1. Finite Element Modelling of Low Density Thermally bonded
Monocomponent Fibre Nonwovens
ABRSTRACT
Due to the manufacturing-induced composite microstructure and random orientation
of fibres, nonwoven demonstrates a complex mechanical behaviour. In order to
understand this behaviour, two micro-scale discontinuous finite element models are
introduced to determine the deformation response in the finite element environment.
One of them is Machine Direction (MD) and the other is in Cross Direction (CD). The
obtained results of FE simulation were compared to the experiments performed
using the tensile tests. Further Analysis will be included by changing the Material
Properties, Fibre Cross sectional Area, bond point thick ness and loading conditions.
A comparative study for both the models with respect to these functions will be
discussed in this project.
Introduction: (web) or a three dimensional (batt)
proceeding to web formation [16]. Web
Nonwovens are polymer based bonding is the next stage, where
structures of randomly oriented fibres polymer based fibres are thermally
bonded together mechanically, bonded which is executed by hot-
thermally or chemically [1]. Nonwoven calendar process. The thermally
materials have a wide range of bonded nonwovens are manufactured
applications spawning from household by interlocking polymeric fibres which
products, medical equipment to major are done by heating down the fibres
technical equipment because of the partially by method of hot calendaring
insulation characteristics. They are [3]. A thermal bond comes into
manufactured in three major types existence when a mechanical bond is
namely dry laid, wet laid and polymer formed due to temperature fall in the
laid. The most widely used Nonwoven bonding material [4]. Industrially, the
manufacturing fabric type is Polymer- thermal bonding refers to generating
based nonwoven. It is otherwise web-like structures from individual
known as ‘spun melt’ nonwoven thermoplastic fibres which are passed
manufactured from polymer extrusion through a hot calendar that is
or melting down the polymer material maintained at high temperature.
[2]. A nonwoven could be sectioned During the process, the individual
into two parts, namely bond points and fibres and the bonding points are
fibres. The bond points formed by plasticised firmly with their respective
heating down the fibres and the bond points. The thermal bonding
remaining fibres constitute a fibrous occurs in three steps (1) heating of
web. filaments (2) formation of bond points
By melting down, these staple fibres (3) cooling and re-solidification of
are converted into two dimensional fibres[5].

2. The material properties used is 20 gsm randomly oriented fibres may be towards
thermally bonded Monocomponent the direction of the bond points but the
nonwoven Polypropylene fibre (PP) which Loading condition of both the models may
is 15 mm (a) in length. The type of differ and the orientation angle remains
nonwoven used in this FE modelling is low the same.
density thermally bonded nonwoven.
Earlier approaches determined the
deformation behaviour for the FE
modelling in the bicomponent material [6]
determining the tensile behaviour and the
mechanical anisotropy, hence determining
the mechanical behaviour of the
Monocomponent discontinuous FE model
is determined to be a challenge, due to
the random orientation of the fibre (b). The
random fibre orientation and the overall
micro structure (c) show the complication (b)
of modelling the nonwoven fibre in the
Finite Environment. One of the models is
in Machine direction (MD), which
coincides with the direction of the
conveyer belt when the nonwovens are
manufactured.
(c)
Fig: 1 (a) SEM image of thermally bonded
nonwoven material (b) Isolated fibres and
fibre bundles within the nonwoven
microstructure [7], overall microstructure
of the polypropylene nonwoven material
(c).
(a)
Development of FE Model:
The other is in Cross Direction (CD) which
is perpendicular to the Machine Direction A parametric modelling technique was
(MD). One of the differences between the developed to generate a model with
FE Model in Machine direction and the subroutine software Patran using the
cross direction is that, the Discontinuous Patran Command language.

3. The model Fig 2 Was generated with the fibres (element type 9) were modelled with
dimensions entered and is generated as truss elements respectively. They do not
an input into the FE simulation software. It transmit the bending stiffness but carry
reads the code and generates the model compression and tension [18]. The model
with the following steps. This decreses the is subjected to 3-Dimensional Analysis
work of reformulating the model to include with its initial loads, Fixed and tension
the actual orientation distribution of fibres setup in the boundary condition.
[8]. These fibres are then arranged in the
Oriental distribution function (ODF).
The nodes seem to enter random but later
will form a complete structure; hence each
node will have a fibre attached to it. A
complete symmetric model is made which
is ready for the insertion of input
parameters, after setting up the boundary
conditions the model is ready to be
simulated. This model actually is
presented after the mesh is generated.
Each bond point is meshed by Bond point
fibre interface and the bond point internal
in order to differentiate the fibres.
Fig 3 Von Misses Stress (MD)
Polypropylene (20 gsm):
There is a tensile extension (Fig 3) and of
100% based on the applied input
parameters. When the model is simulated
150 increments and consistent load is
applied. The failure of the fibre is much
seen even before the failure of the bond
Fig 2: Generation of a new model
point. At almost centre of the extension, it
Finite element modelling is demonstrated is considered to be the area, where the
for two such models. There are total 2318 initiation of the stress tends to begin at
fibres in Machine Direction (MD) and 2103 much higher level. The failure occurs in
fibre in (CD). For creating a bond point the the fibre, when the load applied is more
elements 139 and fibres the element 9 are than that of fibre yield strength. Beyond
used during modelling the nonwovens. that the fibres or the overall model begins
The Bond points (element type139) were to fail.
modelled with shell elements and the

