Impact response and damage tolerance characteristics of
glass±carbon/epoxy hybrid composite plates
N.K. Naik a,*, R. Ramasimha a, H. Arya a, S.V. Prabhu a, N. ShamaRao b
a
Aerospace Engineering Department, Indian Institute of Technology, Powai, Mumbai 400 076, India
b
ADA, Bangalore 560 017, India
Abstract
Impact behaviour and post impact compressive characteristics of glass±carbon/epoxy hybrid composites with alternate stacking sequences
have been investigated. Plain weave E-glass and twill weave T-300 carbon have been used as reinforcing materials. For comparison,
laminates containing only-carbon and only-glass reinforcements have also been studied. Experimental studies have been carried out on
instrumented drop weight impact test apparatus. Post impact compressive strength has been obtained using NASA 1142 test ®xture. It is
observed that hybrid composites are less notch sensitive compared to only-carbon or only-glass composites. Further, carbon-outside/glassinside clustered hybrid con®guration gives lower notch sensitivity compared to the other hybrid con®gurations.
Keywords: A. Fabrics; A. Hybrid; B. Impact behaviour; B. Damage tolerance; D. Ultrasonics
1. Introduction
Composite materials are ®nding increasing applications
in various engineering ®elds because of their superior inplane properties. But these materials are highly susceptible
even to low velocity impacts. Barely visible impact damage
can be formed beneath the surfaces while the surfaces may
appear to be undamaged. One of the ways to achieve the
improved impact resistance of composite materials is by
hybridisation.
Hybrid composites consist of two or more types of reinforcements or matrices or both. By mixing different ®bres, it
is possible to combine the advantages of different ®bres
while simultaneously mitigating their less desirable qualities. Normally, one of the ®bres in a hybrid composite is a
high modulus, high strength and high cost ®bre such as
graphite/carbon, and the second ®bre usually is a low modulus ®bre like Kevlar, E-glass or S-glass. Hybrid composites
are attractive structural materials, because the composite
properties can be tailored to requirements. Other characteristics of hybrid composites are: cost effective utilisation of
different ®bre materials, possible weight savings, reduced
notch sensitivity, improved fracture toughness, longer
fatigue life and improved impact resistance. Hybrid compo-
sites can be classi®ed into two main categories: intermingled or intraply and interlaminated or interply.
Some studies are available on in-plane mechanical properties of hybrid laminated composites [1±11]. It has been
found that the tensile failure strain of brittle composites
consisting of brittle ®bres like carbon is increased when it
is hybridised with ductile ®bres like glass. This is because of
hybrid effect. The phenomenon of hybrid effect is de®ned as
the positive deviation of a property from the rule of
mixtures. In general, hybrid effect leads to the enhancement
of the failure strain and strength than that estimated using
classical lamination theory and the various failure strain
criteria.
Studies have also been made on the impact properties of
hybrid composites [12±19]. Wang et al. [17] have studied
the fracture behaviour of unidirectional laminated hybrid
composites. They have studied single-matrix/double-®bre,
double-matrix/single-®bre, and double-matrix/double-®bre
hybrid composites as well as their single-®bre/single-matrix
control versions. The materials studied have been polyphenylene sul®de±graphite, polyphenylene sul®de±glass,
epoxy±graphite. They have concluded that as the percentage of glass increases, the maximum load tolerated and
impact energy absorbed by the material increases. The
maximum load tolerated was the load corresponding to
either a gross ®bre failure at the back surface or an interlaminar crack across the composite sample. Also the
566
intermixing of glass and graphite ®bre plies helped decrease
the sudden catastrophic failure mode. Jang et al. [15] have
studied the impact properties and energy absorbing capability of graphite composites hybridised with three types of
plain weave fabric: polyethylene (PE), polyester (PET)
and nylon, with epoxy resin. They have measured the
impact load and the impact energy absorbed by the specimen upon penetration. They have observed that the hybrids
containing PE ®bres, which were of high strength and high
ductility were effective in both dissipating impact energy
and resisting through penetration. They have also stated
that for a particular material combination, stacking
sequence is a major factor governing the overall energy
absorbing capability of the hybrid structure. However,
during the service life of the composite structure, low velocity impacts leading to other modes of failure such as delamination are also important considerations. Delamination
and the other secondary modes of failure such as matrix
cracking, debonding, etc. would lead to reduction in residual
inplane strength of impacted composites. Such studies also
need to be carried out.
