This paper presents a study on crushing of CFRP composite laminated plates. The objective of this study is to analyze the influence of crushing speed on the rupture behavior and the energy absorption capability of composite materials.

Two materials are tested: a carbon-epoxy unidirectional prepreg, and a carbon-epoxy fabric. For both materials, three different plate configurations are tested (three different stacking sequences). The crushing device is an improved plate crushing setup with stabilizing guides, which can be used both on a standard static traction/compression test machine, or on a drop tower. For static tests, a 20 mm/min velocity is applied to the specimen all along the 100mm crushing stroke. For dynamic tests, only the initial velocity can be imposed. Three initial speeds were chosen: 2, 5 and 9 m/s. A high-speed camera is used during tests to visualize the global behavior of the plate, and the rupture modes in the crushing front. The load is also recorded, which enables to calculate the load/displacement curve of plates crushing and determinate the energy absorption capability. The analysis of these results enables to discuss on the influence of crushing speed both on the rupture modes and, as a consequence, on the energy absorption capability

Barrau, Jean-Jacques

Duong, Anh Vu

Malherbe, Benoît

Petiot, Caroline

Rivallant, Samuel

Open Archive Toulouse Archive Ouverte

 To cite this document: DUONG Anh Vu, RIVALLANT Samuel,  BARRAU Jean-Jacques, PETIOT Caroline, MALHERBE Benoît. Influence of speed on the crushing behavior of composite plates. In: ACCM 7 – 7th Asian-Australasian Conference on Composite Materials, 15-18 Nov 2010, Taipei, Taiwan.  This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 4875 Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@inp-toulouse.fr                                                                                    Influence of speed on the crushing behavior of composite plates   Anh Vu Duong1*, Samuel Rivallant1, Jean-Jacques Barrau1, Caroline Petiot2, and Benoît Malherbe3   1 Université de Toulouse; INSA, UPS, Mines Albi, ISAE; ICA (Institut Clément Ader); Toulouse, France 2 EADS IW, Suresnes, France 3AIRBUS France, Toulouse, France *Corresponding author：ISAE, 10 avenue E. Belin, BP 54032, 31055 Toulouse, Fance  e-mail：anh-vu.duong@isae.fr    ABSTRACT This paper presents a study on crushing of CFRP composite laminated plates. The objective of this study is to analyze the influence of crushing speed on the rupture behavior and the energy absorption capability of composite materials. Two materials are tested: a carbon-epoxy unidirectional prepreg, and a carbon-epoxy fabric. For both materials, three different plate configurations are tested (three different stacking sequences). The crushing device is an improved plate crushing setup with stabilizing guides, which can be used both on a standard static traction/compression test machine, or on a drop tower. For static tests, a 20 mm/min velocity is applied to the specimen all along the 100mm crushing stroke. For dynamic tests, only the initial velocity can be imposed. Three initial speeds were chosen: 2, 5 and 9 m/s. A high-speed camera is used during tests to visualize the global behavior of the plate, and the rupture modes in the crushing front. The load is also recorded, which enables to calculate the load/displacement curve of plates crushing and determinate the energy absorption capability. The analysis of these results enables to discuss on the influence of crushing speed both on the rupture modes and, as a consequence, on the energy absorption capability.  KEYWORDS: Composite, crushing, energy absorption, speed, CFRP.  1. INTRODUCTION The use of laminated composite in vehicle structure requires a good understanding of their crash behaviour. But the range of crushing mode is very wide and strongly depends on numerous factors. Despite extensive experimental works done in the 90's [1:5], and more recently [6], it is still very hard to predict the crash response of a complex structure. A few works were done concerning dynamic crush tests, [7], but there are very few results concerning the influence of crushing speed on crushing behavior and energy absorption capability. Moreover, conclusions seem often contradictory (problems of dispersion, to few tests…)  The aim of this study is to obtain experimental results providing a better understanding of the speed influence in progressive crushing of composite laminated plates. The main experimental objective of this work is to perform crushing tests on two different materials, with three different stacking sequences for each material, at 4 different speeds (from quasi-static to 9 m/s). A second objective is also to compare energy absorption capability of laminates made of UD plies or fabrics, for the same equivalent modulus.  