DETERMINING THE DEFLECTION OF A THIN COMPOSITE PLATE IN AN UNSTEADY TEMPERATURE FIELD Nguyen Dinh Duc *1 and Nghiem Thi Thu Ha 2 Keywords: composite plate, buckling, unsteady heat transf
Trang 1DETERMINING THE DEFLECTION OF A THIN COMPOSITE
PLATE IN AN UNSTEADY TEMPERATURE FIELD
Nguyen Dinh Duc *1 and Nghiem Thi Thu Ha 2
Keywords: composite plate, buckling, unsteady heat transfer, PVC, titanium particles
The buckling behavior of a thin particle-reinforced composite plate under the influence of an unsteady temperature field and a temperature gradient across its thickness is investigated An analytic solution for bending
of the plate is obtained in the form of double trigonometric series Based on the analytic result, a numerical test is carried out to study the thickness and time dependences of the buckling behavior of a plate made of a PVC matrix and titanium particles.
1 Introduction
In recent years, the behavior of plates under thermal loadings has been investigated by many authors In [1], the thermal buckling of rectangular composite multilayered plates with temperature-dependent material properties was studied by using
a layerwise plate theory Their buckling temperature was determined, and the influence of various mechanical and geometric parameters of the plates on the buckling temperature was investigated In [2], the finite-element method was used to investigate the thermal buckling behavior of composite laminated plates in detail In [3], the first-order shear deformation theory was employed to derive the equilibrium and stability equations for a simply supported moderately thick rectangular plate, made of
a functionally graded material, under two thermal loadings The buckling temperature was determined, and the influence of the aspect ratio of particles, of the relative thickness of layer, and of the gradient index and transverse shear on the buckling temperature was investigated In [4, 5], the thermal buckling of rectangular functionally graded plates is analyzed In [4], the authors investigated a plate under partial heating in its plane and examined the effects of material inhomogeneity, aspect ratio, and heated region on the critical buckling temperature In [5], by using the classical plate theory, the equilibrium, stability,
Mechanics of Composite Materials, Vol 48, No 3, July, 2012 (Russian Original Vol 48, No 3, May-June, 2012)
1University of Engineering and Technology, Vietnam National University, Hanoi
2University of Science, Vietnam National University, Hanoi
*Corresponding author; e-mail: ducnd@vnu.edu.vn
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol 48, No 3, pp 437-448 , May-June,
2012 Original article submitted December 28, 2011
Trang 2and compatibility equations are derived for an imperfect functionally graded plate under three types of thermal loading, and closed-form solutions for the critical buckling temperature are found
In this paper, we investigate the deflection of a rectangular composite plate, made of PVC and titanium particles, subjected to the action of an unsteady heat transfer through its thickness Note that the problem of unsteady heat transfer for a composite engineering tube was investigated in [6] Here, we assume that material components are homogenous and isotropic
In [7], we determined the elastic moduli of a particle-reinforced composite, and in [8] ― the coefficient of the thermal expansion of a composite material as a function of properties of its components and their volume fractions Here, we employ formulas for the elastic moduli of composites that take into account the interaction between the matrix and particles [7]:
ξ
3
G
m
15 1
The coefficient of thermal expansion of a particle-reinforced composite was determined in [8]:
ξ
= m+( c− m) ( +c( )m++ ( m)− )
where ξ =
=
∑V V i
i
N
1
is the volume fraction of the particles; G m , G c , K m , K c, νm, and νc are the shear moduli, bulk mod-uli, and Poission ratios of the matrix and particles, respectively
2 Governing Equations
Since the heat transfer through the thickness of the plate is unsteady, the heat conduction equation is [9]
∂
∂
∂
T
t a
T z
1
2
The initial and boundary conditions are
k T
h
k T
i
∂
− ∂
2 2
1 1
2 2
at at at
,
,
β β
where a k
C
1=
ρ is the thermal diffusivity of plate material; T1 and β1 are the ambient temperature and the convective heat
transfer coefficient, respectively, at z= −h 2 ; T2 and β2 are the ambient temperature and the convective heat transfer
coef-ficient, respectively, at z h= 2 ; k , C , and ρ are the coefficient of thermal conductivity, the specific heat, and mass density,
which are assumed in the form [6]
k= −(1 ξ)k m+ξ ,k c ρ= −(1 ξ ρ) m+ξρc, C C m m C c c
−
1
The strains of the plate are [10, 11]
x z w x
xx= ∂
∂ −
∂
∂
2
2 , e v
y z w y
yy =∂
∂ −
∂
∂
2
2 , e u
y
v
x z
w
x y
xy = ∂
∂ +
∂
∂
− ∂ ∂∂
1 2
2
where, u , v , and w denote the displacements of its midplane points along the x , y , and z axes, respectively.
