Experimental Study on Mechanical Property and Fatigue
Failure of the Bamboo-based Composites
F P Yang
*
and X T Li
School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong
University, Shanghai 200240, PR China
Abstract. Bamboo is a kind of advanced bio-material and has good mechanical behaviour.
Bamboo-based composites have been rapidly developing for use in engineering, especially in
wind turbine structures. In the present study, a series of experiments were performed and the
results were presented concerning the monotonic tension and compression mechanics
properties and fatigue life of bamboo-based composites. The stress-life curve was shown and
the failure models of laminates were discussed. The results suggest that the bamboo-based
composites have different fracture models under tension, compression and reverse fatigue
loading. The composites can support load more abidingly under compression loading.
However, higher strength values can be obtained under tensile loading.
1. Introduction
Bamboo is a kind of bio-material and has good mechanical behaviour. As an economic and friendly
material, bamboo has got increasing use in a wide range of application in engineering [1]. The
properties of outside strip of bamboo are better than those of inside. Thus the grading process was
developed, which can make the laminated bamboo strip lumber of grading [2]. The advanced bio-
composite, compared with other materials, can replace GFRP and wood/epoxy, and be used in wind
turbine blades as a new generation of materials [3]. These materials have many advantages, such as
renewable, less dissipation of energy, low cost, no waste and the worn-out product s can be disposed
easily.
Synthetic fiber/resin composites have been concentrated on all the time, and most of the current
studies focused on their chemical and mechanical properties [4-5]. However, the research and discuss
on the natural fiber composites are relatively new. As more and more interest in and attention to
natural fiber composites, a study on the static and fatigue properties of theses composites is timely
and important. Since bamboo has often been used in engineering structures, some previous research
has been carried out on the basic mechanical and fracture properties of nature bamboo and bamboo
fiber reinforced composites [6-10]. However, bamboo culms or structures made of bamboo
sometimes bore the cyclic forces, such as wind loading. The fatigue damage and failure mode in
bamboo-based composites need to be given serious thought.
Some authors have been focusing on the fatigue properties of bamboo culms [11], structural
bamboo materials [12], textile or biodegradable composites [13-14]. The results show that such
composites did not suffer fatigue damage at stresses well below their static strength, normal and
276
Yang, F. and Li, X.
Experimental Study on Mechanical Property and Fatigue Failure of the Bamboo-Based Composites.
In Proceedings of the International Workshop on Materials, Chemistry and Engineering (IWMCE 2018), pages 276-283
ISBN: 978-989-758-346-9
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

shear strains at the fiber/resin interface could cause deterioration leading to fatigue failure [15]. Static
failure and fatigue damage in such composites take the form of fiber breakage, matrix cracking,
debonding, transverse ply cracking, and delaminating [16]. These processes sometimes occur
interactively or independently depending on the types and properties of the composites. Testing
conditions and material variables may sometimes influence the predominance of one mechanism over
another [17-18].
In order to understand the mechanical properties and fatigue behaviour of bamboo-based
composites, a series of experiments were performed concerning the monotonic tension and
compression mechanics properties and fatigue life of the laminated bamboo lumber used for wind
turbine structures. The stress-life curve was shown and the failure modes of the laminated bamboo
lumber were discussed.
2. Materials and experimental procedure
A novel type of laminated bamboo lumbers was chosen for the present study. The laminate was
comprised of moso bamboo curtain mats which were formed to panels using one-time vacuum
infusion processes. Rectangular slices selected from outside strip of bamboo were used to form the
bamboo curtain mats. Epoxy resin was used as the adhesive. The chemical components of outer
layers in the moso bamboo culm are listed in the Table 1. The processed bamboo laminate has the
physical properties with the bending modulus of elasticity (MOE) 28GPa/gm
3
, specific strength
140MPa/gm
3
, and density 1150kg/m
3
. The specimen was cut with precision machine tools. The
geometric configuration of the specimen employed is shown in Figure 1. according to ISO 527-4,
which is also a common standard used for wood-based products. The bamboo slices were aligned in
the axial direction.
All tests were carried out on an MTS Landmark servo-hydraulic machine as shown in Figure 2. at
room temperature. To obtain the monotonic strength of the laminated bamboo lumber, the specimens
were loaded to failure at a fixed displacement rate of 1mm/minute. The fatigue life tests were
performed utilizing the same specimen geometry used for monotonic tests. All the tests were under
load control at stress ratio R=-1 and the loading frequency f=5Hz.
Table 1. Chemical components of outer layers in the moso bamboo culm.
Components Moisture Ash
Hot Water
solubility
Alcohol-benzene
solubility
Lignin Pentosan Cellulose
(%) 13.7 1.22 8.31 7.15 24.77 31.54 42.59
Figure 1. Details of the specimen
geometry.
Figure 2. Specimen installed in
fatigue machine..
Experimental Study on Mechanical Property and Fatigue Failure of the Bamboo-Based Composites
277

