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  • 7/29/2019 7. a Cell-based Smoothed Discrete Shear Gap Method (CS-DSG3) Based on the C0 Type Higher Order Shear Defor

    1/16

    A cell-based smoothed discrete shear gap method (CS-DSG3) based

    on the C0-type higher-order shear deformation theory for static and free

    vibration analyses of functionally graded plates

    P. Phung-Van a, T. Nguyen-Thoi a,b,, Loc V. Tran a, H. Nguyen-Xuan a,b

    a Division of Computational Mechanics, Ton Duc Thang University, Nguyen Huu Tho St., Tan Phong Ward, Dist.7, Hochiminh City, Viet Namb Department of Mechanics, Facultyof Mathematics & ComputerScience,Universityof Science, Vietnam NationalUniversity HCMC, 227NguyenVan Cu,Dist. 5, HochiminhCity, VietNam

    a r t i c l e i n f o

    Article history:

    Received 27 March 2013

    Received in revised form 19 May 2013

    Accepted 5 June 2013

    Available online xxxx

    Keywords:

    Smoothed finite element methods

    ReissnerMindlin plate

    Cell-based smoothed discrete shear gap

    technique (CS-DSG3)

    Functionally graded plates (FGPs)

    Thermo-mechanical loads

    The higher-order shear deformation plate

    theory (HSDT)

    a b s t r a c t

    A cell-based smoothed discrete shear gap method (CS-DSG3) based on the first-order shear deformation

    theory was recently proposed for static and dynamics analyses of Mindlin plates. In this paper, the CS-

    DSG3 is extended to the C0-type high-order shear deformation plate theory for the static and free vibra-

    tion analyses of functionally graded plates (FGPs). In the FGPs, the material properties are assumed to

    vary through the thickness by a simple power rule of the volume fractions of the constituents. In the sta-

    tic analysis, both thermal and mechanical loads are considered and a two-step procedure is performed

    includinga step of analyzing the temperature field along the thickness of the plate anda step of analyzing

    the behavior of the plate subjected to both thermal and mechanical loads. The accuracy and reliability of

    the proposed method is verified by comparing its numerical solutions with those of other available

    numerical results.

    2013 Elsevier B.V. All rights reserved.

    1. Introduction

    Being first proposed in Sendai (Japan) in 1984, functionally

    graded materials (FGM) are then developed rapidly around the

    world [14]. The FGMs are classified as special composites whose

    material properties change continuously and smoothly along cer-

    tain dimensions of the structure according to a predetermined for-

    mula. This makes FGMs have many advantages in engineering

    applications because the material properties of FGMs can be al-

    tered according to the specific requirements. For the functionally

    graded plates (FGPs), the volume fractions are derived from a func-

    tion of position through their thickness. The FGPs usually consist of

    metal and ceramic which make them both tough and resistant to

    high temperatures. This property makes the FGPs become more

    suitable to apply in aerospace structures, nuclear plants and

    semi-conductor technologies.

    With the advantageous features of FGPs in many practical appli-

    cations and the limitations of analytical methods [59], many

    effective numerical methods have been devised to analyse and

    simulate the behavior of FGPs. For static analysis, Praveen [10]

    investigated the static thermo-elastic response of FGPs using the fi-

    nite element method. Lee [11] presented thermoelastic analysis of

    FGPs using element-free kp-Ritz. Liew et al. [1215] studied the

    thermal behavior of FGPs with temperature-dependent properties.

    Reddy [16,17] presented finite element models for FGPs based on

    the third-order shear deformation theory. Javaheri et al. [18] de-

    rived equilibrium and stability equations of FGPs under thermal

    loads based on a high-order shear deformation plate theory

    (HSDT). Shen [19] studied the non-linear bending response of FGPs

    subjected to thermalmechanical loads, and Woo and Merguid [20]

    carried out the non-linear analysis of FGM plates and shells.

    For dynamic and buckling analyses, Huang and Shen [21] pre-

    sented the non-linear vibration and dynamic response of FGPs in

    thermal environments. Yang and Shen [22] studied the free vibra-

    tion and dynamic response of FGPs subjected to impulsive lateral

    loads combined with initial in-plane actions in a thermal environ-

    ment. Vel and Batra [23] provided a three-dimensional solution for

    the free and forced vibration of simply supported FGPs by using

    different plate theories. Efraim and Eisenberger [24] analysed the

    frequency characteristics of thick annular FGPs of variable thick-

    ness. Matsunaga [25,26] used a two-dimensional global higher-or-

    der deformation theory to analyse free vibration and buckling of

    FGPs. Najafizadeh [27] carried out a thermal buckling analysis of

    0927-0256/$ - see front matter 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.commatsci.2013.06.010

    Corresponding author at: Department of Mechanics, Faculty of Mathematics &

    Computer Science, University of Science, Vietnam National University HCMC, 227

    Nguyen Van Cu, Dist. 5, Hochiminh City, Viet Nam. Tel.: +84 942340411.

    E-mail addresses: [email protected], [email protected](T.Nguyen-Thoi).

    Computational Materials Science xxx (2013) xxxxxx

    Contents lists available at SciVerse ScienceDirect

    Computational Materials Science

    j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m m a t s c i

    Please cite this article in press as: P. Phung-Van et al., Comput. Mater. Sci. (2013), http://dx.doi.org/10.1016/j.commatsci.2013.06.010

    http://dx.doi.org/10.1016/j.commatsci.2013.06.010mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.commatsci.2013.06.010http://www.sciencedirect.com/science/journal/09270256http://www.elsevier.com/locate/commatscihttp://dx.doi.org/10.1016/j.commatsci.2013.06.010http://dx.doi.org/10.1016/j.commatsci.2013.06.010http://www.elsevier.com/locate/commatscihttp://www.sciencedirect.com/science/journal/09270256http://dx.doi.org/10.1016/j.commatsci.2013.06.010mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.commatsci.2013.06.010http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-
  • 7/29/2019 7. a Cell-based Smoothed Discrete Shear Gap Method (CS-DSG3) Based on the C0 Type Higher Order Shear Defor

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    circular FGPs based on a HSDT. In addition, some finite element

    methods [2830] or meshfree approaches [3135] were also de-

    vised to solve the FGM structures. So far, based on the update of

    authors, there have not yet been the papers presenting numerical

    examples using three-node triangular plate elements based on

    the C0-type HSDT [36] for analysis of functionally graded plates

    (FGPs) subjected to thermo-mechanical loads. This paper hence

    will try to fill this gap by using a new three-node triangular plate

    element proposed recently.