2. EXPERIMENTAL 2.1 Fixture design The test fixture (figure 1) has been designed to improve plate crushing fixtures found in literature [8]. It is made of four vertical adjustable guides which avoid buckling of the specimen, and two horizontal adjustable guides. These ones are localised just beneath the vertical guides so that a gap exists between horizontal guides and the metallic base plate where the laminate crashes. Such a concept has been developed at the same time by Feraboli [9]. This avoid tearing of the plate observed in most of the plate crushing fixtures [10], and ensure that the boundary conditions are the same along the whole width of the plate, just above the crushing front. Two main uprights carry the guides without interference with the crush front. Visualisation holes have been made to let the crush front visible. The thickness of the specimen can vary from 0 to 10mm. The gap (unsupported height between the base plate and the horizontal guides) can vary from 0 to 40 mm.  The laminate is fixed to a steel cylinder which is the interface with the static machine or the drop tower (dynamic tests). During crushing, plate and cylinder go                                                                                   down between the uprights and the vertical guides. At the bottom of the cylinder, a 120 kN Kistler piezoelectric sensor measures the crushing load. The small distance between the specimen and the sensor limits the mechanical filtering of the signal, allowing high precision in the dynamic crush load measurement. A high speed camera is used to have a real-time observation of the crushing front on the side of the plate. The filming speed is 20000 fps, with a 512x256 pixels resolution.  Figure 1: Design of the fixture, with (on right) and without (on left) upright  The fixture is used both for quasi-static test on a screw-driven universal testing machine and for dynamic tests on a drop tower apparatus. The load is introduced through the top of the specimen with a steel cylinder. At the bottom of this cylinder, a piezoelectric sensor measures the crushing load. The small distance between the specimen and the sensor limits the mechanical filtering of the signal.  The use of a drop tower does not enable to have a constant speed during dynamic crushing : speed decreases as energy is absorbed. Depending on the test configurations (available weight on the drop tower, energy absorption capability of specimen, initial speed), speed can just slightly decrease, or reach 0 (in that case, the specimen is not totally crushed).  2.2 Design of experiment Specimens are 160*60 mm flat plates. White graduations are drawn on the edge of the specimen each 5 mm. The trigger mechanism is a 45° chamfer machined at the bottom end of the plate. Each test is defined by two parameters: - Crush speed: 20 mm/min for static tests, and three different impact speeds for drop tower tests: 2 m/s, 5 m/s, and 9 m/s. - Laminate configuration: two materials were tested:  1) Material 1: Cytec fabric prepreg 5H (6KHTA) 977-2 Ply thickness: 0.35 mm Three stacking sequence configurations: P1-[(0/45)3]sym P2- [(0)6]sym P3-[(0/45)3,0]sym. 2) Material 2: Hexply unidirectional prepreg T700/M21 (M21/35%/268/T700GC) Ply thickness: 0.26 mm Three stacking sequence configurations:  P4-[(0/45/90/-45)*2]sym,  P5-[(0/90)*4]sym,  P6-[(0/45/90/-45)*2,90,1/2 0°]sym Stacking sequences were chosen so that for each kind of configuration (1 to 3), weight, global thickness and equivalent modulus of the plates are the same for both materials (Table 1). This enables to compare energy absorption efficiency for these two materials. The unsupported height is set to 20 mm for all tests.  Each configuration and speed, two specimens are tested.  Table 1: Specimens characteristics   Config. 1 iso Config. 2 0/90 Config. 3 0° oriented Plate number P1 P2 P3 Number of plies 12 12 14 Total thickness 4.2 4.2 4.9 Material 1 Equiv. Modulus 42700 61000 45700 Plate number P4 P5 P6 Number of plies 16 16 19 Total thickness 4.16 4.16 4.94 Material 2 Equiv. Modulus 45500 62600 46100  2.3 Detailed analysis of progressive crushing mechanisms Figure 3. shows some examples of load-stroke curves obtained from the tests. Each curve may be divided in three phases: the initiation phase, the transition phase and the stable crushing phase on which the specific energy absorption (SEA) is calculated as : SEA = Fmean / ρ.A  Fmean: mean load during the stable crushing phase ρ  specimen density A surface of the cross-section 0500010000150002000025000300000 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1 0,11Deplacement(m)Filtered load (N)P4 (V=0m/s)P4 (V=2m/s)P4 (V=5m/s)P4 (V=9m/s) Figure 3: some examples of load-stroke behaviour                                                                                   3. RESULTS and DISCUSSION The numerous experiments made enabled to observe the different crush modes of composite laminated plates with different configurations and different speeds. Crush mechanisms are homogeneous through the width of the plate, thus the real-time pictures of the side of the crushed laminate (figure 4 and 5) allow observation and understanding of crush modes. Following is shortly described some of the main modes observed.                            