Composites: Part A 43 (2012) 1318–1325
Contents lists available at SciVerse ScienceDirect
Composites: Part A
journal homepage: www.elsevier.com/locate/compositesa
Proposal of the concept of splice-type arrester for foam core sandwich panels
Yasuo Hirose a,⇑, Hirokazu Matsuda b, Go Matsubara b, Masaki Hojo c, Fumihide Inamura b
a
Department of Aeronautics, College of Engineering, Kanazawa Institute of Technology, 7-1 Ohogigaoka, Nonoichi, Ishikawa Pref. 921-8501, Japan
Strength Research Department, Technical Institute, Kawasaki Heavy Industries, Ltd., 1 Kawasaki-cho, Akashi City, Hyogo Pref. 673-8666, Japan
c
Department of Mechanical Engineering and Science, Kyoto University, Sakyo-ku, Kyoto City, Kyoto Pref. 606-8501, Japan
b
a r t i c l e
i n f o
Article history:
Received 7 July 2011
Received in revised form 27 March 2012
Accepted 28 March 2012
Available online 4 April 2012
Keywords:
A. Foams
B. Damage tolerance
B. Delamination
C. Finite element analysis (FE)
a b s t r a c t
A new type of crack arrester concept, named the splice-type crack arrester, was invented and applied to a
core–core splice in a foam core sandwich panel in order to suppress interfacial crack growth. An analytical evaluation of this crack arrester including parametric studies was carried out. It was confirmed by
finite element (FE) analysis that interfacial crack propagation was suppressed by a decrease in the energy
release rate at the crack tip under constant loading owing to the splice-type crack arrester as the crack tip
approached the edge of the arrester. Through this study, it was revealed that the leading edge of the
splice-type crack arrester, its shape and material, have strong effects on the crack suppression capability.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Sandwich structures are structural elements consisting of a
core of low density and two thin, high-stiffness and high-strength
surface skins bonded on both sides of a core material. This element has high stiffness-to-weight and strength-to-weight ratios.
Therefore, adding to many fundamental studies, design procedures were also established [1–9]. As for core materials, a honeycomb core and a foam core are commonly used. Recently, studies
of sandwich structures using new core materials have been conducted [10–12]. Among them, application studies of foam core
sandwich panels in railway vehicles, aircrafts, and hull structures
for a maritime application were carried out owing to the panels’
sufficient operational history, good bending stiffness- and
strength-to-weight ratios, and excellent formability [13–15].
However, there is a serious problem of considerable strength degradation due to interfacial cracks between the surface skin and
the core, initiated in the damaged area. To investigate damage
characteristics and interfacial crack propagation, studies based
on stress analyses were conducted [16–20]. Furthermore, from
the fracture mechanical viewpoint, Shipsha et al. studied the relationship between da/dN and DK [21], and Carlsson and coworkers
[22–24] and Yokozeki [25] conducted research on crack kinking
behavior. Interfacial cracks between the surface skin and the foam
core are a critical problem for the application of foam core sandwich structures because of the difficulty in inspecting interfacial
⇑ Corresponding author. Tel.: +81 76 248 4741; fax: +81 76 294 6711.
E-mail address: hirose_yasuo@neptune.kanazawa-it.ac.jp (Y. Hirose).
1359-835X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.compositesa.2012.03.022
crack together with the considerable degradation of static and fatigue strength.
To increase the durability of foam core sandwich panels, interfacial cracks initiated anywhere and propagated in any direction
should be suppressed. To suppress interfacial cracks, it is necessary
to reduce the energy release rate at the crack tip below the interfacial fracture toughness. To do so, it is effective to install materials
with a higher stiffness than the core material on the crack path and
decrease the energy release rate at the crack tip by redistributing
load from the foam core area near the crack tip to the installed
material. Therefore, on the basis of this concept, we proposed a
structural element named the basic type crack arrester with semicylindrical shape and confirmed the crack suppression effect of the
crack arrester through analyses of the energy release rate and
through experimental validation, i.e., quantitative estimation
based on the fracture mechanical approach showing the reduction
in the energy release rate at the crack tip near the leading edge of
the crack arrester and fracture toughness tests [26–28]. The detection method for an arrested crack was also investigated using
structural health monitoring (SHM) [29]. The structural element
can suppress interfacial cracks initiated anywhere and propagated
in any direction with a systematic arrangement such as a grid pattern owing to its light weight, easy formability and high reliability.
