

    =

    >

  • Rheological model: Elastic spring + frictional device

    1D Plasticity Models > Rate Independent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 7

    ( )( )

    0, , ,

    0, , 0,

    not admissible

    f e e e fe

    e f e fe

    e

    E E E

    E E

    < = = = = =

    = = = = = =

    >

  • Rheological model: Elastic spring + frictional device

    1D Plasticity Models > Rate Independent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 8

  • Hypothesis Within the framework of the infinitesimal deformation theory, we introduce the following hypothesis for a 1D rate-independent linear elastic-perfect plastic model, within the incremental theory of plasticity: H1. Additive split of the infinitesimal strain H2. Set of plastic internal variables: plastic strain

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 9

    e p = +

    { }:p p=E

  • H3. Free energy per unit of volume: quadratic elastic potential H4. Clausius-Planck inequality. Linear elastic constitutive equation, and reduced plastic dissipation inequality

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 10

    ( ) ( ) ( )21: 2e e eW E = =

    ( ): 0e = D( ): 0e e ee p = = + D

    , : 0e e pE = = = D

  • H5. Space of admissible stresses, elastic domain, and yield surface. Yield function.

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 11

    ( ){ }( ) ( ){ }

    ( ){ }

    : 0

    int : 0

    : 0

    Y

    Y

    Y

    f

    f

    f

    = =

    = = Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 12

    0 if 0

    0 if 0

    pY

    pY

    = > = >

    = < = = =

    ( ) ( )0, 0, 0f f =

    ( )( )

    if 0 then 0

    if 0 then

    Plastic loading

    Elastic loading/unloadi0 ng

    f

    f

    > =

    < =

  • H8. Plastic consistency condition Plastic loading: plastic consistency (or persistency) condition

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 13

    ( ) ( ) ( )if 0 then 0, 0, 0f f f = =

    ( ) ( )( ) ( )

    if 0 and 0 then 0

    if 0 and

    Plastic loading

    Elastic0 unloathe di gn n0

    f f

    f f

    = > =

    = < =

    ( ) ( ) ( )sgn sgn sgn 0pf f E E E E = = = =

    ( )1 sgn 0E E = >

    ( ) ( )0 and 0 0f f = > =

  • Trial stress rate Plastic loading: plastic multiplier (or plastic consistency) parameter

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 14

    0trial p trialf f f f E f E = = = =

    ( )1 1 sgn 0trial trialE f E = = >

    : , :trial trial pE E = =

    ( )1 1 sgn 0trial trialE f E = =

  • Plastic loading/elastic unloading from the yield surface Case 1 Case 2

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 15

    if 0 then

    if 0 then 0, 0 0

    trial

    trial

    f

    f f E f

    = < < =

    if 0 the Elastic unloadingn 0trialf < =

    if 0 then Plastic loadi0 ngtrialf > >

    if 0 then

    if 0 then 0 0, 0

    trial

    trial

    f

    f f E f

    >

    = = > > =

  • Plastic loading/elastic unloading from the yield surface Geometric interpretation

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 16

    trial trial

    Y Y

    trialtrial ( )f ( )f

    Elastic unloading Elastic unloading

    Plastic loading Plastic loading

  • Stress-strain curve for a rate-independent elastoplastic model with linear elastic and perfect plastic response

    1D Plasticity Models > Rate Independent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 17

  • Stress-strain curve: hardening plasticity

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 18

  • Stress-strain curve: Bauschinger effect (kinematic hardening)

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 19

  • Stress-strain curve: isotropic/kinematic hardening

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 20

  • Hypothesis Within the framework of the infinitesimal deformation theory, we introduce the following hypothesis for a 1D rate-independent elastoplastic model with linear elastic response, and linear isotropic and kinematic hardening, within the incremental theory of plasticity: H1. Additive split of the infinitesimal strain H2. Set of plastic internal variables

