Verification of dr method in the analysis of isotropic, orthotropic and laminated plates using large deflection theory

13
‫شندي‬ ‫جامعة‬ ‫مجلة‬‫العدد‬‫العاشر‬(‫يناير‬1122‫م‬)ISSN:1858-571X
journal.ush.sd E-mail:journal@ush.sd Box:142-143
Verification of Dynamic Relaxation Method in the
analysis
of isotropic, orthotropic and laminated plates using
large deflection theory
M. Mardi Osama1
‫اسة‬‫ر‬‫الد‬ ‫مستخلص‬:
‫لاص‬ ‫ى‬‫ى‬ ‫ال‬ ‫ااص‬ ‫ى‬‫ى‬‫ش‬‫خ‬ ‫ىادقص‬‫ى‬‫ع‬‫م‬ ‫ىختدام‬‫ى‬‫ع‬‫ا‬ ‫ىم‬‫ى‬‫خ‬ ‫ىس‬‫ى‬‫م‬‫الت‬ ‫ىلا‬‫ى‬‫ا‬ ‫ىه‬‫ى‬‫ف‬
‫ىدي‬‫ى‬‫ى‬‫م‬‫مخعا‬ ‫ىااي‬‫ى‬‫ى‬‫ج‬‫اخ‬ ‫ىد‬‫ى‬‫ى‬‫ف‬ ‫ا‬ ‫ى‬‫ى‬‫ى‬‫ت‬‫ال‬ ‫ىة‬‫ى‬‫ى‬‫ن‬‫المختاي‬ ‫ىه‬‫ى‬‫ى‬‫ل‬ ‫اى‬ ‫ىة‬‫ى‬‫ى‬‫ت‬‫خ‬‫ر‬‫ال‬(FSDT).
‫ى‬‫ى‬‫ى‬‫ع‬ ‫م‬ ‫ى‬‫ى‬‫ى‬‫ع‬‫ما‬ ‫ىام‬‫ى‬‫ى‬‫ن‬‫ر‬‫ت‬ ‫ىختدام‬‫ى‬‫ى‬‫ع‬‫تا‬ ‫ىادقص‬‫ى‬‫ى‬‫ع‬‫الم‬ ‫ىلا‬‫ى‬‫ى‬‫ا‬ ‫ىع‬‫ى‬‫ى‬‫م‬ ‫ير‬ ‫ىل‬‫ى‬‫ى‬‫خ‬ ‫ىخم‬‫ى‬‫ى‬‫ي‬
‫ىخرتا‬‫ى‬‫ى‬‫ى‬‫ع‬‫اق‬ ‫ىل‬‫ى‬‫ى‬‫ى‬‫ع‬ ‫ى‬‫ى‬‫ى‬‫ى‬‫م‬ ‫ا‬ ‫ىاقخد‬‫ى‬‫ى‬‫ى‬‫ت‬ ‫ىددل‬‫ى‬‫ى‬‫ى‬‫م‬‫الم‬ ‫ىاص‬‫ى‬‫ى‬‫ى‬‫د‬ ‫اللر‬ ‫ىا‬‫ى‬‫ى‬‫ى‬‫ي‬‫ت‬ ‫خ‬ ‫ىه‬‫ى‬‫ى‬‫ى‬‫ل‬‫ع‬
‫د‬ ‫ىدينامي‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ل‬‫ا‬(DR).‫ىخرتا‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬‫اق‬ ‫ع‬ ‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ل‬‫م‬ ‫ىة‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫د‬‫د‬ ‫ىار‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬ ‫خ‬ ‫ىي‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬‫خل‬ ‫ىخم‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ي‬
‫د‬ ‫ىدينامي‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ل‬‫ا‬(DR)‫ىاص‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ف‬‫ا‬‫ر‬‫انم‬ ‫لاص‬ ‫اا‬ ‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ل‬‫ى‬‫ل‬‫ر‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ي‬‫ت‬،‫ىة‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ن‬‫ر‬‫م‬‫ة‬ ‫ىات‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ش‬‫مخ‬ ،
‫ا‬ ‫ىه‬‫ى‬‫ف‬ ‫ا‬ ‫ى‬‫ى‬‫ت‬‫ال‬ ‫ىة‬‫ى‬‫ي‬‫مختان‬ ، ‫ا‬ ‫ى‬‫ى‬‫ت‬‫ال‬‫ىدي‬‫ى‬‫م‬‫مخعا‬ ‫ىااي‬‫ى‬‫ج‬‫خ‬‫مية‬ ‫ا‬‫ر‬‫ى‬‫ى‬‫ش‬ ‫اا‬ ‫ى‬‫ى‬‫ل‬ ،
