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Journal of Minera ls & Materials Ch ar ac teri zatio n & Engineeri ng, Vol. 10, No.8, pp.671-682, 2011
jmmce.org Printed in the USA. All rights reserved
Fracture Toughness of Glass-Carbon (0/90)S Fiber Reinforced Polymer
Composite – An Experimental and Numerical Study
P.S. Shivakumar Gouda1*, S.K. Kudari2, Prabhuswamy. S3, Dayananda Jawali3
1Research Scholar, SJCE, Mysore, Karnataka & Department of Mechanical Engineering,
SDM College of Engineering & Technology, Dharwad-580002, Karnataka, India
2Department of Mechanical Engineering, SDM College of Engineering & Technology,
Dharwad-580002, Karnataka, India
3Research Center, SJCE, Mysore-570006, Karnataka, India.
*Corresponding author: email@example.com
Mode-I fracture behavior of glass-carbon fiber reinforced hybrid polymer composite was
investigated based on experimental and finite element analysis. The compact tension (CT)
specimen was employed to conduct mode-I fracture test using special loading fixtures as per
ASTM standards. Fracture toughness was determined experimentally for along and across
the fiber orientation of the specimen. Results indicated that the cracked specimens are
tougher along the fiber orientations as compared with across the fib er orientations. A similar
fracture test was simulated using finite element analysis software ANSYS. Critical stress
intensity factor (K) was calculated at fracture/failure using displacement extrapolation
method, for both along and across the fiber orientations. The fractured surfaces of the glass-
carbon epoxy composite under mode-I loading condition was examined by electron
Key Words: Hybrid polymer composite, Mode -I fracture toughness, Stress intensity factor,
Finite element analysis.
The incorporation of different types of fibers into a single matrix has lead to the development
of hybrid composites. The behavior of hybrid composites is a weighed sum of the individual
components in which there is a more favorable balance between the inherent advantages and
disadvantages. Also, using a hybrid composite that contains two or more types of fiber, the
advantages of one type of fiber could complement with what are lacking in the other. As a
672 P.S. Shivakumar Gouda, S.K. Kudari, Prabhuswamy. S, Dayananda Jawali Vol.10, No.8
consequence, a balance in cost and performance can be achieved through proper material
design . The properties of a hybrid composite mainly depend upon the fiber content, length
of individual fibers, orientation, extent of intermingling of fibers, fiber to matrix bonding and
arrangement of both the fibers. The strength of the hybrid composite is also dependent on the
failure strain of individual fibers. Maximum hybrid results were obtained when the fibers are
highly strain compatible .
Various attempts have been made to characterize fracture toughness under mode-I and mixed
mode loading conditions, but mostly beam type specimens were used. If the so-called end
loaded split (ELS) specimen was loaded by the upper arm, mixed-mode loading conditions at
the crack tip are achieved. The mixed mode bending (MMB) test specimens has been
proposed by combining the schemes used for double cantilever beam (DCB) [3, 4] and end
notched flexure (ENF) tests to study mixed mode fracture toughness. However, for these test
methods there are problems to create a wide range of mixed-mode ratios which limit their
usefulness. Also, different beam type specimens would be required in order to obtain reliable
results for fracture toughness in pure mode-I, pure mode-II and mixed-mode loading
conditions. It is therefore necessary to develop other test methods to evaluate the mixed mode
fracture toughness under in-plane loading conditions starting from pure mode-I to pure mode-
Only limited work could be found in the literature regarding the mode-I fracture behavior of
hybrid composite materials [5 - 10] using compact tension specimens. In the present
investigation mode-I fracture experiments were conducted on compact tension specimen to
determine the fracture toughness of a glass-carbon reinforced epoxy hybrid polymer
composite material. Then, numerical simulations of the interlaminar fracture tests may be
considered as being useful, at least, for two reasons. The first one, numerical simulations or
virtual testing replace many expensive and time consuming experiments. In this case, it is the
necessary to test the numerical model in situation in which experimental results are easily
available. The second one is connected with the necessity to build new analytical models, and
then the numerical model is compared to experimental results for the purpose of fitting the
correct parameters of these models. Hence the title study was undertaken.
