Eng. Mihaela Emilia OLEKSIK

InvesProieResuAxa psocieDomeTitlul Cod CBenef

steşte în oact cofinanţatrselor Umaneprioritară nr.

etăţii bazate peniul major dproiectului: I

Contract: POSficiar: Univer

A

RESBEH

ameni t din Fondul Se 2007 – 2013

1: „Educaţiape cunoaşteree intervenţie Integrarea ceSDRU/88/1.5/rsitatea „Luci

ABST

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Social Europ3 a şi formareae” 1.5.: „Progra

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Abstract of the PhD thesis

2

ABSTRACT - TABLE OF CONTENTS

1. INTRODUCTION............................................................................................ 3

2. THE STATE OF THE ART IN THE AREA OF COMPOSITE MATERIALS

REINFORCED BY FABRICS. PHD THESIS OBJECTIVES.............................. 4

3. THE MECHANICAL BEHAVIOUR OF THE FABRICS USED IN THE

MANUFACTURING OF COMPOSITE MATERIALS.......................................... 6

4. NUMERICAL SIMULATION OF THE MECHANICAL BEHAVIOUR OF THE

COMPOSITE MATERIALS REINFORCED BY FABRICS................................. 7

5. EXPERIMENTAL RESEARCH METHODOLOGY AND THE

EXPERIMENTAL LAYOUTS USED................................................................... 11

6. EXPERIMENTAL RESEARCHES REGARDING THE BEHAVIOUR OF

THE COMPOSITE MATERIALS REINFORCED BY FABRICS......................... 13

7. FINAL CONCLUSIONS. THE MAIN ORIGINAL CONTRIBUTIONS OF

THE THESIS...................................................................................................... 21


3

1. INTRODUCTION

This Ph.D. thesis aims to present a study, from the point of view of the

mechanical behaviour, of the composite materials that have as support polyamide PA

6.6 fabric, also known under the commercial name nylon, and on the influence of the

material with which it is impregnated (silicone in most cases) on the mechanical

properties of these materials. These composite materials are the materials that are

the most often ones used for realising airbags for cars. Knowing the importance

granted by car manufacturers to safety, the author considered as necessary to

realise such a study regarding their mechanical behaviour, but also regarding the

offering of new solution concerning materials that could be used in future. It is a

known fact that airbag producers would like to replace silicon with other materials, so

this Ph.D. thesis also studies the behaviour, from a mechanical point of view, of other

nanocomposite materials that are also based on a polyamide PA 6.6 fabric but are

obtained by means of the deposition of nanoparticles of various oxides on the fibres

that make up the polyamide yarns. Also within the researches comprised in this

thesis, it is sought to determine the influence of stress concentrators (various

perforated holes) on the mechanical behaviour of the material of which the airbag is

made. In order to show the mechanical behaviour of these composite materials, there

were carried out tests not only on the coated or uncoated weaving materials, but

also on the polyamide yarns of which the fabrics are made.

Nowadays, the employment of the computer in the design process is

indispensable, so that it was possible to reduce the time between designing a car

model and its physical realising to just 6 months as compared to 6 years as it was

even at the end of the last century. Of course, within this process, the computer-

aided drawing (CAD) activities are very important, the advantages of using such

software packages being well-known. However, this must not diminish the

importance of the other components that compose an integrated computer-aided

design system and especially the importance of using numerical simulation software

in the verification process.. The best known and at the same time the most used of

the implemented numerical methods is the finite element method. If numerical

simulation software packages managed a few years ago to allow the realising of only

static simulations with a limited number of nodes, nowadays, thanks to the

emergence of powerful computers with multi-core processors and with enough RAM

memory, it is possible to run within a decent timeframe dynamic explicit analyses or

implicit analyses that would allow the presentation of the behaviour in time not only

from a mechanical point of view, but also from a thermal, electrical etc. point of view.