‫ىة‬‫ى‬‫ى‬‫ى‬‫ي‬‫يت‬‫ر‬ ‫خ‬ ‫ة‬ ‫ىت‬‫ى‬‫ى‬‫ى‬ ‫م‬ ‫ع‬ ‫ى‬‫ى‬‫ى‬‫ى‬‫ل‬‫م‬ ‫ىدل‬‫ى‬‫ى‬‫ع‬‫ت‬ ‫ىا‬‫ى‬‫ى‬‫ى‬‫خ‬‫الن‬ ‫ىة‬‫ى‬‫ى‬‫ى‬‫ن‬‫ر‬‫ا‬ ‫تم‬ ‫ىاص‬‫ى‬‫ى‬‫ى‬ ‫ت‬ ‫ىدل‬‫ى‬‫ى‬‫ع‬ ‫لاص‬.
‫د‬ ‫ىدينامي‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ل‬‫ا‬ ‫ىخرتا‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬‫اق‬ ‫ىل‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬ ‫ىر‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬ ‫يظ‬(DR)‫ىل‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬‫تل‬ ‫ىر‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫خ‬ ‫الم‬
‫مختاينة‬ ‫عددية‬ ‫خمليلية‬ ‫عالي‬ ‫م‬ ً‫ق‬ ‫ت‬ ‫م‬ ً‫ا‬ ‫اف‬ ‫خ‬ ‫الممددل‬ ‫داص‬ ‫اللر‬.
‫ىل‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬ ‫ىع‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫م‬ ‫ىة‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫د‬‫د‬ ‫ىار‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬ ‫خ‬ ‫ىة‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ع‬‫ا‬‫ر‬‫الد‬ ‫ىلا‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ا‬ ‫ىه‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ف‬ ‫ىد‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ى‬‫ج‬ُ
،‫ىة‬‫ي‬‫المد‬ ‫الشر‬ ‫خشمع‬ ‫امع‬ ‫ع‬ ‫عدل‬ ‫عله‬ ‫يعخمد‬ ‫د‬ ‫الدينامي‬ ‫اقعخرتا‬
‫ال‬ ،‫ىا‬‫ى‬‫ى‬ ‫ع‬ ‫ن‬ ‫ىدي‬‫ى‬‫ى‬‫م‬‫مخعا‬ ‫ىااي‬‫ى‬‫ى‬‫ج‬‫اخ‬ ‫ىه‬‫ى‬‫ى‬‫ف‬ ‫ا‬ ‫ى‬‫ى‬‫ى‬‫ل‬‫ل‬ ‫ية‬ ‫ىت‬‫ى‬‫ى‬‫ش‬‫ال‬ ‫ىيماص‬‫ى‬‫ى‬‫ع‬ ‫الخ‬‫ىاص‬‫ى‬‫ى‬‫ف‬‫ثا‬
‫ىاد‬‫ى‬‫م‬‫اقت‬ ‫ىامالص‬‫ى‬‫ع‬‫م‬ ،‫ىة‬‫ى‬‫ي‬‫ام‬ ‫ال‬ً‫ا‬‫ى‬‫ى‬ ‫ي‬ ، ‫ىل‬‫ى‬‫ع‬‫الم‬ ‫ىع‬‫ى‬‫م‬‫الم‬ ،‫ىة‬‫ى‬‫ي‬‫الخمن‬ ‫ىادل‬‫ى‬‫ي‬‫خ‬‫ال‬ ،
‫نام‬‫ر‬‫ت‬ ‫اعختدام‬ ‫يم‬‫د‬ ‫ىدينامي‬‫ل‬‫ا‬ ‫ىخرتا‬‫ع‬‫اق‬(DR)‫اا‬ ‫ى‬‫ل‬ ‫ىع‬‫ي‬‫خمل‬ ‫ىه‬‫ف‬
‫اا‬ ‫ى‬‫ل‬ ، ‫ىدي‬‫م‬‫مخعا‬ ‫ىااي‬‫ج‬‫اخ‬ ‫ىه‬‫ف‬ ‫ا‬ ‫ى‬‫ت‬‫ال‬ ‫مختاينة‬ ، ‫ا‬ ‫الت‬ ‫ة‬ ‫مخشات‬
‫مختاينة‬ ‫لثتاناص‬ ‫منخظمة‬ ‫مماع‬ ‫خمص‬ ‫اص‬ ‫ت‬ ‫عدل‬ ‫لاص‬.
‫ىد‬‫ف‬‫ر‬ ‫ال‬ ‫ىي‬‫ع‬‫الت‬ ‫ىناد‬‫ع‬‫اس‬ ‫ىة‬‫ل‬‫لما‬ ‫نة‬‫ر‬‫ا‬ ‫الم‬ ‫نخا‬ ‫جمي‬ ‫مص‬
‫ا‬ ‫ىه‬‫ى‬‫ى‬‫ل‬‫ع‬ ً‫ا‬‫ىي‬‫ى‬‫ى‬‫ع‬‫عا‬ ‫ىد‬‫ى‬‫ى‬‫م‬‫يعخ‬ ‫اع‬‫ر‬‫ى‬‫ى‬‫ى‬‫م‬‫اسن‬‫ا‬ ‫ىع‬‫ى‬‫ى‬‫م‬‫الم‬ ‫ىاا‬‫ى‬‫ى‬‫ج‬‫خ‬‫ىل‬‫ى‬‫ى‬‫ع‬‫لم‬‫ىة‬‫ى‬‫ى‬‫ت‬‫خي‬‫ر‬‫خ‬ ،
‫اص‬ ‫ت‬ ‫ال‬.
Abstract:

