Mode I Fracture Toughness of Interply Hybrid Epoxy Composite Reinforced with Carbon-Basalt Fibers.

Mode I Fracture Toughness of Interply Hybrid Epoxy Composite
Reinforced with Carbon-Basalt Fibers
I.D.G Ary Subagia1,a*, Leonard D. Tijing2,b* and KT. Adi Atmika1,c
1

Mechanical Engineering, Faculty of Udayana University (UNUD), Bukit Jimbaran Badung Bali –
Indonesia 80361.

2

School of Civil and Environmental Engineering, University of Technology, Sydney (UTS), P.O. Box
123, Broadway, NSW 2007, Australia.
a

b

c

arsubmt@gmail.com, ltjing@gmail.com, tutadi2001.yahoo.com

Keywords: Strength, toughness, basalt, carbon, hybrid composite, mode I fracture toughness.

Abstract. In this study, the fracture strength of hybrid composite epoxy matrix reinforced with woven
carbon-basalt fibers were investigated within the framework of Mode I fracture toughness. The
present work aimed to determine the strength and toughness properties of hybrid composite
influenced by the basalt fiber contents on the carbon fiber reinforced plastics composite (CFRP) based
on mode I fracture toughness. A vacuum assisted resin transfer molding technique was conducted to
manufacture the composite. Compact tension specimen form with a single-edge notched was
subjected to realizing fracture toughness behavior of the interply hybrid composite. Fracture
toughness, KIC, of plane-stresses has been calculated from the critical load and crack length based on
the two-dimensional analysis according to ASTM D 5045 standard. We used scanning electron
microscopy to examine the fracture surface, and micro-fracture of matrix cracking as well as the fiber
breakage of interply carbon/basalt/epoxy hybrid composite. The result showed that the toughness of
hybrid composite with increasing basalt fiber contents also increased, as shown by the decrease of the
crack propagation of the notch. De-bonding and fiber pull-out have dominated the failure behavior of
the hybrid composites. Generally, basalt fabric shows potential to improve toughness of a brittle
composite material due to its deformability.
Introduction
Composite materials have shown good potential to replace traditional materials in most of
engineering products in the last two decades. This is largely because of their good mechanical
properties, good stiffness and high strength [1]. In addition, composite materials have good corrosion

resistance, low thermal conductivity, high strength to weight ratio and are light [2]. However, one of
their weaknesses is their brittle behavior. Brittle manner of materials is really dangerous due to sudden
failure without any warning. Fracture toughness of a material is its sensibility towards cracks. Cracks
occurring on a structure or engineering component will decrease the material strength. The fracture
toughness value depends on the specimen thickness. It will be decreased by a surface shear mode.
Many researchers have agreed that the hybridization approach is a good attempt to improve the
fracture toughness of a material [3, 4].
In order to improve the fracture toughness of a composite material, hybridization is a good
methodology. In the present, incorporating a le material with good deformability to enhance the
fracture toughness of brittle composites has been commonly carried out [5]. An example is a hybrid
composite polymer matrix reinforced with carbon fibers and glass fibers [6, 7]. In addition, we can
combine two kinds of fibers such as organic fibers and inorganic fibers that can be bounded using an
epoxy matrix [8]. Considering the government interest to eco-friendly materials and low cost
production, some possibility combinations of fibers as a reinforcement have been studied to improve
the fracture toughness properties of the polymer composites. For example, hybrid composites
containing carbon fiber and carbon nanotubes CNTs have been fabricated [9]. Generally, their results
showed good characteristics and performance as a hybrid material. However, they are far from the

eco-friendly expectation. In the present study, incorporation of both carbon fibers and organic fibers
as composite reinforcements has been conducted. One potential fiber for hybridization with carbon

fiber is basalt fiber [10-12].
Basalt fibers are a new kind of an organic fiber that has a great potential to replace synthetic fiber
(glass fiber) as polymer material reinforcement. Basalt fiber is made from volcanic rock which is
produced through a melting process at high temperatures around 1300˚C-1700˚C [13]. Basalt fibers
have been promoted as a reinforcement due to its good properties and characteristics such as high
tensile and modulus of elasticity [11, 14], eco-friendly, non-combustible [15] and inexpensive [13,
16]. Based from their properties, basalt may have good potential to be applied to engineering products.
In order to improving fracture toughness of composite materials, hybridization of carbon fiber and
basalt fibers have been manufactured based on the vacuum assisted resin transfer molding (VARTM)
technique. The present work aimed to determine the strength and toughness properties of hybrid
composite influenced by the basalt fiber contents of 40 wt% on the carbon fiber reinforced plastics
composite (CFRP) based on mode I fracture toughness. Compact tension (CT) specimen tests have
been carried out in accordance with ASTM D 5045 [17]. Fracture toughness (KIC) of the hybrid
composite was tested under mode I fracture toughness test, and the fracture characteristics were
analyzed using scanning electron microscope (SEM).
Table 1. Basalt fabrics (EcoB4-F210) compounds
Items
%