2. EXPERIMENTAL TECHNIQUES
Hybrid composite materials reinforced with Glass-Carbon Fiber are a new type of laminated
composites, which are becoming increasingly popular for various structural applications in
the automotive, aerospace and other industrial sectors. The present investigation has been
carried out with epoxy resin (LY556) at a room temperature with a curing hardener (HY951)
and Woven glass and carbon bi-directional (0/900)s fiber mesh. The matrix material was of
medium viscosity epoxy resin, which is cost effective because they require minimal setup
costs and the physical properties can be tailored to specific applications. The plain-woven
Vol.10, No.8 Fracture Toughness of Glass-Carbon (0/90)S Fiber Reinforced Polymer 673
glass and carbon fiber mats were the reinforcements; all the fibers in the fabric have
diameters less than 30 μm.
2.2 Fabrication of Composite
The aim of the test is to determine the fracture toughness of Glass-Carbon-Epoxy
thermosetting composite material. For this purpose, the compact tension (CT) specimen was
used. To prepare the specimens by hand layup method [11, 12], 18 layers of cross-ply glass
and carbon laminates each of 0.2 and 0.3mm thickness alternatively 350 mm length and 350
mm width was put together to form a block with dimension of 350*350*20 mm for fracture
test. Similarly for tensile test 6 layers alternatively 350mm length and 350mm width
dimension of 350*350*4 mm, was used.
2.3 Tensile Test
The main aim of the tensile test is to determine the elastic modulus of the selected material.
This test was carried out as per the ASTM D638 standard . Glass-Carbon (0/90)s fiber
reinforced composite was taken in the form of 4mm thick sheets. To test its orthotropic
the specimens were machined from prepared block in two different directions along and
across the fiber direction as shown in Figure 1.
Figure 1. Specimen prepared directions with fiber directions
2.4 Fracture Test
Fracture toughness test for Glass-carbon reinforced epoxy composite was carried out as per
ASTM D 5045  and ASTM E1820  standards. All the details of specimen
preparation, experimental procedure, and formulas used for calculation of critical stress
intensity factor are taken from above mentioned standards. In this test method a notched
specimen was loaded in tension that has been pre-cracked. The load corresponding to a 2.5 %
apparent increment of crack extension was established by a specified deviation from the
linear portion of the record. The KIc value was calculated from this load by equations that
have been established on the basis of elastic stress analysis on specimens of the type
674 P.S. Shivakumar Gouda, S.K. Kudari, Prabhuswamy. S, Dayananda Jawali Vol.10, No.8
described in the standard ASTM D 5045. The validity of the determination of the KIc value
by these test methods depends upon the establishment of a sharp-crack condition at the tip of
the crack, in a specimen of adequate size to give linear elastic behavior.
Figure 2. Standard specimen dimensions
CT geometries were recommended over other configurations because this geometry will
allow smaller specimen sizes to achieve plane strain. Specimen dimensions shown in Figure 2
are taken as per the ASTM D 5045 standard. The material is taken in the form of a sheet, the
specimen thickness, B =20mm was taken and it is identical with the sheet thickness. The
sample width, W = 2B. In the specimen geometry the crack length, a, is selected in such a
way that 0.45 < a/w < 0.55. To tests it’s mode-1 and mixed mode  fracture toughness
specimens were machined from prepared block of composite in two different directions along
and across the fiber directions.
2.5 Test Setup
Specimens are prepared in accordance with ASTM standards were loaded on a computer
controlled Universal Testing Machine. The specimens were clamped in custom-built
Transfixing fixture was designed and fabricated to perform the fracture test for mode-I,
EN150 steel was used to fabricate this fixture. This was subjected to monotonic uniaxial
tension at a displacement rate of 5 mm/min. The tests were closely monitored and conducted
at room temperature. Since it is difficult to detect the first point of damage in laminates, the
elongation recorded corresponds to the applied load the hybrid composite specimen can
withstand. The fracture toughness KIC has been calculated by using load extension curve.
