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Eng. & Technology, Vol.25, Suppl.of No.3, 2007
Experimental Study of Flexural Strength
of Laminate Composite Material
Dr. Jawad Kadhim Uleiwi*
Received on:18/12/2005
Accepted on: 14/5/2006
Abstract
The effect of fiber volume fraction on the flexural properties of the
laminated composite test specimens constructed of two layers, one of them
reinforced with glass fiber and the other layer reinforced with Kevlar fiber
has been investigated experimentally.
The results illustrate that tension stress decreases with the increase in
fiber volume fraction of glass fiber of the lower layer while it increases with
the increase of Kevlar volume fraction of the upper layer. As for compression
stress, it increases with the increase in volume fraction of glass fiber of the
lower layer while it decreases with the increase of volume fraction of Kevlar
fiber of the upper layer.
The results also show the maximum value of tension stress (= 25.3
MPa.) at Vf of Glass fiber (= 15 %) and Vf of Kevlar fiber (= 60 %), while the
maximum value of compression stress (= -17.1 MPa.) at Vf of Glass fiber (= 60
%) and Vf of Kevlar fiber (= 15 %).
ﺍﻟﺩﺭﺍﺴﺔ ﺍﻟﻌﻤﻠﻴﺔ ﻻﺠﻬﺎﺩﺍﺕ ﺍﻷﻨﺤﻨﺎﺀ ﻟﻤﺎﺩﺓ ﻤﺭﻜﺒﺔ ﺼﻔﺎﺌﺤﻴﺔ
ﺍﻟﺨﻼﺼﺔ
ﺃﺠﺭﻱ ﺍﻟﺒﺤﺙ ﻋﻤﻠﻴﺎ" ﻟﺩﺭﺍﺴﺔ ﺘﺄﺜﻴﺭ ﺍﻟﻜﺴﺭ ﺍﻟﺤﺠﻤﻲ ﻟﻸﻟﻴﺎﻑ ﻋﻠﻰ ﺨﻭﺍﺹ ﺍﻷﻨﺤﻨﺎﺀ ﻟﻌﻴﻨﺎﺕ
ﻓﺤﺹ ﻤﺎﺩﺓ ﺼﻔﺎﺌﺤﻴﺔ ﻤﻌﻤﻭﻟﺔ ﻤﻥ ﻁﺒﻘﺘﻴﻥ، ﺍﺤﺩﻯ ﻫﺎﺘﻴﻥ ﺍﻟﻁﺒﻘﺘﻴﻥ ﻤﻘﻭﺍﺓ ﺒﺄﺍﻟﻴﺎﻑ ﺍﻟﺯﺠﺎﺝ ﻭﺍﻟﻁﺒﻘﺔ
.ﺍﻻﺨﺭﻯ ﻤﻘﻭﺍﺓ ﻤﻥ ﺍﻟﻴﺎﻑ ﺍﻟﻜﻔﻠﺭ
ﺒﻴﻨﺕ ﺍﻟﻨﺘﺎﺌﺞ ﺒﺎﻥ ﺃﺠﻬﺎﺩ ﺍﻟﺸﺩ ﻴﻘل ﻤﻊ ﺯﻴﺎﺩﺓ ﺍﻟﻜﺴﺭ ﺍﻟﺤﺠﻤﻲ ﻷﻟﻴﺎﻑ ﺍﻟﺯﺠـﺎﺝ ﻟﻠﻁﺒﻘـﺔ
ﺍﻟﺴﻔﻠﻰ، ﺒﻴﻨﻤﺎ ﻴﺯﺩﺍﺩ ﻤﻊ ﺯﻴﺎﺩﺓ ﺍﻟﻜﺴﺭ ﺍﻟﺤﺠﻤﻲ ﻷﻟﻴﺎﻑ ﺍﻟﻜﻔﻠﺭ ﻟﻠﻁﺒﻘﺔ ﺍﻟﻌﻠﻴﺎ. ﻭﺃﻥ ﺍﺠﻬﺎﺩ ﺍﻟﻀـﻐﻁ
ﻴﺯﺩﺍﺩ ﻤﻊ ﺯﻴﺎﺩﺓ ﺍﻟﻜﺴﺭ ﺍﻟﺤﺠﻤﻲ ﻷﻟﻴﺎﻑ ﺍﻟﺯﺠﺎﺝ ﻟﻠﻁﺒﻘﺔ ﺍﻟﺴﻔﻠﻰ ﺒﻴﻨﻤﺎ ﻴﻘل ﻤﻊ ﺯﻴﺎﺩﺓ ﺍﻟﻜﺴﺭ ﺍﻟﺤﺠﻤﻲ
.ﻷﻟﻴﺎﻑ ﺍﻟﻜﻔﻠﺭ ﻟﻠﻁﺒﻘﺔ ﺍﻟﻌﻠﻴﺎ
ﻷﻟﻴـﺎﻑVf 3.52 = ( ﻋﻨـﺩMPa.) ﻜﻤﺎ ﺒﻴﻨﺕ ﺍﻟﻨﺘﺎﺌﺞ ﺒﺎﻥ ﺃﻋﻠﻰ ﻗﻴﻤﺔ ﻷﺠﻬﺎﺩ ﺍﻟﺸﺩ
( = - ﻷﻟﻴﺎﻑ ﺍﻟﻜﻔﻠﺭ )% 06 =( ، ﺒﻴﻨﻤﺎ ﺃﻋﻠﻰ ﻗﻴﻤﺔ ﻷﺠﻬﺎﺩ ﺍﻟﻀﻐﻁVf ﺍﻟﺯﺠﺎﺝ ) % 51=( ﻭ
.(= 15 %) ﻷﻟﻴﺎﻑ ﺍﻟﻜﻔﻠﺭVf ﻷﻟﻴﺎﻑ ﺍﻟﺯﺠﺎﺝ ) % 06=( ﻭVf 1.71 ﻋﻨﺩMPa.)
Notation: fiber material (N/m2)
b Thickness (m). Ei Modulus of elasticity of each
