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A finite element analysis of a 3D auxetic textile structure for composite reinforcement

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This paper reports the finite element analysis of an innovative 3D auxetic textile structure consisting of three yarn systems (weft, warp and stitch yarns). Different from conventional 3D textile structures, the proposed structure exhibits an auxetic behaviour under compression and can be used as a reinforcement to manufacture auxetic composites. The geometry of the structure is first described. Then a 3D finite element model is established using ANSYS software and validated by the experimental results. The deformation process of the structure at different compression strains is demonstrated, and the validated finite element model is finally used to simulate the auxetic behaviour of the structure with different structural parameters and yarn properties. The results show that the auxetic behaviour of the proposed structure increases with increasing compression strain, and all the structural parameters and yarn properties have significant effects on the auxetic behaviour of the structure. It is expected that the study could provide a better understanding of 3D auxetic textile structures and could promote their application in auxetic composites.
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A finite element analysis of a 3D auxetic textile structure for composite reinforcement
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IOP PUBLISHING SMART MATERIALS AND STRUCTURES
Smart Mater. Struct. 22 (2013) 084005 (8pp) doi:10.1088/0964-1726/22/8/084005
A finite element analysis of a 3D auxetic
textile structure for composite
reinforcement
Zhaoyang Ge1,2, Hong Hu2and Yanping Liu2
1College of Textiles, Donghua University, Shanghai, People’s Republic of China
2Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon,
Hong Kong
E-mail: tchuhong@polyu.edu.hk
Received 25 January 2013, in final form 29 April 2013
Published 22 July 2013
Online at stacks.iop.org/SMS/22/084005
Abstract
This paper reports the finite element analysis of an innovative 3D auxetic textile structure consisting of three
yarn systems (weft, warp and stitch yarns). Different from conventional 3D textile structures, the proposed
structure exhibits an auxetic behaviour under compression and can be used as a reinforcement to manufacture
auxetic composites. The geometry of the structure is first described. Then a 3D finite element model is
established using ANSYS software and validated by the experimental results. The deformation process of the
structure at different compression strains is demonstrated, and the validated finite element model is finally used
to simulate the auxetic behaviour of the structure with different structural parameters and yarn properties. The
results show that the auxetic behaviour of the proposed structure increases with increasing compression strain,
and all the structural parameters and yarn properties have significant effects on the auxetic behaviour of the
structure. It is expected that the study could provide a better understanding of 3D auxetic textile structures and
could promote their application in auxetic composites.
(Some figures may appear in colour only in the online journal)
Nomenclature
2l1Spacing of two adjacent warp yarns in the same
layer
l2Spacing of two neighbouring weft yarns
r1Initial radius of the warp yarn
r2Initial radius of the weft yarn
θInclination angles of the straight line of the weft
yarn
vPoisson’s ratio of the 3D structure
E11 Longitudinal Young’s modulus of yarns
E22,E33 Transverse Young’s moduli of yarns
G23 Transverse shear modulus of yarns
G12,G13 Longitudinal shear moduli of yarns
v12,v13 ,v23 Poisson’s ratios of yarns in the longitudinal and
transverse directions
k1Ratio of r1and r2
k2Ratio of l1and r2
k3Ratio of l2and r2
k4Ratio of the longitudinal Young’s moduli of the
warp and weft yarns
1. Introduction
Auxetic materials are those having negative Poisson’s
ratio (NPR) [1,2]. Unlike conventional materials, an
auxetic material may contract when compressed along
a perpendicular direction, which results in a unique
feature that the material can concentrate itself under
the compressive load to better resist the load [3,4].
This special feature, in combination with other improved
properties, such as enhanced fracture toughness and shear
modulus, has made auxetic materials very attractive for many
potential applications, such as automotive [5], aerospace and
defence [6], sports equipment, etc.
Among many man-made auxetic materials, auxetic
composites occupy an important place. According to Alderson
10964-1726/13/084005+08$33.00 c
2013 IOP Publishing Ltd Printed in the UK & the USA
Smart Mater. Struct. 22 (2013) 084005 Z Ge et al
et al [7], two approaches could be used to fabricate
auxetic composites. The first one is to fabricate laminated
composites by using suitable stacking sequences based
on non-auxetic constituent materials (reinforcement and
matrix) [8], because the auxetic behaviour in a laminated
composite can be achieved through the shear–extension or
extension–shear coupling behaviour of individual lamina
(single layer unidirectional fibre reinforced composite). By
selecting a suitable orientation of the reinforced fibres [9],
auxetic effects could be obtained in in-plane [10,11] or
out-of-plane [12,13] in the composites. The study in [8] also
showed that highly anisotropic behaviour of the individual
lamina material is one of the requirements for obtaining
auxetic behaviour in a laminated composite. This makes
carbon fibre/epoxy resin a more suitable choice than either
Kevlar/epoxy resin or glass fibre/epoxy resin. The second
approach is to include auxetic elements in a composite, or
to use auxetic constituents, for example, an auxetic matrix,
auxetic reinforcement or both [8]. Wei et al theoretically
demonstrated that auxeticity of composites could be obtained
when the auxetic inclusion volume fraction exceeds a critical
value and the ratio of Young’s modulus between the inclusion
and matrix is within a definite interval [14]. Hou et al
presented a numerical analysis of a composite structure
with in-plane isotropic negative Poisson’s ratio by randomly
including re-entrant equilateral triangles [15]. The concept
they proposed could be extended to 3D composite structures
with isotropic negative Poisson’s ratio. Wang et al showed
that composites with inclusions of negative bulk modulus
could lead to a negative Poisson’s ratio and an extreme
damping, which meant that damping tended to infinity and
the composite was globally stable without constraints [16].