Figure 3. Stress-strain curves under tension and compression loading.
(a)
(b)
Figure 4. The failure mode and evolution for the laminated bamboo lumber: (a) under monotonic
tension loading; (b) under compression loading.
3. Results and discussion
3.1. Monotonic tension and compression tests
Tensile test: The standard tensile stress-strain behaviour is shown in Figure 3. In order to ensure the
accuracy of the results, two specimens were chosen to test. The average ultimate tensile strength is
about 190MPa. Under tensile loading, the laminated bamboo lumber failed in a progressive manner
instead of abrupt failure. As shown in Figure 4a, the failure process was involved with the rupture of
individual bamboo slices accompanied by progressive fracture of adjacent bamboo layers. The
fracture was straight and along the plane vertical to the axial direction.
0 3 6 9 12 15
0
50
100
150
200
250
Stress (MPa)
Strain (%)
Tension 1#
Tension 2#
Compression 1#
Compression 2#
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278

Compression test: The compressive stress-strain behaviour is also shown in Figure 3. In the same
way, two specimens were tested and the average compression strength is 179MPa. Compared with
the tensile stress-strain curve, the composites can support load more abidingly under compression
loading. However, higher strength values can be obtained under tensile loading. The similar consults
have been obtained by John W H [3].
Under compressive loading, the laminated bamboo lumber failed in a debonding/buckling manner
as shown in Figure 4b. When the compressive load was up to some value, the composite buckled and
delaminating subsequently occurred.
3.2. Fatigue tests and failure modes
The stress ratio means the ratio of the minimum stress to the maximum stress for a fatigue cycle,
R=σ
min
/σ
max
. Because the laminated bamboo lumber has different failure mode and strength under
tensile loading and compression loading, the tension-compression cycle loading with the stress ratio
R=-1 were applied and analyzed. Six groups of stress levels from 65MPa to 120MPa and total 30
specimens were selected. For each stress level, five specimens were chosen to obtain the fatigue life.
The evaluation of the fatigue life for the composite is usually different with metallic materials. A
critical number of cycles of fatigue failure are defined according to the damage evolution during the
fatigue loading. Stiffness reduction is one of the methods more commonly used [19]. In this study,
the fatigue peak displacement d
max
was introduced as a damage parameter to describe the fatigue
damage. When the peak displacement including the tension and compression values increased up to
25%, the fatigue failure was considered to happen and the corresponding number of cycles is the
fatigue life.
The fatigue stress-life curve, namely S-N curve, is presented in Figure 5. The fitting formula of the
maximum stress S
max
vs. fatigue life N is as follows:
max
log 2.3452 0.08806logSN=−
(1)
In order to predict the fatigue life of the studied bamboo-based composites more efficiently and
accurately, it requires the P-S-N curve and suggests the fatigue life data follow the lognormal
distribution. The P–S–N curves can be established by connecting the Pth percentile points of the
distributions of fatigue life at different stress levels with each other. We can label N
i
as the fatigue
life of the nth specimen under the same stress level. The logarithmic life can be expressed as x
i
=logN
i
.
The mean fatigue life  and standard deviation s can be written as the following equations
respectively.
∑
=
=
n
i
i
x
n
x
1
1
(2)
∑
−
−
=
n
i
xx
n
s
1
2
)(
1
1
(3)
For the fatigue life with the failure probability P, the logarithmic life can be expressed:
suxx
pp
+=
(4)
When the failure probability P=10%, u
p
=-1.282. So we can get the final fatigue life according to the
equation:
pp
xN
1
log
−
=
(5)
Experimental Study on Mechanical Property and Fatigue Failure of the Bamboo-Based Composites
279