We naturally extended this concept to a core–core splice portion
of foam core sandwich structures and proposed the structural element for interfacial crack suppression. The element acquires an
interfacial crack suppression capability with the installation of
some carbon-fiber-reinforced plastic (CFRP) plies into the core–
core splice portion instead of a conventional film adhesive. Without
Y. Hirose et al. / Composites: Part A 43 (2012) 1318–1325
using any fracture mechanical approaches, Olsson and Lönnö proposed a similar structural element of connecting two surface skins
[30]. Our proposed structural element only functions to redistribute
load from a foam core area near the crack tip to thin CFPP plies, not
to confer high strength and high stiffness capabilities in the
through-the-thickness direction to foam core sandwich panel
structures. In other words, it is not necessary for the crack arrester
to transfer loads between surface skins through the foam core because it only serves to induce the redistribution. Therefore, sufficient crack suppression can be expected even without connecting
surface skins using the arrester. The proposed crack arrester can
be arranged systematically such as in a grid pattern within a foam
core sandwich with minimum weight penalty, and it can suppress
interfacial cracks initiated anywhere and propagated in any direction. The slanting angle of the crack arrester to the surface skin is
set below 45° for sufficient curing pressure on the arrester assuming conventional and reliable autoclave curing.
Recently, Zahlen, Rinker and coworker have carried out research
on integral fabrication trials for large foam core sandwich panel
structures with embedded structure elements for reinforcement
together with the development of innovative fabrication processes
such as liquid composite molding (LCM) suitable for integral fabrication [31]. To improve the through-the-thickness stiffness of foam
core sandwich structures, embedded structural elements such as
inserts are commonly used. Note that these structural elements
also have crack suppression capability, the so-called crack stopper,
along with their high strength and high stiffness as thick structural
elements for sustaining concentrated loads [15]. Rinker, Zahlenr
and coworker proposed new reinforcing structural elements with
a suitable shape for the crack stopper because sandwich panels
embedded with complicated reinforcing structures were realized
owing to the development of innovative fabrication processes
[32]. Rinker et al. also evaluated the crack suppression effect of
their crack stop element under fatigue loads with a constant amplitude [33]. No fracture mechanical approaches to investigating the
mechanism of the crack stopper, for example, the changes in the
energy release rate at the crack tip were carried out in their work,
although they experimentally investigated the crack suppression
effect. In contrast, in our study, we showed the crack suppression
effect by determining the reduction in energy release rate at the
crack tip, which was caused by the redistribution of load. Further
progress in Rinker et al.’s research is expected with the use of fracture mechanical approaches [34].
As for other ideas to enhance the through-the-thickness
mechanical property, studies to reinforce the foam core sandwich
panel using pins or stitches were conducted. The former concept
entails connecting surface skins with pins made of Ti–Al–4V alloy
or CFRP materials, and the improvement in compression strength
and energy absorption capability determined through quasi-static
and dynamic tests using Kolsky bar was shown in [35]. The latter
concept entails combining the upper and lower surface skins with
glass or Kevlar threads through the core, the through-the-thickness
mechanical properties were reportedly enhanced using this idea
[36–38]. In the civil engineering field, it was also reported that connecting of the upper and lower skins using a reinforcing element,
named shear ties, through the core improves the through-thethickness mechanical properties of sandwich panels [39]. This
was researched with the aim of the improving of the throughthe-thickness mechanical properties of sandwich panels by
connecting the upper and lower surface skins and a local crack
suppression effect was observed. However, the above studies were
different from ours in terms of firm connection between the upper
and lower surface skins, and the lack of fracture mechanical
analyses of the crack suppression mechanism.
As for other crack suppression ideas, Grenestedt proposed the
peel stopper concept for application in hull structures of high-
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speed vessels [40]. His idea was to suppress interfacial cracks
between the surface skin and the foam core initiated from blisters
located between the surface skin and the foam core. He proposed
two configurations, namely, a peel stopper without skin connection (PS) and a combined peel stopper and panel joint (CPJ). PS
configuration consists of a front skin, a rear skin and a putty
installed in a V-shaped grave machined on the foam core. The
CPJ configuration consists of a front skin, a rear skin and an overlap
by peel stopper, which connects the front and rear skins. In both
configurations, interfacial cracks propagating below the front skin
are suppressed at the peel stopper location by the removal of the
front skin.
Wonderly and Grenestedt estimated the crack suppression effect of the peel stopper proposed by Grenestedt under dynamic
conditions [41]. They confirmed the effect of the crack stopper
using large foam core sandwich panel specimens of 780 mm width,
900 mm width, 1360 mm width and 2000 mm width. Interfacial
cracks propagated dynamically from blisters simulated by blowing
compressed air into them through an accumulator. No fracture
mechanical analyses of the peel stopper effect itself were carried
out in this research though they investigated the relationship between the radius of the expanded blister, the delamination growth,
and the energy release rates at the crack tip.