It was also reported that honeycomb structures with negative
Poisson’s ratio [17] and auxetic fibre networks [18] could be
used as embedding structures for making auxetic composite
structural materials. In recent years, the application of auxetic
fibres and yarns in fabricating composites has attracted a great
deal of attention [1921]. Alderson et al [20] showed that
the use of auxetic fibres as reinforcement could considerably
increase the interface strength between the matrix and fibre
because the diameter of the auxetic fibres becomes bigger
when it is pulled out from the matrix.
3D textile structures including woven, knitted and braided
structures have been widely used as composite reinforce-
ments [22]. Compared to conventional 2D laminated compos-
ites, 3D textile structural composites have superior mechan-
ical performance, such as improved structural integrity, en-
hanced fracture toughness and through-the-thickness strength
against delamination. They have been widely used in aircraft,
marine craft, automotives, civil infrastructure and medical
prostheses [23] and so on. However, most of the 3D textile
structures for composite reinforcement found in the literature
are non-auxetic structures. Although a 2D plain woven fabric
made of auxetic helical yarns was used to manufacture
auxetic composites [21], 3D auxetic textile structures made of
non-auxetic yarns for composite reinforcements are still very
limited.
This paper reports a finite element (FE) analysis of a
novel 3D auxetic textile structure especially developed for
Figure 1. 3D auxetic textile structure: (a) unloaded state; (b) under
compression.
composite reinforcement. Both the 2D geometrical model
and 3D FE model of the structure under compression in the
through-the-thickness direction are presented and compared
with experimental results. The effects of structural parameters
and yarn properties on the auxetic behaviour of the structure
are predicted based on the validated FE model. It is expected
that the study could provide a better understanding of 3D
auxetic textile structures and promote their application in
auxetic composites.
2. 3D auxetic textile structure and its geometry
As shown in figure 1, the 3D auxetic textile structure
developed for composite reinforcement consists of three yarn
systems, i.e., weft yarns, warp yarns and stitch yarns. It was
fabricated on a prototype which had been specially developed
at the Institute of Textiles and Clothing of The Hong Kong
Polytechnic University [24], as shown in figure 2. From
figure 1(a), it can be seen that both the weft and warp yarns
are straight at the initial state. They are alternately placed
along two orthogonal directions of the fabric plane, and are
bound together by the stitch yarns through the fabric thickness
direction. The stitch yarns used were elastic yarns to provide
a better stability of the structure. Since the warp yarns in
each layer are arranged one in and one out, void spaces are
created among the warp yarns. In addition, the positions of the
warp yarns in two adjacent layers are shifted by a half-yarn
spacing. As shown in figure 1(b), this arrangement of the
warp yarns can result in the contraction of the structure in
the weft direction (xdirection) due to crimping of the weft
yarns when compressed in the fabric thickness direction (y
direction). Different from the warp yarns, the weft yarns
are fully arranged. This arrangement makes the warp yarns
still keep a straight state under compression. As a result,
the extension of the fabric structure in the warp direction
(zdirection) is negligible. Therefore, the structure will have
a negative Poisson’s ratio in the weft direction and a zero
Poisson’s ratio in the warp direction under compression.
The cross-section of the structure is shown in figure 3,
in which the auxetic behaviour of the structure in the weft
direction under compression can be better demonstrated. As
shown in figure 3(a), a unit-cell of the structure is outlined
by broken lines. It should be pointed out that the void
spaces of the warp yarns may result in the reduction of the
stability of the structure. Since the structure is developed
for composite reinforcement, the compressible matrix will
be filled in the void spaces of the structure during the
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Smart Mater. Struct. 22 (2013) 084005 Z Ge et al
Figure 2. Prototype for fabricating the 3D auxetic textile structure.
Figure 3. Cross-section of the 3D auxetic structure: (a) unloaded
state; (b) under compression.
composite manufacturing process. Therefore, the stability of
the composite structure can be assured.
According to the previous 2D geometrical model [25],
as shown in figure 4, the Poisson’s ratio of the structure in
the weft direction is given by equation (1), based on the
assumptions in which both the radii and lengths of the weft
and warp yarns are kept constant during the compression of
the structure in the thickness direction.
ν= 2(r1+r2)(sin θθcos θ) +l1(cos θ1)
2(r1+r2)(cos θ+θsin θ1)l1sin θ
×2(r1+r2)
l1
.(1)
3. Finite element analysis
3.1. 3D FE model
The major limitation of the geometrical model is that the
mechanical properties of yarns could not be included in
the analysis. Therefore, it could not provide an accurate
prediction of the auxetic behaviour of the structure. In order
to get more precise prediction of the auxetic behaviour of the
structure under compression, a 3D finite element analysis was
conducted in this work.
According to the observation from the fabricated fabric
sample shown in figure 5, the following assumptions were first
made.
Figure 4. 2D geometrical model of the structure under
compression.
(1) All the unit-cells have the same geometrical shape and
size. They have the same deformation under compression
of the structure. Therefore, a unit-cell is sufficient to
represent the deformation behaviour of the auxetic textile
structure.