Figure 4: Examples of crush modes observed Figure 5: Images from high-speed camera P4     With all specimens tested, there isn’t undamaged splaying mode. The crushing mode observed is mixed mode and fragmentation mode. In mixed crush mode, exterior plies on both sides bend and evacuate in splaying crush mode. The proportion of plies that bend on each side is variable. An obstacle, like a debris wedge, in the front separating two splaying arms is the reason why this mode appears. Fragmentation occurs when plies reach the metallic base at right angle and can not slip on the base. Failure appears continuously at macroscopic scale. Energy absorbed can be very high: up to 50 kJ/kg, depending on the number of fragmented plies. But fragmentation is not a stable crush mode, plies crush evolving from fragmentation to bending, leading to undamaged or fractured splaying crush mode.  3.1 Influence of speed The results of these tests for different stacking sequences of composites plates Cytec and T700/M21 with different initial speeds are shown in figure 6 and figure 7. The dataset of the maximum loads Fmax during the tests for each sample is created. Fmax is the initial peak load (figure 3). Globally, this peak load increases with the speed of the initial velocity before impact.                                Figure 6: Fmax with different initial speeds  However, the results of energy absorption with different speed are difficult to analyze: no clear tendency is observed. The dispersion of the results can be explained by the different observed crush modes which depends on the debris wedge created in the test. A debris wedge made of debris issued from the initiation process or from fracture of central plies can appear at different time and create different crushing modes in which the  (a) Mixed mode: laminate of T700/M21 - chamfer trigger   (b) Fragmentation: laminate of Cytec- chamfer trigger   (b) T700/M21  (a) Cytec                                                                                       0510152025303540451 2 3Stacking SequencesSEA mean (KJ/Kg)Cytec T700/M21 Figure 8: Comparison of SEA for the two materials number of plies in fragmentation is not stable during the test (and not the same from one test to the other). In figure 7, the dataset of each stacking sequence of both materials with different initial velocity of the test is shown. It can be concluded that there is no visible influence of speed on the energy absorption on the two materials tested with the three stacking sequences.                          Figure 7: SEA with different initial speeds  3.2. Comparison unidirectional (UD)/fabrics The Cytec samples and T700/M21 samples have the same equivalent Young modulus for each stacking configuration (iso-rigidity). To compare UD to fabrics, as no visible influence of speed on the results of SEA was found, an average value of SEA was calculated for each material and stacking configuration taking into account the SEA of tests at all speed for a given stacking configuration. Comparison is shown on Figure 8.  The results show that the energy absorption capability of Cytec fabric is much higher (approximately twice) than T700/M21, for the three tested configuration. This can be explained by the fact that in Cytec samples, plies damage happens earlier than in T700/M21, leading to fragmentation whereas in T700/M21, delamination appears between plies, before fiber rupture, developing splaying mode in the external plies, and reducing the number of fragmented plies.     4. CONCLUSIONS The influence of initial velocity on the crushing behavior of composite plates is studied. With two materials tested, the influence of speed to the maximum load is easily observed. However, its influence on the energy absorption is not visible. The results show clearly that Cytec specimen can absorbed more energy than T700/M21 specimen in crush test.  References 1- Hull D. “A unified approach to progressive crushing of fibre-reinforced composite tubes”, Composites science and technology 1991;40:377-421. 2- Farley G.L., Jones M.R. “Crushing characteristics of continuous fibber-reinforced composites tubes”, Journal of composites materials 1992;26:37-50. 3- Mamalis A.G., Robinson M., Manolakos D.E., Demosthenous G.A., Ioannidis M.B., Carruthers J. “Crashworthy capability of composite material structures”, Composite structures 1997; 37:109-134. 4- Ramakrishna S. “Microstructural design of composite materials for crashworthy structural applications”, Materials & Design 1997;18:167-173. 5- Karbhari V.M., Haller J. “Effect of preform structure on progressive crush characteristics of flange-stiffened tubular elements”, Composite Structure 1997; 37:81-96. 6- Ueda M., Hiraga A., Nishimura T. “Energy absorption of unidirectionam CFRP plate unde compression”. 14th European Conference on Composite Materials, Budapest, Hungary, June 2010. 7- Lavoie J.A., Kellas S. “Dynamic crush tests of energy absorbing laminated composites plates”, Composites: Part A 1996;27:467-475. 8- Guillon D., Rivallant S., Barrau JJ., Petiot C., Thevenet P., Pechnik N. : “Initiation and propagation mechanisms of progressive crushing in carbon-epoxy laminated plates”. 13th European Conference on Composite Materials, Stockholm, Sweden, June 2008. 9- Feraboli P., Deleo F., Garattoni F., “Efforts in the standardization of composite materials crashworthiness energy absorption”, 22nd American Society for Composites Technical Conference, Seattle, September 2007.  10- Daniel L., Hogg P.J., Curtis P.T. “The crush behaviour of carbon fibre angle-ply reinforcement and the effect of interlaminar shear strength on energy absorption capability” Composites: Part B 2000;31:435-440.  (a) Cytec (b) T700/M21 