4

As mentioned, the car manufacturers now put more and more emphasis on safety

and this is shown also through the usage, for crash studies, of these simulation

software packages based on the finite element method. In all these studies it is

necessary to also simulate the behaviour of the airbags. In order to obtain from these

analyses results that are as close as possible to reality, it is necessary to precisely

define the material properties and the behaviour of these materials.

The current thesis also aims at setting up a method that is efficient and as fast

as possible, for determining the material data for airbags used in explicit dynamic

simulations, an element that is currently of major importance. This method is based

on the inverse analysis applied with the help of the finite element method.

2. THE STATE OF THE ART IN THE AREA OF COMPOSITE

MATERIALS REINFORCED BY FABRICS. PHD THESIS

OBJECTIVES

Chapter 2 presents the state of the art in the area of composite materials

reinforced with fabrics. A first subchapter presents the types of materials that

compose these composite materials. Then, in a separate subchapter there are

presented the macro and meso forming modes of the fabric materials. The four

modes for the forming at the macro level for fabric-reinforced composite materials

are: transversal compression, plain tension, shear and bending. The macro level

studies the strains while looking at the composite material as a whole. The meso

level of forming exists due to the internal interaction of the fibres that compose the

fabric. The eight forming modes at the meso level are: friction between yarns, shear

between yarns, bending between yarns, yarn buckling, internal friction (between

fibres), yarn tension, yarn compression and yarn torsion. Because the current Ph.D.

thesis aims at studying composite materials reinforced by fabrics that are used for

airbags, an important percentage of the discussion of the state of the art is dedicated

to this type of product. After a short presentation of the history of airbags, there are

reviewed the manufacturing technologies for these components that guarantee the

safety of passengers in cars.

There are presented the technical requirements that the airbags need to meet:

folding-unfolding capacity, resilience, resistance to high temperatures, low

permeability for air, high resistance to dynamic loads, low weight of the fabric, high

strength of the fabric, good abrasion resistance and stability at aging. In the following,

the author presents a history of using polyamide yarns to realising airbags but also of

using silicon as coating material. In a distinct subchapter there are presented the

representative mechanical models for fabrics, namely the Pierce model and the


5

Kawabata model. Two distinct subchapters of the state of the art identify the main

researches in the area of simulating by means of the finite element method the

behaviour of the composite materials used for realising airbags and the main

experimental researches for the same materials. The chapter dedicated to the state

of the art ends with a subchapter that defines the objectives of the Ph.D. thesis.

Based on the analysis of the state of the art in the domain, the objectives of the

Ph.D. thesis were determined as follows:

1. Synthetizing the information presented in the state of the art concerning the

identification: of the types of fabrics used in realising airbags, of the mechanical

properties and functional properties that these must fulfil in order to use them in

manufacturing airbags and of the materials used in realising these fabrics;

2. Elaborating a theoretical study regarding the mechanical behaviour of fabrics

used in realising airbags at the loads at which these are subjected

conventionally during functioning: uniaxial tensile load, biaxial tensile load and

shear load;

3. Three-dimensional geometrical modelling at mesoscopic level of several types

of fabrics and the verification of their mechanical behaviour based on static

numerical simulations using finite element methods for various types of

stresses (uniaxial tensile load and biaxial tensile load);

4. Elaborating explicit dynamic numerical simulations for uniaxial tensile load and

shear at macroscopic level for composite materials manufactured by

impregnating fabrics;

5. Conceiving a new method, based on inverse analysis and finite element method,

in order to identify with a high precision of the mechanical characteristics of the

composite materials manufactured by impregnating fabrics;

6. Designing and realising experimental layouts but also modifying existing

testing setups that would contribute to realising experimental researches on

the composite materials manufactured using impregnated fabrics or

unimpregnated fabrics;

7. Realising experimental researches for identifying the mechanical

characteristics of yarns that form the base of the composite materials

reinforced with fabrics at different load speeds and different load

temperatures;

8. Elaborating comparative studies based on experimental researches regarding

the coated or uncoated fabric materials and regarding the influence of stress

concentrators on these materials;

9. Realising a study based on experimental researches concerning the possibility

of replacing the silicone as coating material for the manufacturing of airbags

with other types of oxides.