    In the other front of the development of numerical methods, Liu

    and Nguyen-Thoi et al. [37] have integrated the strain smoothing

    technique into the FEM to create a series of smoothed FEM (S-

    FEM) [38] such as a cell/element-based smoothed FEM (CS-FEM)

    [39], a node-based smoothed FEM [40], an edge-based smoothed

    FEM [41] and a face-based smoothed FEM [42]. Each of these S-

    FEM has different properties and has been used to produce desired

    solutions for a wide class of benchmark and practical mechanics

    problems. Several theoretical aspects of the S-FEM models have

    been provided in Refs [43,44]. The S-FEM models have also been

    further investigated and applied to various problems such as plates

    and shells [4547], piezoelectricity [48], fluidsolid interaction

    [49], visco-elastoplasticity [50,51], limit and shakedown analysis

    for solids [52], etc.

    Among these S-FEM models, the CS-FEM [38,39] shows some

    interesting properties in the solid mechanics problems. Extendingthe idea of the CS-FEM to plate structures, Nguyen-Thoi et al. [54]

    have recently formulated a cell-based smoothed stabilized discrete

    shear gap element (CSDSG3) for static, and free vibration analyses

    of isotropic Mindlin plates by incorporating the CS-FEM with the

    original DSG3 element [53]. In the CS-DSG3, each 3-node triangular

    element will be divided into three sub-triangles, and in each sub-

    triangle, the stabilized DSG3 is used to compute the strains. Then

    the strain smoothing technique on whole the triangular element

    is used to smooth the strains on these three sub-triangles. The

    numerical results showed that the CSDSG3 is free of shear locking

    and shows four superior properties such as: (1) be a strong

    competitor to many existing three-node triangular plate elements

    in the static analysis; (2) can give high accurate solutions for

    problems with skew geometries in the static analysis; (3) can givehigh accurate solutions in free vibration analysis; (4) can provide

    accurately the values of high frequencies of plates by using only

    coarse meshes.

    Due to these advantages, in this paper, the CS-DSG3 is further

    extended to the C0-HSDT [36] for the static and free vibration anal-

    yses of FGPs. In the FGPs, the material properties are assumed to

    vary through the thickness by a simple power rule of the volume

    fractions of the constituents. In the static analysis, both thermal

    and mechanical loads are considered and a two-step procedure is

    performed including a step of analyzing the temperature field

    along the thickness of the plate and a step of analyzing the behav-

    ior of the plate subjected to both thermal and mechanical loads.

    The accuracy and reliability of the proposed method is verified

    by comparing its numerical solutions with those of other availablenumerical results.

    2. Functionally graded plates and thermal distribution

    A functionally graded plate made of ceramic and metal is shown

    in Fig. 1. The material property is assumed to be graded through

    the thickness by the power law distribution expressed as

    Pz Pc PmVc Pm 1

    Vc 1

    2

    z

    t

    nnP 0 2

    where subscripts m and c refer to the metal and ceramic constitu-ents, respectively; P represents the effective material properties,

    including the Youngs modulus E, density q, Poissons ratio m, ther-mal conductivity k and thermal expansion a; Pc and Pm denote theproperties of the ceramic and metal, respectively; Vc is the volume

    fraction of the ceramic; z is the thickness coordinate of plate and

    varies from t/2 to t/2; n is the volume fraction exponent. The vol-

    ume fraction through the thickness for different volume fraction

    exponents n is illustrated in Fig. 2.

    In the thermal analysis of the FGPs, it is assumed that the tem-

    perature distributions of the ceramic (top) surface and metal (bot-

    tom) surface are the constant temperature, and the temperature

    varies only through the thickness direction. The temperature vari-

    ation along the thickness is attained by solving the one-dimen-

    sional steady state heat conduction equation, which is given by

    d

    dzkz

    dT

    dz

    0 3

    with boundary conditions

    T Ttop at z t=2

    T Tbot at z t=24

    Fig. 1. Functionally graded plate.

    Fig. 2. Volume fraction Vc versus the thickness.

    2 P. Phung-Van et al. / Computational Materials Science xxx (2013) xxxxxx

    Please cite this article in press as: P. Phung-Van et al., Comput. Mater. Sci. (2013), http://dx.doi.org/10.1016/j.commatsci.2013.06.010

    http://dx.doi.org/10.1016/j.commatsci.2013.06.010http://dx.doi.org/10.1016/j.commatsci.2013.06.010
  • 7/29/2019 7. a Cell-based Smoothed Discrete Shear Gap Method (CS-DSG3) Based on the C0 Type Higher Order Shear Defor

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    where Ttop and Tbot are the top and bottom surface temperatures,

    respectively; and k(z) represents the thermal conductivity coeffi-cient at z and is also defined similarly as Eq. (1).

    Fig. 3 illustrates the temperature distributions through the

    thickness of a FGP made by the Aluminum-Ziconia (Al/ZnO2-1)

    for the various value of n, where the top and bottom surfaces are

    hold at 300 C and 20 C, respectively. It is evident that tempera-

    ture in the FGPs constituted by both ceramic and metal

    components.

    3. C0type higher-order shear deformation theory and

    weakform for FGM Mindlin plates

    3.1. C0type HSDT for FGM Mindlin plates

    According to C0-type HSDT model [36], the displacements of an

    arbitrary point in the plate are expressed by

    ux;y;z u0 z4z3

    3t2

    bx

    4z3

    3t2/x

    vx;y;z v0 z4z3

    3t2

    by

    4z3

    3t2/y h=2 6 z6 h=2

    wx;y w

    5

    where tis thickness of plate, u0 = {u0 v0}T and w0 are the membrane

    displacements and the transverse displacement of the mid-plane;

    and b = {bx by}T are the rotations around y-axis and x-axis, respec-

    tively, with the positive directions defined as shown in Fig. 4. Eq.

    (5) is developed from Reddys higher-order theory [55] in which,derivative of deflection is replaced by warping function / = {/x/y}

    T. Thus, the generalized displacement vector with 5 degrees of

    freedom for C1 continuity element can be transformed into the vec-

    tor with 7 degrees of freedom for C0 continuity element as

    u u0 v0 w0 bx by /x /y T

    .

    For a FGM Mindlin plate, the strains in plain is expressed by the

    following equation

    exx eyy cxyT

    e0 zj1 z3j2 6

    where the membrane strains are obtained from the symmetric dis-

    placement gradient

    e0

    @u0@x

    @v0@y

    @u0@y

    @v0@x

    8>>>:9>>=>>; rs u0 7

    and the bending strains are given by

    j1 12 frb rbTg

    j2 k6 fr/ r/T rb rbTg

    with k 4

    t28

    and the transverse shear strains are basically defined as

    cxz cyzT es z

    2js 9

    with

    es rw b

    js cb /10

    where r = [@/@x @/@y]T is the gradient operator.Under the temperature condition, the thermal strain of plate is

    expressed as

    eth azDTz 1 1 0 11

    where DT is the temperature change from a stress-free state.