Novak and DeCrescente [12] have observed that the addition of glass ®bres to carbon/epoxy and boron/epoxy
composites improves the impact strength by a factor of
about three to ®ve, which is higher than that predicted
from the impact properties of the unmixed composites.
Chamis et al. [13] have studied glass/carbon hybrid composites and have observed that hybrid composites failed under
impact by combined fracture modes: ®bre breakage, ®bre
pullout and interply delamination. They also imply that as a
result of this complex failure process, the impact resistance
of hybrid composites may be synergisitically increased over
that predicted from the behaviour of the separate constituents. Harris and Bunsell [14] have conducted Charpy impact
tests on unidirectional hybrid composite rod samples
containing glass reinforcements and carbon reinforcements.
They have stated that the work of fracture by impact and the
¯exural modulus are both simple functions of composition
corresponding to a mixture rule based on the properties of
plain glass reinforced composites and carbon reinforced
composites. In this study, the authors have not observed
the advantages of hybrid effect.
Saka and Harding [16] carried out inplane tensile impact
studies on woven hybrid composites. They also used a
simple laminate theory approach to predict the in-plane
tensile impact behaviour of woven hybrid composites.
They observed that the tensile strength was higher at impact
strain rate compared to that at quasi-static strain rate. Their
experimental studies showed that the tensile strength of
woven glass/carbon hybrid composites was more than that
of only-carbon or only-glass composites. Kowsika and
Mantena [18] have studied the in¯uence of hybridisation
on the characteristics of unidirectional glass/carbon epoxy
composite beams. They have made studies using low velocity instrumented drop weight impact tests. They have
experimentally determined that the strain to failure of
glass/epoxy which is about 0.026 under static loading is
found to increase to 0.044 under impact showing that
glass ®bres are highly sensitive to strain rate of loading.
They have concluded that the peak contact force is the highest for the carbon outside hybrids when compared with the
all-carbon, all-glass and glass outside hybrid composites.
1.1. Effect of strain rate on the mechanical behaviour of
composites
In literature, studies are available on the effect of strain
rate on the mechanical behaviour of composites [20±26].
Harding and Welsh [20] carried out tensile impact testing of
composites using Hopkinson-bar apparatus. They observed
that there is a signi®cant increase in stiffness and strength at
intermediate and impact strain rates for woven fabric
composites. For unidirectional laminated composites, the
increase was marginal. Generally, it was observed that the
increase in elastic and strength properties was signi®cant for
glass plain weave composites [20,21]. The increase was not
signi®cant for satin weave and unidirectional laminated
composites. Generally, the gain was more for glass composites than for carbon composites. Hence, glass plain weave
composites are very attractive materials for impact resistance and damage tolerance applications.
1.2. Composite structures under varying loading conditions
Composite structures experience different loading conditions during their service life. For the effective use of
composite structures, they should have superior impact
resistance and damage tolerance properties. At the same
time, they should have excellent static mechanical properties. The composite laminates/structures which can ful®ll
such contrasting requirements are the hybrid composites.
The objective of the present study is to characterise impact
behaviour and post impact behaviour of hybrid laminated
composite plates. Plain weave E-glass and twill weave T300 carbon fabrics have been chosen as the reinforcing
materials with epoxy resin as the matrix. Studies have
been carried out on instrumented drop weight impact test
apparatus on three hybrid composites and only-carbon and
only-glass composite plates. Post impact compressive
strength and the impact behaviour during the impact event
have been evaluated and compared.
2. Instrumented drop weight impact test apparatus
An instrumented drop weight impact test apparatus was
used in this study for conducting impact tests. Impact parameters such as deceleration/acceleration, contact force,
plate velocity and plate displacement were measured during
impact testing. The recording of parameters was performed
using the instruments: piezoelectric accelerometer, bonded
strain gauge load cell ®tted on the impactor, linear velocity
transducer (LVT) and linear variable differential transformer
567
(LVDT). The instrument outputs were recorded using a data
acquisition card PCL 208 on a computer. The signals were
ampli®ed to match the entire range of the data acquisition
card. Contact force and deceleration/acceleration were
measured directly from the inputs of load cell and accelerometer, respectively. Data obtained from accelerometer was
used to compute the contact force, velocity, displacement
and energy. The velocity and displacement were derived
from deceleration/acceleration data by using incremental
integration. Velocity and displacement values were also
compared with the independently obtained experimental
results. An energy graph was plotted using the derived
contact force and displacement values.