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 21

    e p = +

    { }: , ,p p =E

  • H3. Free energy per unit of volume: quadratic elastic, isotropic hardening and kinematic hardening potentials

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 22

    ( ) ( ) ( ) ( ), , :e eW = + +

    0, 0, 0E K H E K E H+ + > + > + >

    ( ) ( )

    ( )

    ( )

    2

    2

    2

    1 Elastic potential21 Isotropic hardening potential21 Kinematic hardening potential2

    e eW E

    K

    H

    =

    =

    =

  • H4. Clausius-Planck inequality. Linear elastic constitutive equation, linear hardening equations and reduced plastic dissipation

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 23

    ( ): , , 0e = D

    ( ):

    0

    e

    e e

    e

    p

    =

    = +

    D

    , : , :

    : 0

    ee

    p

    E q K q H

    q q

    = = = = = =

    = + + D

  • Linear isotropic hardening Nonlinear isotropic hardening (1) Exponential saturation law + linear isotropic hardening (2) Power law

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 24

    ( ) ( )( ): : 1 expYq K = =

    :q K = =

    ( )1 2: :m

    Yq k k = = +

  • H5. Space of admissible stresses, elastic domain, and yield surface. Yield function.

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 25

    ( ){ }( ) ( ){ }

    ( ){ }

    : , , , , 0

    int : , , , , 0

    : , , , , 0

    Y

    Y

    Y

    q q f q q q q

    q q f q q q q

    q q f q q q q

    = = +

    = = + Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 26

    ( )( ) ( )

    ( )( ) ( )

    if 0, , , 0 then

    , , sgn

    , ,

    , , sgn

    Y

    p

    q

    q

    f q q q q

    f q q q

    f q q

    f q q q

    > = + =

    = =

    = =

    = =

  • H7. Kuhn-Tucker loading/unloading conditions

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 27

    ( ) ( )0, , , 0, , , 0f q q f q q =

    ( )( )

    if 0 then , , 0

    i

    Plastic loading

    Elastic loading/unloadingf , , 0 then 0

    f q q

    f q q

    > =

    < =

  • H8. Plastic consistency condition Plastic loading: plastic consistency (or persistency) condition

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 28

    ( ) ( ) ( )if , , 0 then 0, , , 0, , , 0f q q f q q f q q = =

    ( ) ( )( ) ( )

    if , , 0 and 0 then , , 0

    if , , 0 and

    Plastic loading

    Elastic unlo, , 0 the dingn 0 a

    f q q f q q

    f q q f q q

    = > =

    = < =

    ( ) ( ), , 0 and 0 , , 0f q q f q q = > =

  • Plastic loading: plastic consistency (or persistency) condition

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 29

    ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( )

    2 2

    sgn sgn

    sgn sgn sgn

    sgn sgn sgn

    sgn 0

    q q

    p

    f f f q f q

    q q q q

    q E q E K q H

    q E q E K q H

    q E E K H

    = + +

    = +

    = +

    =

    = + + =

    ( ) ( )1 sgn 0E K H q E = + + >

  • Trial stress rate Plastic loading: plastic multiplier parameter

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 30

    ( ) 0

    q q

    trial pq q

    trial

    f f f q f q

    f f E f K f H

    f E K H

    = + +

    =

    = + + =

    ( ) ( ) ( )1 1 sgn 0trial trialE K H f E K H q = + + = + + >

    : , :trial trial pE E = =

    ( ) ( ) ( )1 1 sgn 0trial trialE K H f E K H q = + + = + +

  • Plastic loading/elastic unloading from the yield surface Case 1 Case 2

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 31

    ( )if 0 and 0 then

    0, 0 0

    trial

    trial

    f

    f f E K H f

    < >

    = + + < < =

    if 0 the Elastic unloadingn 0trialf < =

    if 0 then Plastic loadi0 ngtrialf > >

    ( )if 0 and 0 then

    0 0, 0

    trial

    trial

    f

    f f E K H f

    > =

    = + + > > =

  • Plastic loading/elastic unloading from the yield surface Geometric interpretation