    From Hooks law, the stress in plane is given by

    r Ee0 zj1 z3j2 eth 12

    and the shear stress is expressed as

    s Ges z2js 13

    where the material matrices are given by

    E Ez

    1 mz2

    1 mz 0

    mz 1 0

    0 0 1 mz=2

    264375 14

    G Ez

    21 mz

    1 0

    0 1

    !15

    in which E(z) is Youngs modulus; m(z) is the Poissons ratio varyingaccording to the power law as in Eq. (1).

    Note that the transverse shear strains in Eq. (9) and the shearstress in Eq. (13) are represented parabolically, hence the shear

    correction factor in the C0-type HSDT formulation [36] is not nec-

    essary as shown in Eq. (15).

    Fig. 3. Temperature distribution through the thickness of the Al/ZnO2-1 FGM plate.

    Fig. 4. Positive directions of displacement u, v, w and two rotations bx, by in Mindlin plate.

    P. Phung-Van et al. / Computational Materials Science xxx (2013) xxxxxx 3

    Please cite this article in press as: P. Phung-Van et al., Comput. Mater. Sci. (2013), http://dx.doi.org/10.1016/j.commatsci.2013.06.010

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    3.2. Weakform equation for FGM Mindlin plates

    The standard Galerkin weakform of the static equilibrium equa-

    tions [56] for the FGM Mindlin plate subjected to thermo-mechan-

    ical loads can be written as

    ZXdeTp D

    epdX

    ZXdcTDScdX

    ZXdwpdX

    ZXdeTrthdX 16

    in which p is the transverse loading per unit area; ep, c and rth areexpressed by

    ep e0 j1 j2f gT; c es jsf g

    T; rth Nth Mth Pth

    T

    17

    and material constant matrices D and DS have the forms of

    D

    A B E

    B D F

    E F H

    264375; DS AS BS

    BS

    DS

    " #; 18

    where

    Aij; Bij; Dij; Eij; Fij; Hij Zh=2

    h=2

    1;z;z2;z3;z4;z6Qijdz i;j 1; 2; 6

    Asij; B

    sij; D

    sij

    Zh=2h=2

    1;z2;z4Qijdz i;j 4; 5

    19

    and Nth, Mth, Pth are thermal force and moment resultants and com-

    puted by

    Nth 1 1 0 T

    Zt=2t=2

    Ez

    1 mzkzDTdz

    Mth 1 1 0 T

    Zt=2t=2

    Ez

    1 mzkzzDTdz

    Pth 1 1 0 T

    Zt=2

    t=2

    Ez

    1 mzkzz3DTdz

    20

    4. FEM formulation the FGM ReissnerMindlin plate

    Now, discretize the bounded domain X into Ne finite elements

    such that X SNe

    e1Xe andXi \Xj = ;, ij, then the finite element

    solution uh u0 v0 w0 bx by /x /y T

    of a displacement

    model for the FGM Mindlin plate is expressed as

    uh

    XNn

    i1

    Nix 0 0 0 0 0 0

    0 Nix 0 0 0 0 0

    0 0 Nix 0 0 0 0

    0 0 0 Nix 0 0 0

    0 0 0 0 Nix 0 0

    0 0 0 0 0 Nix 0

    0 0 0 0 0 0 Nix

    2666666666664

    3777777777775

    di Nd

    21

    where Nn is the total number of nodes of problem domain discret-

    ized; Ni(x) is shape function at the ith node;

    di ui vi wi bxi byi /xi /yi T

    is the displacement vector

    of the nodal degrees of freedom of uh associated to the ith node,

    respectively.

    Substituting Eq. (21) into Eqs. (7), (8), (10), then the strains in

    Eq. (17) can be expressed in the general forms of nodal displace-

    ments as

    eh ep cT X

    Nn

    i1

    B

    id

    i22

    where eh is the compatible strain and Bi is the generalized straindisplacement matrix expressed by

    Bi B

    mi

    TB

    b1i

    TB

    b2i

    TB

    s0i

    TB

    s1i

    T !23

    in which

    Bmi

    Ni;x 0 0 0 0 0 0

    0 Ni;y 0 0 0 0 0

    Ni;y Ni;x 0 0 0 0 0

    264 375;B

    b1

    i

    0 0 0 Ni;x 0 0 0

    0 0 0 0 Ni;y 0 0

    0 0 0 Ni;y Ni;x 0 0

    264375;

    Bs0i

    0 0 Ni;x Ni 0 0 0

    0 0 Ni;y 0 Ni 0 0

    !;

    Bs1i c

    0 0 0 Ni 0 Ni 0

    0 0 0 0 Ni 0 Ni

    !;

    24

    Bb2

    i

    c

    3

    0 0 0 Ni;x 0 Ni;x 0

    0 0 0 0 Ni;y 0 Ni;y0 0 0 Ni;y Ni;x Ni;y Ni;x

    264 375where Ni,x and Ni,y are the derivatives of the shape functions in x-

    direction and y-direction, respectively.

    The discretized system of equations of FGM Mindlin plate using

    the FEM for static analysis then can be expressed as

    Kd F 25

    where F is the load vector computed by

    F

    ZX

    pN BmI T

    Nth Bb1I

    TMth B

    b2I

    TPth

    !dX f

    b26

    in which fb is the remaining part of F subjected to prescribed

    boundary loads; and K is the global stiffness matrix assembled from

    the element stiffness matrices Ke as

    K XNee1

    Ke XNee1

    ZXe

    BTi D

    BjdX

    ZXe

    STi D

    s SjdX

    |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

    Ke

    27

    where Bi and Si are defined by

    Bi Bmi

    TB

    b1

    i

    TB

    b2

    i

    T !28

    Si Bs0i

    TB

    s1i

    Th i29

    For free vibration analysis, we have

    K x2Md 0 30

    where x is the natural frequency and M is the global mass matrixcomputed by

    M

    ZX

    NT

    mNTdX 31

    in which m is the matrix defined as

    m

    I1 0 0 I2 0c3

    I4 0

    I1 0 0 I2 0c3

    I4

    I1 0 0 0 0

    I3 0c3

    I5 0

    I3 0c3

    I5

    c3

    2I7 0

    sym c3 2I7

    26666666666664

    37777777777775

    32

    4 P. Phung-Van et al. / Computational Materials Science xxx (2013) xxxxxx

    Please cite this article in press as: P. Phung-Van et al., Comput. Mater. Sci. (2013), http://dx.doi.org/10.1016/j.commatsci.2013.06.010

    http://dx.doi.org/10.1016/j.commatsci.2013.06.010http://dx.doi.org/10.1016/j.commatsci.2013.06.010
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    with