Their ideas were very interesting and creative. However,
strictly speaking, the ideas did not suppress interfacial cracks
but only swerved them from the interface, and no fracture
mechanical approach to studying the effect of a peel stopper were
carried out.
Jakobsen et al. also proposed an interfacial crack suppression
idea called the new crack stopper. Their idea was to embed a material with elastic properties close to the sandwich core properties,
called the new crack stopper, in the sandwich panel, leading interfacial cracks to the surface of the new crack stopper. With the new
crack stopper, interfacial cracks swerved the interface and propagated along the surface of the new crack stopper. The effect of
the new crack stopper was confirmed experimentally through a
three-point bending test [42]. Furthermore, Jakobsen and coworkers investigated a suitable shape for the new crack stopper and a
material for rerouting interfacial cracks, and studied crack kinking
behavior [43–46]. However, no evaluation of the crack arrest effect
was carried out. Their idea was very innovative and important for
suppressing interfacial cracks, but different from ours in the point
of swerving interfacial cracks, instead of stopping them.
The splice-type crack arrester is a different idea from the
mechanical viewpoint, notwithstanding shape similarity, although
some structural elements with apparently similar shapes for suppressing interfacial cracks have been proposed.
In this paper, we describe the interfacial crack suppression effect of the splice-type crack arrester and the effect of its key
parameters such as slanting angle, and mechanical properties on
the crack suppression effect determined through numerical analyses based on a fracture mechanical approach.
2. Numerical method
The FE method was used to estimate the crack suppression effect by calculating the energy release rate at the crack tip using a
crack closure integral [47].
In the FE method, linear fracture mechanics was applied for the
following reasons. (1) The core material of WF110 was brittle and
showed a linear relationship between tensile stress and strain. (2)
We have already confirmed that the data of numerical analyses are
in agreement with the experimental data for the basic type crack
arrester with semicylindrical shape [27]. (3) In this case, the size
of the plastic zone under a small scale yielding assumption was
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about 0.2 mm under the plane strain condition. This size was cal2
culated on the basis of the data of KI = 2.32 108 Nm3 and
rY = 3.6 MPa. It is much less than the crack length of 40 mm. These
results satisfy the small scale yielding condition and confirm the
applicability of linear fracture mechanics to our study. In the FE
analysis, two-dimensional plane strain FE models were used. These
models consist of upper and lower surface skins, two tapered cores
and a splice-type crack arrester. The two tapered cores were
spliced together with butt joints. A schematic diagram of the FE
model with the splice-type crack arrester is shown in Fig. 1. Carbon
fiber reinforced plastic (CFRP) was used for the surface skins and
the splice-type arrester. The FE model consisted of the surface
skins and the crack arrester made of Toho Tenax UT500/#135,
which comprised a 12 K twill weave fabric carbon fiber and toughened epoxy resin, and the foam core made of Rohacell WF110 PMI
(polymethacrylimide) with thickness of 35 mm. The mechanical
properties of the materials are shown in Table 1. In the modeling
of the surface skin, each lamina of the surface skin with the symmetrical stacking sequence of the ply orientation was modeled.
The assumed ply orientation of a surface skin was [(+45°, 45°)/
(0°, 90°)/(0°, 90°)/(+45°, 45°)] and its nominal thickness was
1.52 mm. The fiber volume fraction of this material is 56%. The
FE model of the splice-type arrester uses UT500/#135 fabric plies
with the ply orientations of (+45°, 45°) and (0°, 90°). The fiber
volume fraction of these materials is 46%. The other arrester material used for evaluation was neat resin for parametric studies. The
slanting angle of the arrester was also varied as a parameters. Each
ply of the splice-type crack arrester and surface skins, and the foam
core were modeled with two-dimensional plane strain elements.
The following parameters were selected for numerical
evaluations:
– Crack suppression effect
The crack suppression effect of the splice-type arrester
was first evaluated under the following conditions and
then was compared with that of a basic type arrester with
a semicylindrical shape.
– Slanting angle h: 30°.
The definition of the slanting angle shown in Fig. 1.
– Arrester material: UT500/#135 fabric (+45°, 45°).
– Applied load: 350 N.
– Effect of the material
The effect of the arrester material was estimated for the
following materials.
– UT500/#135 fabrics [(+45°, 45°) and (0°, 90°)] and
neat resin
Here, h was fixed at 30° and the applied load was
fixed at 350 N.
– Effect of the slanting angle
The effect of the slanting angle was estimated for
h = 15°, 30°, 45°and 60°.
Here, the crack arrester material was UT500/#135
fabric (+45°, 45°) and the applied load was fixed at
350 N.
Arrester leading edge
L
– Direction of the crack propagation relative to the splice
portion
Crack propagation in the direction of the obtuse angle
side of the splice, denoted by direction A, and that in the
direction of the acute angle side of the splice, denoted by
direction B, were compared under the following
conditions.