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 32

    trial trial

    ( )Y q q Y q q +

    trialtrial ( ), ,f q q ( ), ,f q q

    Elastic unloading Elastic unloading

    Plastic loading Plastic loading

  • Isotropic hardening Geometric interpretation: expansion (without translation) of the yield surface

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 33

    Y0Y

    Y q ( )Y q

  • Kinematic hardening Geometric interpretation: translation (without expansion) of the yield surface

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 34

    Y0Y

    Y q +( )Y q

  • Isotropic + Kinematic hardening Geometric interpretation: expansion and translation of the yield surface

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 35

    Y0Y

    Y q q +( )Y q q

  • Stress-strain curve for a rate-independent elastoplastic model with linear elastic and linear isotropic hardening plasticity

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 36

  • Stress-strain curve for a rate-independent elastoplastic model with linear elastic and linear kinematic hardening plasticity

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 37

  • Stress-strain curve for a rate-independent elastoplastic model with linear elastic, linear isotropic/linear kinematic hardening plasticity

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 38

  • Reduced plastic dissipation Plastic dissipation rate per unit of volume

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 39

    ( ) ( )( )( ) ( )( )( )

    ( )( )

    :

    sgn sgn

    sgn

    , ,

    0

    p

    Y

    Y

    q qq q q q

    q q q

    q q

    f q q

    = + +

    = +

    = +

    = +

    = +

    =

    D

  • Maximum plastic dissipation principle Given a strain rate and a rate of the plastic internal variables the maximum plastic dissipation principle states that the stress state satisfies where,

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 40

    { } { }: ,0,0 , : , ,p p = = E E

    ( ) ( ), ,p p D S E D ET T

    { } { }: , , , : , ,q q p p = =S T

    ( ) ( ), : , :p p p p= = D S E SE , D E ET T

  • Maximum plastic dissipation principle Maximum plastic dissipation Constrained minimization problem

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 41

    ( ) ( ), ,p p D S E D ET T( ) ( ), : 0p p = D S E S ET T T

    ( )arg max , p = S D ET T( )( )arg min , p = S D ET T

  • Maximum plastic dissipation principle Maximum plastic dissipation, given by, is equivalent to associative plastic flow rule, Kuhn-Tucker loading/unloading conditions, and convexity of the yield surface, given by,

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 42

    ( )( )arg min , p = S D ET T

    ( )( ) ( )

    ( ) ( ) ( ) ( )0, 0, 0

    p f

    f f

    f f f

    =

    =

    S

    S

    E S

    S S

    S S ST T T

  • Maximum plastic dissipation principle Proof 1. Maximum plastic dissipation implies associative plastic flow rule and Kuhn-Tucker loading/unloading conditions

    Constrained minimization problem Unconstrained minimization problem: Lagrange multipliers

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 43

    ( )( )arg min , p = S D ET T

    ( ) ( ) ( ), , : ,p p f = + E D ET T TL( )arg min , ,p = S ET TL

  • The optimality conditions of the unconstrained minimization problem yield

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 44

    ( ) ( ) ( )( )

    , , ,

    0

    p p

    p

    f

    f

    == =

    = +

    = + =

    T T T T ST S T S

    S

    T E D T E T

    E S

    L

    ( ) ( )0, 0, 0f f =S S( )p f= SE S

  • Maximum plastic dissipation principle Proof 2. Maximum plastic dissipation implies convexity of the yield surface

    Unconstrained minimization problem

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 45

    ( ) ( )( ) ( ) ( ) ( )( ) ( ) ( ) ( )( )( ) ( ) ( ) ( )( )

    ( ) ( ) ( ) ( )