Trang 3Hooke’s law for the stress–strain relationship at a varying temperature is [9]
σ
σ
ν
xy = E e xy
+
Inserting (3) into (4), we get the relations between stresses and displacements
σ
x
v
y z
w x
w
=
−
∂
∂ +
∂
∂ −
∂
∂
∂
2 2
2
2 ∆ ,
σ
y
u
x z
w y
w
=
−
∂
∂ +
∂
∂ −
∂
∂
∂
2 2
2
2 ∆ ,
σ
ν
y
v
x z
w
x y
= + ( ) ∂∂ +
∂
∂ −
∂
∂ ∂
2
The moments and membrane forces are
x
v y
N
−
∂
∂ +
∂
∂
− −
y
u x
N
−
∂
∂ +
∂
∂
− −
y
v x
xy =
+ ( ) ∂∂ +
∂
∂
x
w y
M
∂
∂
22 − −
2
2 1
ν
y
w x
M
∂
∂
22 − −
2
2 1
ν
x y
xy = − (1−ν)∂ ∂∂2 , (6)
where
h
h
−∫
α
2
2
, M T E z Tdz
h
h
=
−∫
2
2
, D= Eh
−
3 2
The basic equations for determining the deflection of the plate are the equilibrium equations [10]
∂
∂
N x
N y
x xy 0, ∂∂ +∂
N x
N y
(8)
∂
∂
∂
∂
∂
∂ ∂ +
∂
2 2
2
2 2
2
M x
M
x y
M
w
w
x y N
w y
3 Deflection of a Simply Supported Plate
Let
τ = a t
h12 , ζ = z
h, γ1= β1h
k , γ2 = β2h
k ;
then Eq (1) becomes:
∂
∂
∂
2
Trang 4with the initial and boundary conditions
T T
i
∂
−∂
at at at
τ
0
1 2 1 2
1 1
2 2
,
Using the Laplace transformation
T*=∞∫Te d−pτ τ
0
,
Eqs (9) and (10) are put into the form
d T
T
p i
2
2* * 0
dT
T p dT
T p
*
*
*
*
,
2
2
at
(12)
The solution of Eq (11) is
*= + 1cosh ζ + 2sinh ζ,
where D1 and D2 are determined from boundary conditions (12)
Introducing T* into (12), we obtain
p
A p
B p i
*= + ( )
( ), where
i
2
1 2
2
1 2
The solution of Eq (1) with conditions (2) is found in the form
B
A
n n
n
′( )+
−
( )
′ −( ) −
=
∞
∑
0 0
2 2 1
2
µ µ
µ τ, where
1 2
,
′( )= + +
B 0 γ1 γ2 γ γ ,1 2
Trang 5A( )− n = (T T− i) −
2
2
1 2
n n
(13)
2
1 2
µ
2
1 2 2 1 2 2 1 2
1
and µn =i p n+1 is the solution of the equation
tanµ γ γ
−
1 2 2
1 2
Let T0 =T i (T0is the absolute temperature in natural conditions); then
′( )+
−
( )
′ −( )
=
∞
−
∑
B
A
n n n
n
0 0
2 2 1
2
µ µ
where A( ),0 ′B ( ), 0 A(−µn2), and ′ −B( µn2) are determined as in (13) We assume that the midplane is free of strains; then (5) becomes
N x= − N T
−
1 ν, N y= − N T
−
Inserting DT (determined from (14)) into the expressions of N T and M T into (7), integrating them, and considering
Eqs (15), we get that N x=N y =N0 and M T =M0 With the forces and moments found and Eqs (6) inserted into Eqs (8), the first two equations are satisfied automatically, but the third one takes the form
D∇ ∇2 2w −N ∇ w=
0 2 0, or ∇ ∇ −
=
2 2w N0 0
The boundary conditions of a simply supported plate are
x
w y
x
∂
∂
0
2 2
2
2 0
y
w x
y
∂
∂
0
2 2
2
2 0
Equation (16) can be rewritten as
∂
∂
∂
∂
∂
∂
2 2
2 2 2 2
2
0
N
D w f
,
(17)
On the other hand, we can consider the boundary conditions
2 2 2 2
(18)
Trang 6Thereby, using boundary conditions (18), we obtain the boundary conditions for the unknown function f
D
+
− (10ν)=0 at x = 0 and x a= ,
D
+
− (10ν)=0 at y = 0 and y b=
From these equations, we find the unknown function f appearing in the first equation of system (17):
D
= −
−
(1 ν0 ),
The second equation of system (17) becomes
∂
∂
∂
−
2 2
2
N
D w
M
which is used for determining the deflection w of the plate in the case of unsteady heat transfer The boundary condition w = 0