2.6. Finite Element Analysis of the Fracture Model
A 3D Finite Element model was created to simulate fracture test in ANSYS 10. Solving a
fracture mechanics problem involves performing a linear elastic or elastic-plastic static
analysis and then using specialized post processing commands or macros to calculate desired
fracture parameters . In this section, we will concentrate on two main aspects of this
procedure: Modeling the crack region and calculating fracture parameters. The most
important region in a fracture model is the region around the edge of the crack. In linear
elastic problems, it has been shown that the displacements near the crack tip (or crack front)
Vol.10, No.8 Fracture Toughness of Glass-Carbon (0/90)S Fiber Reinforced Polymer 675
vary as √r, where r is the distance from the crack tip. The stresses and strains are singular at
the crack tip, varying as 1/√r. To pick up the singularity in the strain, the crack faces should
be coincident, and the elements around the crack tip (or crack front) should be quadratic, with
the middle side nodes placed at the quarter points. Such elements are called singular.
Figure 3. Singular element of ANSYS
Figure 4. Nodes on the quarter point
elements at the tip of the crack.
The recommended element type for 3-D models is SOLID95, the 20-node brick element. As
shown in Figure 3, the Figure 4 shows the first row of elements at a distance of 0.1mm from
the crack tip around the crack front should be singular elements. After modeling the crack
model as per the standard dimensions, a quarter point elements are created at the crack tip.
Applied boundary conditions: The model is constrained in all degrees of freedom other
than y direction at the bottom half hole region and the load is applied on the top half hole
region, where the pin load is acting as shown in the Figure 5.
Figure 5. Meshed specimen with applied boundary conditions
3. RESULTS AND DISCUSSION
Experiment have been carried out to characterize the candidate composite material under
different loading conditions and with various specimen configurations, the analysis of the
around the crack
676 P.S. Shivakumar Gouda, S.K. Kudari, Prabhuswamy. S, Dayananda Jawali Vol.10, No.8
results and the influence of various parameters on the properties are summarized in the
3.1 Tensile Behavior of Hybrid Polymer Composite
Six specimens from each fiber orientation of the composite were tested. The dimensions of
the test coupons were 165 mm in length, 12 mm in width, and, 4 mm in thickness
respectively. The 12 sample specimens were tested at a cross-head speed of 5 mm / min.
Stress versus Strain responses were plotted and are shown in Figure 6 and Figure 7.
Figure 6. Stress v/s strain (%) plot for across the specimen.
Figure 7. Stress v/s strain (%) plot for along the specimen
Table 1. Young’s modulus for along and across specimen
Specimen Young’s Modulus for
Young’s Modulus for
1 3404 3102
2 2432 3167
3 1495 2402
4 3402 2318
5 1756 2410
6 1606 3198
Average 2349.167 2766.17
Vol.10, No.8 Fracture Toughness of Glass-Carbon (0/90)S Fiber Reinforced Polymer 677
The initial tensile response is typical for visco-elastic materials, in that they are initially linear
and later become nonlinear. The elastic modulus for six composite specimens was calculated
using the slope of stress v/s strain curve. The average modulus for along and across the fiber
directions of the glass-carbon epoxy composite was found to be 2766.17 MPa and 2349.16
Mpa respectively. These values are low for these types of composite structures especially for
the woven fiber case. It is observed that the difference in Young’s modulus of along and
across specimens is 417 MPa, this data is used to calculate mode-I fracture property of the
glass-Carbon fiber reinforced epoxy hybrid composite polymer.
