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Towards green engineering designs: Natural fibre-based
hybrid composites for structural applications
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Yang, N., Zou, Z., Potluri, P., & Katnam, K-B. (2022). Towards green engineering designs: Natural fibre-based
hybrid composites for structural applications. 33-36. Paper presented at Proceedings of the MACE PGR
conference, Manchester, United Kingdom.
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Download date:21. Aug. 2023
Towards green engineering designs: Natural fibre-
based hybrid composites for structural applications
Nenglong Yang, Zhenmin Zou, Prasad Potluri, Kali-Babu Katnam
Department of Mechanical, Aerospace and Civil Engineering
University of Manchester
Manchester, UK
nenglong.yang@manchester.ac.uk
Abstract—In this paper, the effect of intra-yarn hybridisation on
the macroscopic homogenised properties of natural fibre-based
hybrid composites (NFHCs) was computationally investigated.
Many researchers have experimentally investigated hybrid effects
on their mechanical properties. Only a limited number of
computational studies on NFHCs have been reported. Four hybrid
plain weave laminates: jute-glass, hemp-glass, jute-carbon and
hemp-carbon were studied using a two scale modelling approach.
The approach is based on homogenisation in which
micromechanical representative volume element (RVE) model
and mesomechanical repeating unit cell (RUC) model are
established separately. The results indicate that hemp-glass hybrid
2D woven composites may be more cost-effective than glass woven
composites in structural applications.
I. INTRODUCTION
Composites are made of reinforcing fibres and a polymer
matrix that, when used in combination, achieve optimal material
properties. Synthetic fibres, such as glass or carbon fibres, have
excellent specific strength and stiffness, but a major problem is
that they are not biodegradable and not environmentally
friendly. On the other hand, natural fibres such as jute, hemp,
kenaf, flax, ramie or sisal fibres, are biodegradable and
environmentally friendly, and at the same time, they are very
cheap and readily available [1]. However, natural fibres may not
be sufficient for structural applications. Because the quality of
natural fibres is lower than synthetic fibres. Since natural fibres
are short in length, it is difficult to arrange them into an orderly
composite structure. In addition, the interface between natural
fibre and polymer matrix is weak because natural fibre absorbs
moisture [2]. Although synthetic fibre reinforced composite
offers several advantages over metal and metal alloys in
structural applications, some synthetic fibres can be replaced
with natural fibres to achieve similar structural performance.
The use of two or more fibres in a matrix is called fibre
hybridisation. The mechanical properties of hybrid composites
are between two fibres and a matrix, in which one fibre balances
the deficiencies of the other fibre. Hybrid composites achieve
certain characteristics that non-hybrid composites cannot
achieve.
The combination of synthetic and natural fibres has been
experimentally studied [3-9]. However, different fibre and
matrix combinations with different fibre volume fractions
require extensive experimental testing. Therefore, experimental
methods to study all these combinations seem to be expensive
and time-consuming. On the other hand, Finite Element
Analysis (FEA) of natural fibre-based hybrid composites
(NFHCs) appears to be an economic method that has not been
widely studied. There are three main hybrid configurations:
inter-layer, intra-layer and intra-yarn [10]. The first two
configurations [11] have been extensively studied, while the
third configuration has received little attention. Hence, this
paper investigates the effect of intra-yarn hybridisation on the
macroscopic homogenised properties of four hybrid plain weave
laminates: jute-glass, hemp-glass, jute-carbon and hemp-carbon.
II. METHODOLOGY
A. Overview
A two scale modelling approach was developed to study the
mechanical behaviour of NFHCs, in which the micromechanical
representative volume element (RVE) model and
mesomechanical repeating unit cell (RUC) model were
developed separately. These models are based on the volume
averaging in the homogenisation process. In micromechanical
RVE model, the distribution of fibres within one impregnated
yarn is considered. The homogenised material properties of the
yarn at the microscale are obtained first. This is done by
homogenising the mechanical properties of both matrix and
fibres constituents within one impregnated yarn. Then, the
homogenised material properties of yarns can be input into
mesomechanical RUC model. Consequently, the homogenised
material properties of the textile composite at the mesoscale are
then obtained. This is done by considering the internal structure
of textile composites, in this case, repeating textile unit cell.