– Slanting angle: 60°.
This angle was selected as the angle giving the
greatest effect of crack suppression within the parametric
studies discussed later.
– Crack arrester material: UT500/#135 fabric
(+45°, 45°).
– Applied load: 350 N.
For the loading condition, a mode-I type loading condition was
selected as a typical case. The energy release rates were calculated
for crack tip locations of L = 0.085 mm, 5 mm, 20 mm and 40 mm
under a constant load of 350 N with mode-I type loading condition.
Here, the parameter L is defined as the distance from the crack tip
to the leading edge of the arrester. As references, the energy release
rates at the crack tip obtained from the FE model without the crack
arrester and those of the FE model with the basic type crack arrester with a semicylindrical shape were calculated. A schematic diagram of the FE model with the semicylindrical crack arrester is
shown in Fig. 2.
The ABAQUS Ver.6.4.1 FEM code was used in the FE analysis,
and the total energy release rate was selected in order to estimate
the effect of the crack arrester considering the mixed-mode condition at the crack tip. In a previous study, the resin layer immediately below the surface skin was modeled and mode separation
for the energy release rate was conducted [26]. However, the resin
layer was not modeled in this study for simplicity because it has
little influence on estimating the effect of the major parameters
of the splice-type arrester. A schematic diagram of the FE model
is shown in Fig. 3. The external dimensions of the FE model and
the mode-I type loading condition are shown in Fig. 4. A schematic
diagram of the FE model used to compare crack propagation in
directions A and B is shown in Fig. 5.
The definitions of the energy release rates used in this paper are
summarized below [27].
– G0: Energy release rate at crack tip without the crack arrester.
This energy release rate was derived from FE analysis using the
FE model without the crack arrester for a given load, P, and various
crack lengths.
– GA: Energy release rate at crack tip with the crack arrester.
This energy release rate was calculated using the FE model with
the crack arrester for a given load, P, and various crack lengths.
In the analysis of the crack suppression effect, the normalized
energy release rate was introduced to estimate the crack arrester
effect quantitatively. This parameter is defined as GGA0 . Here, GA and
Surface skin
Splice-type crack arrester
Interfacial crack
Slanting angle
Fig. 1. FE model with splice-type crack arrester.
Foam core
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Table 1
Mechanical properties of materials used in the analysis.
Surface plate
CFRP (0°, 90°)
Vf = 46%
CFRP (+45°,
Vf = 46%
EXX (GPa)
EYY (GPa)
EZZ (GPa)
54.9
8.61
54.9
mXY
mYZ
mXZ
lXY (GPa)
lYZ (GPa)
lXZ (GPa)
45°)
Foam core
CFRP UD 90°
Vf = 56%
Neat resin
Rohacell WF110
CFRP (0°, 90°)
Vf = 56%
CFRP (+45°,
Vf = 56%
12.6
8.61
12.6
66.3
8.61
66.3
15.1
8.61
15.1
8.61
8.61
127
4.1
0.17
0.33
0.052
0.33
0.33
0.023
0.33
0.33
0.043
0.33
0.33
0.019
0.33
0.55
0.022
0.022
0.33
0.18
3.23
3.23
3.53
3.23
3.23
26.1
3.23
3.23
4.24
3.23
3.23
31.6
2.78
4.23
4.23
1.54
0.071
G0 were calculated by FE analysis under constant loading for the
same crack length.
3. Results and discussion
3.1. Crack suppression effect of the splice-type arrester
The crack suppression effect of the splice-type arrester is shown
in Fig. 6. The relationship GGA0 and the distance from the crack tip to
the leading edge of the arrester, L at a constant load of P = 350 N is
shown in this figure. The figure indicates that the normalized energy release rate at the crack tip for the FE model with the crack
arrester abruptly decreases near the leading edge of the arrester,
within approximately 5 mm, under the constant applied load. This
means that the splice-type crack arrester exhibits satisfactory suppression. This crack suppression effect is realized by the redistribution of load, which is similar to the basic type crack arrester with a
semicylindrical shape [26]. The stress distribution near the crack
tip and in the crack arrester with h = 30° and L from 40 mm to
0.085 mm is shown in Fig. 7. This figure shows that the stress in
the crack arrester increases as the crack tip approaches the leading
edge of the arrester. This increase in stress appears throughout the
entire length of the arrester when L = 0.085 mm, which leads to a
significant reduction of the energy release rate at the crack tip in
spite of the relatively thin crack arrester.