Influence of speed on the crushing behavior of composite plates

International audienceThis paper presents a study on crushing of CFRP composite laminated plates. The objective of this study is to analyze the influence of crushing speed on the rupture behavior and the energy absorption capability of composite materials.Two materials are tested: a carbon-epoxy unidirectional prepreg, and a carbon-epoxy fabric. For both materials, three different plate configurations are tested (three different stacking sequences). The crushing device is an improved plate crushing setup with stabilizing guides, which can be used both on a standard static traction/compression test machine, or on a drop tower. For static tests, a 20 mm/min velocity is applied to the specimen all along the 100mm crushing stroke. For dynamic tests, only the initial velocity can be imposed. Three initial speeds were chosen: 2, 5 and 9 m/s. A high-speed camera is used during tests to visualize the global behavior of the plate, and the rupture modes in the crushing front. The load is also recorded, which enables to calculate the load/displacement curve of plates crushing and determinate the energy absorption capability. The analysis of these results enables to discuss on the influence of crushing speed both on the rupture modes and, as a consequence, on the energy absorption capability

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Influence of speed on the crushing behavior of composite
plates
Anh Vu Duong, Samuel Rivallant, Jean-Jacques Barrau, Caroline Petiot,
Benoît Malherbe
To cite this version:
Anh Vu Duong, Samuel Rivallant, Jean-Jacques Barrau, Caroline Petiot, Benoît Malherbe. Influence
of speed on the crushing behavior of composite plates. ACCM 7 – 7th Asian-Australasian Conference
on Composite Materials, Nov 2010, Taipei, Taiwan. pp.0. ￿hal-01852293￿
 
To cite this document: DUONG Anh Vu, RIVALLANT Samuel,  BARRAU Jean-Jacques, 
PETIOT Caroline, MALHERBE Benoît. Influence of speed on the crushing behavior of 
composite plates. In: ACCM 7 – 7th Asian-Australasian Conference on Composite 
Materials, 15-18 Nov 2010, Taipei, Taiwan. 
 
This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ 
Eprints ID: 4875 
Any correspondence concerning this service should be sent to the repository 
administrator: staff-oatao@inp-toulouse.fr 
 
                                                                                
 
 
Influence of speed on the crushing behavior of composite plates 
 
 
Anh Vu Duong1*, Samuel Rivallant1, Jean-Jacques Barrau1, Caroline Petiot2, and Benoît 
Malherbe3 
 
 1 Université de Toulouse; INSA, UPS, Mines Albi, ISAE; ICA (Institut Clément Ader); Toulouse, France 
2 EADS IW, Suresnes, France 
3AIRBUS France, Toulouse, France 
*Corresponding author：ISAE, 10 avenue E. Belin, BP 54032, 31055 Toulouse, Fance  
e-mail：anh-vu.duong@isae.fr 
 
 
 