(2) The stitch yarn is totally flexible and cannot withstand
the compression loads. Therefore, its effect on the
deformation behaviour of the structure under compression
loads in the fabric thickness direction could be omitted
from the FE analysis.
(3) Both the weft and warp yarns are totally straight at the
initial state when no compression load is applied to the
structure.
(4) No slippage takes place at the initial contacting points of
the weft and warp yarns during the compression process.
(5) All the yarns are considered as transversely isotropic
elastic materials having linear elastic properties and their
moduli are kept constant during the deformations of the
structure.
On the basis of the above assumptions, a 3D FE model
was first set up. As the compression process of the structure
is a large deformation process, and involves interactions of
several yarn objects, a solid element type was selected in order
to improve convergence during the calculations.
The 3D FE model of a complete unit-cell of the fabric
structure is shown in figure 6. It was built according to the
geometrical shape of the structure and meshed with solid
element SOLID186 of ANSYS via a mapped mesh method.
SOLID186 could be used as a high order 3D 20-nodes solid
element which exhibits quadratic displacement behaviour.
It has the properties of large deflection and large strain
capabilities.
The boundary conditions applied to the FE model under
compression in the vertical direction (ydirection) are shown
in figure 7. Due to the symmetrical feature of the structure,
two vertical planes X0–X00and Z0–Z00, which were defined
as the central plane of the unit-cell perpendicular to the xaxis
(figure 7(a)) and the central plane perpendicular to the zaxis
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Smart Mater. Struct. 22 (2013) 084005 Z Ge et al
Figure 5. 3D auxetic fabric sample.
Figure 6. 3D FE model of the structure at the initial state.
(figure 7(b)), were set up to be fixed during the compression
process. Meanwhile, the vertical boundary planes A–A0and
B–B0perpendicular to the xaxis were set up to be freely
moved in the xdirection (figure 7(a)), and the vertical
boundary planes C–C0and D–D0perpendicular to the zaxis
were set up to be freely moved in the zdirection (figure 7(b)).
To make them remain as vertical planes under compression,
a set of coupled degrees of freedom were applied to these
boundary planes by using the ‘CP’ command. To simulate
the compression test, the bottom plane of the FE model in
the ydirection was fixed and a displacement in the negative y
direction was applied to the top plane of the model.
The interactions of yarns are also defined. The contact
pairs, defined as the surface to surface contacts, are applied
for the contacts between the weft and warp yarns. The
3D contact elements ‘CONTA174’ and ‘TARGE170’ are
alternately placed on the contact surfaces of the solid elements
from bottom to top. The behaviour of the contact elements is
always bonded.
Figure 7. Boundary conditions of the FE model: (a) front view;
(b) lateral view.
Transversely isotropic elastic properties were defined for
the solid elements. The longitudinal Young’s moduli E11 for
the warp and weft yarns were obtained from the experimental
results. From the nature of transversely isotropic materials,
the following relationships exist: E22 =E33,G12 =G13, and
G23 =0.5E22/(1+v23 ). The transverse Young’s moduli E22
were assumed to be equal to E11/15 based on the braided
yarns used. Data for G12 were assumed to be G23, since the
braided yarns used in this study had similar shear behaviour
in both longitudinal and transverse directions. The Poisson’s
ratio in both the transverse and longitudinal directions of
the yarns was 0.2 [26]. The specified geometrical parameters
and yarn material properties for the FE analysis are listed in
table 1.
3.2. Validation by experiment
In order to verify the validity of the above FE model, the
auxetic fabric sample shown in figure 5was compressed
at a speed of 2 mm min1on an Instron 5566 machine
equipped with two circular compression platens of 150 mm in
diameter and a 10 kN load cell. The same method as proposed
in [25] was used to measure the lateral size change of the
structure and to obtain the Poisson’s ratio values at different
compression strains.
A comparison of the Poisson’s ratio–compression strain
curves obtained from the 2D geometrical model, the 3D
FE model and the experiment is shown in figure 8. It
can be seen that the curve from the FE model is very
close to the curve from the experiment. This implies that a
very good agreement is obtained between the FE analysis
and the experiment. Therefore, the proposed FE model is
validated by the experiment. However, the difference between
the geometrical analysis and the experiment is very large
although the variation trends of their curves are similar,
i.e., the auxetic behaviour of the structure increases with
increasing compression strain. This is normal, because the
yarn properties could not be included in the geometrical
analysis. Therefore, many factors such as the changes in
yarn cross-section and length were omitted in the geometrical
analysis. As a result, the geometrical analysis could not
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Smart Mater. Struct. 22 (2013) 084005 Z Ge et al
Table 1. Geometrical parameters and yarn properties.
Radius
(mm)
Yarn spacing
(mm) E11 (MPa) E22 (MPa) G12 (MPa) G23 (MPa) v12 v23
Warp yarns 3.08 7.50 131.76 8.78 3.66 3.66 0.2 0.2
Weft yarns 1.01 7.50 144.96 9.66 4.03 4.03 0.2 0.2
Figure 8. Poisson’s ratio–compression strain curves obtained from
geometrical analysis, FE model and experiment.
provide an accurate prediction of the auxetic behaviour of the
structure.
4. Demonstration and simulation of auxetic
behaviour
The above validated FE model can be used to simulate the
auxetic behaviour of 3D textile structures made with different
structural parameters and yarn properties. First of all, the FE
model can provide a very clear demonstration on how a 3D
auxetic textile structure deforms under compression. Figure 9
shows the front view of the deformation process of the auxetic
structure calculated with the values listed in table 1at different
compression strains. It can be clearly seen that the structure
laterally contracts when compressed in the vertical direction
and the maximal auxetic effect is obtained when the weft
yarns in two adjacent layers come into contact each other.