6

3. THE MECHANICAL BEHAVIOUR OF THE FABRICS USED FOR THE MANUFACTURING OF THE COMPOSITE MATERIALS

Chapter three presents the types of fabrics that are used for the manufacturing of

the composite materials that have as support textile materials. The fabric is a textile

product obtained by crossing under a right angle two fibre systems, the warp and the

weft, in a certain order. The manner in which the warp fibres cross the weft fibres is

called link. Also in this chapter there is presented the classification of fabrics by several

criteria: by the nature of the raw material, by destination, by the technological process of

weaving or finishing and by the width of the weaving machine.

Another subchapter of the Ph.D. thesis presents the properties of fabrics used

for manufacturing airbags, namely the physical, mechanical and functional properties.

A third subchapter is dedicated to the types of basic links used in the woven

materials that serve as support for airbags.

Basic weaves are weaves in which, within the limits of connection ratio, each

warp fibre has a single connection point with the weft fibres and each weft fibre has a

single connection point with the warp fibres.

The weave is defined through two important elements: the linking ratio and the

displacement. The displacement is the distance of the linking point of a fibre from the

linking point of the previous fibre.

The basic links presented in the current thesis are:

- the plain weave, with a ratio of 2/2;

- the twill weave, with the smallest ratio: 3/3;

- the satin weave, with the smallest ratio: 5/5.

The fourth subchapter of this chapter presents the theories that describe the

nonlinear ratios between the stress and strain in fabrics, focusing more on the woven

materials than on the knitted ones.

As it is known, the mechanical behaviour of weavings and knitting’s is, usually,

a nonlinear behaviour. It should be noted that the weavings and knitting’s consist of

yarns and initially have a high flexibility. There are two reasons that explain this

flexibility. The first is the flexibility of the yarn itself, whose structure consists of

parallel, thin fibres in which the movement of the individual fibres is limited only by

the friction between fibres during the loading. The other reason is that the structure of

weavings and knitting’s consists of fibres connected without any type of fastening in

the places where they intersect. This means that the displacement of fibres and yarns

in this structure during the application of a load is complex and that their mechanical

properties must be considered as a structural assembly and not as a material

continuum. For a better understanding of the mechanical behaviour of the fabrics

discussed in the thesis, there is presented the mathematical model of Kawabata, a


7

model that is also implemented in the commercial software packages for simulation

through the finite element method. This model is based on the biaxial extension theory of

yarns.

The loading process of fabrics is divided into two stages. The first stage is the

bending one, in which the fibre is stressed at pure bending, without being subjected

also to tensile stress. The second stage is the one in which the bent fibre is subjected

to tensile stress in the connection points between warp and weft. From the

combination of the two types of loads and based on the stresses occurring in the

fabric fibres there can be obtained the complete stress-strain relation for these textile

materials. There are taken into account two cases, the case of the incompressible

yarn and the case of the compressible yarn. At the end there is introduced into the

model also the shear deformation theory. The main characteristic of the shear

deformation theory is given by the torque that appears at the intersection of the

woven fibres. This appears in the weaving process as a consequence of the need to

change the angle between weft and warp.

The last subchapter of this chapter is dedicated to conclusions. The study of the

mechanics of fabric materials has been applied to everything from airships to bullet-

proof protections. Kawabata's method of the unit cell proved to be efficient in

evaluating the mechanical behaviour at the uniaxial tensile test, but the prediction of

the shear behaviour had less success. Continuous-type approaches are easy to

implement for the structure analysis, but require a large amount of tests to present

the anisotropic and nonlinear nature of the fabric. The 3D finite element models offer

the most details regarding the mechanical behaviour of the fabrics, but are very

demanding from the point of view of calculation needs for the modelling of large

structures. The current high-end techniques offer a favourable compromise between

the methods with mechanicist unit cell and finite element analysis, offering precision

and detail without an extensive calibration of the elastic constants.