Figure 8. Glass-Carbon epoxy hybrid composite test coupon after tensile test showing (a)
front view and (b) side view. With a magnification of 4X
This may be the result of insufficient wetting of fibers and manual errors encountered during
the hand layup method of manufacturing process. A microscopic analysis was conducted in
order to verify this hypothesis. The resulting microscopic images are shown in Figure 8. The
fracture of the Glass-Carbon epoxy hybrid composite test coupon, shown in the above Figure
8(a), began at points A and B. At these points an accumulation of stresses occurred and this is
shown by the crazing (white area) on the coupon. This stress concentration was greater than
the threshold of the material and failure occurred at points A and B. Thereafter there was
catastrophic failure along the width of the specimen as the load bearing area decreased.
The test coupon shown in Figure 8 exhibits a fracture path that is angled. This angle was
determined to be approximately 20º to the vertical in Figure 8(a). In Figure 8(b) the fracture
path is angled at 45º to the vertical, and this is typical of a shear crack. When the load was
applied to the specimen, stresses were transversely induced along the fiber edges. Due to the
random nature of the fibers, high stress concentration areas were created. The induced
stresses in these areas were not greater than the allowable stress but they were sufficient to
rupture the matrix. The angled fracture shown in Figure 8(a) is actually the path taken by
these stresses, along the fiber edges, throughout the width of the coupon.
3.2 Mode-I Fracture Behavior of Hybrid Polymer Composite
Mode-I Fracture toughness test for Glass- Carbon fiber reinforced epoxy polymer composite
was carried out as per ASTM D 5045  and ASTM E1820  standards. All the details of
678 P.S. Shivakumar Gouda, S.K. Kudari, Prabhuswamy. S, Dayananda Jawali Vol.10, No.8
specimen preparation, experimental procedure, and formulas used for calculation of critical
stress intensity factor are taken from above mentioned standards. The figures 9 and 10, show
a Load versus displacement response for the glass-carbon reinforced epoxy composite
specimen, from this curve the hybrid polymer composite achieved a average maximum
critical stress intensity factor (KIC) of 29.68 MPa√m at a average peak load of 2958N, while
an average minimum critical stress intensity factor (KIC) of 23.59 MPa√m at a average peak
load of 2860N has been obtained.
For the CT specimens tested in mode-I loading, the crack growth was not so smooth nor
continuous instead, fewer crack jumps of a few millimeters each time were observed in load
versus displacement curves ( Figure 9 and 10) for across and along the fiber orientation of the
Figure 9. Load Vs displacement plot for across the fiber direction
Figure 10. Load Vs displacement plot along the fiber direction
Further the study has been extended to know the fewer crack jumps during fracture, the
mode-I fracture surfaces were examined using a microscope. The microscopic study of
fracture surfaces of the mode-I specimens are shown in Figure 11a and b. Figure 11a shows
the fractrograph of the mode-I fracture along the fiber orientation of the initiation area taken
just beyond the pre crack of the glass- carbon-epoxy composite. Therefore, the fracture
surfaces show the first increment of crack growth which corresponds to the measured fracture
The mode-I fracture surface is indicative of a brittle cleavage failure with relatively smooth
and flat matrix fracture (11a-A) and shows very small debonding between fiber and matrix,
Vol.10, No.8 Fracture Toughness of Glass-Carbon (0/90)S Fiber Reinforced Polymer 679
also a pull out of glass fibers, which would explain the low mode-I fracture toughness.
Figure11b shows the fractrograph of a the mode-I fracture loading across the fiber orientation
of the initiation area taken just beyond the pre crack of the glass-carbon-epoxy composite Its
characteristic is overall flatness (11b-C) on the matrix fracture (11b-D). Also a brittle
cleavage failure with relatively smooth and flat matrix fracture (11a-A) shows very small
debonding between fiber and matrix (11b-A and B) also a large pull out of glass fibers,
shown in Figure 11b.