    , , , ,

    , ,

    , ,

    if 0 then

    p p

    p p

    p p

    f f

    f f

    f f f

    f f f

    + +

    >

    S

    S

    S E E

    D S E S D E

    D E D S E S

    S S S

    S S S

    T T

    T T T

    T T T

    T T T

    T T T

    L L

  • Maximum plastic dissipation principle Proof 3. Associative plastic flow rule, Kuhn-Tucker loading/ unloading conditions and convexity of the yield surface implies maximum plastic dissipation

    Using associative plastic flow rule Using convexity of the yield surface

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 46

    ( )( ) ( ) ( )

    p

    p

    f

    f

    =

    =

    S

    S

    E S

    S E S ST T T

    ( ) ( ) ( )( )p f f S E ST T T

  • Maximum plastic dissipation: elastic unloading (trivial case) Maximum plastic dissipation: plastic loading

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 47

    ( )( ) ( )

    if 0 then 0 and

    , ,

    p

    p p

    =

    S E

    D S E D E

    T

    T T

    ( )( ) ( )

    ( ) ( )

    if 0 then 0 and

    0

    , ,

    p

    p p

    f

    f

    > =

    S

    S E

    D S E D E

    T T T

    T T

  • Hypothesis H1. Additive split of the infinitesimal strain H2. Set of plastic internal variables H3. Free energy per unit of volume H4. Clausius-Planck inequality. Linear elastic constitutive equation, linear hardening equations and reduced dissipation H5. Space of admissible stresses, elastic domain, and yield surface. Yield function. H6. Associative plastic flow rule H7. Kuhn-Tucker loading/unloading conditions

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 48

  • Hypothesis H1. Additive split of the infinitesimal strain H2. Set of plastic internal variables H3. Free energy per unit of volume H4. Clausius-Planck inequality. Linear elastic constitutive equation, linear hardening equations and reduced dissipation H5. Space of admissible stresses, elastic domain, and yield surface. Yield function. H6. Maximum plastic dissipation

    1D Plasticity Models > Rate Independent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 49

  • Contents 1. 1D Rate independent plasticity models

    1. Motivation 2. Perfect plasticity model 3. Hardening plasticity model

    2. 1D Rate dependent plasticity models 1. Motivation 2. Perfect plasticity model 3. Hardening plasticity model

    1D Plasticity Models > Contents

    Contents

    April 1, 2015 Carlos Agelet de Saracibar 50

  • Rheological model: dashpot

    1D Plasticity Models > Rate Dependent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 51

    1 =

  • Rheological model: elastic spring + frictional device | dashpot

    1D Plasticity Models > Rate Dependent Plasticity Models

    Motivation

    April 1, 2015 Carlos Agelet de Saracibar 52

    e p = +

    e p

    E

    No se puede mostrar la imagen en este momento.

    ( ) ( ) ( ): sgn sgnex Y f = =

    ( ) ( ) ( ) ( )1 1 1sgnp ex f f f = = =

  • Hypothesis Within the framework of the infinitesimal deformation theory, we introduce the following hypothesis for a1D rate-dependent linear elastic-perfect plastic model, within the incremental theory of plasticity: H1. Additive split of the infinitesimal strain H2. Set of plastic internal variables: plastic strain

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 53

    e p = +

    { }:p p=E

  • H3. Free energy per unit of volume: quadratic elastic potential H4. Clausius-Planck inequality. Linear elastic constitutive equation, and reduced plastic dissipation inequality

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 54

    ( ) ( ) ( )21: 2e e eW E = =

    ( ): 0e = D( ): 0e e ee p = = + D

    , : 0e e pE = = = D

  • H5. Elastic domain, plastic domain, and yield surface. Yield function.