The contact force was obtained using the expression:
with the laminate axis. The rate of loading was maintained
as 1.27 mm/min.
F…t† ˆ ma…t†
Orthogonal plain weave E-glass fabric of 0.26 mm thickness was selected for glass reinforcements. Orthogonal twill
weave T-300 carbon fabric of 0.40 mm thickness was
selected for carbon reinforcements. Epoxy resin (LY 556)
with hardener (HY 951) was used for the matrix. Laminates
were cured at room temperature for 24 h. Five types of
laminates of nominal thickness 5.0 mm were prepared.
The laminates were GLE-12, [G4/C4]S, [G/C]4S, [C4/G4]S,
and CTE-1. The GLE-12 laminates consisted of 19 layers
of E-glass reinforcement. The CTE-1 consisted of 13 layers
of T-300 carbon reinforcement. The hybrids [G4/C4]S, [G/
C]4S and [C4/G4]S consisted of eight layers of E-glass and
eight layers of T-300 carbon reinforcement arranged
symmetrically in the three stacking sequences. The hybrid
laminate [C4/G4]S is of carbon-outside/glass-inside clustered
con®guration, whereas [G4/C4]S is of glass-outside/carboninside clustered con®guration. The hybrid laminate [G/C]4S
is of dispersed con®guration. For all the laminates, overall
®bre volume fraction (Vf0 ) was 44%. Laminates of dimensions 350 mm £ 350 mm £ 5 mm were fabricated using
matched die moulding technique. Specimens of dimensions
150 mm £ 150 mm £ 5 mm were prepared from the laminates. Required quality of the laminates/specimens was
ascertained through C-scan results. All the experiments
were done at room temperature.
The study was carried out at constant incident impact
energy, EII ˆ 19.76 J. The impactor mass was M ˆ 4.7 kg,
and the incident impact velocity was, V0 ˆ 2.9 m/s. Four
identical specimens of 5 mm thickness were tested for all
the ®ve types of laminates. Visual inspection was conducted
by observing the damage patterns by viewing the specimens
against a strong source of light. The damage area was
thus marked, and measured using a 10 £ magnifying
glass. C-scans and A-scans were also obtained to identify
the maximum area of delamination and location of major
delamination.
where m is the mass of the impactor and a(t) the recorded
accelerometer data as a function of time.
Impactor velocity wrt time was computed as:
Z
V…t† ˆ V0 2 a…t† dt
where V0 is incident impact velocity.
On further integration, displacement of the impactor wrt
time was derived as:
Z
d…t† ˆ V…t† dt
The energy exchanged at time t, due to work done by
contact force during the loading and unloading was
computed as:
Z
E…t† ˆ F…t† D…t† dt
where D(t) ˆ dd(t)/dt
Impact testing was conducted on the specimens clamped
on all the four sides. The unsupported area of the specimen
during impact loading was 127 mm £ 127 mm.
2.1. Compression after impact test ®xture
Post impact compression testing of impacted specimens
was carried out using compression after impact (CAI) test
®xture fabricated as per NASA 1142 standard [27]. Specimens were cut to have a width of 125 mm. The specimens
were clamped along the top and bottom edges during CAI
tests. Anti-buckling guides were used to provide simple
support along the lateral edges to prevent overall buckling
of the specimen. The side supports were snug ®t so that the
transverse deformation due to Poisson's effect was not
constrained. A gap of 6 mm between the supports and end
plate was provided to allow for the compression of the
specimen. The CAI testing was carried out by loading the
specimen on a universal testing machine with a maximum
capacity of 200 kN. The loading axis was carefully aligned
2.2. Compression testing
Compressive behaviour of all the ®ve types of composite
specimens has been experimentally determined. Lockheed
test ®xture with a modi®ed specimen geometry was used for
the experimental studies. The lower end of the specimen
was tapered to avoid end crushing during loading. The loading rate was 0.3 mm/min.
3. Design of experiments
4. Data analysis and presentation
To study the impact behaviour of composites, deceleration/acceleration and contact force histories were recorded
568
Fig. 1. Variation of contact force, velocity, displacement and energy versus time for GLE-12.
Fig. 2. Variation of contact force, velocity, displacement and energy versus time for [G4/C4]S.