is satisfied if w is expressed in the Fourier series [11]:
a
n y b
mn n m
=
=
∞
=
∞
∑
1 1
, (20)
where m and n are natural numbers We also express M0 in a Fourier series:
a
n y b
mn n m
0
1 1
=
=
∞
=
∞
∑
where
a
M
m n
=
0 2
if
, , , , , , , ,
Inserting (20), (21) into Eq (19), we get
w
a
a
n b
N D
m n
m n mn
mn
= 1
2 2 2
2 2
2 0
if
Thus, the analytic solution for the deflection of the plate under the conditions of unsteady heat transfer is
a
n b
N D
m mn
n m
=
−
=
1 3 5
2
2 2
2 0
, , ,
, , ,
a
n y b
This is a familiar solution form of the buckling problem of plates; however, unlike the known results, its coefficients are determined from geometric parameters of the plate, the properties and volume fractions of material components, and the parameters of the unsteady heat transfer process
Trang 74 Numerical Result
To study a specific case, we considered a composite plate containing titanium particles, whose material components had the following characteristics [6, 8]
PVC matrix: E m= 3 GPa, νm=0 2 , αm= ⋅8 10−5 /K, k m=0 16 W/(m·K), C m=900 J/(kg·K), and
ρm=1380 kg/m3
Titanium particles: E c =100 GPa, νc =0 34 , αc=4 8 10 ⋅ −6/K, k c=22 1 W/(m·K), C c=523 J/(kg·K), and
ρc=4500 kg/m3
The plate had a length a = 2 25 m, width b = 1 5 m, and thickness h = 0 02 m The surrounding medium was air with
β1=60 W/(m2·K) and T1=330K at z= −h 2 and T2 =300K, β2 =40 W/(m2 · K), and T0 =293 K at z h= 2
Inserting these data into the expression determining the deflection of the plate and using Matlab 7.1 for calculation, the results shown in Figs 1 and 2 were obtained
As seen from Fig 1, the volume fraction ξ of titanium particles has a significant effect on the bending behavior of the plate At ξ = 0.1, the deflections are positive and vary greatly along the plate At ( 0 1 < ≤ξ 0 2 ), the deflections are smaller and vary more uniformly when the volume fraction of the particles is increased When ξ reaches the value 0.3, the deflections
0
3.0
2.0
1.0
0
1.0 1.5
1 2 3
x, m
w, mm
4
Fig 1 Deflection w of the plate along its length at t = 1200 s and ξ = 0.1 (1), 0.15 (2), 0.21 (3), and
0.3 (4)
0
0.10 0.05 0 0.05 0.10 0.15 0.20 0.25
t, s
w, mm
=0.3
=0.2
Fig 2 Deflection w at the midpoint of the plate according to time t.
Trang 8and their differences at various points along the plate increase From Fig 2, we notice that, at the beginning, the deflection of the plate varies continuously with time, but at certain periods of time, the deflection of the plate at the midpoint remains almost unchanged
5 Conclusion
The results obtained show that, at a suitable volume content, the reinforcing titanium particles allows one to increase the bending resistance and thermal stability composite plates
Acknowledgment This work was financially supported by Project 107 02 — 2010 08 of the National Foundation for
Science and Technology Development of Vietnam — NAFOSTED The authors are grateful for this support
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