Exceeding this critical state, if we continue to compress the
structure, the changes in the yarn cross-sections become the
main deformation mode of the structure, which may lead to a
positive Poisson’s ratio of the structure. In this case, the above
FE model is no longer valid due to changes in the boundary
conditions.
The parameters that can influence the auxetic behaviour
of the proposed 3D auxetic textile structure include the radii
and longitudinal Young’s moduli of the warp and weft yarns,
the spacing of two adjacent warp yarns in the same layer 2l1
and the spacing of two adjacent weft yarns in the same layer
l2. Keeping the same assumptions that yarns are transversely
isotropic elastic materials and E22 =E11/15, G12 =G23 , the
Figure 9. Front view of the deformation process of an auxetic
structure at different compression strains.
effects of the non-dimensional parameters k1,k2,k3, and k4as
listed in the nomenclature were analysed. In order to facilitate
the analysis, the radius of the weft yarn, set as 1 mm, and
its longitudinal Young’s modulus, set as 100 MPa, were kept
unchanged.
The effect of k1, which was defined as the radius ratio
of the warp and weft yarns, is shown in figure 10, in which
the Poisson’s ratio–compression strain curves of the structure
were plotted with different values of k1(k1=1–3) when other
non-dimensional parameters were kept unchanged (k2=7,
k3=7, k4=1). It should be noted that the variation scope
of the compression strain for each curve is from 0 to the
maximal value where the weft yarns in the two adjacent layers
come into contact. It can be seen that k1has a significant
effect on the auxetic behaviour of the structure and this effect
increases with increasing k1. This phenomenon is normal
because the void spaces between two adjacent layers of the
weft yarns become increased when k1increases. Therefore,
more void spaces are provided for the weft yarns to be more
easily crimped under compression of the structure. As high
crimping of the weft yarns will lead to a high contraction
of the structure, a high auxetic effect is obtained. Therefore,
the auxetic behaviour of the structure can be increased by
increasing k1, i.e., by increasing the difference in radii of the
warp and weft yarns.
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Smart Mater. Struct. 22 (2013) 084005 Z Ge et al
Figure 10. Poisson’s ratio–compression strain curves for different
k1values.
Figure 11. Poisson’s ratio–compression strain curves for different
k2values.
The effect of k2, which was defined as the ratio of the
half spacing of two adjacent warp yarns in the same layer
and the radius of the weft yarns, is shown in figure 11, in
which the Poisson’s ratio–compression strain curves of the
structure were plotted with different values of k2(k2=7–10)
when other non-dimensional parameters were kept unchanged
(k1=3, k3=7, k4=1). It can be seen that k2can influence
the auxetic behaviour of the structure, but the effect is not
so significant as that of k1. It can be also seen that the
auxetic effect increases with decreasing k2. This is because
with decreasing k2, the spacing between the two adjacent warp
yarns in the same layer decreases. Therefore, the contraction
of the structure in the transverse direction with the same
compression strain will lead to a high transverse strain. As
a result, the auxetic effect of the structure increases with
decreasing k2. However, with decreasing k2, the void spaces
for the weft yarns to be freely deformed will be decreased,
which may limit the further contraction of the weft yarns in the
Figure 12. Poisson’s ratio–compression strain curves for different
k3values.
horizontal direction when compressed. Therefore, the auxetic
effect can be decreased when k2becomes too small.
The effect of k3, which was defined as the ratio of the
spacing of two adjacent weft yarns in the same layer and
the radius of the weft yarn, is shown in figure 12, in which
the Poisson’s ratio–compression strain curves of the structure
were plotted with different values of k3(k3=5, 7, 9) when
other non-dimensional parameters were kept unchanged (k1=
3, k2=7, k4=1). It can be seen that the change of k3cannot
cause a fluctuation of Poisson’s ratio of the structure. This
means that the weft yarn has no obvious effect on the auxetic
behaviour of the structure. Since the arrangement of the weft
yarns in all the layers of the structure is the same, all the weft
yarns have the same bending shape during the compression
process, regardless of their spacing. Therefore, the auxetic
behaviour of the structure would remain nearly unchanged
when the value of k3changes.
The effect of k4, which was defined as the ratio of the
longitudinal Young’s moduli of the warp and weft yarns, is
shown in figure 13, in which the Poisson’s ratio–compression
strain curves of the structure were plotted with different values
of k4(k4=1/81, 1/9, 1, 9) when other non-dimensional
parameters were kept unchanged (k1=3, k2=7, k3=7).
It can be seen that k4has a significant effect on the auxetic
behaviour of the structure and this effect increases with
increasing k4.k4=1/81 is a special case for k1=3. In this
case, both the warp and weft yarns have the same bending
rigidity. As the two kinds of yarns have the same ability to
resist the deformation, the Poisson’s ratio of the 3D structure
becomes nearly zero. However, when k4is greater than 1/81,
the weft yarns become relatively softer than the warp yarns.
Since the auxetic behaviour comes from the deformation of
the weft yarns, the easy deformation of softer weft yarns can
lead to a high auxetic effect. Therefore, the auxetic effect of
the structure can be increased by increasing k4, i.e., increasing
the difference of the moduli of the warp and weft yarns.
An interesting phenomenon is observed when k4=9.