569
Fig. 3. Variation of contact force, velocity, displacement and energy versus time for [G/C]4S.
using accelerometer and load cell, respectively. The deceleration/acceleration data, a, obtained from the accelerometer, curve ®t deceleration/acceleration, a-cf, contact
force, F, derived from the deceleration/acceleration data
and contact force data, F-lc, obtained from the load cell
wrt time were analysed for the ®ve types of specimens.
Contact force, F, plate velocity, V, plate displacement, d
and energy, E, wrt time, t were derived using recorded
Fig. 4. Variation of contact force, velocity, displacement and energy versus time for [C4/G4]S.
570
Fig. 5. Variation of contact force, velocity, displacement and energy versus time for CTE-1.
deceleration/acceleration a data. Typical plots have been
presented in Figs. 1±5.
The duration of impact, tf, indicated the time duration
after which there was no contact between the plate and
the impactor. At the end of impact event, impact force
and deceleration/acceleration were zero. The maximum
deceleration, am, maximum contact force, Fm, zero velocity,
V ˆ 0, maximum plate displacement, d m, and maximum
plate energy, Em, occur simultaneously.
The characteristic impact parameters: peak contact
force, maximum displacement, duration of impact,
maximum plate energy, maximum deceleration and
time to reach peak contact force for each type of lami-
nate are presented in Table 1. The values of maximum
plate energy, absorbed energy and plate strain energy
are presented in Table 2. The results are the averages
of four tests. The quantities in the bracket indicate the
scatter.
4.1. Deceleration/acceleration plots
The deceleration/acceleration data measured is for the
impactor. During the entire impact event, since there was
contact between the impactor and the plate, the deceleration
data measured is also that of the plate.
Table 1
Characteristic impact parameters
Laminate
Peak contact force,
Fm (kN)
Maximum
displacement,
d m (mm)
Duration of
impact, tf (ms)
Maximum plate
energy, Em (J)
Maximum
deceleration,
am (m/s 2)
Time to reach
Fm, tfm (ms)
GLE-12
6.0
(0.1, 20.3)
6.3
(0.3, 20.1)
6.9
(0.3, 20.1)
7.1
(0.6, 20.1)
6.8
(0.2, 20.1)
6.5
(0.5, 20.1)
7.0
(0.1, 20.1)
5.6
(0.4, 20.1)
4.2
(0.1, 20.3)
3.9
(0.5, 20.1)
7.5
19.5
(0.1, 20.8)
19.5
(0.1, 20.1)
19.6
(0.1, 20.1)
19.6
(0.1, 20.1)
19.6
(0.1, 20.1)
1277
3.5
1340
3.6
1468
3.0
1510
2.5
1447
2.4
[G4/C4]S
[G/C]4S
[C4/G4]S
CTE-1
7.1
5.7
5.2
4.0
571
Table 2
Characteristic impact energies
Laminate
Maximum plate
energy, Em (J)
Energy absorbed,
Ea (J)
Plate strain energy,
Es ˆ Em 2 Ea (J)
GLE-12
[G4/C4]s
[G/C]4s
[C4/G4]s
CTE-1
19.5
19.5
19.6
19.6
19.6
7.8
8.6
10.2
15.0
13.5
11.7
10.9
9.4
4.6
6.1
compared with the duration of impact event. This was
con®rmed by independently measuring the residual displacements by the LVDT, which were much lower than the
derived values.
4.5. Energy plots
4.2. Contact force plots
Contact force was derived from the deceleration/acceleration data. Contact force was also obtained from the
load cell. The value of contact force obtained from the
load cell was marginally lower than the contact force
computed from the accelerometer data. The variation was
of the order of 5%. Data from accelerometer was used to
derive the value of contact force by multiplying the acceleration values with the mass of the impactor. The contact
force measured indicates the resistance offered by the plate
during the impact event.
The energy±time relation was plotted using the contact
force and displacement results obtained from accelerometer
data. The maximum plate energy, Em, represents the maximum energy transferred to the plate by the impactor during
the impact event. The maximum plate energy consists of the
plate strain energy, Es, and the energy absorbed, Ea, for
fracture propagation. The plate strain energy is responsible
for the rebound of the impactor. The energy absorbed is the
energy lost in the plate for creating damages. The energy
absorbed also contained the kinetic energy of the plate since
the plate had not come back to its initial position. Thus, the
energy absorbed does not completely represent the fracture
energy, if the separation takes place between the plate and
the impactor before the plate reaches to its original position.