    I1; I2; I3; I4; I5; I7

    Zh=2h=2

    qz1;z;z2;z3;z4;z6dz 33

    5. Formulation of a cell-based smoothed discreate shear gap

    (CS-DSG3) method based on the C0-type HSDT for FGM Mindlin

    plates

    5.1. Formulation of the DSG3 based on the C0 -type HSDT

    In the original DSG3 [53], the problem domain is discretized

    into Nn nodes and Ne three-node triangular elements. The first-or-

    der shear deformation plate theory (FSDT) is used for Mindlin

    plates behavior and each node only has 3 degrees of freedom

    di wi bxi byi T

    . The formulation of the DSG3 is based on the

    concept shear gap of displacements along the edges of the ele-

    ments. In the DSG3, the shear strain is linear interpolated from

    the shear gaps of displacement by using the standard element

    shape functions. The DSG3 element is shear-locking-free and has

    several superior properties as presented in Ref [53]. In the

    present paper, the DSG3 is extended to the C0-type HSDT formula-

    tion [36] and each node will have 7 degrees of freedom

    di ui vi wi bxi byi /xi /yi T

    as mentioned in Section 4.

    Using a mesh of 3-node triangular elements, the approximation

    ue ue ve we bex be

    y /e

    x /e

    y

    Tfor a 3-node triangular

    element Xe for Mindlin FGM plates can be written as

    uex

    X3i1

    Nei x 0 0 0 0 0 0

    0 Nei x 0 0 0 0 0

    0 0 Nei x 0 0 0 0

    0 0 0 Nei x 0 0 0

    0 0 0 0 Nei x 0 0

    0 0 0 0 0 Nei x 0

    0 0 0 0 0 0 Nei x

    2666666666664

    3777777777775

    |fflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflffl fflffl{zfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflffl}Nei x

    dei

    X3i1

    Nei xd

    ei

    34

    where de

    i uei v

    ei w

    ei b

    exi b

    eyi /

    exi /

    eyi

    Tare the nodal degrees

    of freedom of ue associated to ith node and Nei x

    diag Nei x; Nei x; N

    ei x; N

    ei x; N

    ei x; N

    ei x; N

    ei x

    , i = 1, 2, 3, in

    which Nei x are the linear shape functions of the 3-node triangular

    elementXe.

    Substituting Eq. (34) into Eqs. (23) and (24), we obtained the

    membrane strain ee0, the curvatures of the deflection je1; j

    e2 and

    the shear strains ch [53] of the element in the forms of

    ee0 Bm

    de

    35

    je1 Bb1 d

    e; je2 B

    b2 de

    36

    ce ee

    s

    jes& ' Bs0

    Bs1

    & 'de 37where d

    e d

    e1 d

    e2 d

    e3

    Tis the nodal displacement vector of

    element; andBm, Bb1 ; Bb2 ; Bs0 , Bs1 arethe gradient matricesexpressed

    by

    Bm

    1

    2Ae

    b c 0 0 0 0 0 0

    0 d a 0 0 0 0 0

    d a b c 0 0 0 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    m1

    c 0 0 0 0 0 0

    0 d 0 0 0 0 0

    d c 0 0 0 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    m2

    b 0 0 0 0 0 0

    0 a 0 0 0 0 0

    a b 0 0 0 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    m3

    266664377775 12Ae Bm1 Bm2 Bm3 38

    Bb1

    1

    2Ae

    0 0 0 b c 0 0 00 0 0 0 d a 0 0

    0 0 0 d a b c 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflfflffl}B

    b11

    0 0 0 c 0 0 00 0 0 0 d00

    0 0 0 d c00|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflfflffl}B

    b12

    0 0 0 b 0 0 00 0 0 0 a00

    0 0 0 a b00|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflffl}B

    b13

    266664377775 12Ae Bb11 Bb12 Bb13

    h i39

    Bb2

    1

    2Ae

    0 0 0 b c 0 b c 0

    0 0 0 0 d a 0 d a

    0 0 0 d a b c d a b c|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    b21

    0 0 0 c 0 c 0

    0 0 0 0 d 0 d

    0 0 0 d c d c|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflffl}B

    b22

    0 0 0 b 0 b 0

    0 0 0 0 a 0 a

    0 0 0 a b a b|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    b23

    266664377775 12Ae Bb21 Bb22 Bb23

    h i

    40

    Bs0 12Ae

    0 0 b c Ae 0 0 0

    0 0 d a 0 Ae 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    s01

    0 0 c ac=2 bc=2 0 0

    0 0 d ad=2 bd=2 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflfflfflffl}B

    s02

    0 0 b bd=2 bc=2 0 0

    0 0 a ad=2 ac=2 0 0|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    s03

    264 375 12Ae Bs01 Bs02 Bs03 41

    Bs1

    1

    2Ae

    0 0 0 1 0 1 0

    0 0 0 0 1 0 1

    |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    s11

    0 0 0 1 0 1 0

    0 0 0 0 1 0 1|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    s12

    0 0 0 1 0 1 0

    0 0 0 0 1 0 1|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}B

    s13

    266664377775 12Ae Bs11 Bs12 Bs13 42

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    in which a, b, c, d arecomputed from the coordinates of three nodes of

    theelement as shown in Fig. 5, andAe is thearea of thetriangular ele-

    mentXe.

    Substituting Eqs. (38)(42) into Eq. (27), the global stiffness ma-

    trix now becomes

    KDSG3

    XNe

    e1

    KDSG3e 43

    where KDSG3e is the element stiffness matrix of the DSG3 element,

    and is computed by

    KDSG3e

    ZXe

    BTi D

    BjdX

    ZXe

    STi D

    s SjdX B

    Ti D

    BjAe S

    Ti D

    s SjAe

    44

    From Eqs. (38)(42) and (44), it is seen that the element stiff-

    ness matrix in the DSG3 depends on the sequence of node numbers

    of elements, and hence the solution of DSG3 is influenced when the

    sequence of node numbers of elements changes, especially for the

    coarse and distorted meshes. The CS-DSG3 is hence proposed to

    overcome this drawback and also to improve the accuracy as well

    as the stability of the DSG3.

    5.2. Formulation of CS-DSG3 based on the C0-type HSDT

    In the CS-DSG3 [54] using the C0-type HSDT formulation [36],

    the domain discretization is the same as that of the DSG3 using

    Nn nodes and Ne triangular elements. However in the formulation

    of the CS-DSG3, each triangular element Xe is further divided into

    three sub-trianglesD1,D2 andD3 by connecting the central point O

    of the element to three field nodes as shown in Fig. 6.