E1 Modulus of elasticity parallel layer (N/m2)
to the fiber direction (N/m2) Em Modulus of elasticity of the
E2 Modulus of elasticity matrix material (N/m2)
perpendicular to the fiber hi Height of the layer i (m)
direction (N/m2) I Moment of inertia (m4)
Ef Modulus of elasticity of the L Length of the specimens (m)
* Mat. Eng. Dept./ University of Technology
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
M Bending Moment (N.m) (%)
n Number of layer Y Distance from bottom outer
P Applied load (N) surface to a certain level
R Radius of curvature (m) distance (m)
S Equivalent stiffness (N.m2) yo Distance from bottom outer
Vf Volume fraction of the fiber surface to neutral axis (m)
(%) εi Strain components
Vi Volume fraction of each layer σi Stress components (N/m2)
(%)
Vm Volume fraction of the matrix
made from two layers to flexural
Introduction strength.
In general the flexural strength of The tension stresses of the lower
the laminate composite beam can be surface and compression stresses of the
improved considerably by the addition of upper surface at the mid point of the
fibers with a certain volume fraction of laminate composite beam were measured
each layer. experimentally depending on the
Unidirectional fiber-epoxy technique of strain gauge and strain
matrix laminate composites are meter.
commonly used for advanced In this research the fiber volume
applications, such as blade, the flexural fraction of the reinforcing layer of the
strength represents the major forms of laminate composite material represents
loading for this type of components. Here the major factor on the flexural strength
the bending test is used to test and of the laminated composite beam.
evaluate the strength properties of Most of the work is concentrated
laminate composite materials with on determining the stresses of the
constant span–to–thickness ratio and composite beam with different boundary
constant width–to-thickness ratio. conditions.