In this case, the auxetic behaviour of the structure decreases
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Smart Mater. Struct. 22 (2013) 084005 Z Ge et al
Figure 13. Poisson’s ratio–compression strain curves for different
k4values.
during the initial compression stage. This phenomenon
could be explained by analysing the deformation behaviour
of the weft yarns during the compression process. Under
compression, the weft yarns are subjected to both bending
and stretching deformations. While the bending deformation
produces an increased effect on the auxetic behaviour of the
structure, the stretching deformation produces a decreased
effect on the auxetic behaviour of the structure. Since the
weft yarns are more easily stretched at the initial deformation
due to straightening effect of braided yarns, a greater impact
on the auxetic behaviour is produced at the beginning of the
compression process. In particular, with increasing k4, the
difference in the longitudinal Young’s moduli of the warp and
weft yarns is increased, which makes the weft yarns more
easily stretched during the initial stage. As a result, an obvious
decreasing trend of the auxetic effect at the initial compression
is observed when k4=9.
5. Conclusions
The geometry of an innovative 3D auxetic textile structure
for composite reinforcement was described. Its FE model
was established using ANSYS software and validated
by the experimental results. The deformation process at
different compression strains was demonstrated and the
auxetic behaviour at different structural parameters and yarn
properties were simulated by using transversely isotropic
elastic materials in the FE model. The following conclusions
can be drawn from the analysis.
(1) The FE model can provide an accurate prediction
of the auxetic behaviour of the 3D auxetic textile
structure. Further work will consider the influence of
the structural parameters and yarn properties on the
mechanical behaviour of the structure under compression.
(2) The auxetic behaviour of the 3D auxetic textile structure
increases with increasing compression strain. It is
significantly affected by the structural parameters and
yarn properties. An increase of the ratios of the radii
and moduli between the warp and weft yarns and a
decrease of the spacing between two adjacent warp yarns
can increase the auxetic behaviour of the structure. The
spacing between two adjacent weft yarns in the same layer
has no obvious effect on the auxetic behaviour of the
structure.
Acknowledgment
The author would like to thank Research Grants Council
of Hong Kong Special Administrative Region Government
for funding support in the form of a GRF project (grant
no. 516510).
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... The effective material properties of anisotropic composites with hexachiral, anti-tetrachiral, rotachiral, and honeycomb auxetic lattices were calculated by Dirrenberger et al. [7] via a theoretical point of view. A three-dimensional finite element (3D-FE) constitutive modeling of auxetic textile composites was presented by Ge et al. [8] with the aid of ANSYS commercial software. Another FE-based study concerned with material properties of composites with out-of-plane auxeticity was carried out by Grima et al. [9]. ...
... In all of the following numerical examples, the slenderness ratio of the beam-type element is assumed to be identical with L h 100 in order to present precise responses for thin-walled beams. Prior to express the results of present work, the accuracy of the proposed methodology is checked as illustrated in Fig. 3 8.96 GPa, and ρ F 1750 kg m 3 . ...
... In this part, stability margins of case studies whose transient behaviors tracked in Figs. 4,5,6,7,8,9, and 10 will be probed. As the first case, the impact of changing the thickness of piezoelectric ply's thickness on the stability path of the system is drawn in Fig. 11. ...
Article
In this paper, a combination of mechanics- and control-based frameworks are employed for the purpose of probing the actively controlled acoustic wave propagation behaviors of smart three-layered laminated composite beams with an auxetic core for the first time. The material properties of auxetic ply are achieved using an analytical micromechanical scheme. Afterward, the kinematic motion equation of thin-walled beams, rested on a viscoelastic medium, is assessed by inserting the displacement field of the classical beam theorem into the dynamic form of the virtual work’s principle. Afterward, the problem is solved in both temporal and spatial domains with the help of the separation of the variables. Once the spatial part of solution is inserted into the governing equation, a time-dependent nonlinear dynamic equation will be reached whose solution over the time domain will be extracted using the perturbation technique. Thereafter, the stability analysis will be carried out according to the Lyapunov method. The highlights of this work indicate the significant role of the thicknesses of piezoelectric and auxetic layers on the stability region of the smart laminate. Indeed, the system moves toward being stabilized when the thickness of the auxetic layer is increased. Similarly, an increase in the thickness of the piezoelectric layer stabilizes the waveguide.
... These 2D woven auxetic fabrics can be used as wearable protection. As shown in Fig. 4c, Ge et al. [177] proposed a 3D auxetic textile structure whose behavior depends on the structural parameters and properties of yarns. In addition, a numerical method was developed to reveal the deformation mechanism of 3D auxetic textile structure [178]. ...
... Jiang and Hu [187] proposed and fabricated a tubular auxetic braided structure with 16 yarns using a standard braiding technique to overcome the yarn slippage problem. and (b) woven [176] technique, (c) 3D auxetic textile structure [177], (d) auxetic double-helix yarn [142], (e) helical auxetic yarns manufactured using semi-coextrusion process [184], and (f) yarn fabric-based multi-scale auxetic composites [189]. ...