4.6. Damage pattern
4.3. Plate velocity plots
The velocity plots were derived from the deceleration/
acceleration plots. The incident impact velocity indicates
the velocity of the impactor at the beginning of the impact
event. The velocity of the impactor was also measured using
a LVT. In general, experimentally observed incident impact
velocities and rebound velocities matched the derived data.
The rebound velocity was less than V0.
4.4. Plate displacement plots
Plate displacement plots were derived from the deceleration/acceleration plots. At the end of the impact event, the
plate might not have come back to its original position.
Hence, the plate displacement at this time derived from
the deceleration/acceleration plot may not indicate the residual displacement. The residual displacement is signi®cantly lower than the displacement at F ˆ 0. The duration
for the plate to come back to rest is signi®cantly longer as
The damage sizes measured visually and through C-scans
are given in Table 3. Damage shapes obtained visually and
through C-scans are given in Figs. 6 and 7, respectively. The
C-scans showed that damage areas consist of both delamination and matrix cracks. The location of maximum delamination/damage has been determined using A-scans. In
general, the major damage/delamination was found at a
distance of about 2.0 mm from the top surface.
4.7. Post impact compression testing
Post impact compression testing was performed for all the
specimens using the compression after impact test ®xture.
The loading during CAI testing was along the warp direction. The results of CAI testing have been presented in Table
3. Unnotched compressive strength values have been
obtained experimentally. The results are the averages of
four tests.
Table 3
Damage tolerance characteristics
Laminate
GLE-12
[G4/C4]S
[G/C]4S
[C4/G4]S
CTE-1
Damage dimensions (mm)
Visual observation, top
C-scan results
Along warp
Along ®ll
Along warp
Along ®ll
19.0
23.5
28.0
27.0
21.0
17.0
27.3
27.3
24.5
26.5
21.0
23.8
28.5
20.9
21.0
17.0
27.6
27.6
22.8
26.6
Post impact compressive
strength, Xcn (MPa)
loading along warp
Compressive
strength, Xc (MPa)
loading along warp
Xcn =Xc (%)
172.0 (14, 28)
196.8 (8, 27)
186.4 (5, 26)
200.0 (7, 28)
220.8 (11, 210)
225.0 (30, 210)
238.2 (7, 25)
239.5 (4, 27)
240.1 (5, 2 4)
300.0 (20, 28)
76.4
82.6
77.8
83.3
73.6
572
Fig. 6. Damage shapes and sizes obtained from visual observation for plates subjected to impact.
5. Results and discussion
The area of damage has been estimated by visual observation and by C-scan results. The area of damage is found to
be least for the all-glass specimen, GLE-12 and found to
increase in the order GLE-12, [C4/G4]S, CTE-1, [G4/C4]S,
[G/C]4S. The damage area is indicative of the area of the
sublaminate formed by delamination of a certain region
from the rest of the laminate. The reduction in compressive
strength is expected to be due to the buckling of the sublaminate. The sublaminate buckling load is higher for a subla-
minate of smaller area. Hence, under similar conditions of
laminate stiffness, strength and sublaminate thickness, the
laminate having lesser area of delamination is expected to
have higher compressive strength.
The damage length transverse to the loading direction is
indicative of the size of the notch, since this length is
perpendicular to the line of loading. The damage length
is the least for the all-glass specimen GLE-12, and is
found to increase in the order GLE-12, [C4/G4]S, CTE-1,
[G4/C4]S, [G/C]4S. This hierarchy is exactly the same as
that for the damage area. Since the damage length along
573
Fig. 7. Damage shapes and sizes for different glass±carbon/epoxy hybrid
laminates, EII ˆ 19.76 J, LZ ˆ 5.0 mm: C-scans.
®ll represents the size of the notch, there is more reduction
in strength for a laminate having bigger notch size. Under
similar conditions of laminate in-plane stiffness and
strength, the laminate having smaller notch size is expected
to have higher compressive strength.
