environmental study on gfrp composite laminates · 2017. 6. 30. · dr.m.satyanarana gupta...
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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 6, June 2017, pp. 480–493, Article ID: IJMET_08_06_050
Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
ENVIRONMENTAL STUDY ON GFRP
COMPOSITE LAMINATES
G. Dhanajayan
Assistant Professor, Aeronautical Department,
MLR institute of technology, Hyderabad, India
Veeranjaneyulu Kalavagunta, V.Vamshi, Dr.M.Satyanarana Gupta
Aeronautical Department,
MLR institute of technology, Hyderabad, India
ABSTRACT
This paper investigates the structural behavior of composite material under
different environment conditions. The mechanical properties of composite materials
may vary when the material is exposed to high temperature, high humidity
environments. Therefore, in order to utilize the full potential of composite materials,
their performance at elevated temperatures and at high moisture content must be
known. The objective of this investigation was to evaluate the changes in the tensile
strength and flexural strength of composite materials exposed to fresh water, 3%
NaCl, and engine oil in which the temperature is maintained about 60oC and 95%
relative humidity. Hot-air oven is used to maintain the above condition. The flexural
and tensile strength were tested for period of 2, 4 and 8 days after continuous aging.
The results of mechanical deformation in the GFRP samples were studied and
compared for above environmental condition.
Key words: Composites, Accelerated aging, GFRP, Humidity
Cite this Article: G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and
Dr.M.Satyanarana Gupta Environmental Study on Gfrp Composite Laminates
International Journal of Mechanical Engineering and Technology, 8(6), 2017, pp.
480–493.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6
1. INTRODUCTION
Fibers or particles embedded in matrix of another material are the best example of modern
day composite material, which are mostly structural.
Though fiber composites have been in use for many years in application of aircraft,
marine, automobile etc. but still there is little information available on their environmental
impacts.
G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and Dr.M.Satyanarana Gupta
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The strength of composites may be hindered as a result of different environmental
interaction. As recent study under accelerating aging shows that the tensile and flexural
strength of composite resins demonstrate lower values after immersed and test in water, NaCl
and engine oil as compared to dry condition due to their absorption.
Accelerated testing is an approach for obtaining more information from a given test time
than would normally be possible. It does this by using a test environment that is more severe
than that experienced during normal equipment use. Since higher stresses are used,
accelerated testing must be approached with caution to avoid introducing failure modes that
will not be encountered in normal use. The strength of a material in bending, expressed as the
stress on the outermost fibers of a bent test specimen, at the instant of failure is called flexural
strength. The tensile strength of a material is the maximum amount of tensile stress that it can
be subjected to before failure.
2. DESIGN AND FABRICATION OF GFRP LAMINATES
Laminates are composite material where different layers of materials give them the specific
function to perform. Fabrics have no matrix to fall back on, but in them, fibers of different
compositions combine to give them a specific character. Reinforcing materials generally
withstand maximum load and serve the desirable properties.
A. Hand lay-up method
Hand lay-up is a simple method for composite production. A mould must be used for lay-up
parts unless the composite is to be joined directly to another structure. The mould can be as
simple as a flat sheet or have infinite curves and edges. For some shapes, moulds must be
joined in sections so they can be taken apart for removal after curing. Before lay-up, the
mould is prepared with release agent to insure that the part will not adhere to the mould.
Reinforcement fibers can be cut and laid in the mould. It is up to the designer to organize
the type, amount and direction of the fibers being used. Resin must then be catalyzed and
added to the fibers. A brush, roller or squeegee can be used impregnate the fibers with the
resin. The lay- up technician is responsible for controlling the amount of resin and the
quantity of saturation.
B. Raw Materials Used
Epoxy resin - ARALDITE LY 556 Hardener - HY 951
Figure 2.1 Epoxy Resin and Hardener
Glass fiber - Bidirectional woven textile
Environmental Study on GFRP Composite Laminates
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Figure 2.2 Bidirectional woven textile
C. Fabrication of Material
The fabrication of the polymer matrix composites was done at room temperature. The
required ingredients of resin and hardener were mixed in beaker and the mixture used to
laminate the material. A ten layered structure was formed as per ASTM standards. Then the
material kept for 24hrs to set properly.