Article
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Auxetic mechanical metamaterials are artificially architected materials that possess negative Poisson’s ratio, demonstrating transversal contracting deformation under external vertical compression loading. Their physical properties are mainly determined by spatial topological configurations. Traditionally, classical auxetic mechanical metamaterials exhibit relatively lower mechanical stiffness, compared to classic stretching dominated architectures. Nevertheless, in recent years, several novel auxetic mechanical metamaterials with high stiffness have been designed and proposed for energy absorption, load-bearing, and thermal-mechanical coupling applications. In this paper, mechanical design methods for designing auxetic structures with soft and stiff mechanical behavior are summarized and classified. For soft auxetic mechanical metamaterials, classic methods, such as using soft basic material, hierarchical design, tensile braided design, and curved ribs, are proposed. In comparison, for stiff auxetic mechanical metamaterials, design schemes, such as hard base material, hierarchical design, composite design, and adding additional load-bearing ribs, are proposed. Multi-functional applications of soft and stiff auxetic mechanical metamaterials are then reviewed. We hope this study could provide some guidelines for designing programmed auxetics with specified mechanical stiffness and deformation abilities according to demand.
... Ge et al. [11] investigated a novel 3D auxetic textile structure using finite element analysis. This structure incorporates the following three yarn systems: weft, warp, and stitch. ...
Article
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The demand for robust yet lightweight materials has exponentially increased in several engineering applications. Additive manufacturing and 3D printing technology have the ability to meet this demand at a fraction of the cost compared with traditional manufacturing techniques. By using the fused deposition modeling (FDM) or fused filament fabrication (FFF) technique, objects can be 3D-printed with complex designs and patterns using cost-effective, biodegradable, and sustainable thermoplastic polymer filaments such as polylactic acid (PLA). This study aims to provide results to guide users in selecting the optimal printing and testing parameters for additively manufactured/3D-printed components. This study was designed using the Taguchi method and grey relational analysis. Compressive test results on nine similarly patterned samples suggest that cuboid gyroid-structured samples perform the best under compression and retain more mechanical strength than the other tested triply periodic minimal surface (TPMS) structures. A printing speed of 40 mm/s, relative density of 60%, and cell size of 3.17 mm were the best choice of input parameters within the tested ranges to provide the optimal performance of a sample that experiences greater force or energy to compress until failure. The ninth experiment on the above-mentioned conditions improved the yield strength by 16.9%, the compression modulus by 34.8%, and energy absorption by 29.5% when compared with the second-best performance, which was obtained in the third experiment.
... Arising from the allusion by Saint-Venant [3] on the possibility of negative Poisson's ratio in anisotropic solids and some related early reports [4][5][6][7][8][9], research in auxetic systems began in earnest with the pioneering works of Lakes [10,11], Evans et al. [12], Wojciechowski [13], Yeganeh-Haeri et al. [14], Alderson and Evans [15], Baughman et al. [16], Scarpa et al. [17], Grima and Evans [18] and Ishibashi and Iwata [19], to name a few. Along the way, the performance of auxetic materials have been evaluated against conventional materials for various applications such as safety fasteners [20], surgical and biomedical implants [21][22][23][24][25], cushions [26,27], chemical filters [28][29][30][31], technical textiles [32,33], footwear [34,35], vibration controllers and shock absorbers [36][37][38][39][40][41], aircraft structures [42,43], composites [44,45] and sports gear [46,47]. Geometrical and deformation mechanism models that give rise to auxetic behaviour have been extensively surveyed; the reader is referred to some recent reviews [48][49][50][51][52][53][54][55][56][57] and monographs [58][59][60][61] that include auxetic systems. ...
... Poisson's coefficient is defined for a given range of deformation (under the elastic regime), there is to say, it is not constant under any stress value. This parameter has a dependence on the applied strain, which is represented inFigure 14for a textile material under compression(GE, 2013). Typical ν -compression strain curve for a textile material (Simulation, Experiment and geometrical analysis).Reference: (GE; HU; LIU, 2013). ...
Thesis
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Selective Laser Melting (SLM) figures as one of the most promising Additive Manufacturing (AM) methods at present day. The principle of SLM is to sinter and melt powder layer by layer using a laser beam. This process brings many possibilities, such as a vast range of geometries that can be produced, rapid fabrication, high dimensional accuracy and high densification of parts, nevertheless, a significant amount of Residual Stresses (RS) are created. On the other hand, auxetic materials present a series of peculiar properties (Negative Poisson Ratio - NPR, enhanced indentation resistance, increased shear modulus), which make this class of materials very unique. Still, most of the research in auxetics is more intensive in polymers, because of the ease to obtain this property. Up to date, very little research has been done in auxetic metallic materials produced by SLM. Because of their unique combination of mechanical, physical and chemical properties, Titanium alloys represent a promising research subject. It is known that parts containing Ti and alloys are more easily fabricated using SLM. Associating titanium alloys unique properties with the proper geometries that lead to auxetic properties, SLM method can be used to create several applications. The first aim of this research is to simulate and manufacture re-entrant auxetic structures composed of Titanium - Ti-6Al-4V using SLM. The second aim is to formulate high energy absorption impact applications. Preliminary numerical simulation results illustrate the great potential of auxetics research: a 7.62 mm projectile traveling between 100 m/s to 400 m/s can be completely suppressed by a single Ti-6Al-4V auxetic structure. Keywords: SLM, Auxetic materials, Titanium, Ti-6Al-4V, high energy absorption impact applications, Residual Stresses (RS).