The compression after impact (CAI) strength for the ®ve
types of laminates are found to be decreasing in the order
CTE-1, [C4/G4]S, [G4/C4]S, [G/C]4S, GLE-12. The damage
tolerance is de®ned as the ratio of compressive strength after
impact to the compressive strength of the unnotched laminates. It is found to be highest for [C4/G4]S and found to be
decreasing in the order [C4/G4]S, [G4/C4]S, [G/C]4S, GLE-12,
CTE-1. It can be seen that the damage tolerance is higher for
hybrid composites compared to those of only-glass or
only-carbon. On comparison of the heirarchy amongst
the three hybrid composites, it is found that the decreasing order of compressive strength and decreasing order
of damage tolerance is [C4/G4]S, [G4/C4]S, [G/C]4S. This
heirarchy is found to remain consistent under considerations of damage area, damage length transverse to the
loading direction, compressive strength after impact and
notch sensitivity. Also on comparison it is found that
although the CAI strength of CTE-1 is the highest
among the ®ve types of laminates studied, the CTE-1
laminate has the highest notch sensitivity and the highest reduction in compressive strength. This clearly shows
the advantage of hybridisation in decreasing the notch
sensitivity.
The displacement of the plate under the impactor is found
to increase in the order CTE-1, [C4/G4]S, [G/C]4S, GLE-12,
[G4/C4]S. This indicates that CTE-1 has the least displacement and it is maximum for [G4/C4]S. The hierarchy of
increasing displacement amongst the three hybrid composites is [C4/G4]S, [G/C]4S, [G4/C4]S.
The duration of impact is indicative of the time during
which the transfer of energy takes places during the impact.
The duration of impact is highest for GLE-12, and decreases
in the order GLE-12, [G4/C4]S, [G/C]4S, [C4/G4]S, CTE-1.
The chances of catastrophic failure is reduced if the duration
of impact is higher.
From the study of Figs. 2±4 and Table 3 it is noticed that
the heirarchy amongst the three hybrid composites for
decreasing peak contact force and increasing maximum
displacement is [C4/G4]S, [G/C]4S, [G4/C4]S. The consistency
of these heirarchies match the reasoning that the plate
having higher peak contact force has more resistance to
deformation and lesser maximum displacement under the
impactor.
These observations match those obtained by Kowsika and
Mantena [18]. They observed during their studies on impact
behaviour of hybrid composite beams made of unidirectional laminae that the peak contact force is the highest
when the layers are symmetrically arranged such that carbon
layers are on the outer surfaces and glass layers are near to
neutral axis.
From Figs. 6 and 7, and from Table 3, the heirarchy for
increasing damage area, increasing size of notch perpendicular to the loading direction and the decreasing compressive strength after impact is [C4/G4]S, [G4/C4]S, [G/C]4S. This
heirarchy is expected due to the following reasons.
The hybrid composite [C4/G4]S has the highest ¯exural
modulus because the layers are arranged such that the laminate contains the high stiffness carbon reinforcement away
from the neutral axis and the low stiffness glass reinforcements at the neutral axis. Additionally, carbon being a stronger and stiffer material, it is able to withstand higher
stresses. Hence placing the carbon layers at highly stressed
regions would be bene®cial. Hence [C4/G4]S con®guration
has lowest damage and least notch sensitivity.
6. Conclusions
The following are the important conclusions based on the
experimental studies carried out.
² Glass±carbon/epoxy hybrid composites have lower
notch sensitivity compared with only-carbon or onlyglass composites.
² Carbon-outside/glass-inside clustered hybrid con®guration gives higher post impact compressive strength and
lower notch sensitivity. Also, with this con®guration,
574
damage area and the crack lengths along warp and
®ll directions are less compared with the other hybrid
con®gurations.
² The transverse displacement is less for carbon-outside/
glass-inside clustered hybrid con®guration compared
with the other hybrid con®gurations.
² Impact duration is higher for glass-outside/carbon-inside
clustered hybrid con®guration compared with the other
hybrid con®gurations.
Acknowledgements
This work was supported by the Structures Panel, Aeronautics Research and Development Board, Ministry of
Defence, Government of India, Grant No. Aero/RD-134/
100/10/95-96/890.
References
[1] Bunsell AR, Harris B. Hybrid carbon and glass ®bre composites.
Composites 1974;5:157±64.
[2] Aveston J, Sillwood JM. Synergistic ®bre strengthening in hybrid
composites. Journal of Materials Science 1976;11:1877±83.
[3] Zweben C. Tensile strength of hybrid composites. Journal of Materials Science 1977;12:1325±37.
[4] Maron G, Fischer S, Tuler FR, Wagner HD. Hybrid effects in composites: conditions for positive or negative effects versus rule-ofmixtures behaviour. Journal of Materials Science 1978;13:1419±26.
[5] Summerscales J, Short D. Carbon ®bre and glass ®bre hybrid reinforced plastics. Composites 1978;9:157±66.