Figure 2.3 Fabrication of Composite
D. Cutting of Samples
A diamond cutter was used to cut each laminate into smaller pieces, having dimensions of
250x25x3mm for tension test and 127x12.7x3mm for flexural test. This was done in
accordance with ASTM standards.
Figure 2.4 Samples
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E. Accelerated Environmental Testing In GFRP
The basis for this test as an indicator of the long term behavior of fiber reinforced composites
is that elevated temperature and moisture content accelerate the formation of the products
hydration of the cement in the matrix. Accelerated degradation from the combined action of
temperature and moisture. As a result of these environmental factors, the utility of composite
materials is terminated when the stiffness is reduced sufficiently to cause structural instability,
and/or failure or rupture of the material is induced. The samples are immersed in water, 3%
of NaCl, engine oil and accelerated at a temperature of 60oC and 95% humidity were placed
in a humid chamber. The samples are tested in above condition in time interval for 2, 4 and 8
days.
- - .
Figure 2.5 Accelerated Aging
F. Three Point Bending
The flexural test measures the force required to bend under three point loading conditions.
The data used to select materials for parts that will support loads without flexing. The data is
often used as an indication of a material stiffness when flexed. Since the physical properties
of many materials (especially thermoplastics) can vary depending on ambient temperature, it
is sometimes appropriate test materials at temperature that simulate the intended end user
environment.
Flexural strength:
S=���
����(�)
Where
P = maximum load (N)
L = support span (min)
b = specimen width (mm)
d = specimen thickness (mm)
Figure 2.6 Schematic of 3-point bend
Environmental Study on GFRP Composite Laminates
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3. TESTING MACHINES
A. Universal Testing Machine
This UTM used to test the tensile properties of unreinforced and reinforced plastics in the
form of standard dumbbell-shaped test specimens when tested under defined conditions of
pre-treatment, temperature, humidity, and testing machine speed.
Specification:
Company Unico
Load capacity 2.5ton
ASTM D638
Speed of test 50mm/min
Figure 2.7 Universal Testing Machine
Figure 2.8 Hot-Air Oven
B. Hot-Air-Oven
Double walled thermostatically controlled: Inner chamber made of aluminium /stainless steel.
Outer body is made of MILD STEEL. Beaded heading elements are placed under the ribs at
the bottom and sides. Temperature controlled by hydraulic thermoset from 10oC above
ambient to 40oC. Dial setting approximate basis. Correct reading as per L-shape thermometer
fitted on the front panel at the top. Suitable to work on 220 volt A.C supply.
4. RESULTS, DISCUSSION AND INTERPRETATION
FRP composites consist of fiber and matrix. The mechanical behavior or performance of the
composites is determined by the local response of the fiber matrix. There is load transfer from
G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and Dr.M.Satyanarana Gupta
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fiber to fibre through the matrix. The region including the contact region between matrix and
fiber extending on both sides, and having some finite thickness called as interphase. The
interphase possesses unique properties to the bulk matrix. It can include impurities un reacted
polymers components non polymerized additives etc. The thickness and properties of this
interphase have crucial impact on the composite properties. Apart from allowing the load
transfer between fibers through matrix, interphase provides a match of chemical and thermal
compatibility between the constituents.
Below are the variations of moisture content with time for different mediums.