The flexural strength is also B.P. Hughes and N.I. Fattuhi
known as bending strength. It describes determined the various efficiency factors
how much of a non-moving load can be for steel and polypropylene fibers in
applied before a specimen yields or cement–based composites with particular
breaks, or it is the resistance of a material reference to flexural specimens [1].
to being broken by bending stresses. Yail J. Kim and Andrew Kong
High numbers mean that the material is studied a new composite material,
strong and can withstand a heavy load. namely steel reinforced polymer (SRP),
The composite used in this study in flexural strengthening of rectangular
was unidirectional laminate material reinforced concrete beams and found that
(glass fiber and Kevlar fiber) – epoxy increasing the flexural strength up to 53
matrix composite. % was achieved in the beams
The unidirectional specimens strengthened with SRP sheets [2].
were bend tested using universal material G.J. Turvey determined the
testing machine equipped with three - initial flexural failure loads as associated
point loading apparatus. central deflections for simply supported
The aim of this work is to composite plates subjected to a uniform
evaluate the laminated composite beam lateral pressure [3].
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
J. Kosoric, M.Cattani, S. Bouill, Laminated fiber reinforced
Ch. Godin, and J. Meyer evaluated the composite material consists of multi
composite reinforced with glass fibers of layers of various material and each layer
two dental materials: laboratory is called lamina, defined as a composite
composite resins and provisional resins. made by a single layer of material,
The analysis showed that glass fibers usually a flat arrangement of
reinforceing the laboratory composite unidirectional fibers or woven fibers in
resins have greater effect on the flexural matrix.
strength than modulus of elasticity [4]. Lamination may also be
Zsolt R'ACZ studied the analysis constructed using fabric material such as
of the flexural strength of the cotton, paper, or woven glass fibers
unidirectional composite carbon fiber embedded in plastic matrix [9].
composites and estimated the magnitude The laminate fiber reinforced
of size effect in carbon fiber composite composite specimen used in this research
and the result revealed that a specimen is composed of two layers of orthotropic
with lower span – to thickness ratio material. The upper layer is made up of
exhibits a lower flexural strength [5]. glass fiber – Epoxy matrix while the
Lassila J. and Vallittu P. K. lower layer is made up of Kevlar fiber –
investigated the influence of the position Epoxy matrix with the same thickness for
of fiber rich layer on the flexural each layer but with different fiber volume
properties of fiber – reinforced composite fraction.
construction. They found that the Any beam bending problem may
specimens with FRC positioned on the be solved in the usual fashion except that
compression side showed flexural " EI " will be replaced by the function
strength of approximately 250 MPa., "S" (Equivalent stiffness) computed from
while FRC positioned on the tension side the values of moment of the beam so as
showed strength ranging from 500 to 600 to determine the theoretical value of
MPa. [6]. deflection and stresses.
Johnston, C.D. and Zemp, R.W.
examined the influence of fiber content Derivation of Neutral Axis
(0.5-1.5 % of volume ), fiber aspect ratio The determination of neutral
(47-100), and fiber type (4 types) on the axes of laminate composite material is
flexural fatigue performance of steel fiber based on the equilibrium equation of the
reinforced concrete [7]. body. Therefore, the equilibrium can be
T. Waki and T. Nakamura written as [10] :-
studied and compared the flexural
strength of three types of Glass-fiber h1 h2 hi
reinforced composite systems. They ∫ σ1.b. dy + ∫ σ 2 . b. dy +
h0 h1
∫ σ . b. dy = 0
hi −1
i
found that the BR-100 (686 MPa.) and
vectris (634 MPa.) beams demonstrated …..(1)
significantly higher flexural strength than y − y0
the fiber Kor (567 MPa.) beam and also σ i = Εi . ε i = Εi …..(2)
R
found that ( Estenia / BR-100) composite
had a good mechanical strength for metal because εi = ( y – y0)/ R
– free restorations [8].