ABSTRACT 
This paper presents a study on crushing of CFRP 
composite laminated plates. The objective of this study is 
to analyze the influence of crushing speed on the rupture 
behavior and the energy absorption capability of 
composite materials. 
Two materials are tested: a carbon-epoxy 
unidirectional prepreg, and a carbon-epoxy fabric. For 
both materials, three different plate configurations are 
tested (three different stacking sequences). 
The crushing device is an improved plate crushing 
setup with stabilizing guides, which can be used both on 
a standard static traction/compression test machine, or on 
a drop tower. For static tests, a 20 mm/min velocity is 
applied to the specimen all along the 100mm crushing 
stroke. For dynamic tests, only the initial velocity can be 
imposed. Three initial speeds were chosen: 2, 5 and 9 
m/s. 
A high-speed camera is used during tests to visualize 
the global behavior of the plate, and the rupture modes in 
the crushing front. The load is also recorded, which 
enables to calculate the load/displacement curve of plates 
crushing and determinate the energy absorption 
capability. 
The analysis of these results enables to discuss on the 
influence of crushing speed both on the rupture modes 
and, as a consequence, on the energy absorption 
capability. 
 
KEYWORDS : Composite, crushing, energy absorption, 
speed, CFRP. 
 
1. INTRODUCTION 
The use of laminated composite in vehicle structure 
requires a good understanding of their crash behaviour. 
But the range of crushing mode is very wide and strongly 
depends on numerous factors. Despite extensive 
experimental works done in the 90's [1:5], and more 
recently [6], it is still very hard to predict the crash 
response of a complex structure. 
A few works were done concerning dynamic crush 
tests, [7], but there are very few results concerning the 
influence of crushing speed on crushing behavior and 
energy absorption capability. Moreover, conclusions 
seem often contradictory (problems of dispersion, to few 
tests…) 
 
The aim of this study is to obtain experimental results 
providing a better understanding of the speed influence 
in progressive crushing of composite laminated plates. 
The main experimental objective of this work is to 
perform crushing tests on two different materials, with 
three different stacking sequences for each material, at 4 
different speeds (from quasi-static to 9 m/s). A second 
objective is also to compare energy absorption capability 
of laminates made of UD plies or fabrics, for the same 
equivalent modulus. 
 
2. EXPERIMENTAL 
2.1 Fixture design 
The test fixture (figure 1) has been designed to 
improve plate crushing fixtures found in literature [8]. It 
is made of four vertical adjustable guides which avoid 
buckling of the specimen, and two horizontal adjustable 
guides. These ones are localised just beneath the vertical 
guides so that a gap exists between horizontal guides and 
the metallic base plate where the laminate crashes. Such 
a concept has been developed at the same time by 
Feraboli [9]. This avoid tearing of the plate observed in 
most of the plate crushing fixtures [10], and ensure that 
the boundary conditions are the same along the whole 
width of the plate, just above the crushing front. Two 
main uprights carry the guides without interference with 
the crush front. Visualisation holes have been made to let 
the crush front visible. 
The thickness of the specimen can vary from 0 to 
10mm. The gap (unsupported height between the base 
plate and the horizontal guides) can vary from 0 to 40 
mm.  
The laminate is fixed to a steel cylinder which is the 
interface with the static machine or the drop tower 
(dynamic tests). During crushing, plate and cylinder go 
                                                                                
 
 
down between the uprights and the vertical guides. At the 
bottom of the cylinder, a 120 kN Kistler piezoelectric 
sensor measures the crushing load. The small distance 
between the specimen and the sensor limits the 
mechanical filtering of the signal, allowing high 
precision in the dynamic crush load measurement. A high 
speed camera is used to have a real-time observation of 
the crushing front on the side of the plate. The filming 
speed is 20000 fps, with a 512x256 pixels resolution. 
 
Figure 1: Design of the fixture, with (on right) and 
without (on left) upright 
 
The fixture is used both for quasi-static test on a 
screw-driven universal testing machine and for dynamic 
tests on a drop tower apparatus. The load is introduced 
through the top of the specimen with a steel cylinder. At 
the bottom of this cylinder, a piezoelectric sensor 
measures the crushing load. The small distance between 
the specimen and the sensor limits the mechanical 
filtering of the signal. 
 