13
First – order orthotropic shear deformation equations
for the nonlinear elastic bending response of rectangular
plates are introduced. Their solution using a computer
program based on finite differences implementation of the
Dynamic Relaxation (DR) method is outlined. The
convergence and accuracy of the DR solutions for elastic
large deflection response of isotropic, orthotropic, and
laminated plates are established by comparison with various
exact and approximate solutions. The present Dynamic
Relaxation method (DR) coupled with finite differences
method shows a fairly good agreement with other analytical
and numerical methods used in the verification scheme.
It was found that: The convergence and accuracy of the
DR solution is dependent on several factors including
boundary conditions, mesh size and type, fictitious densities,
damping coefficients, time increment and applied load. Also,
the DR large deflection program using uniform finite
differences meshes can be employed in the analysis of
different thicknesses for isotropic, orthotropic or laminated
plates under uniform loads. All the comparison results for
simply supported (SS5) edge conditions showed that
deflection is almost dependent on the direction of the applied
load or the arrangement of the layers
Notations
a, b plate side lengths in x and y directions respectively.
 6,2,1, jiA ji
Plate in plane stiffness.
5544
, AA Plate transverse shear stiffness.
 6,2,1, jiD ji
Plate flexural stiffness.

yxyx
 Mid – plane direct and shear strains

zyzx
 , Mid – plane transverse shear strains.

11
     xyyx GGEEEE  1221 ,, In – plane elastic longitudinal,
transverse and shear moduli.
   yzxz GGGG  2313 , Transverse shear moduli in the x – z and y
– z planes respectively.
yxyx
MMM ,, Stress couples.
  yxyyxx MMhEaMM ,,412 
 Dimensionless stress couples.
yxyx
NNN ,, Stress resultants.
  yxyyxx NNhEaNN ,,312 
 Dimensionless stress resultants.
q Transverse pressure.
 412 
 hEqaq y Dimensionless transverse pressure.
yx
QQ , Transverse shear resultants.
vu, In – plane displacements.
w Deflections
 1
 whw Dimensionless deflection
zyx ,, Cartesian co – ordinates.
 t Time increment
, Rotations of the normal to the plate mid – plane
yx
 Poisson’s ratio
  ,,,, wvu In plane, out of plane and rotational
fictitious densities.

zxyx
 ,, Curvature and twist components of plate
mid – plane
1 – Introduction
Composites were first considered as structural
materials a little more than half a century ago. From
that time to now, they have received increasing
attention in all aspects of material science,
manufacturing technology, and theoretical analysis.