y − y0
n hi
∑∫Ε
Theoretical Analysis of Laminate
Composite Material i b. dy = 0 ....(3)
i = 1 hi −1 R
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
h1 h2
Εi . b i
n h
∑ R ∫ ( y − y0 ) dy = 0 …(4)
i =1
Μ = ∫ σ 1. b. dy. y + ∫ σ 2 . b. dy. y
h0 h1
hi −1
hi
n + − − − − + ∫ σ i ⋅ b ⋅ dy ⋅ y …(10)
hi −1
y − y0
n hi
Ei hi i ∴Μ = ∑ ∫ Ε .b i y. dy
Ei - 1 hi - 1 i-1 i = 1 hi −1 R
….(11)
[( )
n
b
E2
E3 h3
h2
Μ= ∑ Εi 2 hi3 − hi3− 1
6 R i =1
E1 h1 (
− 3 y0 hi2 − hi2−1 )] ….(12)
hi
n
Εi . b y2
∑1 R − y0 . y = 0 …(5)
∑ Ε [2 (h )
n
2 hi −1 b
i=
S = ΜR = i i
3
− hi3−1
6 i =1
n
Εi . b hi2 − 3 y0 (hi2 − hi2−1 ) ]
∑ R
…..(13)
− y0 hi
i =1 2
h 2
S = ΜR = [
∑ Εi 2 (hi3 − hi3− 1 )
b n
− − y0 hi − 1 = 0
i −1
…(6) 6 i =1
2
− 3 y0 (hi2 − hi2−1 ) ] ….(14)
Εi . b hi2
∴ MR ==EI = IS= E/ R
n
∑ R
2 − y0 hi
i =1 ∴ σ/ of the beam)
theory
y M/ (simple bending
hi2− 1
− + y0 hi − 1 = 0 …(7)
and S = EI = MR "equivalent stiffness"
2 I = bd3/ 12
n
h 2 − h 2−1
∑E
The Composite beam is simply
i ⋅ i
i
i =1 2 supported, the deflection of the beam is
n
therefore: The deflection (δ) = PL3/ 48EI
− yo ∑ (hi − hi −1 ) = 0 ….(8)
And the stresses are:
σmax = M * ymax / I
i =1
(may be compression or tension)
∑ Ε (h − hi2− 1 )
n
2 σmin = M * ymin / I
i i
1 i =1
y0 = ….(9)
∑ Εi (hi − hi − 1 )
2 n (may be compression or tension)
i =1
Composite Material:
Some properties of the laminar
Determination of Bending Moment:- composite materials in the longitudinal
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
direction and in the lateral direction are Figure (2) represents the three-
estimated from the rule of mixtures point test machine with a test specimen
Modulus of elasticity in the longitudinal of the laminated composite beam
direction (parallel to the laminas (Ec) supplied with strain gauge at both faces (
upper and lower face) to measure the
n strain from the strain gauge in order to
E c = ∑ E i ⋅ Vi …(15) calculate both the bending compression
i =1
and the tension stresses of the faces.
Modulus of elasticity in the lateral
direction (perpendicular to the laminas Instrumentation
(E2) The following instrumentations were
needed in the experimental work:
n
1 V
=∑ i ..(16)
1-) Digital strain meter.
Ec i =1 E i
2-) Specimens equipped with strain
gauges.
On the other hand the properties 3-) Weights.
of a unidirectional lamina are found by
using the following equation. Results and Discussion
The results obtained from the
experimental work of the flexural
E1 = E f ⋅ Vf + E m ⋅ Vm ..(17) analysis of the laminated composite test
specimen are illustrated in Table (1)
E f ⋅E m which represents the position of neutral
E2 = E3 = …(18) axis of the beam, deflection of the beam,
E f ⋅ Vm + E m ⋅ Vf
compression and tension stress of the
composite test specimen which is
Experimental Work
measured by using strain gauge and
The experimental work was
strain meter technique.
carried out in the field to determine
Figure (3) represents the
experimentally the deflection, tension
schematic diagram for the thickness of
and compression stress of the test
the laminate composite test specimen
specimens.
illustrating the values of stresses (tension
The unidirectional fibrous
and compression) with the position of
composite test specimen is composed of
neutral axis at different values of glass
two layers. The upper one is made from
fiber volume fraction of the upper layer
Kevlar fiber – Epoxy matrix composite
and a constant value of Kevlar fiber
and the lower one is made from glass
volume fraction of the lower layer.
fiber – Epoxy matrix with different fiber
It is also clear from this figure
volume fraction for each layer as
that the position of neutral axis decreases
following.
with the decrease of the glass fiber
volume fraction of the upper layer, where
Vf of Glass fiber (upper layer) = 15%, 30
as the value of the tension stresses
%, 45 %, and 60 %.
increases with the increase of the glass
Vf of Kevlar fiber (lower layer) = 15%,
fiber volume fraction of the upper layer.