B. Micromechanical model
The random sequential expansion (RSE) algorithm [12] was
modified in this paper to generate random fibre distributions of
two fibres with two different radii. In this algorithm, one fibre is
around the first fibre within the bounded inter-fibre spacing
without overlapping. When no more fibres can be added around
the first fibre, the algorithm proceeds to add fibres around the
second fibre. The matrix is assumed to be an isotropic material
and the fibres are assumed to be transversely isotropic material.
All fibres are assumed to have a constant circular cross-section.
MACE PGR Conference 2022 University of Manchester
Perfect bonding between matrix and fibres is assumed and
interphase between matrix and fibre is neglected. The length and
width of RVE model are set 20 the radius of larger fibre, as
this is sufficient to compute homogenised material properties.
The micromechanical RVE model was meshed using linear
elastic 8-node hexahedral 3D solid reduced integration and
hourglass control (C3D8R) elements. The element size of
approximately 0.7 𝜇m is considered to be the optimum mesh
size to accurately characterise the effective elastic constants of
unidirectional FRCs [13]. Thus, it is adopted in this study. A
total of seven simulations were generated for each set of volume
fractions with an average element size of 0.7 𝜇m, and only one
element through the thickness direction.
C. Mesomechanical model
TexGen is used to generate the geometry of the 2D woven
textile. The modelling of yarn is based on three geometric
properties: yarn cross-section, yarn path, and yarn volume
fraction. In this study, yarns were assumed to be orthotropic
materials with lenticular cross-sections and sinusoidal paths.
The fibre volume fraction within one yarn is (𝑉) and the
volume of yarn in the RUC is (𝛺yarn ). The volume of RUC is
(𝛺). Hence the effective fibre volume fraction (𝑉
ˆ) of the
RUC is calculated as follows:
𝑉
ˆ𝑉
𝛺yarn
𝛺
(1)
The mesomechanical RUC model was meshed using voxel
elements. Voxel mesh is formed by dividing the overall volume
into rectangular parallelepiped cuboid elements (C3D8). The
voxel elements are automatically generated in TexGen. Voxel-
based meshing method is employed because voxels can be
repetitively refined without mesh distortion problems, yarn
volume fractions can be easily controlled and periodic boundary
conditions can be easily applied [15].
D. Homogenisation of mechanical properties
The unit cell model developed by Li and Wongsto [16] is
faithfully utilised in this paper to investigate NFHCs. This
includes creating geometries, meshing parts, applying periodic
boundary conditions (PBCs) and extracting material properties
of the model. The mesomechanical models follow a similar
approach to the micromechanical models. The difference
between micromechanical models and mesomechanical models
lies in different geometries and meshes, while the rest procedure
remains the same. All simulations are performed in ABAQUS
[17]. A complete set of constraint equations for the PBCs of a
unit cell and loading cases can be found in [18] and will not be
repeated here.
III. RESULTS AND DISCUSSION
A. Micromechanical model
Four NFHCs were investigated using the two-scale
modelling framework: jute-glass, hemp-glass, jute-carbon and
hemp-carbon. The total fibre volume fraction was fixed at 0.6,
and the volume fraction of the two types of fibres was different.
The material properties of each constituent used in the
simulations are shown in Table I. For all four NFHCs, seven
different volume fractions were examined and for each volume
fraction, seven different microstructures were generated.
The predicted specific material properties of yarns in all four
NFCHs were compared with rule of hybrid mixtures (RoHM)
[19] (Figure 1). The predicted specific longitudinal modulus
(𝐸) does not vary microstructures as the standard deviation is
close to zero and matches well with those predicted by RoHM.
For hemp-carbon and jute-carbon hybrid composites, the overall
specific 𝐸 decreases as the volume fraction of natural fibre
increases. This is because the specific 𝐸 of carbon fibre is much
higher than the specific 𝐸 of hemp fibre and jute fibre. The
overall specific 𝐸 increases with the increase of the hemp fibre
volume fraction for hemp-glass hybrid composites. This means
that adding hemp fibre to the hemp-glass hybrid composite will
optimise the specific 𝐸. For the jute-glass hybrid composites,
as the volume fraction of natural fibre increases, the specific 𝐸
decreases slightly. Hence jute-glass composites can be a cost-
effective alternative for glass FRCs if high specific 𝐸 is not
required. The highest significant variation can be seen in the
predicted specific longitudinal Poisson’s ratio (𝜈) and they are
all higher than the specific 𝜈 predicted by RoHM, especially
hemp-carbon hybrid composite. The diameter ratio of hemp
fibre and carbon fibre is highest in the four cases (Table I).