13
The term composite could mean almost any thing if
taken at face value, since all materials are composites of
dissimilar subunits if examined at close enough details. But in
modern engineering materials, the term usually refers to a
matrix material that is reinforced with fibers. For instance, the
term “FRP” which refers to Fiber Reinforced plastic, usually
indicates a thermosetting polyester matrix containing glass
fibers, and this particular composite has the lion’s share of
today commercial market.
In the present work, a numerical method known as
Dynamic Relaxation (DR) coupled with finite differences is
used. The DR method was first proposed in 1960s and then
passed through a series of studies to verify its validity by
Turver and Osman Refs. [4], [8] and [9] and Rushton [2],
Cassel and Hobbs [10], and Day [11]. In this method, the
equations of equilibrium are converted to dynamic equations
by adding damping and inertia terms. These are then
expressed in finite difference form and the solution is
obtained through iterations. The optimum damping coefficient
and time increment used to stabilize the solution depend on a
number of factors including the matrix properties of the
structure, the applied load, the boundary conditions and the
size of the mesh used.
Numerical techniques other than the DR include finite
element method, which widely used in the present studies i.e.
of Damodar R. Ambur et al [12], Ying Qing Huang et al [13],
Onsy L. Roufaeil et al [14],… etc. In a comparison between
the DR and the finite element method, Aalami [15] found that
the computer time required for finite element method is eight
times greater than for DR that analysis, whereas the storage
capacity for finite element analysis is ten times or more than
that for DR analysis. This fact is supported by Putcha and
Reddy [16] who noted that some of the finite element
formulations require large storage capacity and computer
time. Hence, due to less computations and computer time
involved in the present study, the DR method is considered
more efficient than the finite element method. In another
comparison Aalami [15] found that the difference in
accuracy between one version of finite element and
another may reach a value of 10% or more, whereas a
comparison between one version of finite

13
element method and DR showed a difference of more than
15%. Therefore, the DR method can be considered of
acceptable accuracy. The only apparent limitation of DR
method is that it can only be applied to limited geometries.
However, this limitation is irrelevant to rectangular plates
which are widely used in engineering applications.
The Dynamic Relaxation (DR) program used in this
paper is designed for the analysis of rectangular plates
irrespective of material, geometry, edge conditions. The
functions of the program are to read the file data; compute the
stiffness of the laminate, the fictitious densities, the velocities
and displacements and the mid – plane deflections and
stresses; check the stability of the numerical computations, the
convergence of the solution, and the wrong convergence;
compute through – thickness stresses in direction of plate
axes; and transform through – thickness stresses in the lamina
principal axes.
The convergence of the DR solution is checked at the
end of each iteration by comparing the velocities over the
plate domain with a predetermined value which ranges
between 9
10
for small deflections and 6
10
for large
deflections. When all velocities are smaller than a
predetermined value, the solution is deemed converged and
consequently the iterative procedure is terminated. Sometimes
DR solution converges to an invalid solution. To check for
that the profile of the variable is compared with an expected
profile over the domain. For example, when the value of the
function on the boundaries is zero, and it is expected to
increase from edge to center, then the solution should follow a
similar profile. When the computed profile is different from
the expected values, the solution is considered incorrect and
can hardly be made to converge to the correct value by
altering the damping coefficients and time increment.
Therefore, the boundary conditions should be examined and
corrected if they are improper.
The errors inherent in the DR technique include
the discretization error which is due to the
replacement of a continuous function with a discrete
function, and there is an additional error because the
discrete equations are not solved exactly due to the
variations of the velocities from the edge of the plate
to the center.

13
Finer meshes reduce the discretization error, but increase
the round – off error due to the large number of
calculations involved.
2 - Large deflection theory
The equilibrium, strain, constitutive equations and
boundary conditions are introduced below without
derivation
2.1 Equilibrium equations:
0





y
N
x
N yxx
0





y
N
x
N yyx
 102 2
22
2
2















q
y
Q
x
Q
y
w
N
yx
w
N
x
w
N yx
yyxx
0





x
yxx
Q
y
M
x
M
0





y
yyx
Q
y
M
x
M
2.2 Strain equations
The large deflection strains of the mid – plane of
the plate are as given below:
x
z
x
w
x
u
x
















2
2
1


13
y
z
y
w
y
v
y
















2
2
1

 2























xy
z
y
w
x
w
x
v
y
u
yx




 



y
w
zx

 



x
w
zy

2.3 The constitutive equations
The laminate constitutive equations can be represented in
the following form:
 














































zx
zy
x
y
j
j
jiji
jiji
i
i
AA
AA
Q
Q
DB
BA
M
N




5545
4544
3
Where i
N denotes x
N , y
N and yx
N and i
M
denotes x
M , y
M and yx
M . ji
A , ji
B and ji
D
 6,2,1, ji are respectively the membrane
rigidities, coupling rigidities and flexural rigidities
of the plate. 
j
 denotes
yx 