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 55

    ( ){ }( ) ( ){ }

    ( ){ }

    : 0

    ext : 0

    : 0

    Y

    Y

    Y

    f

    f

    f

    = =

    = = >

    = = =

    YY

  • H6. Associative plastic flow rule

    The associative plastic flow rule can be cast as

    Geometric interpretation

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 56

    ( ) ( ) ( )1sgn , 0p f f = = =

    ( ) ( ) ( ) ( )1 1 sgnp f f f = =

    ( ) ( ) ( ) ( )( )1 1 1sgn sgnp Y Yf f = = =

  • Closest-point-projection (cpp)

    Natural relaxation time

    Associative plastic flow rule

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 57

    ( )sgn if extif

    Y

    = =

    * P

    1: E =

    ( )11 *p E

    =

  • Associative plastic flow rule: geometric interpretation

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 58

    ( )11 *p E

    =

    Y Y

    ( )EP=*

    Y Y

    ( )EP=*

  • Stress-strain curve for a rate-dependent linear elastic, perfect plastic model

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 59

  • Perzyna model The associative plastic flow rule given by

    is equivalent to the maximization of a regularized plastic dissipation, and can be obtained as the solution of the following unconstrained minimization problem

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 60

    ( ) ( ) ( ) ( )1 1 sgnp f f f = =

    ( )( )arg min , p = D( ) ( ) ( ) 21, : , 2

    p p f = D D

  • Perzyna model Proof. The solution of the unconstrained minimization problem reads,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 61

    ( ) ( ) ( )

    ( ) ( ) ( ) ( )

    ( ) ( )

    2

    :

    1, : ,2

    1, : , 0

    1 0

    p p

    p p

    p

    f

    f f

    f f

    =

    =

    ==

    =

    D D

    D D

    ( )( )arg min , p = D

  • Duvaut-Lions model The associative plastic flow rule given by

    is equivalent to the maximization of a regularized plastic dissipation, and can be obtained as the solution of the following unconstrained minimization problem written in terms of the cpp

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 62

    ( )( )arg min , p = D

    ( )11 *p E

    =

    ( ) ( ) 121, : , 2p p

    E

    = D D *

  • Closest-point-projection (cpp) The closest-point-projection is obtained as the solution of the following constrained minimization probem, written in terms of the complementary energy

    Using the Lagrange multipliers method it can be transformed into the following unconstrained minimization problem

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 63

    ( )arg min = * * *

    ( ) ( ) ( )121 1 12 2E E = = * * * *

    ( ) ( ) ( ), ; : f = +* * * * *L( )arg min , ; = * * * *L

  • Proof 1. The solution of the unconstrained minimization problem reads,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 64

    ( ) ( )( ) ( ) ( )

    ( )

    1

    212

    1 1

    1 1:

    , : ,

    , : , 0

    0

    p pE

    p p

    p

    E

    E

    =

    = =

    = =

    D D *

    D D *

    *

    ( )( )arg min , p = D

    ( )11p E

    = *

  • Proof 2. The solution of the closest-point-projection, obtained as the solution of an unconstrained minimization probem written in terms of the complementary energy, reads,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 65

    ( ) ( ) ( )( ) ( ) ( )

    ( ) ( )1:

    , ; :

    , ; : 0

    0

    f

    f

    E f

    = +

    = + =

    + ==* * *

    *

    * * * * *

    * * * * *

    * * *

    L

    L

    ( )arg min , ; = * * * *L

    ( ) ( )0, 0, 0f f =* ** *

  • The solution of the unconstrained minimization problem yields the following results for the closest-point-projection,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 66

    ( ) ( )( )

    ( )

    1 0

    sgn sgn sgn

    sgn sgn

    , sgn sgn

    E f

    E f

    E

    E

    E

    + =

    + =

    + =

    + =

    = =

    *

    *

    * * *

    * * *

    * * * *

    * * *

    * * *

  • For the non-trivial case (plastic loading), using the Kuhn-Tucker complementarity conditions for the cpp, the Lagrange multiplier reads,

    and the closest-point-projection takes the form,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Perfect plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 67

    ( )( ) ( )