45°)
Resin layer
3.3. Effect of the arrester material on interfacial crack suppression
To evaluate the influence of the mechanical properties of the arrester material on the crack suppression effect, the energy release
rate at a crack tip location of L = 0.085 mm with h = 30° was calculated and compared for three types of arrester material, UT500/
#135 fabric (0°, 90°)/EXX = 54.9 GPa, UT500/#135 fabric (+45°,
45°)/EXX = 12.6 GPa and resin/EXX = 4.1 GPa, as typical examples.
The relationship between Young’s modulus and the energy release
rate at the crack tip is shown in Fig. 10. This figure indicates that a
crack arrester with greater stiffness, EXX, results in a greater reduction of the energy release rate at the crack tip, which decreases
with increasing Young’s modulus.
3.4. Influence of the crack propagation direction on the crack
suppression effect
To estimate the effect of the crack propagation direction, the
relationship between the energy release rate and the distance L
was investigated for crack propagation directions A and B defined
in Fig. 5. A slanting angle of h = 60° was selected, which resulted
in the strongest effect on crack suppression in this study. A comparison of the crack suppression effect for the two crack directions
is shown in Fig. 11. It can be seen that the crack arrester has almost
the same effect on crack suppression for both directions in case of a
slanting angle of h = 60°.
3.2. Influence of the slanting angle on the crack suppression effect
The relationship between the energy release rate at the crack tip
location of L = 0.085 mm and the slanting angle is shown in Fig. 8.
This figure indicates that the energy release rate at L = 0.085 mm,
very near the leading edge of the arrester, decreases as the slanting
angle increases. A comparison of the stress, rYY, distribution for different slanting angles at L = 0.085 mm is shown in Fig. 9, indicating
that a crack arrester with a larger slanting angle has lower stress
near the crack tip. This means that load redistribution mainly depends on the distance between the area of higher stress near the
crack tip and the leading edge of the arrester. An arrester with a
larger slanting angle has a smaller area of high stress near the crack
tip owing to the shorter distance between the region of higher
stress and the crack arrester. Therefore, an arrester with a larger
slanting angle has a stronger effect on crack suppression.
3.5. Comparison of crack suppression effect with basic type crack
arrester with a semicylindrical shape
To compare the crack suppression effect between the basic type
crack arrester with the semicylindrical shape and the splice-type
crack arrester, the energy release rate at the crack tip for various
crack tip locations is calculated and compared under constant
loading of P = 350 N with h = 30° as shown in Fig. 12. This figure
shows that the basic type crack arrester has an approximately
75% lower energy release rate near the leading edge of the arrester
than the splice-type crack arrester. This result indicates that a concentrated mass of material with higher stiffness, such as the semicylindrical shape, near the crack tip has a stronger crack
suppression effect than a thin layer of the same material distributed over a wide area, such as the splice-type arrester. It is
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Y. Hirose et al. / Composites: Part A 43 (2012) 1318–1325
Arrester leading edge
Surface skin
L
Interfacial crack
Crack arrester
R: Radius
Foam core
Fig. 2. FE model of crack arrester with semicylindrical shape.
Surface skin: CFRP fabric UT500/#135 (45o, -45o) 0.38t mm
Surface skin: CFRP fabric UT500/#135 (0o, 90o) 0.38t mm
Surface skin: CFRP fabric UT500/#135 (0o, 90o) 0.38t mm
Surface skin: CFRP fabric UT500/#135 (45o, -45o) 0.38t mm
Core 35t mm
Interfacial crack
L
Arrester
Arrester
Surface skin: CFRP fabric UT500/#135(45o, -45o) 0.38t mm
Surface skin: CFRP fabric UT500/#135 (0o, 90o) 0.38t mm
Surface skin: CFRP fabric UT500/#135 (0o, 90o) 0.38t mm
Surface skin:
CFRP fabric UT500/#135(45o, -45o) 0.38t mm
Fig. 3. Schematic diagram of FE model of foam core sandwich panel with arrester. (For interpretation of the references to color in this figure legend, the reader is referred to
the web version of this article.)
120
Unit: mm
P
70
a
Arrester material: CFRP fabric (+45o, -45o)
L
Interfacial crack
300
Fig. 4. External dimensions of the FE model and mode-I type loading condition.
Note: Width of FE model: 100 mm for mode-I type loading condition. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
Load P
Direction A
60o
Direction B
Fig. 5. Definition of the crack propagation directions. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
Fig. 6. Crack suppression effect of the splice-type arrester.
suggested that the concentrated mass at the leading edge of splicetype arrester also enhances the crack suppression capability. It
leads to the future modification of the splice-type crack arrester.