A). SAMPLES IMMERSED IN WATER:
Table 1 environmental conditions in water
Test method ASTM D638,D790,D573
Test condition Temperature 60oC, humidity 95%
Room temperature 23oC
Relative humidity 50%
Table 2 variation of mechanical properties
GFRP Before
aging
After Aging in Water
48 hours 96 h0urs 192 hours
Tensile strength, N/mm2 215.3 214.86 208.95 211.63
Flexural Strength, n/mm2 26.40 25.96 24.81 21.97
Difference in Weight, g - 0.2 .36 .41
B). SAMPLES IMMERSED IN 3% NaCl:
Table .3 environmental conditions in Nacl
Test method ASTM
D638,D790,D573
Test condition Temperature 60oC,
humidity 95%
Room temperature 23oC
Relative humidity 50%
Table 4 variation of mechanical properties
GFRP Before aging After Aging in 3% Nacl
48 hours 96 hours 192 hours
Tensile strength,
N/mm2 215.3 213.42 207.46 210.23
Flexural Strength,
n/mm2 26.40 25.83 23.75 20.62
Difference in
Weight, g 0.1 .32 .38
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c). SAMPLES IMMERSED IN ENGINE OIL
Table .5 environmental conditions engine oil
Test method ASTM
D638,D790,D573
Test condition Temperature 60oC,
humidity 95%
Room temperature 23oC
Relative humidity 50%
Table 6 variation of mechanical properties
GFRP Before aging After Aging in Engine Oil
48 hours 96 hours 192 hours
Tensile strength, N/mm2 215.3 213.02 206.27 209.48
Flexural Strength,n/mm2 26.40 25.81 22.10 19.83
Difference in Weight, g - 0.1 .2 .32
5. LOAD Vs ELONGATION IN TENSILE STRENGTH TEST
Table .7 Tensile strength test for sample after-48 hrs aging in Engine oil:
Breaking load 14869 N
Elongation at break 2mm
Percent elongation 9.1%
Tensile strength 2171.5kg/sq.cm
213.03MPa
Figure 2.9 Load Vs Elongation in sample after aging in 48-hrs in Engine oil
Table .8 Tensile strength test for sample after-48 hrs aging in 3% NaCl:
Breaking load 14929 N
Elongation at break 2mm
Percent elongation 9.1%
Tensile strength 2175.6kg/sq.cm
213.42MPa
G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and Dr.M.Satyanarana Gupta
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Figure 2.10 Load Vs Elongation in sample after aging in 48-hrs in 3% NaCl.
Table .9 Tensile strength test for sample after-96 hrs aging in water
Breaking load 13989 N
Elongation at break 2mm
Percent elongation 9.1%
Tensile strength 2129.9kg/sq.cm, 208.95MPa
Figure 2.11 Load Vs Elongation in sample after aging in 96-hrs in water
Table .10 Tensile strength test for sample after-96 hrs aging in Engine Oil:
Breaking load 13779 N
Elongation at break 2.5 mm
Percent Elongation 11.45 %
Tensile strength 2102.7 kg/sq.cm, 206.27 MPa
Figure 2.12 Load Vs Elongation in sample after aging in 96-hrs in Engine oil.
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Table.11 Tensile strength test for sample after-96 hrs aging in 3% NaCl
Breaking load 13879 N
Elongation at break 2.7 mm
Percent elongation 12.3 %
Tensile strength 2114.8 kg/sq.cm, 207.46MPa
Figure 2.13 Load Vs Elongation in sample after aging in 96-hrs in 3% NaCl.
Table.12 Tensile strength test for sample after -192 hrs aging in water
Breaking load 13629 N
Elongation at break 2.2 mm
Percent Elongation 10.0 %
Tensile strength 2157.3 kg/sq.cm 211.63MPa
Figure 2.14 Load Vs Elongation in sample after aging in 192-hrs in water.
Table .14 Tensile strength test for sample after-192 hrs aging in Engine Oil:
Breaking load 13459 N
Elongation at break 2 mm
Percent Elongation 9.1 %
Tensile strength 2135.4 kg/sq.cm, 209.48MPa
Figure 2.15 Load Vs Elongation in sample after aging in 192-hrs in Engine Oil.
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Table 13 Tensile strength test for sample after-192 hrs aging in 3% NaCl:
Breaking load 13497 N
Elongation at break 2 mm
Percent Elongation 9.1 %
Tensile strength 2143.1 kg/sq.cm, 210.23MPa
Figure 2.16 Load Vs Elongation in sample after aging in 192-hrs in 3% NaCl.
6. MOISTURE ABSORPTION OF SAMPLES AGING IN DIFFERENT
ENVIRONMENT
6.1. MOISTURE CONTENT IN WATER
The graphical representation shows the absorption of water in the GFRP samples in
accelerated environment.
Figure 2.17 Moisture content Vs square root time in water
6.2. MOISTURE CONTENT IN 3% NaCl
The graphical representation shows the absorption of 3%NaCl in the GFRP samples in
accelerated environment.