For the S-N curve of the composite with the expression equation (1), the P-S-N curve with P=10%
can be calculated. The results were shown in Figure 5. and the following equation. From the picture,
we can see that the S-N curve and P-S-N curve are almost same, and the experimental data show
good consistency with each other.
p
NS log08933.034113.2log
max
−=
(6)
Figure 5. Stress-life curve for bamboo-
b
ased composites at R=-1.
(a)
(b)
Figure 6. The failure mode of the laminated bamboo lumber under cyclic tension-compression
loading (R=-1): (a) in low-cyclic fatigue (N
f
=1043); (b) in high-cyclic fatigue (N
f
=126020).
100 1000 10000 100000 1000000 1E7
50
75
100
125
150
σ
max
N
S-N curve
P-S-N curve
IWMCE 2018 - International Workshop on Materials, Chemistry and Engineering
280

The fatigue failure of the laminated bamboo lumber under cyclic loading was shown in Figure 6.
When under low-cyclic fatigue loading, the fracture was propagated along a plane to some angle with
the axial direction (Figure 6a). In some local position, the delaminating happened. The failure
mechanism was similar with the “compressive mode”. Some reasons can be guessed that since
ultimate tensile strength of the laminated bamboo lumber was higher than compressive strength, at
the same stress value, the composite began to damage during supported the compression loading.
The stress-strain curves under low-cyclic fatigue loading are plotted in Figure 7a according to
every fixed cycle numbers. It can be shown that from the beginning of fatigue test, the maximum
strain was on the increase under compressive loading, but it kept unchanged in the tensile process
until the last dozens of cycles. The non-linear relationship between stress and strain at the stage of
compression was more obvious than tension loading. The conclusion can be suggested again that
under low-cyclic fatigue loading, the damage always began to occur during compressive loading.
When the damage accumulation was up to some extent, the composite was not able to bear more
loading and the failure happened.
Under high-cyclic fatigue loading, the failure happened with the progressive rupture of bamboo
slices, sometimes accompanied by debonding of bamboo layers. The fracture was propagated along a
plane vertical to the axial direction (Figure 6b). The failure mechanism was similar with the “tensile
mode”. The stress-strain curves for laminated bamboo under high-cyclic fatigue loading are plotted
in Figure 7b. Contrary to the behavior under low-cyclic fatigue loading, the maximum tension strain
increased more obviously than compression strain during the test. The damage introduced by tension
loading contributed more to the failure of the composite. It is suggested that at the low stress level,
the laminated bamboo lumber can support the cyclic compressive loading longer.
-3 -2 -1 0 1 2 3
-150
-100
-50
0
50
100
150
20
1020
1040
cycle numbers
N
f
=1043
1040
Stress (MPa)
Strain (%)
20
(a)
-2 -1 0 1 2
-100
-50
0
50
100
12.6k
20
20
12.5k
Stress (MPa)
Strain (%)
Cycle numbers
N
f
=126020
12.6k
(b)
Figure 7. Stress-strain curves of the laminated bamboo lumber for every fixed cycle numbers:
(a) under low-cyclic loading; (b) under high-cyclic loading.
4. Conclusions
In the present study, a series of experiments were performed and the results were presented
concerning the static and fatigue mechanics properties of bamboo-based composites. The stress-life
curve was obtained and the failure modes of the laminated bamboo lumber were discussed. Some
conclusions were obtained.
Experimental Study on Mechanical Property and Fatigue Failure of the Bamboo-Based Composites
281

The laminated bamboo lumber showed no exactly the same behavior under monotonic tensile and
compressive loading. The laminates can support the loading more abidingly under compression
condition. However, higher strength values can be obtained under tensile loading.
Under tensile loading, the laminated bamboo lumber failed in a progressive manner with a straight
fracture. The process was involved with the rupture of individual bamboo slices accompanied by
progressive fracture of adjacent bamboo layers. Under compressive loading, the failure was in a
debonding/buckling manner.
The failure mechanism of the laminated bamboo lumber was similar with the “compressive mode”
under low-cyclic fatigue loading. The fracture plane was at an angle to the axial direction. Under
high-cyclic fatigue loading, the failure happened with the progressive rupture of bamboo slices,
sometimes accompanied by debonding of bamboo layers.
Further investigation would be conducted on the microscopic damage mechanism and the
interface strength between the bamboo slices. An effective finite element analysis model is expected
to create and verify the experimental data.
Acknowledgements
This work is supported by Shanghai Natural Science Fund of China (Grant No. 16ZR1417700) and
the National Natural Science Foundation of China (Grants No. 11102107).
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