The use of a drop tower does not enable to have a 
constant speed during dynamic crushing : speed 
decreases as energy is absorbed. Depending on the test 
configurations (available weight on the drop tower, 
energy absorption capability of specimen, initial speed), 
speed can just slightly decrease, or reach 0 (in that case, 
the specimen is not totally crushed). 
 
2.2 Design of experiment 
Specimens are 160*60 mm flat plates. White 
graduations are drawn on the edge of the specimen each 
5 mm. The trigger mechanism is a 45° chamfer machined 
at the bottom end of the plate. Each test is defined by two 
parameters: 
- Crush speed: 20 mm/min for static tests, and three 
different impact speeds for drop tower tests: 2 m/s, 5 m/s, 
and 9 m/s. 
- Laminate configuration: two materials were tested:  
1) Material 1: Cytec fabric prepreg 5H (6KHTA) 977-2 
Ply thickness: 0.35 mm 
Three stacking sequence configurations: 
P1-[(0/45)3]sym 
P2- [(0)6]sym 
P3-[(0/45)3,0]sym. 
2) Material 2: Hexply unidirectional prepreg T700/M21 
(M21/35%/268/T700GC) 
Ply thickness: 0.26 mm 
Three stacking sequence configurations: 
 P4-[(0/45/90/-45)*2]sym, 
 P5-[(0/90)*4]sym, 
 P6-[(0/45/90/-45)*2,90,1/2 0°]sym 
Stacking sequences were chosen so that for each kind of 
configuration (1 to 3), weight, global thickness and 
equivalent modulus of the plates are the same for both 
materials (Table 1). This enables to compare energy 
absorption efficiency for these two materials. 
The unsupported height is set to 20 mm for all tests.  
Each configuration and speed, two specimens are tested. 
 
Table 1: Specimens characteristics 
  Config. 1 
iso 
Config. 2 
0/90 
Config. 3 
0° oriented 
Plate number P1 P2 P3 
Number of plies 12 12 14 
Total thickness 4.2 4.2 4.9 
M
at
er
ia
l 1
 
Equiv. Modulus 42700 61000 45700 
Plate number P4 P5 P6 
Number of plies 16 16 19 
Total thickness 4.16 4.16 4.94 
M
at
er
ia
l 2
 
Equiv. Modulus 45500 62600 46100 
 
2.3 Detailed analysis of progressive crushing 
mechanisms 
Figure 3. shows some examples of load-stroke curves 
obtained from the tests. Each curve may be divided in 
three phases: the initiation phase, the transition phase and 
the stable crushing phase on which the specific energy 
absorption (SEA) is calculated as : 
SEA = Fmean / ρ.A 
 
Fmean: mean load during the 
stable crushing phase 
ρ  specimen density 
A surface of the cross-section 
0
5000
10000
15000
20000
25000
30000
0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1 0,11
Deplacement(m)
F
ilt
er
ed
 lo
ad
 (N
)
P4 (V=0m/s)
P4 (V=2m/s)
P4 (V=5m/s)
P4 (V=9m/s)
 
Figure 3: some examples of load-stroke behaviour 
                                                                                
 
 
3. RESULTS and DISCUSSION 
The numerous experiments made enabled to observe 
the different crush modes of composite laminated plates 
with different configurations and different speeds. Crush 
mechanisms are homogeneous through the width of the 
plate, thus the real-time pictures of the side of the 
crushed laminate (figure 4 and 5) allow observation and 
understanding of crush modes. Following is shortly 
described some of the main modes observed. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 4: Examples of crush modes observed 
Figure 5: Images from high-speed camera P4 
 
   With all specimens tested, there isn’t undamaged 
splaying mode. The crushing mode observed is mixed 
mode and fragmentation mode. In mixed crush mode, 
exterior plies on both sides bend and evacuate in 
splaying crush mode. The proportion of plies that bend 
on each side is variable. An obstacle, like a debris wedge, 
in the front separating two splaying arms is the reason 
why this mode appears. Fragmentation occurs when plies 
reach the metallic base at right angle and can not slip on 
the base. Failure appears continuously at macroscopic 
scale. Energy absorbed can be very high: up to 50 kJ/kg, 
depending on the number of fragmented plies. But 
fragmentation is not a stable crush mode, plies crush 
evolving from fragmentation to bending, leading to 
undamaged or fractured splaying crush mode. 
 