    In the CS-DSG3, we assume that the displacement vector deO at

    the central point O is the simple average of three displacement vec-

    tors de1; d

    e2 and d

    e3 of three field nodes

    deO 13de1 d

    e2 d

    e3

    45On the first sub-triangleD1(triangle O-1-2), a linear approxima-

    tion ueD1 ueD1 veD1 weD1 beD1x beD1

    y /eD1

    x /eD1

    y

    h iTis con-

    structed by

    ueD1 NeD11 deO N

    eD12 d

    e1 N

    eD13 d

    e2 N

    eD1 deD1 46

    where deD1 d

    eO d

    e1 d

    e2

    Tis the vector of nodal degrees of free-

    dom of the sub-triangle D1 and NeD1 NeD11 N

    eD12 N

    eD13

    contains

    the linear shape functions created by the sub-triangle D1.

    Using the DSG3 formulation based on the C0-type HSDT pre-

    sented in Section 5.1 for the sub-triangle D1, the membrane strain

    eD10 , the bending strains jD11 ; jD12 and the shear strains eD1s ; jD1s inthe sub-triangle D1 are then obtained, respectively, by

    eD10 bmD11 b

    mD12 b

    mD13

    |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}bmD1

    deO

    de1

    de2

    26643775 bmD1 deD1 47

    jeD11 bb1D11 b

    b1D12 b

    b1D13

    h i|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

    bb1D1

    deO

    de1

    de2

    264375 bb1D1 deD1 ;

    jeD12 bb2D11 b

    b2D12 b

    b2D13h i|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}bb2D1

    deO

    de1

    d

    e2

    264

    375

    bb2D1 d

    eD1

    48

    eeD1s bs0D11 b

    s0D12 b

    s0D13

    |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}b

    s0D1

    deO

    de1

    de2

    264375 bs0D1 deD1 ;

    jeD1s bs1D11 b

    s1D12 b

    s1D13

    |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}b

    s1D1

    deO

    de1

    de2

    264375 bs1D1 deD1

    49

    where bmD1 ; b

    b1D1 ; bb2D1 ; b

    s0D1 and bs1D1 are, respectively, com-

    puted similarly as the matrices Bm; Bb1 ; Bb2 ; Bs0 and Bs1 of the

    DSG3 in Eqs. (38)(42) but with two following changes: 1) the coor-

    dinates of three nodexi xi yi T; i 1; 2; 3 are replaced byxO, x1

    andx2, respectively; and 2) the areaAe is replaced by the areaAD1 ofsub-triangle D1.

    Substituting deO in Eq. (45) into Eqs. (47)(49), and then rear-

    ranging we obtain

    eD10 13

    bmD11 b

    mD12

    13

    bmD11 b

    mD13

    13

    bmD11

    h i|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

    BmD1

    de1

    de2

    de3

    264375 BmD1 de

    50

    jD11 13

    bb1D11 b

    b1D12

    13

    bb1D11 b

    b1D13

    13

    bb1D11

    h i|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflffl}Bb1D1

    de1

    de2

    de3

    264

    375

    Bb1D1 de

    jD12 13

    bb2D11 b

    b2D12

    13

    bb2D11 b

    b2D13

    13

    bb2D11

    h i|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflffl}

    Bb2D1

    de1

    de2

    de3

    264 375 Bb2D1 de51

    eD1s 13

    bs0D11 b

    s0D12

    13

    bs0D11 b

    s0D14

    13

    bs0D11

    h i|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl fflfflfflfflfflfflfflfflffl}

    Bs0D1

    de1

    de2

    de3

    264375 Bs0D1 de

    jD1s 13

    bs1D11 b

    s1D12

    13

    bs1D11 b

    s1D13

    13

    bs1D11

    h i

    |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Bs1D1

    de1

    de2

    de3

    264375 Bs1D1 de

    52

    Fig. 5. Three-node triangular element and local coordinates in the DSG3.

    Fig. 6. Three sub-triangles (D1, D2 and D3) created from the triangle 1-2-3 in theCS-DSG3 by connecting the central point O with three field nodes 1, 2 and 3.

    6 P. Phung-Van et al. / Computational Materials Science xxx (2013) xxxxxx

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    Similarly, by using cyclic permutation, we easily obtain the bending

    and shear strains eDj0 ; j

    Dj1 ; j

    Dj2 ; e

    Djs ; j

    Djs and matrices

    BmDj ; Bb1Dj ; Bb2Dj ; Bs0Dj ; Bs1Dj ; j 2; 3, for the second sub-triangle

    D2 (triangle O-2-3) and third sub-triangle D3 (triangle O-3-1),

    respectively.

    Now, applying the cell-based strain smoothing operation in the

    CS-FEM [38,39], the membrane strain eDj0 , bending strains j

    Dj1 ; j

    Dj2

    and shear strainse

    Dj

    s ; j

    Dj

    s ;j

    1;

    2;

    3 are, respectively, used to cre-

    ate a smoothed membrane strain ~ee0, smoothed bending strains~je1; ~j

    e2 and smoothed shear strains ~e

    es ; ~j

    es on the triangular element

    Xe, such as:

    ~ee0 ZXe

    eh0UexdX X3j1

    eDj0

    ZDj

    UexdX 53

    ~je1 ZXe

    jh1UexdX X3j1

    jDj1

    ZDj

    UexdX;

    ~je2 ZXe

    jh2UexdX X3j1

    jDj2

    ZDj

    UexdX 54

    ~ees ZXeebsUexdX X

    3

    j1 ZDjeDjs UexdX;

    ~jes ZXe

    jhsUexdX X3j1

    ZDj

    jDjs UexdX 55

    where Ue(x) is a given smoothing function that satisfies the unity

    propertyRXeUexdX 1. Using the following Heaviside constant

    smoothing function

    Uex 1=Ae x 2 Xe

    0 x R Xe

    &56

    where Ae is the area of the triangular element, the smoothed mem-

    brane strain ~ee0, the smoothed bending strains ~je1; ~j

    e2 and the

    smoothed shear strains ~ees ; ~jes in Eqs. (53)(55) become

    ~ee0 1

    Ae X3

    j1ADje

    Dj0 57

    ~je1 1

    Ae

    X3j1

    ADjjDj1 ;

    ~je2 1

    Ae

    X3j1

    ADjjDj2 58

    ~ees 1

    Ae

    X3j1

    ADjeDjs ; ~j

    es

    1

    Ae

    X3j1

    ADjjDjs 59

    Substituting eDj0L; j

    Dj1 ; j

    Dj2 ; e

    Djs , and j

    Djs ; j 1; 2; 3, into Eqs. (57)