4. Each individual bond point begins to than that of the cross direction. At initial
dislocate form its original position condition, there is constant force at the
damaging its neighbouring bond point. load 0 N, this is due to the stiffness of the
There is distortion of stress at these levels material at initial condition. It may be also
due to the Fibre-Bond Point Collision. The due to the surrounding temperature and
fibres (Fig 4) at the corner of the model other climatic conditions.
exhibit higher stress, there is a necking
curvature exhibited at the end as it is In the test, there is not much extension
resulting higher level of stress exerted and there is regular drop in the
concentration. force which results in non-uniformity of the
results obtained. Therefore, the FE
simulation results gave a very softer
movement that that of the real fabric
giving a constant elongation with respect
to the applied force.
Previous model [8] determines lack of
inter-fibre friction and interaction, because
of the current model having the same
material properties as the current model.
The model in cross direction, in the test,
there is not much extension exerted and
there is regular drop in the force which
results in non-uniformity of the results
obtained.
Therefore, the FE simulation results gave
a very softer movement that that of the
real fabric giving a constant elongation
with respect to the applied force. Several
Fig 4 Von Misses Stress (CD) other conditions were also considered to
understand the deformation response,
Results: including change in the thickness of the
bond point for both loading directions,
In this result, Force-Elongation of the
Polypropylene fibre 20 gsm in Cross change in the fibre cross section area etc.
direction both the test give 100 % the results were analysed using the Von
Misses stress.
elongation with respect to the applied
tensile load. The results from the test Change in fibre cross sectional area
show that the material does not exhibit
at (MD)
constant elongation due to the reason the
Post Simulation, Various Parameters are
load is at the longitudinal direction. During
changed to analyse the behaviour of the
the thermal bonding process, the
Polypropylene fibre 20 gsm in order to
preference of the nonwoven manufactured
analyse the deformation response,
in the machine direction is much more

5. Task 1 was changing the cross sectional transferred to the Bond-point interface.
area of the fibre (Truss) and analysing the These results in higher stress at the bond-
variation of stress-strain relation observed. point interface, the thick shell bond point
This will be discussed by a graph plotted element begins to breakdown. The figure
between the models both MD & CD 50 below shows that the bond point fails
Respectively. The reason for the selection at immediate apply of the tensile load in
of fibre cross section area for the analysis the loading direction also known as
was due to its less stiffness compared to machine direction. The analysis was
the bond point and the accurate undertaken using the Polypropylene
visualisation of the results. polymeric material fibre with all the similar
material properties, boundary conditions
as discussed earlier in table 4 apart from
decreased bond point thickness which
resulted in the change in the entire
geometry of model.
Fig 5 Force-Extension curve (MD & CD)
Each individual bond point begins to
Effect of Bond point deformation: dislocate form its original position
damaging its neighbouring bond point.
The bond point is considered to be stiffer
There is distortion of stress at these levels
throughout the deformation, but when
due to the Fibre-Bond Point Collision.
their thickness is decreased to around 10 %
of the original thickness, the bond points Increase in bond point thickness
tends to disobey its geometrical property. (CD)
During the FE simulations, change in the
material properties, fibre cross sectional
area result in stress only at the fibres and With the same material properties given to
Bond Point-Fibre interface. Even at high the polypropylene in table 4 but change in
tensile loading conditions, this is the case. the bond point thickness from 0.035 to
But when it comes to decreasing the 0.1, to understand the effect of bond point
thickness of the bond point, the load is thickness towards the overall stress

6. distribution of the model. It is clear from completely give a different result finally.
the result that the fibres which join two By decreasing the thickness, several
bond points close to each other determine activities of the Bond point fibre structure
more stress. This is observed only are the has been identified. The resultant von
two areas where the load applied is fully in misses’ stress clearly visualizes, the
affect. This is due to the fact that there is stress distributed throughout the fibres
even a change in the geometric and even some part of the bond point are
arrangement of the bond point at some very high. But post increment at 150, it
areas very near the stress region (i.e.) normalizes and all the stresses are
fibres between two bond points. transferred to the end of the fibre,
proportional to the tensile direction.
Conclusion:
The behaviour of the thermally bonded
mono component fibre nonwoven was
discussed in a finite element environment.
Generation of the model was determined
by using the Patran command language,
further simulated using the MSC Marc
software. Initially, the von misses stress
and the plastic, elastic strain results were
obtained and discussed further. Several
input parameters were changed and
simulated in order to understand the
deformation characteristics of the material
Von Misses stress for bond point
thickness behaviour of polymer materials such as
polypropylene, poly amide and Low
Decreased Bond Point Thickness (MD):
density poly ethylene were analysed by
The initial bond point thickness was including their input parameters in the
0.0035 mm, it was reduced to 0.0025 mm.
current FE model. The geometric
There was a sudden transformation of the
stresses from maximum stress throughout properties of the bond point and fibre were
the region at initial levels of post changed, in order to understand the
increment, but later on reduced. Hence
behaviour of the fibres and the
we understand that, when there is a
change in fibre cross sectional area then corresponding bond-point structure. This
there may be stress obtained lesser included changing the fibre cross section
throughout the region at the initial level. area and thickness of bond point. The
But resultant Von Misses stress would

7. results obtained were the force-elongation Nonwovens Farukh Farukh a,⇑, Emrah
plot for poly propylene fibres of both Demirci a, Baris Sabuncuoglu a, Memis_
Acar a, Behnam Pourdeyhimi b,
Machine Direction and cross direction.
Vadim V. Silberschmidt a
Some of the damage behaviour in the
models such as the bond point collision, [8] Farukh Farukh. (2012). Computational
Material science. Numerical modelling of
fibre damage behaviour due to the less damage initiation in low0density thermally
thickness of the bond point was analysed bonded nonwovens. 1 (1), 1-4.
and the results were obtained.
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Properties
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(2011) Finite element modelling of
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wowens: Tensile behaviour
[7] Numerical modelling of damage
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