    ( )1

    if 0 then 0

    0

    0

    Y

    Y

    f

    f E f E

    E f

    > = =

    = = =

    = >

    * * *

    * * *

    *

    ( ) , sgn sgnsgn sgn

    Y

    Y

    f

    = = =

    = =

    * *

    * * *

  • Hypothesis Within the framework of the infinitesimal deformation theory, we introduce the following hypothesis for a 1D rate-dependent linear elastic-hardening plasticity model, within the incremental theory of plasticity: H1. Additive split of the infinitesimal strain H2. Set of plastic internal variables

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 68

    e p = +

    { }: , ,p p =E

  • H3. Free energy per unit of volume: quadratic elastic, isotropic hardening and kinematic hardening potentials

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 69

    ( ) ( ) ( ) ( ), , :e eW = + +

    0, 0, 0, 0E E K H E K E H> + + > + > + >

    ( ) ( )

    ( )

    ( )

    2

    2

    2

    1 Elastic potential21 Isotropic hardening potential21 Kinematic hardening potential2

    e eW E

    K

    H

    =

    =

    =

  • H4. Clausius-Planck inequality. Linear elastic constitutive equation, linear isotropic/linear kinematic hardening, and reduced plastic dissipation inequality

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 70

    ( ): , , 0e = D

    ( ):

    0

    e

    e e

    e

    p

    =

    = +

    D

    , : , :

    : 0

    ee

    p

    E q K q H

    q q

    = = = = = =

    = + + D

  • H5. Elastic domain, plastic domain, and yield surface. Yield function

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 71

    ( ){ }( ) ( ){ }

    ( ){ }

    : , , , , 0

    ext : , , , , 0

    : , , , , 0

    Y

    Y

    Y

    q q f q q q q

    q q f q q q q

    q q f q q q q

    = = +

    = = + >

    = = + =

    Y q q +( )Y q q

  • H6. Associative plastic flow rule H7. Plastic multiplier

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 72

    ( ) ( )( )( ) ( )

    , , sgn

    , ,

    , , sgn

    p

    q

    q

    f q q q

    f q q

    f q q q

    = =

    = =

    = =

    ( )1 , , 0f q q

    =

  • Reduced plastic dissipation Plastic dissipation rate per unit of volume

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 73

    ( ) ( )( )( ) ( )( )( )

    ( )( )( )

    :

    sgn sgn

    sgn

    , ,

    0

    p

    Y

    Y

    q qq q q q

    q q q

    q q

    f q q

    = + +

    = +

    = +

    = +

    = +

    = +

    D

  • Perzyna model The plastic flow rule can be obtained as the solution of an unconstrained minimization problem, arising from the maximization of a regularized plastic dissipation, given by,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 74

    ( )( )arg min , p= T TS D E( ) ( ) ( ) 21, : , 2

    p p f = D S E D S E S

  • The solution of the unconstrained minimization problem, arising from the maximization of a regularized plastic dissipation, yields the following plastic flow rule,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 75

    ( ) ( ) ( )

    ( ) ( )

    21, : ,2

    1:

    p p

    p

    f

    f f

    =

    = = 0

    S S

    S

    D S E D S E S

    E S S

    ( )( )arg min , p= T TS D E

    ( ) ( )1p f f

    = SE S S

  • Duvaut-Lions model The plastic flow rule can be obtained as the solution of an unconstrained minimization problem, arising from the maximization of a regularized plastic dissipation, given by,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 76

    ( )( )arg min , p= T TS D E( ) ( ) ( )

    ( ) 12

    1, : , *

    1: , *2

    p p

    p

    =

    =

    D S E D S E S S

    D S E S SC

  • The solution of the unconstrained minimization problem, arising from the maximization of a regularized plastic dissipation, yields the following associative plastic flow rule,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 77

    ( )( )arg min , p= T TS D E( ) ( ) ( )

    ( )

    1

    1

    1, : , *

    1: *

    p p

    p

    =

    = = 0

    S SD S E D S E S S

    E S S

    C

    C

    ( )11 *p

    = E S SC

  • Closest-point-projection The closest-point-projection (cpp) is obtained as the solution of the following constrained minimization problem, written in terms of the complementary energy as,