 
, and
xy 



 
.
4544
, AA And 55
A denote the stiffness Coefficients
and are calculated as follows:-

13
 



1
5,4,,
1
k
k
z
z
ji
n
k
jiji
jizdckkA
Where ji
c are the stiffness of a lamina referred to the plate
principal axes and i
k , j
k are the shear correction factors.
2.4 Boundary conditions
Five sets of simply supported boundary conditions are used in
this paper, and are denoted as SS1, SS2, SS3, SS4 and SS5 as
has been shown in Fig (1) below.
0
0
0
0
0





xy
x
xy
x
M
M
w
N
N
a
b
y
xx
SS2
b
SS1
0 yxyyxy
MMwNN
0 yxyyxy
MMwNN
0
0
0
0
0






x
xy
x
M
w
N
N
0
0
0
0
0





xy
x
xy
x
M
M
w
N
N
0 yyxy
MwNN 
0 yyxy
MwNN 
a

13
Fig. (1) Simply supported boundary conditions
0
0
0
0
0







x
x
M
w
N
0 yy
MwNu 
b
a
y
x
SS3
a
b
0
0
0
0
0






x
xy
M
w
N
u
 yxy
MwvN 
b
a
SS4
0 yxy
MwvN 
a
b
0 yy
MwNu 
x
0
0
0
0
0







x
M
w
u
y
x
0 y
Mwvu 
a
b
0
0
0
0
0







x
x
M
w
N
0
0
0
0
0







xM
w
u
0 y
Mwvu 
SS4
SS5

34
3. Dynamic Relaxation of the plate equations
An exact solution of the plate equations is obtained using
finite differences coupled with dynamic relaxation method.
The damping and inertia terms are added to equations (1).
Then the following approximations are introduced for the
velocity and acceleration terms:
 
t
ttt
ttt
ba
ba




























/
4
2
1
2
2


In which  ,,,, wvu . Hence equations (1) becomes:
 





























y
N
x
Nt
t
u
k
kt
u yxx
u
b
u
u
a

*
*
1
1
1
 





























y
N
x
Nt
t
v
k
kt
v yxy
v
b
v
v
a

*
*
1
1
1
   521
1
1
2
22
2
2
*
*







































q
y
Q
x
Q
y
w
N
yx
w
N
x
w
N
t
t
w
k
kt
w yx
yyxx
w
b
w
w
a


 






























x
yxy
ba
Q
y
M
x
Mt
t
k
kt 

 
 *
*
1
1
1
 






























y
yyx
ba
Q
y
M
x
Nt
t
k
kt 

 
 *
*
1
1
1
The superscripts a and b in equations (4) and (5) refer
respectively to the values of velocities after and before
the time increment t and 1*
2
1 
   tkk . The
displacements at the end of each time increment, t ,
are evaluated using the following integration
procedure:

33
 6
t
t
b
ba





Thus equations (5),(6),(2) and (3) constitute the set of
equations for solution. The DR procedure operates as follows:
(1) Set initial conditions.
(2) Compute velocities from equations (5).
(3) Compute displacement from equation (6).
(4) Apply displacement boundary conditions.
(5) Compute strains from equations (2).
(6) Compute stress resultants and stress couples from
equations (3).
(7) Apply stress resultants and stress couples boundary
conditions.
(8) Check if velocities are acceptably small (say 6
10
).
(9) Check if the convergence criterion is satisfied, if it does
not repeat the steps from 2 to 8.
It is obvious that this method requires five fictitious densities
and a similar number of damping coefficients so as the
solution will be converged correctly.
4 –Verification of the dynamic relaxation (DR) method
using large deflection theory
Table (1) shows deflections, stress resultants and stress
couples in simply supported in – plane free (SS3) isotropic
plate. The present results have been computed with 66
uniform meshes. These results are in a fairly good agreement
with those of Aalami et al [1] using finite difference method
(i.e. for deflections, the difference ranges between 0.35% at
8.20q and 0 % as the pressure is increased to 97). A
similar comparison between the two results is shown in Table
(2) for simply supported (SS4) condition. It is apparent that
the center deflections, stress couples and stress resultants
agree very well. The mid – side stress resultants do not show
similar agreement whilst the corner stress resultants show
considerable differences. This may be attributed to the type of
mesh used in each analysis. A set of thin plate results
comparisons presented here with Rushton [2] who employed
the DR method coupled with finite olifferences. The present results