4. NUMERICAL SIMULATION OF THE MECHANICAL BEHAVIOUR

OF THE COMPOSITE MATERIALS REINFORCED WITH FABRICS

Chapter four is dedicated to the numerical simulations using the finite element

method. In the first part of this chapter there were carried out numerical analyses

using the finite element method applied at mesoscopic level (at the level of fibres

composing the fabric) and in the second part analyses at macroscopic level,

considering the composite material as a whole.

In order to study the mechanical behaviour of the various types of fabrics, the

author has preferred to use the finite element method, in a first stage, applied to a

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9

Following the unfolding of the static analyses for the uniaxial tensile test, there

can be drawn following conclusions: the maximal value of the Von Mises equivalent

stress occurs in the case of the twill weave, 61.34 MPa, being followed by the basket

weave with 53.17 MPa, the satin weave with 38.08 and the plain weave 26.69, the

lowest values of the nodal displacement being determined for the plain weave (0.023

mm) and the twill weave (0.024 mm).

Following the unfolding of the static analyses for the biaxial tensile test, there

can be drawn following conclusions: the maximal value of the Von Mises equivalent

stress occurs in the case of the satin weave – 128.9 MPa, being followed by the

basket weave with 67.11 MPa, the twill weave, 61.92 MPa and the plain weave

37.35, the lowest values of the nodal displacement being determined for the plain

weave (0.012 mm) and the twill weave (0.020 mm).

The analyses at macroscopic level were dynamic explicit analyses and based

on them there was elaborated a method of identifying the material properties that are

introduced as input data in simulation software systems based on inverse analysis. The study of the behaviour at mesoscopic level is surely very useful when

studying the behaviour of a unit cell or of a few such cells. Due to the manner in

which the model is built, there are limits because of the number of finite elements.

Also, there can be studied only static or quasi-static behaviours, also due to the large

number of elements that are necessary. In the case that is most often encountered,

that of the study of the behaviour of complex parts, it is necessary to use another

approach, namely the macroscopic one. This approach implies the geometrical

modelling of the whole part and its discretisation with solid-type or shell-type

elements that would reflect the fabrics' behaviour at macroscopic scale.

In a first phase there were realised two explicit dynamic analyses for simulating

the uniaxial tensile test and for simulating the Bias test. The Bias test is a test that

aims to emphasise the shear behaviour of fabric materials or of composite materials

reinforced by fabrics. Specific for this test is the fact that the rectangular shape

sample, is extracted on a direction at 450 from the direction of the warp yarns and

implicitly also from the direction of the weft yarns. Another particularity of this test is

that the sample has to have the width equal to half of its free length (the length

between the jaws).

The analysis phase is realised, for both simulations, using the software Ls-Dyna

971. For the test sample's material there was used the material model Composite

Fabric (material no. 34 from the material library of Ls-Dyna). The finite element type

was Thin Shell 163 with a number of 7 integration points along the shell thickness.

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current case with regard to the fastening of the test sample in the area of the fixed

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made of

analysis,

cient were

modulus on

son's ratio

e test with

he results

e final stage the optical

int of view

of view of

HE

ed on two

g the real

s

t

s

s

a

l

e

f

,

e

n

o

h

s

w

f

o

l


12

material characteristics of polyamide PA 6.6 yarns used both for the numerical

simulation (analysis through the finite element method) and experimental researches

related to the mechanical behaviour of polyamide PA 6.6 fabrics coated or uncoated

with silicone or with other oxides that appeared more recently in the textile industry.

The elaborated experimental research methodology aims at comparing the

results obtained theoretically with those determined experimentally in order to

validate the theoretical results obtained by numerical analysis, using the finite

element method, with regard to the behaviour of the composite materials reinforced

by fabrics.