    Using the Lagrange multipliers method, it can be transformed into the following unconstrained minimization problem

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 78

    ( )* arg min * * = T T S S

    ( ) ( ) ( )121 1 12 2* * * * = = S S S S S S S SC C

    ( ) ( ) ( ), *; * : * * *f = +SS S S SL( )* arg min , *; * *= T TS SL

  • Closest-point-projection The solution of the unconstrained minimization problem, defining the closest-point-projection, yields,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 79

    ( ) ( ) ( )( ) ( )

    * * *

    1*

    , *; * : * * *

    : * * *

    f

    f

    = +

    = + = 0S S S

    S

    SS S S S

    S S S

    L

    C

    ( )* arg min , *; * *= T TS SL

    ( )** * *f= SS S SC

    ( ) ( )* 0, * 0, * * 0f f =S S

  • Closest-point-projection The solution of the unconstrained minimization problem, defining the closest-point-projection, yields,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 80

    ( ) ( )( )( ) ( )

    *

    *

    *

    * * *, *, * * sgn * *

    * * *, *, * *

    * * *, *, * * sgn * *q

    q

    E f q q E q

    q q K f q q q K

    q q H f q q q H q

    = =

    = =

    = = +

    ( )** * *f= SS S SC

    ( ) ( )* 0, *, *, * 0, * *, *, * 0f q q f q q =

  • Closest-point-projection The solution of the unconstrained minimization problem, defining the closest-point-projection, yields,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 81

    ( ) ( )( ) ( )

    ( ) ( )( )( ) ( ) ( )

    * * * sgn * *

    * * sgn * * sgn

    * sgn * *

    * * * sgn * * sgn

    q q E H q

    q q q q

    E H q

    q E H q q q

    = +

    =

    +

    + + =

    ( ) ( ) ( )* * * , sgn * * sgnq q E H q q = + =

  • For the non-trivial case, using the Kuhn-Tucker complementarity conditions for the cpp, the Lagrange multiplier reads,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 82

    ( )if * 0 then *, *, * * * * 0Yf q q q q > = + =( ) ( )

    ( )( )

    ( ) ( )

    *, *, * * *

    * *

    *

    , , * 0

    Y

    Y

    Y

    f q q q E H q

    q E H q K

    q E K H q

    f q q E K H

    = + +

    = + +

    = + + +

    = + + =

    ( ) ( )1* , , 0E K H f q q = + + >

    ( ) ( )* 0, *, *, * 0, * *, *, * 0f q q f q q =

  • Closest-point-projection The solution of the unconstrained minimization problem, defining the closest-point-projection, yields,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 83

    ( ) ( ) ( )( ) ( )( ) ( ) ( )

    1

    1

    1

    * , , sgn

    * , ,

    * , , sgn

    E E K H f q q q

    q q K E K H f q q

    q q H E K H f q q q

    = + +

    = + +

    = + + +

    ( )** * *f= SS S SC

  • Associative plastic flow rule The associative plastic flow rule takes the form,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 84

    ( ) ( ) ( ) ( )

    ( ) ( ) ( )

    ( ) ( ) ( ) ( )

    11

    11

    11

    1 1* , , sgn

    1 1* , ,

    1 1* , , sgn

    p E E K H f q q q

    K q q E K H f q q

    H q q E K H f q q q

    = = + +

    = = + +

    = = + +

    ( )11 *p

    = E S SC

  • Associative plastic flow rule The associative plastic flow rule equations can be recast in the form,

    where the relaxation time takes the form,

    1D Plasticity Models > Rate Dependent Plasticity Models

    Hardening plasticity model

    April 1, 2015 Carlos Agelet de Saracibar 85

    ( )

    ( )

    sgn

    sgn

    p q

    q

    =

    =

    =

    ( ) ( ) ( )11 1, , , ,E K H f q q f q q

    = + + =

    ( ) 1: E K H = + +

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