This paper contains of the proposal of the splice-type crack arrester and the results of parametric studies for optimizing the
shape of the splice-type crack arrester by numerical analyses using
the conceptual FE model based on a simplified actual structure. As
for the experimental validation in our study, the data of preliminary studies of fracture mechanical investigations based on the results derived from numerical analyses were compared with those
of fracture toughness tests. Here, the shape and stacking sequence
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Y. Hirose et al. / Composites: Part A 43 (2012) 1318–1325
Unit: MPa
L = 40.0 mm
L = 20.0 mm
L = 5.0 mm
L = 0.085 mm
Energy release rate G A, N/mm
Fig. 7. Distribution of the maximum principal stress. Note: Arrester material: CFRP fabric (+45°,
L = 0.085 mm
Arrester material: CFRP fabric (+45o, -45o)
Slanting angle
, degree
Fig. 8. Relationship between energy release rate and slanting angle.
of the specimens were slightly different from the ideal ones.
According to the preliminary studies, a 13-fold higher crack
suppression effect was observed for the splice-type crack arrester
compared with that of the sandwich panel without the crack
arrester [34,48]. No crack kinking of the interfacial crack was
confirmed in the evaluation of the basic type crack arrester with
semicylindrical shape [27] and in the preliminary study of the
splice-type crack arrester [48].
45°), slanting angle: h = 30°, P = 350 N.
Rinker et al. estimated the crack suppression effect of the
crack stopper under fatigue loads [33]. In this study, they estimated two types of crack stop element, named a CFRP hollow
profile, which was a rectangular solid core with CFRP plies placed
on the periphery, and double-T beams, which was a T-shape CFRP
solid element, embedded in the foam core sandwich panel fabricated by liquid composite molding. The crack stopper effects of
the crack stop elements were estimated by change of the relationship between the crack length and the number of cycles under a fatigue load with a constant amplitude. It was reported
that interfacial cracks penetrated between the crack stop element
and the surface skin, and a part of the crack stop element separated from the surface skin under mode I and II type fatigue loading before the cracks were suppressed. This phenomenon
indicated that the estimation of the crack stop element was
meaningful but that some additional studies are needed. We also
confirmed a similar interfacial crack penetration between the
crack arrester and the surface skin in the fracture toughness test
[27]. We found that this crack penetration could be prevented by
placing a CFRP ply cover on intersection of the crack arrester and
surface skin [49]. A similar countermeasure was taken for the test
specimen configuration for the experimental validation of the
splice-type crack arrester [34,48].
We have already obtained preliminary results of the crack
suppression effect for the splice-type crack arrester in both
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Y. Hirose et al. / Composites: Part A 43 (2012) 1318–1325
θ = 30ο
θ = 15 o
θ = 45ο
θ = 60ο
1.6
P = 350 N
DCB
1.4
L = 0.085mm
1.2
θ = 30o
1
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
60
Young’s modulus of the arrester, GPa.
Normalized energy release rate
Energy release rate GA, N/m
Fig. 9. Relationship between distribution of rYY near the crack tip and slanting angle.
Fig. 10. Effect of Young’s modulus.
Distance L, mm
Crack propagation Crack propagation
direction A
direction B
P = 350 N
θ
Arrester material: CFRP (+45o, -45o)
Normalized energy release rate
Fig. 12. Comparison with basic type crack arrester.
θ = 60o
experimental and numerical studies under mode II type loading
[50], and there will be presented in our follow-up paper.
4. Concluding remarks
θ = 60 (Direction A)
o
θ = 60o (Direction B)
Distance L, mm
Fig. 11. Effect of the crack propagation direction.
An innovative crack arrester using the splice portion of a foam
core sandwich panel is proposed. The crack suppression method
of this splice-type crack arrester was analyzed by finite element
method, and the suppression of interfacial cracks under mode-I
type loading was confirmed. Through parametric studies, the following results are obtained:
– The splice-type arrester has a satisfactory crack suppression
effect.
– A larger slanting angle, h, has a greater effect on crack suppression, although manufacturing constraints should be considered
for configurations with a larger slanting angle.
Y. Hirose et al. / Composites: Part A 43 (2012) 1318–1325
– A splice-type crack arrester with greater stiffness has a stronger
effect on crack suppression, and this tendency saturates as the
stiffness increases.
– The crack propagation direction has little influence on the crack
suppression effect for h = 60°.
– It is suggested that a concentrated mass of material with higher
stiffness near the crack tip has a strong influence on the crack
suppression effect through the reduction of the energy release
rate at the crack tip.
– It is reasonable to predict that the configuration of the splicetype arrester, particularly the configuration of the leading edge
of the arrester, should be modified to consider actual aircraft
structures in order to enhance effect of the crack suppression
because the FE model used in this estimation was very simple
and idealized.