Therefore, it can be asserted that specific 𝜈 has a higher
variability because of the higher diameter ratio between the
natural and synthetic fibres.
TABLE I. MATERIAL PROPERTIES OF THE CONSTITUENTS [1, 20-22]
Material 𝑬𝟏
(GPa)
𝑬𝟐
(GPa)
𝑮𝟏𝟐
(GPa)
𝑮𝟐𝟑
(GPa) 𝝂𝟏𝟐 𝝂𝟐𝟑 Density
(𝒈/𝒄𝒎𝟑)
Diameter
(𝝁𝒎)
E-glass 73 73 30.4 30.4 0.2 0.2 2.5 15
Jute 27.6 5.5 2.5 2* 0.34* 0.40* 1.3 20
Hemp 70.0 14 6 5* 0.40* 0.40* 1.5 30
Carbon 230 40 24 14.3 0.27 0.35 1.8 10
Epoxy 3.4 3.4 1.49 1.49 0.14 0.14 1.046
* Assumed
MACE PGR Conference 2022 University of Manchester
Figure 1. Comparison of the predicited micromechanical material properties: (a) 𝐸, (b) 𝜈, (c) 𝐸, (d) 𝜈, (e) 𝐺, (f) 𝐺 , calculated using FEA with sample
size N=7, with those calculated using rule of hybrid mixtures (RoHM) over a range of natural fire volume fractions for all four hybrid systems: jute-glass, hemp-
glass, jute-carbon, hemp-carbon
B. Mesomechanical model
The geometry of mesomechanical RUC model is shown in
Figure 2. 𝛺yarn , 𝑉 and 𝑉
ˆ are 0.60, 0.54 and 0.32 respectively.
The predicted specific material properties of plain weave for all
four cases using both coarse voxel mesh with 64,000 elements
and fine voxel mesh with 125,000 elements were compared with
the analytical plain weave model developed by Szablewski [23]
and is shown in Figure 3. In the figure, the bottom x-axis
represents the relative volume fraction of natural fibres in one
impregnated yarn, and the top x-axis represents the relative
volume fraction of synthetic fibres in one impregnated yarn. The
difference between the predicted specific material properties
using fine mesh and coarse mesh is negligible (Figure 3), thus
the selected fine mesh size should be sufficient to obtain a
convergence result of homogenised material properties.
Similarly, for hemp-carbon and jute-carbon hybrid composites,
the overall specific 𝐸 decreases as the volume fraction of
natural fibre increases. The overall specific 𝐸 increases with the
increase of the natural fibre volume fraction for hemp-glass
hybrid composites. This means that adding hemp fibre to the
hemp-glass hybrid composite will optimise the mesoscale
specific 𝐸. For all four NFHCs, except for the specific 𝐸, the
matching of the specific material properties is inconsistent. This
is because the textile geometry modelling in FEA and analytical
solution are different. However, the trends for specific 𝐺 and
𝐺 are similar.
Figure 2. Plain weave composite (Unit: mm)
IV. CONCLUSION
In summary, macroscopic homogenised properties are a
function of relative volume fraction of the fibres constituent. The
overall specific 𝐸 increases with the increase of the hemp fibre
volume fraction for hemp-glass hybrid composites. This
happens in both micro and meso scales. The results indicate that
hemp-glass hybrid 2D woven composites may be a cost-
effective alternative to glass woven composites for secondary
structure applications.
ACKNOWLEDGEMENT
The authors acknowledge the financial support of Physical
Sciences Research Council (EPSRC) [Grant Number:
EP/T517823/1]. The authors also acknowledge the use of the
Computer Shared Facility 3 at The University of Manchester.
MACE PGR Conference 2022 University of Manchester
Figure 3. Comparison of the predicited mesomechanical material properties: (a) 𝐸, (b) 𝜈, (c) 𝐸, (d) 𝜈, (e) 𝐺, (f) 𝐺, calculated using FEA with fine and
coarse voxel meshses, with those calculated using the analytical model developed by Szablewski [23] over a range of natural fire volume fractions for all four
hybrid systems: jute-glass, hemp-glass, jute-carbon, hemp-carbon
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