    (59), the smoothed bending strain ~ee0, the smoothed bending strains~je1; ~j

    e2 and the smoothed shear strains ~e

    es ; ~j

    es are expressed by

    ~ee0 eBmde; ~je1 eBb1 de; ~je2 eBb2 de; ~ees eBs0 de;

    ~jes eBs1 d

    e60

    where eBm; eBb1 ; eBb2 ; eBs0 and eBs1 are the smoothed bending andshear strain gradient matrices given by

    eBm 1Ae

    X3j1

    ADj BmDj ; eBb1 1

    Ae

    X3j1

    ADj Bb1Dj ; eBb2 1

    Ae

    X3j1

    ADj Bb2Dj

    eBs0 1Ae

    X3j1

    ADj Bs0Dj ; eBs1 1

    Ae

    X3j1

    ADj Bs1Dj

    61

    Therefore the global stiffness matrix of the CS-DSG3 are assembledby

    eK XNee1

    eKe 62where eKe is the element smoothed stiffness matrix for FGMMindlinplates given by

    ~Ke

    ZXe

    eBTi DeBjdX ZXe

    ~STi Ds~SjdX eBTi DeBjAe ~STi Ds~SjAe 63

    in which

    eBi

    eB

    mi

    TeB

    b1

    i

    TeB

    b2

    i

    T !;

    eSi

    eB

    s0i

    TeB

    s1i

    T !64

    From Eqs. (61) and (63), it is clearly seen that the element stiff-ness matrix in the CS-DSG3 does not depend on the sequence of

    node numbers, and hence the solution of CS-DSG3 is unchanged

    when the sequence of node numbers changes. In addition, due to

    using the cell-based strain smoothing technique in the CS-FEM

    [38,39], the CS-DSG3 can help to improve the accuracy as well as

    the stability of the DSG3 [54].

    6. Numerical results

    In this section, various numerical examples are performed to

    show the accuracy and stability of the CS-DSG3 compared to re-

    sults to several published ones in the literature. The ceramicmetal

    FGM plates are used, and their material properties, including

    Youngs modulus, Poissons ratio, thermal expansion coefficient,conductivity and density of pure plates are given in Table 1.

    6.1. Temperature field distribution in the FGPs subjected to only

    surface temperatures

    A functionally graded plate shown in Fig. 1 is made of

    Aluminum-Ziconia (Al/ZnO2-2). The thermal analysis is conducted

    by imposing constant surface temperatures at the Aluminum

    (metal) at 20 C and Ziconia (ceramic) surface at 300 C. The varia-

    tion of temperature varies only through the thickness direction.

    The distribution of temperature through the thickness is attained

    by solving the one-dimensional steady state heat conduction

    equation, which is shown in Eq. (3). In this analysis, the standard

    Table 1

    Material properties of FGM components.

    Properties Aluminum Alumina

    (Al2O3)

    Zirconia (ZrO2-

    1)

    Zirconia (ZrO2-

    2)

    E (GPa) 70 380 200 151

    m 0.3 0.3 0.3 0.3k (W/mK) 204 10.4 2.09 2.09

    a (106/C)

    23 7.2 10 10

    q (kg/m3) 2707 3800 5700 3000Fig. 7. Two square plate models: (a) clamped plate; (b) simply supported plate.

    P. Phung-Van et al. / Computational Materials Science xxx (2013) xxxxxx 7

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    Fig. 8. Four lowest frequencies of square plates by the CS-DSG3 corresponding to different values of volume fraction exponents: (a) n = 0; (b) n = 0.5; (c) n = 1; (d) n = 2.

    Fig. 9. Effect of volume fraction exponent n to four lowest frequencies of square FGM plates: (a) Mode 1; (b) Mode 2; (c) Mode 3; (d) Mode 4.

    8 P. Phung-Van et al. / Computational Materials Science xxx (2013) xxxxxx

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    one-dimensional finite element method is used.

    Fig. 3 illustrates the temperature distributions through the

    thickness Aluminum-Ziconia (Al/ZnO2-2) FGM plate for the various

    value of volume fraction exponent n. With the results of the tem-

    perature through the thickness, the thermal force and moment

    resultants Nth, Pth and Mth can be computed according to Eq. (20).

    6.2. Free vibration analysis of FGPs

    In this section, we investigate the accuracy and efficiency of theCS-DSG3 element for analyzing natural frequencies of plates. The

    plate may have simply (S) supported or clamped (C) edges. The

    symbol, CCCC or SSSS, for instance, represents clamped or simply

    supportted boundary conditions along the four edges of the

    rectangular plate, respectively. A non-dimensional frequency

    parameter - is often used to stand for the frequencies. The numer-ical results by the CS-DSG3 are then compared to analytical solu-

    tions and other available numerical results in the literature.

    6.2.1. Square FGM plates

    We now consider two square Al/Al203 plates of length L = 10and thickness t= 1 with two boundary conditions, CCCC and SSSS,

    Fig. 10. Shape of six lowest eigenmodes of a clamped square FGM plate by the CS-DSG3: (a) Mode 1; (b) Mode 2; (c) Mode 3; (d) Mode 4; (e) Mode 5; (f) Mode 6.

    Fig. 11. (a) a skew plate model; (b) a discretization of skew plate using triangular elements.

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    Fig. 12. Four lowest frequencies of the Al/ZrO2-2 skew plates with h = 15: (a) n = 0; (b) n = 0.5; (c) n = 1; (d) n = 3.

    Fig. 13. Four lowest frequencies of skew plates with h = 45: (a) n = 0; (b) n = 0.5; (c) n = 1; (d) n = 3.

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    as shown in Fig. 7a and b. A regular discretization using 144 3-node

    triangular elements and a non-dimensional frequency parameter

    - xL2=tffiffiffiffiffiffiffiffiffiffiffiffiqc=Ec

    pare used. Fig. 8 shows the four first non-dimen-

    sional frequencies of the FGM plate by the CS-DSG3 corresponding

    to different values of volume fraction exponents, n = 0, n = 0.5, n = 1

    and n = 2. It is seen that the present results match well with those

    ofkp-Ritz [33].

    Next, the effect of volume fraction exponent n to the non-

    dimensional frequency of Al/Al203 plate is investigated and the re-

    sults are shown in Fig. 9. Again, it is seen that the present results

    match well with those by kp-Ritz [33]. Fig. 10 plots the shape of

    six lowest eigenmodes of the clamped square FGM plates by the

    CS-DSG3. It is observed that the shapes of eigenmodes express cor-rectly the real physical modes of the plate.