... [10][11][12][13][14]). This can therefore thought of as a starting point, which led to exploratory works on their applications such as aircraft structures [15,16], technical textiles [17,18], shock absorber and vibration controller [19][20][21][22][23][24], chemical filters [25][26][27][28], surgical and biomedical implants [29][30][31][32][33], safety devices [34], sports gear [35,36], composite structures [37,38], footwear [39,40] and cushions [41,42], to name a few. In addition to the experimental evidence of negative Poisson's ratio in the form of foams by Lakes [9], it is worth mentioning that auxetic 2D foams were studied by Pozniak et al [43]. ...
Article
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This paper explores a new anisotropic auxetic system that consists of rotating rhombi and right triangles by inspiration from tangram pieces. The Poisson’s ratio was developed by geometrical analysis on the representative unit with prescribed boundary requirements. Upon assigning rotational stiffness to the hinges, the Young’s modulus was established by matching the potential energy stored in the spiral springs with the strain energy of the deformation for the homogenized continuum. Results indicate that the on-axes Poisson’s ratio and dimensionless Young’s moduli are governed by the shapes and separation angles of the rigid units which, in turn, determine the dimension of the representative unit of the metamaterial. For the special case where the Poisson’s ratio is -1 when stretched on either axis, the Young’s moduli are equal. For this special case, the separation angles and the on-axes Young’s moduli increase monotonically with the shape descriptor of the rigid units. The capability of combining rotating rigid units of quadrilateral and triangular shapes suggests that new combinations of mechanical properties can be designed from rotation-based auxetic systems.
... 3DP has been much utilized in producing fashion accessories but not much for wearable apparel products because of its limited stretchability, bendability, or flexibility which are essential material properties related with wearers' comfort and functionality (Lee, 2022). Integrating with auxetic structures -novel and non-conventional patterns that possess the unique elongation characteristic when being stretched (Ge et al., 2013;Saxena et al., 2016), 3D printed textiles have a greater potential to mimic traditional textiles which perform better drapability for fulfilling users' functional and aesthetic needs (Spahiu et al., 2020). Although drapability is an important factor determining the aesthetic and usability of textiles for wearable products (Lee & Kim, 2006), based on our knowledge, little attention has been given to explore drapability of 3D printed textiles. ...
Article
This study aimed to explore drapability of 3D-printed auxetic structure textiles with different geometries through the digital image processing technique in order to showcase their potential applications in 3D-printed wearable product development. A 13 (textile samples) × 3 (repetition) experimental research design consisting of 10 3D-printed auxetic structure textiles and three traditional lace fabrics were utilized in this study. The findings indicate that 3D-printed multi-angular auxetic structures exhibited the highest level of drapability followed by sinusoidal and triangular auxetic structures; these multi-angular structure textiles with draping coefficient ranging from 26.82% to 31.43% have a great potential to simulate traditional lace-like fabrics. A statistically significant correlation also was found between drapability and weight of 3D-printed auxetic structure textiles. This study demonstrates a true potential of 3D-printed auxetic structure textiles as alternatives of traditional lace textiles and their application in the wearable product development.
Article
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This paper presents an innovative three-dimensional (3D) fabric structure for composite reinforcement. Different from most conventional 3D fabric structures, the new structure displays a negative Poisson’s ratio (NPR) effect under compression. Based on a manufacturing process developed by combining both non-weaving and knitting technologies, four NPR 3D fabric samples with different warp yarn diameters were first manufactured manually. Then, their Poisson’s ratio (PR) values under compression along the fabric thickness direction were experimentally evaluated. A geometrical model was also proposed for the theoretical calculation of PR values of these fabrics and was compared with experimental data. The good agreements were obtained between the calculation and experiment. The results show that all the 3D fabrics display NPR effect under compression, which results in a unique feature that allows the structure to concentrate itself under the compressive load to better resist the load. This special feature makes this innovative 3D fabric structure very attractive for many potential applications such as automobile, aerospace, defense and sports equipment, where impact protection can be a highly desirable property.
Article
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Materials with negative Poisson ratios are known to have high shear rigidities – a useful property for many types of structural and functional materials. To improve upon relatively low Young’s modulus of existing auxetics, one may consider embedding such components in an elastic material with sufficiently high modulus. We show theoretically that such composite materials do exhibit auxeticity when the inclusion volume fraction exceeds a critical value and the ratio of Young’s modulus of inclusion to that of a matrix falls within a definite interval. The existence of these auxeticity windows, once verified experimentally, opens up a new avenue of auxetics research.
Article
Materials that become thicker when stretched and thinner when compressed are the subject of this review. The theory behind the counterintuitive behavior of these so-called auxetic materials is discussed, and examples and applications are examined. For example, blood vessels made from an auxetic material will tend to increase in wall thickness (rather than decrease) in response to a pulse of blood, thus preventing rupture of the vessel (see Figure).
Article
It is feasible to design laminated composites with negative Poisson's ratio. Although the minimum value of negative Poisson's ratio design can be done via numerical approach, it is possible to use the analytical method in this paper to perform the following tasks: (a) evaluate the approximated ply orientation angles to obtain maximum transverse strain cy, (b) determine the necessary conditions of design negative Poisson's ratio, and (c) investigate the influence of laminae properties on the Poisson's ratio of a composite laminate. In this study, it is also found that, in general, the ply orientations for obtaining maximum transverse strain, sy, in a composite laminate are close to ⁷⁰ '/ ²⁰ I%.