References
[1] Zenkert D. An introduction to sandwich construction. London: EMAS; 1995.
[2] Zenkert D. The handbook of sandwich construction. London: EMAS; 1997.
[3] Groth HL, Zenkert D. Fracture of defect foam core sandwich beam. J Test Eval
1990;18(6):390–5.
[4] Zenkert D. Strength of sandwich beam with mid-plane debonding in the core.
Compos Struct 1990;15:279–99.
[5] Zenkert D. Strength of sandwich beams with interface debonding. Compos
Struct 1991;17:331–50.
[6] Carlsson LA, Sendlein LS, Merry SL. Characterization of sheet/core shear
fracture of composite sandwich beams. J Compos Mater 1991;25:101–16.
[7] Carlsson LA, Prasad S. Interfacial fracture of sandwich beams. Eng Fract Mech
1993;44:581–90.
[8] Thomson RS, Shah Khan MZ, Mouritz AP. Shear properties of a sandwich
composite containing defects. Compos Sci Technol 1998;42:107–18.
[9] Cantwell WJ, Scudamore R, Ratcliffe J, Davies P. Interfacial fracture in sandwich
laminate. Compos Sci Technol 1999;59:2079–85.
[10] Kazemahvazi S, Zenkert D. Corrugated all-composite sandwich structures.
Part1: Modeling. Compos Sci Technol 2009;69:913–9.
[11] Kazemahvazi S, Zenkert D. Corrugated all-composite sandwich structures. Part
2: Failure mechanisms and experimental programme. Compos Sci Technol
2009;69:920–5.
[12] Alfredsson KS, Gawandi AA, Gillespie Jr JW, Carlsson LA, Bogetti TA. Stress
analysis of axially and thermally loaded discontinuous tile core sandwich with
without adhesive filled core gaps. Compos Struct 2011;93:1621–30.
[13] Wennhage P, Olsson KA. Analysis of sandwich structures for railway vehicles.
In: Proc. 4th international conference on sandwich construction, Stockholm,
Sweden, 1998. p. 95–105.
[14] Moyer Jr. ET, Amir GG, Olsson KA, Hellbratt SE. Response of GRP sandwich
structures subjected to shock loading. In: Proc. 2nd international conference of
sandwich construction, Gainesville, USA, 1992. p. 49–57.
[15] Herrmann AS, Zahlen PC, Zuardy I. Sandwich structure technology in
commercial aviation. In: 7th International conference on sandwich
structures, Aalborg, Denmark, 2005. p. 13–26.
[16] Kulkarni N, Mahfuz H, Jeelani S, Carlsson LA. Fatigue crack growth and life
prediction of foam core sandwich composite under flexural loading. Compos
Struct 2003;59:499–505.
[17] Burman M, Zenkert D. Fatigue of foam core sandwich beam-2: effect of initial
damage. Int J Fatigue 1997;19(7):563–78.
[18] Vadakke V, Carlsson LA. Experimental investigation of compression failure of
sandwich specimen with face/core debond. Composite Part B 2004;35:583–90.
[19] Rizov V, Shipsha A, Zenkert D. Indentation study of foam core sandwich
composite panels. Compos Struct 2005;69:95–102.
[20] Zenkert D, Shipsha A, Bull P, Hayman B. Damage tolerance assessment of
composite sandwich panels with localized damage. Compos Sci Technol
2005;65:2597–611.
[21] Shipsha A, Burman M, Zenkert D. Interfacial fatigue crack growth in foam core
sandwich structures. Fatigue Fract Eng Mater Struct 1999;22(2):123–31.
[22] Carlsson L, Prasad S. Debonding and crack kinking in foam core sandwich
beams-I analysis of fracture specimen. Eng Fract Mech 1994;47:813–24.
[23] Carlsson L, Prasad S. Debonding and crack kinking in foam core sandwich
beams-II experimental investigation. Eng Fract Mech 1994;47:825–41.
1325
[24] Carlsson LA, Matteson RC, Aviles F, Loup DC. Crack path in foam cored DCB
sandwich fracture specimens. Compos Sci Technol 2005;65:2612–21.
[25] Yokozeki T. Analysis of crack kinking in foam core sandwich beams. Composite
Part A 2011;42:1493–9.
[26] Hirose Y, Hojo M, Fujiyoshi A, Matsubara G. Suppression of interfacial crack for
foam core sandwich panel with crack arrester. Adv Compos Mater
2007;16(1):11–30.
[27] Hirose Y, Matsuda H, Matsubara G, Hojo M, Inamura F. Evaluation of new crack
suppression method for foam core sandwich panel via fracture toughness tests
and analyses under mode-I type loading. J Sandwich Struct Mater
2009;11(6):451–70.