SiO2

52.8

Al2O3
17.5

Fe2O3
10.3

MgO
4.63

CaO
8.59

Na2O
3.34

K2O
1.46

TiO2
1.38

P2O5
0.28

MnO
0.16

CrO
0.06

Experimental procedure
Materials
In the present study, two kinds of fabrics for reinforcement had been employed [15]. Plain carbon
fabrics (C120-3K) are the main reinforcements, manufactured by Hyundai Fiber Co. Ltd. (Korea). We
used a plain basalt fabric (EcoB4-F210) that was fabricated by Seco-Tech (Korea). Basalt fabric
components are shown in Table 1. Additionally, epoxy resin (HTC-667C), a thermoseting polymer,
was used as matrix bought from Jet. Korea Industrial Corporation. The hardener used was a modified
aliphatic amine.

Table 2. Variation of interply hybrid composite panel
Hybrid
Composite
CFRP
C36B8C36
C32B16C32
C28B24C28
C27B32C27
B8C64B8
C16B16C16B16C16
BFRP

CT code
CF
C1
C2
C3
C4
BCB
CBCBC

BF

Fracture
Tensile yield
Toughness,
strength,
B [mm] W [mm] a [mm] σ ys, [MPa] K Q , [Mpa.√m]
Average dimension

15
15
14.8
14.75
14.72
14.55
14.25
14.35

60
60

59.2
59
58.88
58.2
57
56

3.33
3.33
3.26
3.25
3.24
3.2
3.13
3.08

687
630
602
558

536
571
556
402

14.495
13.583
13.492
12.555
11.497
12.183
12.704
8.358

Fabrication of hybrid composite
Vacuum assisted resin transfer molding (VARTM) technique [18, 19] (Fig. 1) was employed for
the fabrication of hybrid composites. Generally, this technique consists of five steps as follows: 1)
mold preparation, 2) sealing of the mold and creating a vacuum, 3) resin preparation and degassing, 4)
resin impregnation, and 5) panel curing. In the present study, according to the VARTM steps, six
panels with plain carbon fabrics and plain basalt fabrics were designed as shown in Table 2. After that,

compact tension (CT) specimen was produced by cutting the panel using a water jet machine. The CT
dimension is 75mm high, 72 mm wide and 15 mm thick (see Fig.1). The crack length, a (crack

pre-notch plus razor notch), is equal with the specimen thickness, B. In this case, the specimen is used
accordance to standard: 2 < w/B < 4. Then, the applied PQ was 5% of the secant line which is, P5 = PQ.

Figure 1. Compact tension specimen geometry.
Test setup and Mode I Fracture toughness analysis
In the present study, the CT specimen of hybrid interply composites was determined based on the
mode I fracture toughness using a universal testing machine (Unitec-M, R&B). Two tonnes load cell
was used with cross head speed of 1 mm/min. Crack propagation of the specimen is measured using
the clip-on gage of 0.25 mm (Epsilon Technology Corp. Jackson, WY USA). According to ASTM D
5045 standard, the fracture toughness was measured five times for each variety of hybrid composite.
Theoretically, fracture toughness of plain strain condition is strongly dependent on the specimen
thickness. The plastics zone at the crack tip has to be appreciably less than the specimen thickness, B,
as shown in Eq. 1 [17]:
K
B, a, (W − a ) ≥ 2.5  Q
σ
 ys





2

(1)

where. KQ is fracture toughness, σys the yield stress, a the crack length, and W the specimen width.
Here, the width of specimen followed the recommended size, which is:
K
W ≥ 2.5  Q
σ
 ys

2


 ≥ 2 B


(2)

In this work, the toughness for CT specimen is calculated following Eq. 3:
K IC = K Q =

where, f ( δ ) =

PQ
BW

1

2

(3)

f (δ )

(2 + x)
(1 − x )
3

2

( )

 0.886 + 4.64(δ ) − 13.32(δ ) 2 + 14.72(δ )3 − 5.60(δ ) 4  , and δ = a
w

(4)