    Fig. 14. Shape of six lowest eigenmodes of a clamped skew plate by the CS-DSG3: (a) Mode 1; (b) Mode 2; (c) Mode 3; (d) Mode 4; (e) Mode 5; (f) Mode 6.

    Table 2

    Non-dimensional center deflection w 100wcEmt3=121 m2qL4 of a Al/ZrO2-1

    plate (L/t= 5) subjected to a uniform load.

    Boundary condition Method n

    0 0.5 1 2

    CCCC DSG3 0.0731 0.0970 0.1137 0.1334

    CS-DSG3 0.0732 0.0972 0.1139 0.1336

    MLPG 0.0718 0.1073 0.1253 0.1444

    kp-Ritz 0.0774 0.1034 0.1207 0.1404

    SSSS DSG3 0.1768 0.2336 0.2679 0.3051

    CS-DSG3 0.1774 0.2343 0.2688 0.3060

    MLPG 0.1671 0.2505 0.2505 0.3280

    kp-Ritz 0.1722 0.2403 0.2403 0.3221

    Fig. 15. Non-dimensional central deflection w 100wcEmt3=121 m2qL4

    of asimply supported FGM plate subjected to a uniform load by the CS-DSG3.

    Fig. 16. Non-dimensional central deflection w 100wcEmt3=121 m2qL4 of a

    clamped FGM plate subjected to a uniform load by the CS-DSG3.

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    6.2.2. Skew FGM plates

    We now consider a Al/ZrO2-2 skew plate with various skew an-

    gles h as shown in Fig. 11a. Two boundary conditions (SSSS and

    CCCC) are studied, and the plate is discretized into 144 three-node

    triangular elements as shown in Fig. 11b.

    Figs. 12 and 13 show the first four non-dimensional frequencies

    of the Al/ZrO2-2 skew plate with skew angles h = 15 and h = 45 by

    the CS-DSG3, corresponding four different values of volume frac-

    tion exponents, n = 0, 0.5, 1.0 and 3.0. It is seen that the results

    by the CS-DSG3 agree well with those by kp-Ritz [33]. Furthermore,

    Fig. 14 plots the shape of six lowest eigenmodes of the clamped

    skew plate with skew angle h = 60 by the CS-DSG3. It is again ob-

    served that the shapes of eigenmodes express correctly the real

    physical modes of plate.

    6.3. Static analysis

    6.3.1. Square FGM plates

    6.3.1.1. Behavior of FGM plates subjected to only the mechanical

    load. We now perform a static analysis for two square Al/ZrO2-1

    plates (length L, thickness t) with clamped and simply supported

    boundary conditions as described in Fig. 7a and b. The plate is sub-

    jected to a uniform load q = 1 and the volume fraction exponent n

    ranges from 0 to 2. Using the uniform discretization of 13 13

    nodes, the non-dimensional center deflectionsw 100wcEmt

    3=121 m2qL4 of the plate (L/t= 5) by the CS-DSG3 are presented in Table 2, and compared with those of Mesh-

    less Local Petrov Galerkin (MLPG) [31] and kp-Ritz [11]. It is seen

    that the numerical results by the CS-DSG3 agree well to reference

    solutions. In addition, the ability of overcoming the shear locking

    of the CS-DSG3 for the cases of FGM plates with different boundary

    conditions is illustrated clearly in Figs. 15 and 16. It isseen thatthe

    non-dimensional central deflection of the FGM plate is almost

    independent with the change of the length-to-thickness ratio L/t

    when the plates become thin. The conclusion is correct for the

    plates with two simply supported and clamped boundary condi-

    tions, and also for four different volume fraction exponents, n = 0,

    0.5, 1.0 and 2.0.

    Next, Fig. 17 shows the effect of volume fraction exponent n to

    the deflection of the center line position of simply supported FGM

    plate by the CS-DSG3. It is seen that when the volume fraction

    Fig. 17. Effect of volume fraction exponent n to the non-dimentional deflectionw wcEmt

    3=121 m2qL4 of the center line position of a simply supported FGMplate by the CS-DSG3.

    Fig. 18. Non-dimentional axial stress profile rx rxt2=qL2

    through thethickness of a simplysupported FGM plate subjectedto a uniformload by the CS-DSG3: (a) n = 0;(b)n = 0.5; (c) n = 1; (d) n = 2.

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    exponent n increases, the deflection also increases, as expected.

    This result is quite similar to those by MLPG [31] and kp-Ritz [11].

    6.3.1.2. Behavior of FGM plates subjected to the thermo-mechanical

    load. In this example, the proposed CS-DSG3 is used to analyse the

    behavior of the FGPs subjected to both mechanical and thermal

    loadings. The temperature is assumed to be constant in the plane

    of the plate and varies through the thickness. The FGM plate (Al/

    ZrO2-2) is made from aluminum at the bottom surface and the Zir-conia at the top surface with the length L = 0.2 m and thickness

    t= 0.01 m. Material properties vary through the thickness of plate

    with respect to the power law as shown in Eqs. (1) and (2).

    We first investigate the behavior of the FGM plate subjected to a

    uniform mechanical load q, and the volume fraction exponents n of

    the plate are varied by n = 0, 0.5, 1 and 2. Figs. 18 and 19 show the

    axial stress profile through the thickness of FGM plates

    corresponding to two boundary conditions, simply supported and

    clamped ones. It is seen that the present results by the CS-DSG3

    match well with those by MLPG [31]. Fig. 20 shows the effect ofthe volume fraction exponent and the mechanical load parameter

    Fig. 19. Non-dimensional axial stress profile rx rxt2=qL2 through the thickness of a clamped FGM plate subjected to a uniform load by the CS-DSG3: (a) n = 0; (b) n = 0.5;

    (c) n = 1; (d) n = 2.

    Fig. 20. Effect of the volume fraction exponent and the mechanical load parameter

    P qL4=Emt4 (without thermal load) to non-dimensional central deflection

    wc wc=t of a simply supported FGM plate by the CS-DSG3.

    Fig. 21. Effect of the volume fraction exponent and the thermal load Tc to non-

    dimensional central deflection wc wc=t of a simply supported FGM plate by the

    CS-DSG3.

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    Fig. 22. Effect of the volume fraction exponent and the mechanical load parameter

    P qL4=Emt4 (with thermal loads, Tm = 20 C and Tc = 300 C) to non-dimen-

    sional central deflection wc wc=t of a simply supported FGM plate by the CS-

    DSG3.

    Fig. 23. Non-dimensional deflection wc wc=t of the central line position of a

    simply supported FGM plate subjected to a mechanical, thermal and thermo-

    mechanical loads by the CS-DSG3.