Article
In isotropic materials, it is known that values of Poisson's ratio larger than one half are thermodynamically inadmissible, for such values would lead to negative strain energy under certain loads. Although a negative Poisson's ratio is not forbidden by thermodynamics, it is rare in crystalline solids. With the development of modem fiber reinforced composite materials, the effective Poisson's ratio of laminated fiber reinforced composites shows a peculiar behavior as it becomes larger than one half or less than zero. In this article, a study of negative in-plane Poisson's ratio for a general class of randomly-oriented composite laminates is presented. A simple random statistical analysis has been presented. It is demonstrated that composite laminates with negative in-plane Poisson's ratio could be achieved by using the specific values of independent elastic constants E 1 , E 2 , G 12 , and v12 in each lamina. Also, the influence of the lamina material properties to the negative in-plane Poisson's ratio of the composite laminates is presented. The results from this statistical analysis provide a set of general guidelines for designing composite laminates with a special character-the negative in-plane Poisson's ratio.
Article
Either an in-plane or out-of-plane negative Poisson’s ratio,, in continuous carbon fibre/epoxy resin composites can be achieved, providing the fibre volume fraction and anisotropy are high enough, by selecting suitable stacking sequences. This paper examines the use of specially designed software which allows the designer to match the mechanical properties of laminates with predicted negative to those with similar mechanical properties but positive. This has allowed auxetic and matched carbon fibre/epoxy resin laminates to be specifically designed. These laminates were then fabricated and tested, with good agreement found to theoretical predictions. This study, then, provides a route to evaluating the effect of a negative alone on properties such as fracture toughness and impact resistance.
Article
Relatively few negative Poisson’s ratio (auxetic) composites have been manufactured and characterised and none with inherently auxetic phases [Milton G. J. Mech. Phys. Solids 1992;40:1105–37]. This paper presents the use of a novel double-helix yarn that is shown to be auxetic, and an auxetic composite made from this yarn in a woven textile structure. This is the first reported composite to exhibit auxetic behaviour using inherently auxetic yarns. Importantly, both the yarn and the composite are produced using standard manufacturing techniques and are therefore potentially useful in a wide range of engineering applications.
Article
The current status of research into auxetic (negative Poisson's ratio) materials is reviewed, with particular focus on those aspects of relevance to aerospace engineering. Developments in the modelling, design, manufacturing, testing, and potential applications of auxetic cellular solids, polymers, composites, and sensor/actuator devices are presented. Auxetic cellular solids in the forms of honeycombs and foams are reviewed in terms of their potential in a diverse range of applications, including as core materials in curved sandwich panel composite components, radome applications, directional pass band filters, adaptive and deployable structures, MEMS devices, filters and sieves, seat cushion material, energy absorption components, viscoelastic damping materials, and fastening devices. The review of auxetic polymers includes the fabrication and characterization of microporous polymer solid rods, fibres, and films, as well as progress towards the first synthetic molecular-level auxetic polymer. Potential auxetic polymer applications include self-locking reinforcing fibres in composites, controlled release media, and self-healing films. Auxetic composite laminates and composites containing auxetic constituents are reviewed and enhancements in fracture toughness, and static and low velocity impact performance are presented to demonstrate potential in energy absorber components. Finally, the potential of auxetics as strain amplifiers, piezoelectric devices, and structural health monitoring components is presented. JAERO185
Article
2 (1 + ν) . Most common materials have a Poisson's ratio close to 1/3, however rubbery materials have values approaching 1/2; they readily undergo shear deformations but resist volumetric (bulk) deformation, so G > K. In several cases negative Poisson's ratio was observed in an existing material; in several it was deliberately introduced by design. This article deals with materials with negative Poisson's ratios, how they can be created with specified properties, implications of these unusual physical properties, and recent advances. 2. Negative Poisson's ratio cellular solids We consider first cellular solids with a negative Poisson's ratio, since the physical causes of the behavior of these solids are most readily appreciated. Two dimensional honeycombs with inverted cells (Fig. 1; compare with conventional honeycomb in Fig. 2) were reported with negative Poisson's ratios in the honeycomb plane (2-5), and these honeycombs have been recently analyzed (6,7). Honeycombs are sufficiently simple that the Poisson effect can be easily visualized. Macroscopic structures in two or three dimensions consisting of rods, springs, and sliders, were devised to give a negative Poisson's ratio (5); these structures have an inverted characteristic similar to the honeycombs. Structures of the above type require some form of individual assembly. Foam materials with a negative Poisson's ratio as small as -0.7 were developed (8) in which an inverted or re-entrant cell structure was achieved by isotropic permanent volumetric compression of a conventional foam, resulting in microbuckling of the cell ribs. Polymer foams which exhibit a softening point (8,9), ductile metallic foams (8,9), and thermosetting polymer foams (9) can be prepared with a negative Poisson's ratio; ν ≈ -0.8 can be attained in copper foam (Fig. 3). The negative Poisson's ratio occurs over a range of strain (10,11) and that range is larger in the polymer than in the metal foams. In the above structures and materials, the negative Poisson's ratio arises from the unfolding of the re-entrant cells, and isotropy can be achieved along with the negative Poisson's ratio. Anisotropic microcellular foams were recently reported to exhibit an unintentional negative Poisson's ratio in some directions (12,13). Since these are anisotropic materials, the bounds on Poisson's ratio are wider (- ∞ < ν < ∞) than in the isotropic case; indeed Poisson's ratios smaller than -1 have been reported. The physical mechanism appears to be associated with tilting of particulates linked by microfilaments. Microcracks in a material can be viewed as flattened pores with minimal volume. Several types of rocks with microcracks have been reported to exhibit a negative Poisson's ratio (14,15) of