Figure 2.18 Moisture content Vs square root time in 3% NaCl
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6.3. MOISTURE CONTENT IN ENGINE OIL
The graphical representation shows the absorption of Engine Oil in the GFRP samples in
accelerated environment
Figure 2.19 Moisture content Vs square root time in Engine Oil
7. DEGRADATION IN FLEXURAL STRENGTH OF SAMPLES AGING
IN DIFFERENT ENVIRONMENT
7.1. SAMPLES IN WATER
The following graph shows the degradation in flexural strength of GFRP samples immersed
in water at 60oC with 95% of humidity. The strength were tested in period of time interval 2,
4 and 8 days.
Figure 2.20 Degradation in flexural strength agter aging in water.
7.2. SAMPLES IN 3% NaCl
The following graph shows the degradation in flexural strength of GFRP samples immersed
in 3% NaCl at 60oC with 95% of humidity. The strength were tested in period of time interval
2, 4 and 8 days.
Figure 2.21 Degradation in flexural strength agter aging in 3% NaCl.
G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and Dr.M.Satyanarana Gupta
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7.3. SAMPLES IN ENGINE OIL
The following graph shows the degradation in flexural strength of GFRP samples immersed
in Engine oil at 60oC with 95% of humidity. The strength were tested in period of time
interval 2, 4 and 8 days.
Figure 2.23 Degradation in flexural strength agter aging in Engine oil.
8. COMPARISION OF FLEXURAL STRENGTH DEGRADATION IN
DIFFERENT ENVIRONMENT
The following graph shows the degradation of flexural strength in the environment like water,
NaCl, Engine Oil. The strength degradation is high in engine oil compare to water and NaCl.
Figure 2.24 Comparion of Degradation in flexural strength
9. DEGRADATION IN TENSILE STRENGTH OF SAMPLES AGING IN
DIFFERENT ENVIRONMENT SAMPLES IN WATER
The following graph shows the degradation in Tensile strength of GFRP samples immersed in
water at 60oC with 95% of humidity. The strength were tested in period of time interval 2, 4
and 8 days.
Figure 2.25 Degradation in Tensile strength agter aging in water.
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9.1. SAMPLES IN 3% NaCl
The following graph shows the degradation in Tensile strength of GFRP samples immersed in
3% NaCl at 60oC with 95% of humidity. The strength were tested in period of time interval 2,
4 and 8 days.
Figure 2.26 Degradation in Tensile strength agter aging in 3% NaCl.
9.2. SAMPLES IN ENGINE OIL
The following graph shows the degradation in Tensile strength of GFRP samples immersed in
Engine oil at 60oC with 95% of humidity. The strength were tested in period of time interval
2, 4 and 8 days
Figure 2.27 Degradation in Tensile strength after aging in Engine oil.
10. CONCLUSION
Glass fiber reinforced composite when exposed to degrading atmosphere like 3% NaCl
solution, water and Engine oil, and this exposure generally decreases the mechanical
properties. It was found experimentally by the accelerated aging method the properties
degraded.
The moisture absorption was found to be maximum in water than 3% NaCl and engine oil.
This diffusivity in moisture decreases the mechanical property of composites by decreasing
the saturation of matrix.
The flexural strength decreases periodically in an aging environment. It decreases more in
engine oil, compared to water and 3% NaCl. The percentage of flexural strength reduces in
the following environment, Water-16.7%, 3% NaCl-21.87%, and engine oil-24.88%
The tensile strength decreases for certain period of time and its strength varies continuous
aging process with elevated temperature but it does not attain its original strength. Therefore
when composites are exposed to different environment the tensile strength decreases. The
percentage of decrease of the tensile strength in the following environment: Water by 2.94%,
3% NaCl by 3.64%, engine oil- 4.14%
Therefore the decrease in flexural strength is more than that of tensile strength in
composites due to environmental degradation.
G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and Dr.M.Satyanarana Gupta
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[5] T.P. Meikandaan and Dr. A. Ramachandra Murthy, Flexural Behaviour of RC Beam
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[6] T. P. Meikandaan and Dr. A. Ramachandra Murthy, Retrofittng of Reinforced Concrete
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[7] Hooper, S. J., Toubia, R. F., and Subramanian, R., “Effects of Moisture Absorption on
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[8] Parvati T S and Dr. P.S. Joanna, Double Skin Tubular Columns Confined with GFRP.
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