33
for simply supported (SS5) square plates were computed for
two thickness ratios using an 88 uniform mesh are listed in
table (3). In this instant, the present results differ slightly from
those found in Ref. [2]. Another comparison for simply
supported (SS5) square isotropic plates subjected to uniformly
distributed loads are shown in Tables (4) and (5) respectively
for deflection analysis of thin and moderately thick plates. In
this comparison, it is noted that, the centre deflection of the
present DR analysis, and those of Azizian and Dawe [3] who
employed the finite strip method are in fairly good agreement
(i.e. with a maximum error not exceeding 0.09%).
A large deflection comparison for orthotropic plates
was made with the DR program. The results are compared
with DR results of Turvey and Osman [4], Reddy’s [5], and
Zaghloul et al results [6]. For a thin uniformly loaded square
plate made of material I which its properties are stated in
Table (6) and with simply supported in – plane free (SS3)
edges. The center deflections are presented in Table (7) where
DR showed a good agreement with the other three.
A large deflection comparison for laminated plates was
made by recomposing sun and chin’s results [7] for [ 
44
0/90 ]
using the DR program and material II which its properties are
cited in Table (6). The results were obtained for quarter of a
plate using a 55 square mesh, with shear correction
factors 6/52
5
2
4
 kk . The analysis was made for different
boundary conditions and the results were shown in Tables (8),
and (9) as follows: The present DR deflections of two layer
antisymmetric cross – ply simply supported in – plane fixed
(SS5) are compared with DR results of Turvey and Osman [8]
and with sun and chin’s values for a range of loads as shown
in Table (4-8). The good agreement found confirms that for
simply supported (SS5) edge conditions, the deflection
depends on the direction of the applied load or the
arrangement of the layers. Table (9) shows a comparison
between the present DR, and DR Ref. [8] results, which are
approximately identical. The difference between laminates
 
90/0 and  
0/90 at 5/ ab is 0.3% whilst it is 0%
when 1/ ab .

31
The comparison made between DR and alterative
techniques show a good agreement and hence the present DR
large deflection program using uniform finite difference
meshes can be employed with confidence in the analysis of
moderately thick and thin flat isotropic, orthotropic or
laminated plates under uniform loads. The program can be
used with the same confidence to generate small deflection
results.
Table (1) comparison of present DR, Aalami and
Chapman’s [1] large deflection results for simply
supported (SS3) square isotropic plate subjected to
uniform pressure  3.0,02.0/  vah
q S c
w
 
 2
1
y
x
M
M  
 2
1
y
x
N
N
20.8
1
2
0.7360
0.7386
0.7357
0.7454
0.7852
0.8278
41.6
1
2
1.1477
1.1507
1.0742
1.0779
1.8436
1.9597
63.7
1
2
1.4467
1.4499
1.2845
1.2746
2.8461
3.0403
97.0
1
2
1.7800
1.7800
1.4915
1.4575
4.1688
4.4322
S (1): present DR results ( 66 uniform mesh over
quarter of the plate)
S (2): Ref. [1] results ( 66 graded mesh over quarter
of the plate)
  0,
2
1
1  zayx

33
Table (2) Comparison of present DR, Aalami and
Chapman’s [1] large deflection results for simply
supported (SS4) square isotropic plate subjected to
uniform pressure  3.0,02.0/  vah
q S c
w
 
 1
1
2
1
M
M  
 1
1
2
1
N
N  
 3
2
2
1
N
N  
 2
3
2
1
N
N  
 4
4
2
1
N
N
20.8
1
2
0.5994
0.6094
0.6077
0.6234
1.0775
1.0714
0.2423
0.2097
1.1411
1.1172
0.1648
0.2225
41.6
1
2
0.8613
0.8783
0.8418
0.8562
2.2435
2.2711
0.5405
0.4808
2.4122
2.4084
0.3177
0.4551
63.7
1
2
1.0434
1.0572
0.9930
1.0114
3.3151
3.3700
0.8393
0.7564
3.6014
3.6172
0.4380
0.6538
97.0
1
2
1.2411
1.2454
1.1489
1.1454
4.7267
4.8626
1.2604
1.1538
5.1874
2.2747
0.5706
0.9075
S (1): present DR results ( 66 uniform mesh over quarter of
the plate)
S (2): Ref. [1] results ( 66 graded mesh over quarter of the
plate)
  0)4(;0,
2
1
,0)3(;0,
2
1
)2(;0,
2
1
1  zyxzayxzyaxzayx