Figure 11a. Fracture surfaces loading along the fiber
Figure 11b. Fracture surfaces loading across the fiber
orien tat ion
3.2 Finite Element Analysis of Mode-1 Fracture Behavior of Hybrid Polymer Composite
The general-purpose finite element (FE) code ANSYS is used in this study. A several test
samples of Compact tension (CT) specimen under mode-I loading has been considered in the
Glass fibers pull out Carbon fibers
Brittle cleavage of Epoxymatrix
Glass fibers pull out Carbon fibers
Brittle cleavage of Epoxymatrix
Glass fibers pull out Carbon fibers
Brittle cleavage of EpoxymatrixGlass fibers pull out
Glass fibers pull out Carbon fibers
Brittle cleavage of Epoxymatrix
680 P.S. Shivakumar Gouda, S.K. Kudari, Prabhuswamy. S, Dayananda Jawali Vol.10, No.8
present study with orthotropic material properties as inputs from the tensile test and
maximum load and crack length as inputs from experimental fracture test. A series of finite
element calculations have been made on the several specimens considering full specimen
geometry due to lack of loading symmetry. A typical 3-dimensional FE mesh used in the
analysis is shown in Figure.5. The loading and displacement boundary conditions were used
in this analysis. Three-dimensional elastic FE calculations were performed using SOLID95,
the 20-node higher order brick elements considering plane strain condition. In these
calculations, the material behavior has been considered to be linear elastic. The stress
intensity factors in mode-I loading (KI) have been computed for various loadings and crack
lengths using ANSYS post processor. The magnitudes of KI have also been computed
experimentally and cited in the Table 2. This result in Table 2 indicates that there exists some
discrepancy in estimation of stress intensity factors by experimental fracture test and present
FE results. It is found that there is 15% and 24% error in estimation of KI. This discrepancy
in estimated magnitudes of stress intensity factor attributed to varied loading condition in
experimental fracture test through loading fixtures.
Table 2. Experimental and FE results for across the specimen
Table 3. Experimental and FE results for along the specimen
The computed magnitudes of KI for the CT specimens are tabulated and it can be seen that
the stress intensity factors for mode I is greater along the fiber orientation as compared with
the across the fiber orientation.
The difference in the magnitude of elastic modulus along and across the fiber orientation is
417 MPa. Also the elastic modulus is dominant in along the fiber orientation of the tensile
specimen. Similarly the magnitude of the critical stress intensity factor (KIC) is dominant in
along the fiber orientation of the CT specimen.
1 2860 6.50 34.07 28.95 15.02
2 2232 8.0 21.67 27.26 22.93
3 2123 6.0 18.35 24.85 24.46
4 2367 7.0 20.30 23.38 19.90
1 2852 5.0 32.84 39.46 17.29
2 2958 5.0 26.34 32.54 23.31
3 2607 5.0 29.23 34.45 17.85
4 2639 13.0 30.34 38.75 21.68
Vol.10, No.8 Fracture Toughness of Glass-Carbon (0/90)S Fiber Reinforced Polymer 681
The fracture surfaces of the glass-carbon-epoxy hybrid composite under mode-I loading
condition were examined by electron microscopy to gain insight into the failure responses.
The fracture surface observations showed that the mode-I fracture surface is indicative of
brittle cleavage failure with relatively smooth and flat matrix fracture and shows a little
debonding between fiber and matrix with small amount of glass fiber pullout can be
The finite element result indicates that the magnitude of the critical stress intensity factor
(KIC) is dominant in along the fiber orientation of the CT specimen also it is found that there
is 15% and 24% error in estimation of KIC. This discrepancy in estimated magnitudes of
stress intensity factor attributed to varied loading condition and method of composite
fabrication, experimental fracture test through the loading fixtures.
The authors express their thanks to Dr. S.Mohankumar, Principal, and Management, S.D.M
College of Engineering and Technology, Dharwad, Karnataka, India- 580002, and Prof.
V.K.Heblikar Professor & Head, Mechanical Engineering, and Dr.S.T.Nandibewoor,
Chairman, Department of PG Studies, Karnatak University, Dharwad also to the staff of
Mechanical Engineering Department, S.D.M College of Engineering and Technology, and
the facility provided for microscopic examinations at Geology laboratories, S.D.M College of
Engineering and Technology, Dharwad, India.
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