The researches were carried out using experimental installations from the the

”Lucian Blaga” University of Sibiu, from the University of Debrecen or from

specialised companies present in Sibiu:

• Universal tension, compression and buckling testing machine Instron 5587;

• Universal tension, compression and buckling testing machine Instron 4303;

• Aramis optical device;

• SEM electron microscope for determining the microstructural behaviour.

The universal tension, compression and buckling testing machines Instron 5587

and 4303 are universal testing instruments consisting of two main systems: a mobile

beam and the control system, that applies the tensile or compression loads to the

material. The Aramis optical device allows the determination of strains both at the

uniaxial tensile test or Bias test and at the equibiaxial test. A Scanning Electron

Microscope – SEM is an electron microscope that produces images of the studied

test sample by scanning it with a focused electron beam. The electrons in the beam

interact with the atoms in the sample and produce signals that can be detected

optically and that contain information on the topography of the sample's surface, but

also on its composition.

In order to realise the experiments in practice it was necessary to design

several experimental installations that would allow the applying of the various work

variants. Among the designed installations, one is for determining the mechanical

characteristics of fabrics subjected to uniaxial stress and is used also for the Bias

type test, another is used for determining the shear behaviour of this type of materials

and a third one is dedicated to equibiaxial tensile tests.

The installation used for the uniaxial tensile tests and for the Bias test (Fig. 9)

consists of two identical parts. The upper part is fastened on the upper beam of the

Instron machine (1) that glides on the guiding columns (2). The upper part (4) is

fastened to the force transducer (3) by means of a flange. The lower part of the

installation (5) is fastened, also using a flange, on the table with ”T” type grooves (6)

by means of six M10 screws. On its turn, the table with ”T” type grooves is fastened

to the chassis of the machine (7) also by means of screws. The installation is

conc

from

Fig. t

com

com

four

faste

end

texti

avoid

the a

test

the m

of th

6

two

ceived so t

m the roll on

9 The installhe Bias test mpression a

Another

posite ma

arms of e

ening the u

(5) is fast

le compos

d crushing

adherence

sample is

material, th

he test sam

6. EXPERBEHAVBY FA

The expe

important

that when

n which it w

ation for reafastened on nd buckling t

5587

r test that

terials rein

equal leng

upper free

tened in th

site materia

g the mater

e between

fastened b

he test sam

mple there a

RIMENTAVIOUR O

ABRICS

erimental r

directions

the mobile

was placed

lising the tenthe universa

testing mach7

uses the

nforced by

gth (2) is f

end (1) in

he lower j

al is fasten

rial, there w

the test sa

by means o

mple has c

are also tw

AL RESEOF THE C

researches

s, namely

13

e beam mo

d.

nsile test andal tensile, hine Instron

e installatio

fabrics. F

fastened o

nto the upp

aw (the fix

ned betwee

were glued

ample and

of four M5

cut outs in

wo cylindric

EARCHECOMPOS

s presente

the beha

oves, the t

d Fig. 1

on from fig

For this tes

on a uniax

per jaw (th

xed jaw).

en the arm

d rubber ba

d the faste

screws (3

the four c

cal joints (4

S REGASITE MAT

ed in this P

aviour of

A

extile sam

10 Installatioshearing

gure 10 is

st, a metal

xial tensile

he mobile

The test s

m pairs (2) o

ands that a

ning syste

3). In order

corners. O

4) that allow

RDING TTERIALS

Ph.D. thes

the mater

bstract of the

ple would

on for determg behaviour

s the fram

frame co

testing m

jaw) while

sample ma

on which,

also help to

em. Each s

r to avoid a

n the othe

w the arms

THE S REINFO

sis are stru

rials comp

e PhD thesis

not unfold

mining the

me test for

nsisting of

machine by

e the lower

ade of the

in order to

o increase

side of the

a folding of

er diagonal

s to rotate.