33
Table (3) Comparison of present DR, and Rushton’s [2]
large deflection results for simply supported (SS5) square
isotropic plate subjected to uniform pressure  3.0v
q S c
w  11

8.2
1
2
3
0.3172
0.3176
0.2910
2.3063
2.3136
2.0900
29.3
1
2
3
0.7252
0.7249
0.7310
5.9556
5.9580
6.2500
91.6
1
2
3
1.2147
1.2147
1.2200
11.3180
11.3249
11.4300
293.0
1
2
3
1.8754
1.8755
1.8700
20.749
20.752
20.820
S (1): present DR results ( 88;02.0/ ah uniform mesh
over quarter of the plate)
S (2): present DR results ( 88;01.0/ ah uniform mesh
over quarter of the plate)
S (3): Ref. [2] results (thin plate 88 uniform mesh over
  hzayx
2
1
,
2
1
1 
Table (4) Comparison of the present DR, and Azizian and
Dawe’s [3] large deflection results for thin shear
deformable simply supported (SS5) square isotropic plate
subjected to uniform pressure  3.0,01.0/  vah

33
q S c
w
9.2
1
2
0.34693
0.34677
36.6
1
2
0.80838
0.81539
146.5
1
2
1.45232
1.46250
586.1
1
2
2.38616
2.38820
S (2): Azizian and Dawe [3] results.
Table (5) Comparison of the present DR, and
Azizian and Dawe’s [3] large deflection results for
moderately thick shear deformable simply
supported (SS5) square isotropic plates subjected
to uniform pressure  3.0,05.0/  vah
q S c
w
0.92
1
2
0.04106
0.04105
4.6
1
2
0.19493
0.19503
6.9
1
2
0.27718
0.27760
9.2
1
2
0.34850
0.34938
S (2): Azizian and Dawe [3] results.

33
Table (6) Material properties used in the
orthotropic and laminated plate comparison
analysis.
Material 21
/ EE 22
/ EG 213
/ EG 223
/ EG 12
  2
5
2
4
kkSCF 
I 2.345 0.289 0.289 0.289 0.32 6/5
II 14.3 0.5 0.5 0.5 0.3 6/5
Table (7) Comparison of present DR, DR results of
Ref. [4], finite element results Ref. [5] and
experimental results Ref. [6] for a uniformly
loaded simply supported (SS3) square orthotropic
plate made of material I  0115.0/ ah
q  1c
w  2c
w  3c
w  4c
w
17.90.58590.58580.58 0.58
53.61.27101.27101.30 1.34
71.51.49771.49771.56 1.59
89.31.68621.68621.74 1.74
S (1): present DR results ( 55 uniform non –
interlacing mesh over quarter of the plate).
S (2): DR results of Ref. [4].
S (3): Reddy’s finite element results [5].
S (4): Zaghloul’s and Kennedy’s Ref. [6]
experimental results as read from graph.

33
Table (8) Deflection of the center of a two – layer anti
symmetric cross ply simply supported in – plane fixed
(SS5) strip under uniform pressure 01.0/,5/  ahab .
q S  
90/01
w  
0/902
w  0ji
Bw
 1%  2%  3%
33
3
3
1
0.6851
0.6824
0.6800
0.2516
0.2544
0.2600
0.2961
131.4
130.5
- 15.0
- 14.1
172.3
168.2
13
3
3
1
0.8587
0.8561
0.8400
0.3772
0.3822
0.3900
0.4565
88.1
87.5
- 17.4
- 16.3
127.7
124.0
33
3
3
1
1.0453
1.0443
1.0400
0.5387
0.5472
0.5500
0.6491
61.0
60.9
- 17.0
- 15.7
94.0
90.8
343
3
3
1
1.1671
1.1675
1.1500
0.6520
0.6630
0.6600
0.7781
50.0
50.0
- 16.2
- 14.8
79.0
76.1
333
3
3
1
1.2611
1.2629
1.2300
0.7418
0.7551
0.7600
0.8780
43.6
43.8
- 15.5
- 14.0
70.0
67.2
334
3
3
1
1.3390
1.3421
1.0300
0.8173
0.8327
0.8400
0.9609
39.3
39.7
- 14.9
- 13.3
63.8
61.2
S (1): present DR results
S (2): DR results Ref. [8].
S (3): Values determined from sun and chin’s results Ref. [7].
(1):   
www /100 1