[6] Manders PW, Bader MG. The strength of hybrid glass/carbon ®bre
composites. Journal of Materials Science 1981;16:2233±45.
[7] Hancox NL. Fibre composite hybrid materials. London: Applied
Science Publishers, 1981.
[8] Ji X. On the hybrid effect and fracture mode of interlaminated hybrid
composites. In: Hayashi T, Kawata K, Umekawa S, editors. Progress
in Science and Engineering of Composites, Proceedings of ICCM-IV,
Tokyo: Japan Society for Composite Material, 1982. p. 1137±44.
[9] Fukuda H, Chou TW. A statistical approach to the strength of hybrid
composites. In: Hayashi T, Kawata K, Umekawa S, editors. Progress
in Science and Engineering of Composites, Proceedings of ICCM-IV,
Tokyo: Japan Society of Composite Material, 1982. p. 1145±52.
[10] Kretsis G. A review of the tensile, compressive, ¯exural and shear properties of hybrid ®bre-reinforced plastics. Composites 1987;18:13±23.
[11] Khatri SC, Koczak MJ. Thick- section AS4-graphite/e-glass/pps
hybrid composites: Part 1. Tensile behaviour. Composites Science
and Technology 1996;56:181±92.
[12] Novak RC, DeCrescente MA. Impact behavior of unidirectional resin
matrix composites tested in the ®ber direction. In: Composite materials: testing and design (Second Conference), ASTM STP 497, 1972.
p. 311±23.
[13] Chamis CC, Hanson MP, Sera®ni TT. Impact resistance of unidirectional ®ber composites. In: Composite materials: testing and design
(Second Conference), ASTM STP 497, 1972. p. 324±49.
[14] Harris B, Bunsell AR. Impact properties of glass ®bre/carbon ®bre
hybrid composites. Composites 1975;6:197±201.
[15] Jang BZ, Chen LC, Wang CZ, Lin HT, Zee RH. Impact resistance and
energy absorption mechanisms in hybrid composites. Composites
Science and Technology 1989;34:305±35.
[16] Saka K, Harding J. A simple laminate theory approach to the prediction of the tensile impact strength of woven hybrid composites.
Composites 1990;21:439±47.
[17] Wang CJ, Jang BZ, Panus J, Valaire BT. Impact behavior of hybrid®bre and hybrid-matrix composites. Journal of Reinforced Plastics
and Composites 1991;10:356±78.
[18] Kowsika MVSLN, Mantena PR. Static and low-velocity impact
response characteristics of pultruded hybrid glass±graphite/epoxy
composite beams. In: Gibson RF, Newaz GM, editors. Proceedings
of the 12th American Society for Composites, Lancaster: Tecnomic
Publishing Co, 1997. p. 610±9.
[19] Naik NK, Ramasimha R. Impact response of hybrid glass±carbon/
epoxy composite plates. In Proceedings of ICEM-9, Bethel: Society
for Experimental Mechanics, Inc., 2000. p. 198±201.
[20] Harding J, Welsh LM. A tensile testing technique for ®bre-reinforced
composites at impact rates of strain. Journal of Materials Science
1983;18:1810±26.
[21] Welsh LM, Harding J. Effect of strain rate on the tensile failure of
woven reinforced polyester resin composite. Journal De Physique
1985;46:405±14.
[22] Werner SM, Dharan CKH. The dynamic response of graphite ®breepoxy laminates at high shear strain rates. Journal of Composite
Materials 1986;20:365±74.
[23] Harding J, Li YL. Determination of interlaminar shear strength for
glass/epoxy and carbon/epoxy laminates at impact rates of strain.
Composites Science and Technology 1992;45:161±71.
[24] Bouette B, Cazeneuve C, Oytana C. Effect of strain rate on interlaminar shear properties of carbon/epoxy composites. Composites
Science and Technology 1992;45:313±21.
[25] Harding J. Effect of strain rate and specimen geometry on the
compressive strength of woven glass-reinforced epoxy laminates.
Composites 1993;24:323±32.
[26] Leber H, Lifshitz JM. Interlaminar shear behavior of plain-weave
GRP at static and high rates of strain. Composites Science and Technology 1996;56:391±405.
[27] NASA/aircraft industry standard speci®cation for graphite ®bre
toughened thermoset resin composite materials. NASA Reference
Publication 1142. 1985.