30 %, 45 %, and 60 %.
As for the compression stress, it
decreases with the increase of the glass
The Geometry of the test specimen has a
fiber volume fraction.
length of (170 mm) and width of (13
Figure (4) shows the relationship
mm) and a thickness of (3.5 mm) as
between stress (compression and tension
shown in figure (1) [11].
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
stress) with the volume fraction of Glass It can be seen from this figure
fiber of the upper layer at a constant that deflection decreases in nonlinear
volume fraction of Kevlar fiber (=30 %) relationship with the increase of both
of the lower layer. glass fiber volume fraction and Kevlar
It is clear from this figure that the fiber volume fraction.
tension stress resulting from the bending It is found that the maximum
of the lower face decreases in nonlinear value of deflection is (=0.85 mm) at Vf of
relationship from (19.8 MPa.) to (13.7 glass (=15 %) and Vf of Kevlar (=15 %),
MPa.) with the increas of the glass fiber while the minimum value of deflection is
volume fraction from (15 %) to (60 %) (= 0.24 mm) at Vf of Glass (= 60 %) and
respectively due to the increase of the Vf of Kevlar (=60 %).
reinforcing material. On the other hand, Figure (7) shows the 3-
the compression stress of the upper Dimensional relationship between
surface increases from (-10.6 MPa.) to (- tension stress of the lower face and the
14.3 MPa.) with the increase in the glass ratios of glass and Kevlar fiber volume
fiber volume fraction from (15 %) to (60 fraction of each layer.
%) respectively. It can be seen from this figure
Figure (5) shows the relationship that the tension stress of the lower face
between the position of neutral axis increases in nonlinear relationship with
(measured from the reference of the the increase in Kevlar fiber volume
lower face ) and the glass fiber volume fraction because the Kevlar fiber
fraction of the upper layer at different reinforces the lower layer while it
Kevlar fiber volume fraction of the lower decreases in nonlinear relationship with
layer. the increase of glass fiber volume
It is clear from this figure that the fraction. Also it is clear from this figure
fiber volume fraction of each layer that the maximum value of the tension
influences the position of neutral axis, stress (= 25.3 MPa.) at Vf of Glass fiber
where the position increases in nonlinear (= 15 %) of the upper layer and Vf of
relationship with the increase in the glass Kevlar ( = 60 %) of the lower layer,
fiber volume fraction of the upper layer, while the minimum value of tension
while it decreases with the increase of stress (= 11.8 MPa.) at Vf of Glass fiber
Kevlar fiber volume fraction of the lower (= 60 %) of upper layer and Vf of Kevlar
surface. ( = 15 %) of lower layer.
It is found that the position of the Figure (8) shows the 3-
neutral axis (=1.12 cm) at Vf of Glass ( Dimensional relationship between
=15 %), while (= 1.5 cm) at Vf of Glass compression stress of the upper face due
(= 60 %) for the same value of Vf of to bending and ratios of glass and Kevlar
Kevlar (= 60 %). It has also been found fiber volume fraction of each layer.
that the highest value of the position of It can be seen from this figure
the neutral axis (=2.051 cm ) at Vf of that the compression stress of the upper
Glass (=60 %) of the upper surface and face decreases in nonlinear relationship
Vf of Kevlar (=15 %) of the lower with the increase of Kevlar fiber volume
surface. fraction. While it increase in nonlinear
Figure (6) shows the 3- relationship with the increase of Glass
dimensional relationship between the fiber volume fraction. It is also clear
lateral deflection of the laminated from this figure that the maximum value
composite beam and the volume fraction of the compression stress (= -17.1 MPa.)
of glass fiber and volume fraction of at Vf of Glass fiber (= 60 %) of upper
Kevlar fiber. layer and Vf of Kevlar (= 15 %) of the
459
Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
lower layer, while the minimum value of of glass of the lower layer while it
compression stress (= -9.6 MPa.) at Vf of decreases with the increase of Kevlar
Glass fiber (= 15 %) of the upper layer volume fraction of the upper layer.
and Vf of Kevlar ( = 60 %) of the lower The maximum value (= -17.1 MPa.)
layer. at Vf of Glass fiber (= 60 %) of the
And the comparison between the upper layer and Vf of Kevlar (= 15
theoretical results and experimental work %) of the lower layer, while the
at Vf of Kevlar fiber (= 60 %) Vf of Glass minimum value of tension stress (= -
fiber (= 15 %) illustrated in table (2). 9.4 MPa.) at Vf of Glass fiber (= 15
%) of the upper layer and Vf of
Conclusions Kevlar (= 60 %) of the lower layer.