(2):   
www /100 2

(3):   221
/100 www 

33
Table (9) Center deflection of two – layer anti – symmetric
cross – ply simply supported in – plane free (SS1) plate
under uniform pressure and with different aspect ratios
 18;01.0/  qah .
ab / S  
90/01
w  
0/902
w  0ji
Bw
 1%  2%  3%
5.0
1
2
0.8691
0.8683
0.8718
0.8709
0.3764
0.3764
130.9
129.1
131.6
130.2
- 0.3
- 0.3
4.0
1
2
0.8708
0.8708
0.8758
0.8557
0.3801
0.3801
129.1
129.1
129.1
130.4
- 0.6
- 0.6
3.0
1
2
0.8591
0.8593
0.8677
0.8678
0.3883
0.3883
121.2
121.3
123.5
123.5
- 1.0
- 1.0
2.5
1
2
0.8325
0.8328
0.8422
0.8424
0.3907
0.3907
113.1
113.2
115.6
115.6
- 1.15
- 1.1
2.0
1
2
0.7707
0.7712
0.7796
0.7799
0.3807
0.3807
102.4
102.6
104.8
104.9
- 1.14
- 1.1
1.75
1
2
0.7173
0.7169
0.7248
0.7251
0.3640
0.3640
97.0
97.0
99.1
99.2
- 1.0
- 1.1
1.5
1
2
0.6407
0.6407
0.6460
0.6455
0.3335
0.3325
92.1
92.7
93.7
94.1
- 0.82
- 0.70
1.25
1
2
0.5324
0.5325
0.5346
0.5347
0.2781
0.2782
91.4
91.4
92.2
92.2
- 0.4
- 0.4
1.0
1
2
0.3797
0.3796
0.3797
0.3796
0.1946
0.1949
95.1
94.8
95.1
94.8
0.0
0.0
S (1): present DR results
S (2): DR results Ref. [8].
(1):   
www /100 1

(2):   
www /100 2

(3):   221
/100 www 

34
5 – Conclusions
A Dynamic relaxation (DR) program based on finite
differences has been developed for large deflection analysis of
rectangular laminated plates using first order shear
deformation theory (FSDT). The displacements are assumed
linear through the thickness of the plate. A series of new
results for uniformly loaded thin, moderately thick, and thick
plates with simply supported edges have been presented.
Finally a series of numerical comparisons have been
undertaken to demonstrate the accuracy of the DR program.
These comparisons show the following:-
1. The convergence of the DR solution depends on several
factors including boundary conditions, mesh size, fictitious
densities and applied load.
2. The type of mesh used (i.e. uniform or graded mesh) may
be responsible for the considerable differences in the mid –
side and corner stress resultants.
3. For simply supported (SS5) edge conditions, all the
comparison results confirmed that deflection depends on the
direction of the applied load or the arrangement of the layers.
4. The DR large deflection program using uniform finite
differences meshes can be employed with confidence in the
analysis of moderately thick and flat isotropic, orthotropic or
laminated plates under uniform loads.
5. The DR program can be used with the same confidence to
generate small deflection results.
6. The time increment is a very important factor for speeding
convergence and controlling numerical computations. When
the increment is too small, the convergence becomes tediously
slow; and when it is too large, the solution becomes unstable.
The proper time increment in the present study is taken as 0.8
for all boundary conditions.
7. The optimum damping coefficient is that which produces
critical motion. When the damping coefficients are large, the
motion is over – damped and the convergence becomes very
slow. At the other hand when the coefficients are small, the
motion is under –

33
damped and can cause numerical instability. Therefore, the
damping coefficients must be selected carefully to eliminate
under – damping and over – damping.
8. Finer meshes reduce the discretization errors, but increase
the round – off errors due to large number of calculations
involved.
References
[1] Aalami , B. and Chapman J.C. “ large deflection behavior
of rectangular orthotropic plates under transverse and in –
plane loads”, proceedings of the institution of civil Engineers,
(1969), 42, pp. (347 – 382).
[2] Rushton K. R., “large deflection of variable – thickness
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