3.1 Influence of speed 
The results of these tests for different stacking 
sequences of composites plates Cytec and T700/M21 
with different initial speeds are shown in figure 6 and 
figure 7. The dataset of the maximum loads Fmax during 
the tests for each sample is created. Fmax is the initial 
peak load (figure 3). Globally, this peak load increases 
with the speed of the initial velocity before impact. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 6: Fmax with different initial speeds 
 
However, the results of energy absorption with 
different speed are difficult to analyze: no clear tendency 
is observed. The dispersion of the results can be 
explained by the different observed crush modes which 
depends on the debris wedge created in the test. A debris 
wedge made of debris issued from the initiation process 
or from fracture of central plies can appear at different 
time and create different crushing modes in which the 
 
(a) Mixed mode: laminate of T700/M21 - 
chamfer trigger 
 
 
(b) Fragmentation: laminate of Cytec- chamfer trigger 
 
 
(b) T700/M21 
 
(a) Cytec     
                                                                                
 
 
0
5
10
15
20
25
30
35
40
45
1 2 3
Stacking Sequences
S
E
A
 m
ea
n 
(K
J/
K
g)
Cytec T700/M21
 
Figure 8: Comparison of SEA for the two materials 
number of plies in fragmentation is not stable during the 
test (and not the same from one test to the other). In 
figure 7, the dataset of each stacking sequence of both 
materials with different initial velocity of the test is 
shown. It can be concluded that there is no visible 
influence of speed on the energy absorption on the two 
materials tested with the three stacking sequences.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 7: SEA with different initial speeds 
 
3.2. Comparison unidirectional (UD)/fabrics 
The Cytec samples and T700/M21 samples have the 
same equivalent Young modulus for each stacking 
configuration (iso-rigidity). To compare UD to fabrics, as 
no visible influence of speed on the results of SEA was 
found, an average value of SEA was calculated for each 
material and stacking configuration taking into account 
the SEA of tests at all speed for a given stacking 
configuration. Comparison is shown on Figure 8.  
The results show that the energy absorption capability 
of Cytec fabric is much higher (approximately twice) 
than T700/M21, for the three tested configuration. This 
can be explained by the fact that in Cytec samples, plies 
damage happens earlier than in T700/M21, leading to 
fragmentation whereas in T700/M21, delamination 
appears between plies, before fiber rupture, developing 
splaying mode in the external plies, and reducing the 
number of fragmented plies. 
 
 
 
 
4. CONCLUSIONS 
The influence of initial velocity on the crushing 
behavior of composite plates is studied. With two 
materials tested, the influence of speed to the maximum 
load is easily observed. However, its influence on the 
energy absorption is not visible. 
The results show clearly that Cytec specimen can 
absorbed more energy than T700/M21 specimen in crush 
test. 
 
References 
1- Hull D. “A unified approach to progressive crushing 
of fibre-reinforced composite tubes”, Composites 
science and technology 1991;40:377-421. 
2- Farley G.L., Jones M.R. “Crushing characteristics of 
continuous fibber-reinforced composites tubes”, 
Journal of composites materials 1992;26:37-50. 
3- Mamalis A.G., Robinson M., Manolakos D.E., 
Demosthenous G.A., Ioannidis M.B., Carruthers J. 
“Crashworthy capability of composite material 
structures”, Composite structures 1997; 37:109-134. 
4- Ramakrishna S. “Microstructural design of composite 
materials for crashworthy structural applications”, 
Materials & Design 1997;18:167-173. 
5- Karbhari V.M., Haller J. “Effect of preform structure 
on progressive crush characteristics of 
flange-stiffened tubular elements”, Composite 
Structure 1997; 37:81-96. 
6- Ueda M., Hiraga A., Nishimura T. “Energy 
absorption of unidirectionam CFRP plate unde 
compression”. 14th European Conference on 
Composite Materials, Budapest, Hungary, June 
2010. 
7- Lavoie J.A., Kellas S. “Dynamic crush tests of energy 
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(a) Cytec 
(b) T700/M21 


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Influence of speed on the crushing behavior of composite plates

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