The main conclusions of the
experimental investigation of flexural
analysis of laminated composite material References
are:- [1-] Hughes, B.P. and N.I. Fattuhi, "
1- Position of neutral axis measured Predicting the Flexural Strength of
from the lower face increases with Steel and Polypropylene Fiber –
the increase of glass fiber volume Reinforced Cemented Based Beams
fraction while it decreases with the ", Composites, Butterworth and Co.
increase of Kevlar fiber volume Ltd., January, (1977).
fraction. [2-] Yail J. Kim and Andrew Kong,"
2- The maximum value of deflection (= Flexural Strengthening of RC Beams
0.85 mm) is at Vf of Glass (=15 %) Using Steel Reinforced Polymer
and Vf of Kevlar (=15 %), while the (SRP) Composite ", M.Sc. Thesis,
minimum value of deflection (= 0.24 Queen's University, Kingstom,
mm ) is at Vf of Glass (=60 %) and Canada, (2005).
Vf of Kevlar (=60 %). [3-] Turvey G.J.," Uniformly loaded
3- Tension stress decreases from (19.8 Antisymmetric Cross-ply Laminated
MPa.) to (13.7 MPa.), while Rectangular Plates in an Initial
compression stress increases from (- Flexural Failure Analysis ", Fiber
10.6 MPa.) to (-14.3 MPa.) with the Science and Technology, No.16,
increase of Vf of Glass from (15 %) England, (1982).
to (60 %) of the lower layer and at Vf [4-] Kosoric J., M. Cattani, S. Bouill,
of Kevlar = 30 % of the upper layer. CH.Godin and J.Meyer,"
4- Tension stress decreases with the Reinforcement of Composite Resins
increase in fiber volume fraction of with Unidirectional Glass Fibers",
glass of the lower layer while European Cells and Materials, Vol. 3,
increase with increase Kevlar volume Suppl.1, (2002).
fraction of the upper layer. The [5-] Zsolt R'ACZ, "Analyzing the
maximum value (= 25.3 MPa.) is at Flexural Strength Properties of
Vf of glass fiber (= 15 %) of the Unidirectional Carbon / Epoxy
upper layer and Vf of Kevlar (= 60 Composites", Hungarian Scientific
%) of the lower layer, while the Research Fund, (2002).
minimum value of tension stress (= [6-] Lassila L.J. and Vallittu P.K., "The
11.8 MPa.) is at Vf of glass fiber (= Effect of Fiber Position and
60 %) of the upper layer and Vf of Polymerization Condition on the
Kevlar (= 15 %) of the lower layer. Flexural Properties of Fiber –
5- Compression stress increases with Reinforced Composite", Journal of
the increase of fiber volume fraction
460
Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
Contemp Dent, Vol.5, No.2, May Systems", IADR/AADR/CADR 80th
(2004). General Session, (San Dieg.), (2002).
[7-] Johnston, C.D. and Zemp, R.W.," [9-] T.J. Reinhard," Engineering Material
Flexural Fatigue Performance of Handbook Volume 1", Composite
Steel Fiber Reinforced Concrete- ASM International, (1987).
Influence of Fiber Content, Aspect [10-] Jones, R.M.," Mechanics of
Ratio, and Type," ACI Materials Composite Materials ", McGraw –
Journal, Vol.88,No.4, Jul-Aug, Hill, New York, (1975).
(1991). [11-] I. Ychang, " Composite Science and
[8-] T. Waki and T. Nakamura," Flexural Technology ", Elsvier applied
Strength and Bending Elasticity of Science Pub., Vol.24, No.1, (1985).
Fiber Reinforced Composite
Table: (1) Results of Experimental Work.