Here, PQ is critical load that was measured by projecting a line whose slope is 5% less than the original
slope of curve, and f (δ) is the geometry function that depends on the crack size of specimen width
ratio.
Result and Discussion
Mode I fracture toughness behavior hybrid composite
Toughness is the resistance of material against fracture and crack propagation. Figures 2a and b
show the load-displacement curve of a single edge notched specimen of hybrid interply composite in
accordance to fracture Mode I (tensile mode). Generally, the results show that the load for tensile
mode of all CT specimens increases linearly, which was due to the elastic behavior of the specimen.
The load then continues to raise until the plastic mode. Here, we marked a bright color ahead of the
notch in Fig. 2 (plastically deformed) and the curve has slightly deviated from linearity. Crack then
started to show and followed by a sudden decrease of loads(Fig.2a). In this case, a pop-in occurred
until at point "D", which started from point "C" (see insets of Fig. 2a). This condition is different with

Applied Load, P (Kgf)

basalt fiber reinforced plastic (BFRP) (Fig. 2b). At point "B" (inset of Fig. 2b), only quasi-elastic
deformation occurred ahead of the notch as marked by a bright color in the figure. At this point, the
crack started, but pop-in behavior did not occur. This result indicates that CFRP has semi-stable crack
growth failure compared with BFRP composite.

Fracture Toughness, KQ, [MPa√m]

Figure 2. Load-displacement curves of the compact tension specimens: a. carbon fabric, b. basalt
fabric.

(a)

(b)

Figure 3. Mode I fracture toughness results: a) effect of the amount of basalt fabrics inserted into the
carbon fabric, and; b) effect of the lamination sequences mode between the basalt fabrics with carbon
fabrics.
Figure 3 shows the average fracture toughness behavior of interply hybrid epoxy composite
reinforced with plain woven carbon fabrics and basalt fabrics. We can see from the results that an
opposite trends has occurred for fracture toughness of interply hybrid composites. Here, the fracture
toughness of each hybridization variation of carbon fabrics increased with increasing the amount of
basalt fabrics content , which may be due to the deformability of basalt fabrics. This result indicates
that basalt fiber can potentially improve the fracture toughness of CFRP. Similar results have been
reported [20]. In the present work, increasing the amount of plain woven basalt content (40 wt%) has
given influence on the deformable toughness of the composites increasing up to 20.68%. The interply
hybrid epoxy composite with sequence laminate mode between the carbon fabrics and basalt fabrics
showed some effect on the fracture toughness of the composites compared with CFRP and CBC mode
(B1) (see Fig.3b). From the result, it can be seen that the sequence laminate mode CBCBC showed the
best result and is therefore a potential configuration for improving the fracture toughness (KIC) of
composite materials.
Failure behavior of interply hybrid composite under mode I
Figure 4 shows the fracture surfaces of interply hybrid composites. From the figure, we can see
that the failure morphology of CFRP (Fig. 4a) showed warp and weft formation and is of brittle

nature. This was different with the failure mode of the epoxy composite reinforced with plain woven
basalt fibers (Fig. 4b). This difference could be due to the good deformability of basalt fabrics.
Generally, the failure of interply epoxy hybrid composite reinforced with plain woven carbon and
basalt fabrics were dominated by failure via pull-out, de-lamination and de-bonding form. For BFRP,
the basalt yarn failure is by individual fiber rupture [21]. Figures 4a, b and c show the failure shape of
the CT specimen of CFRP, BFRP and interply hybrid composite of carbon fabric with 40 wt% basalt
fabrics, respectively.

Figure 4. Fracture surfaces of interply hybrid composites showing region of failure along transversely
as well as longitudinally arranged fiber bundles, and sites of brittle matrix fracture; a) CFRP, b) BFRP
and, c) 40wt% of basalt fabrics hybrid with carbon fabrics.
Conclusions
In this study, we successfully investigated the fracture toughness and failure characteristics of
interply hybrid epoxy composites reinforced with carbon fabrics and basalt fabrics under mode I
fracture toughness test. The specimen was manufactured using VARTM process. CT specimen test
was carried out. From this investigation, the results showed that the strength fracture toughness, KIC,
decreased with the increase of basalt fibres contents (40 wt%) in the CFRP. The toughness of hybrid
composite with increasing basalt fibre contents also increased, as shown by the decrease of the crack
propagation of the notch. De-bonding and fiber pull outs dominated the failure behaviour of the hybrid
composites. This is an indication of instances of shear deformations, which occurred locally in such
structures. Here, due to the deformability of basalt fibres hybridization with carbon fibres shows
potential to improve the fracture toughness of hybrid composites under the mode-I test.
Acknowledgements
The authors would like to thank Udayana University, Bali, Indonesia for the support of this study and
in realizing this paper.
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