[28] Matsuda H, Matsubara G, Hirose Y, Hojo M. Effect of crack arrester for foam
core sandwich panel under mode I, mode II and mixed mode condition. In:
Proc. 16th international conference on composite materials, Kyoto, Japan,
2007.
[29] Minakuchi S, Yamaguchi I, Takada N, Hirose Y. Detecting an arrested crack in
foam-core sandwich structure using an optical fiber sensor. Adv Compos
Mater 2011;20(5):419–33.
[30] Olsson KA, Lönnö A. Recent research and development: GRP-sandwich
technology for high-speed marine vessels. In: Proc. 2nd international
conference of sandwich construction, Gainesville, USA, 1992. p. 807–823.
[31] Zahlen PC, Rinker M, Heim C. Advanced manufacturing of large, complex foam
core sandwich panels. In: 8th International conference on sandwich
structures, Porto, Portugal, 2008.
[32] Rinker M, Zahlen PC, Schäuble R. Damage and failure progression of CFRP foam
core sandwich structure. In: 8th International conference on sandwich
structures, Porto, Portugal, 2008.
[33] Rinker M, John M, Schäulbe R. Investigation of sandwich crack stop elements
under fatigue loading. In: Proc. 9th International conference on sandwich
structures, California, USA, 2010.
[34] Hirose Y, Matsuda M, Matsubara G, Hojo M, Inamura F. Experimental
evaluation of splice-type crack arrester with filler under mode-I type
loading. J Compos Struct, submitted for publication.
[35] Cartié DD, Fleck NA. The effect of pin reinforcement upon the throughthickness compressive strength of foam core sandwich panels. Compos Sci
Technol 2003;63:2401–9.
[36] Kim J, Lee Y, Park B, Kim D. Evaluation of durability and strength of stitched
foam-cored sandwich structures. Compos Struct 1999;47:543–50.
[37] Potluri P, Kusak E, Reddy T. Novel stitch-bonded sandwich composite
structures. Compos Struct 2003;59:251–9.
[38] Lascoup B, Abouora Z, Khellil K, Benzeggagh M. On the mechanical effect of
stitch addition in sandwich panel. Compos Sci Technol 2006;66:1385–98.
[39] Naito C, Beacraft M, Hoemann J, Bewick B. Performance and characterization of
shear ties for use in insulated precast concrete sandwich wall panels. Air Force
Research Laboratory, Report, FRL-RX-TY-TP-2010-0082; November 2010.
[40] Grenestedt JL. Development of a new peel-stopper for sandwich structures.
Compos Sci Technol 2001;61:1555–9.
[41] Wonderly C, Grenestedt JL. Dynamic performance of a peel stopper for
composite sandwich ship structures. J Compos Mater 2004;38:805–31.
[42] Jakobsen J, Bozhevolnaya E, Thomsen OT. New peel stopper concept for
sandwich structures. Compos Sci Technol 2007;67:3378–85.
[43] Jakobsen J, Andreasen JH, Bozhevolnaya E. Crack kinking of a delamination at
an inclined core junction interface in a sandwich beam. Eng Fract Mech
2008;75(16):4759–73.
[44] Bozhevolnaya E, Jakobsen J, Thomsen OT. Performance of sandwich panels
with peel stoppers, strain. Int J Exp Mech 2009;45:349–57.
[45] Jakobsen J, Thomsen OT, Andreasen JH, Bozhevolnaya E. Crack deflection
analyses of different peel stopper design for sandwich structure. Compos Sci
Technol 2009;69:870–5.
[46] Jakobsen J, Andreasen JH, Thomsen OT. Crack deflection by core junctions in
sandwich structures. Eng Fract Mech 2009;76(14):2135–47.
[47] Ryubicki EF, Kannine MF. A finite element calculation of stress intensity factors
by a modified crack closure integral. Eng Fract Mech 1997;9:931–8.
[48] Hirose Y, Matsuda M, Matsubara G, Hojo M. Evaluation of advanced crack
arrester for foam core sandwich panel – mode I type loading. In: Proc. 17th
international conference on composite materials, Edinburgh, UK, 2009.
[49] Hirose Y, Matsubara G, Hojo M, Matsuda H, Inamura F. Evaluation of modified
crack arrester by fracture toughness tests under mode I type and mode II type
loading for foam core sandwich panel. In: Proc. US-Japan conference on
composite materials 2008, Tokyo, Japan, 2008.
[50] Hirose Y, Matsuda M, Matsubara G, Hojo M. Proposal of interfacial crack
suppression method using splice-type crack arrester under mode II type
loading for foam core sandwich panel. In: Proc. 16th composite durability
workshop, Seoul, Korea, 2011.