SAMPE Journal - September/October 2020 - 8

FEATURE / COMPOSITE BONDED JOINTS
arrester is expected to lead to significantly higher
crack growth resistance when compared with the
conventional bonded interface.

(a)

(b)

Figure 1. Interlocking-fiber-based crack arrester: (a) schematic and (b)
photograph.

the interface with adherends (Figure 1b), whereas
the 90° layers are bridging between the 0° layers
(Figure 1b). Therefore, for crack propagation along
the bonded interface, it is necessary to fracture
the bridging 0° layers or to break the 90° layers
progressively. In any case, carbon fiber fracture
is necessary for crack propagation. Therefore,
introducing a interlocking-fiber-based crack
Figure 2. Schematic of DCB specimen with interlocking-fiber-based crack
arrester.

SAMPE JOURNAL

S E P T E M B E R /O C TO B E R 2 0 2 0

EXPERIMENTAL EVALUATION:
INTERLOCKING FIBER CONFIGURATION
EFFECT
Materials and Methods
DCB tests were performed to evaluate the effect of
the interlocking fiber configuration on resistance
to mode-I failure. The schematic of the DCB
specimen is shown in Figure 2. The length of
the specimen was 200 mm, and three 25 mmwide specimens were cut from a plate of 100 mm
width. We used a unidirectional carbon/epoxy
prepreg sheet (T700SC/2592, Toray Industries,
Inc.) for the adherends ([0]16, thickness: 2.25 mm)
and arrester, and an epoxy adhesive film (FM3002M, Cytec Industries, Inc., thickness: 0.2 mm).
The manufacturing method of the crack arrester
is shown in Figure 3. First, the part behind the
intersection of the 0° layers was cut into a 5-mmwide-slit shape. Next, an adhesive film was placed
on the part next to the intersection of the 0° layers.
A sheet of polytetrafluoroethylene (PTFE) film
(thickness: 50 µm) was placed on the adhesive film
to introduce an initial crack. The initial crack was
80 mm in length from the tip of the specimen. The
0° layers, cut into the opposite slit shape of the first
0° layers, were placed on the PTFE film, and the
slit parts of each of the 0° layers were interlocked.
The crack reached the intersection of the 0° layers
at 30 mm from the initial crack. Finally, the crack
arrester was fabricated by inserting 90° layers
between the interlocked slit parts. A DCB specimen
was prepared by sandwiching the crack arrester
between the adherends (Figure 4). To evaluate the
effect of the interlocking fiber configuration, three
types of the configurations were used; the first
one with two plies of the prepreg sheets for both
the 0° layers and the 90° layers (02-902 specimen),
the second one with three plies for the 0° layers
and two plies for the 90° layers (03-902 specimen),
and the third one with two plies for the 0° layers
and one ply for the 90° layer (02-901 specimen).
In addition, specimens without the arrester were
used for comparison. Specimens were cured in
an autoclave under 0.3 MPa pressurization. The
curing cycle was 2°C/min heating, 2 h holding at
130°C, and 2°C/min cooling. The specimen with
two loading blocks bonded on the surfaces was
mounted on a precision universal tester (AG-100kN
Xplus, Shimadzu Co.). Tensile loading was applied
at a speed of 3 mm/min.

w w w. s a m p e . o r g

http://www.sampe.org

SAMPE Journal - September/October 2020

Table of Contents for the Digital Edition of SAMPE Journal - September/October 2020