    Fig. 24. Effect of the thermal load Tc on central deflection wc wc=t of a simply

    supported FGM plate (with n = 1) subjected to a thermo-mechanical load by the CS-DSG3.

    Fig. 25. Effect of the skew angle on the axial stress through the thickness of a

    simply supported Al/ZnO2-1 plate (n = 0.5) subjected to a mechanical load by the

    CS-DSG3.

    Fig. 26. Effect of the skew angle on the axial stress through the thickness of a

    simply supported Al/ZnO2-1 plate (n = 2) subjected to a mechanical load by the CS-

    DSG3.

    Fig. 27. Effect of the skew angle on the axial stress through the thickness of a

    simply supported Al/ZnO2-1 plate (n = 0.5) subjected to a thermo-mechanical loadby the CS-DSG3.

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    P qL4=Emt4 to non-dimensional central deflection wc wc=t

    of the simply supported FGM plate. It is observed that the central

    deflection of the plate varies linearly with respect to the change

    of the load parameter. In addition as expected, the central deflec-

    tion increases correspondingly to the increase of the volume frac-

    tion exponent n. This is because a FGM plate with a larger volume

    fraction exponent means that it has a smaller ratio of ceramic com-

    ponent, and hence its stiffness is reduced.

    We next study the behavior of the FGM plate subjected to the

    thermal load. The temperature at the bottom surface is hold at

    Tm = 20 C and the temperature at the top surface is varied from

    0 C to500 C. Fig. 21 shows the effect of the volume fraction expo-

    nent and the thermal load to non-dimensional central deflection

    wc wc=t of the simply supported FGM plate. It is observed thatthe central deflection of the plate also varies linearly with respect

    to the change of the thermal load. In addition, when the thermal

    load increases highly at the top surface, the deflection of the plate

    increases upwardly. This implies that the FGM plates subjected to

    mechanical loads in the high temperature condition will have the

    deflection smaller than that of the FGM plates subjected to only

    mechanical loads in the normal temperature conditions. In other

    words, the FGM plates can resist mechanical loads in the high tem-

    perature conditions very well, as illustrated in the following

    numerical results.

    We nowinvestigate the behavior of FGM plates subjected to the

    thermo-mechanical load. The temperature is now holdTm = 20 C at

    the bottom surface and Tc = 300 C at the top surface. Fig. 22 shows

    the effect of the volume fraction exponent and the mechanical load

    parameter

    P qL

    4

    =Emt

    4

    (from

    14 to 0) to non-dimensional cen-

    tral deflection wc wc=t of the simply supported FGM plate. It is

    seen that the behavior of deflection under thermo-mechanical load

    is quitedifferent fromthe pure mechanical load. When the mechan-

    ical load parameter equals to zero,the deflection of FGMplate is dif-

    ferent from zero. This is because the high temperature at the top

    surface causes the thermal expansion, and hence makes the plates

    deflect upwardly. In addition as expected, the central deflection in-

    creasescorrespondinglyto the increaseof the volumefractionexpo-

    nent. Next, Fig. 23 shows the non-dimensional deflection of the

    central line position of a simply supported FGM plate subjected to

    a mechanical, thermal and thermo-mechanical loads. As expected,

    it is observedthat when theplate is subjectedto the themo-mechan-

    ical load, thedeflection of plate is smaller than that of the plate sub-

    jected to onlythe mechanical load. Lastly, Fig. 24 shows theeffect of

    the temperature Tc on the central deflection of a simply supported

    FGM plate subjected to a thermo-mechanical load and the volume

    fraction exponent n = 1. Again, it is seen that when the temperature

    Tcat the topsurfaceof FGMplate increases, the upwarddeflection by

    the thermal load is also increased and hence the total deflection of

    FGM plate becomes smaller than those of the FGM plate subjected

    to only pure mechanical loads.

    6.3.2. Skew FGM plate

    Wenow applytheproposedCS-DSG3to analysea simplysupported

    Al/ZrO2-1 skewplate as shown in Fig. 11a. The geometry of plate is gi-

    ven by length L = 10, thickness t= 0.1 and the plate is discretized by a

    uniformmesh of 13 13 nodes as shown in Fig. 11b. Wefirstconsider

    the effect of the skew angleh

    to the axial stress of the FGM plate sub-

    jectedto a uniformmechanical load q = 104 N/m2. The resultsfor three

    volume fraction exponents at n = 0.5 and n = 2.0 are shown in Figs. 25

    and 26, respectively. It is seen that when the skew angle becomes lar-

    ger, the absolute axial stress induced in the plate becomes higher.

    These results agree very well with those given in the reference [11].

    A similar observation for thecase of the FGM plate subjected to a ther-

    mo-mechanical load is also illustrated in Figs. 27and28. Lastly, Fig. 29

    shows the effect of the temperature on the axial stress through the

    thickness of the FGM plate subjected to a thermo-mechanical load at

    the volume fraction exponent n = 1. It is again observed that when

    the temperature becomes larger, the absolute axial stress induced

    in the plate becomes higher.

    7. Conclusions

    The paper presents an extension of the CS-DSG3 using three-

    node triangular elements to the C0-type high-order shear deforma-

    tion plate theory for the static and free vibration analyses of func-

    tionally graded plates (FGPs). In the FGPs, the material properties

    are assumed to vary through the thickness by a simple power rule

    of the volume fractions of the constituents. In the static analysis,

    both thermal and mechanical loads are considered and a two-step

    procedure is performed including a step of analyzing the tempera-

    ture field along the thickness of the plate and a step of analyzing

    the behavior of the plate subjected to both thermal and mechanical

    loads. The accuracy and reliability of the proposed CS-DSG3 is ver-

    ified by comparing its numerical solutions with those of other

    available numerical results. In addition, the numerical results bythe CS-DSG3 confirm that the FGM plates can resist mechanical

    Fig. 28. Effect of the skew angle on the axial stress through the thickness of a

    simply supported Al/ZnO2-1 plate (n = 2.0) subjected to a thermo-mechanical load

    by the CS-DSG3.

    Fig. 29. Effect of the thermal load Tc on the axial stress through the thickness of a

    simply supported Al/ZnO2-1 plate (n = 1.0) subjected to a thermo-mechanical loadby the CS-DSG3

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    loads in the high temperature conditions very well. This is due to

    the opposite responses of the FGM plate to the thermal loads and

    mechanical loads.

    Acknowledgements

    This work was supported by Vietnam National Foundation for

    Science & Technology Development (NAFOSTED), Ministry of Sci-

    ence & Technology, under the basic research program (Project

    No.: 107.02-2012.05).

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