Volume fraction Position of Tension
Neutral Deflection Compression
Kevlar Glass Stress
axis * 10^-3 *10^-3 (m) Stress (MPa.)
Fiber Fiber (MPa.)
(m)
15 % 1.12 0.49 -9.6 25.3
30 % 1.273 0.35 -10.4 20.3
60 %
45 % 1.4 0.28 -11.4 17.9
60 % 1.5 0.24 -12.2 16.4
15 % 1.184 0.55 -10.9 22.8
30 % 1.365 0.39 -11.2 18.4
45 %
45 % 1.506 0.31 -12.2 16.4
60 % 1.618 0.27 -13 15.2
15 % 1.294 0.65 -10.6 19.8
30 % 1.512 0.46 -12.3 16.3
30 %
45 % 1.668 0.37 -13.4 14.7
60 % 1.785 0.326 -14.3 13.7
15 % 1.528 0.84 -12.4 16.1
30 % 1.784 0.617 -14.3 13.8
15 %
45 % 1.943 0.52 -15.8 12.6
60 % 2.051 0.46 -17.1 11.8
Table: (2) Comparison between the Experimental Work
and Theoretical Study.
461
Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
Deflection *10^-3 Compression Stress Tension Stress
(m) (MPa.) (MPa.)
Experimentally 0.49 -9.6 25.3
Theoretically 0.52 -10.25 23.8
0.0035 m
Glass Fiber – Epoxy Matrix
Kevlar Fiber – Epoxy Matrix
0.17 m 0.013 m
Figure (1): Test Specimen.
Strain Gauge
Test
Specimen Applied
Load
Figure (2): Flexural Apparatus with Test Specimen.
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
σt = 22.8 MPa. σt = 18.4 MPa.
Yo= 1.184 cm Yo= 1.365 cm
σc = -10.9 MPa. σc = -11.2 MPa.
Vf Glass = 15 % Vf Glass = 30 %
(a) Vf Kevlar = 45 % (b) Vf Kevlar = 45 %
σt = 16.4 MPa. σt = 15.2 MPa.
Yo= 1.506 cm Yo= 1.618 cm
σc = -12.2 MPa. σc = -13 MPa.
Vf Glass = 45 % Vf Glass = 60 %
(C) Vf Kevlar = 45 %
(d) Vf Kevlar = 45 %
Figure (3): Schematic Diagram for Tension and Compression Stresses with Position of
Neutral Axis of Laminated Composite Material at Different Fiber
Volume Fraction.
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
30
25
20
15
Stress (MPa.)
10
5 Vf of kevlar = 30 %
Tension Stress
0 Compression Stress
-5
-10
-15
-20
15 30 45 60
Vf of Glass %
Figure (4): Relationship Between Stress (Tension and Compression) of Laminate
Composite Beam and Fiber Volume Fraction of Glass at Constant Fiber
Volume Fraction of Kevlar = 30 %.
2.4
Vf of kevlar = 15 %
2.2 Vf of kevlar = 30 %
Position of Neutral axis (m) * 10^-2
Vf of kevlar = 45 %
Vf of kevlar = 60 %
2.0
1.8
1.6
1.4
1.2
1.0
15 30 45 60
Vf of Glass %
Figure (5): Relationship Between Position of Neutral Axis of the Laminate Composite
Beam and Fiber Volume Fraction of Glass at Different Fiber Volume
Fraction of Kevlar.
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
15 60
30 45
45 30
60 15
Figure (6): 3-Dimensional Relationship Between Deflection of the Laminate Composite
Beam, Fiber Volume Fraction of Glass and Fiber Volume Fraction of
Kevlar.
15 60
30 45
45 30
60 15
Figure (7): 3-Dimensional Relationship Between Tension Stress, Fiber Volume Fraction
of Glass and Fiber Volume Fraction of Kevlar.
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Eng. & Technology, Vol.25, Suppl.of No.3, 2007 Experimental Study of Flexural Strength
of Laminate Composite Material
15 60
30 45
45 30
60 15
Figure (8): 3-Dimensional Relationship Between Compression Stress, Fiber Volume
Fraction of Glass and Fiber Volume Fraction of Kevlar.
466
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