ORCED

uctured on

posing the

s

d

r

f

y

r

e

o

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e

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l

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com

reinf

char

rese

the

char

carry

adeq

dete

in w

mod

orde

prog

notic

first

PA 6

indic

cont

true

Fig.

polya

the l

posite mat

forced by f

In order

racteristics

earch algor

significan

racteristics

ying out t

quancy of

ermining th

In this ca

which the i

dified on th

er to deter

gramme wa

From the

ced that th

area is the

6.6. The s

cating the

tains the ar

The grap

stress and

11 Dependestres

The main

amide PA

oading spe

terials with

fabrics.

to carry o

of the pol

rithm that c

t factors,

, programm

he experi

the deter

e confiden

ase, there h

ndependen

ree variatio

rmine the

as repeate

e graphs o

here exist t

e starting

second are

decrease

rea where

phs in figur

d true strai

ence graph fs function of

n conclusi

6.6 decrea

eed.

h textile sup

out the ex

yamide PA

contains fo

selecting

ming the e

ments, de

rmined mo

nce interva

has been u

nt variable

on levels.

experimen

d five time

obtained fo

two distinc

area whic

ea is chara

of the te

the materi

res 11 and

n of the tw

for the maximf T and v

on that ca

ases with t

14

pport and t

xperimenta

A 6.6 fibres

ollowing sta

g the mat

experiment

etermining

odels, che

ls.

used a fact

es (loading

This progr

ntal error

es, thus lea

or the tens

ct areas on

h defines

acterised b

ensile cap

ial breaks.

d 12, resp

wo analysed

mal true

an be dra

the increas

the behavi

al research

s, there ha

ages: emp

thematical

t, selecting

the mode

ecking the

torial expe

g speed a

ramme con

in each e

ading to a n

ile tests fo

n the true

the hypere

by the sud

ability of

ectively, p

d paramete

Fig. 12 Depes

awn is tha

se of the te

A

iour of the

hes regard

as been set

hasising a

models

g the exper

els' coeffic

coefficien

rimental p

nd loading

ntains nine

experiment

number of

or polyami

stress-true

elastic beh

dden drop

the fibre.

present the

ers.

endence grastrain functio

t the ultim

emperature

bstract of the

composite

ding the m

t up an exp

nd hierarc

of the c

rimenting c

cients, che

nts' signific

rogramme

g temperat

e experime

tal point,

45 experim

de PA 6.6

e strain cu

haviour of

of the stre

The last

e depende

ph for the mn of T and v

mate streng

e and incre

e PhD thesis

e materials

mechanical

perimental

hisation of

considered

conditions,

ecking the

cance and

of type 32

ture) were

ents, but in

the whole

ments.

6 it can be

urves. The

polyamide

ess value,

area also

nce of the

aximal true

gth of the

eases with

s

s

l

l

f

d

e

d

2

e

n

e

e

e

e

,

o

e

e

h

fabri

into

mec

test

test.

cons

mea

an

expe

unive

optic

in co

mate

6.6 f

direc

this t

Fig. 1optic

tests

fibre

load

load

In order

ics from a

the num

chanical tes

and the sh

The olde

The test

stant or no

asured usin

extensome

erimental

ersal tens

cal device A

oordinate’s

For unfol

erial type,

fabric coa

ction of the

type of tes

13 The testincal measurem

un

The main

s for coate

es, are as f

- at the

ing is done

- at the u

ing is done

to determ

macrostru

erical sim

sts such as

hear test or

est method

sample is

t, on a ten

ng a force

eter. For

installation

ile, compr

Aramis (fig.

force-elong

ding the te

i.e. for bas

ted with s

e weft fibre

st.

ng machine Iment system iaxial tensile

n conclusio

ed or unco

follows:

uniaxial te

e on the wa

uniaxial ten

e on the we

ine the be

ctural poin

mulation so

s the uniax

r frame tes

d for testin

fastened

nsile testing

transduce

the unfo

n designe

ession and

. 13). The o

gation (fig.

ests there

sic (uncoat

silicone bot

es. The sh

nstron 5587 Aramis used

e tests

ons that ca

oated fabri

ensile load

arp directio

nsile loadin

eft directio

15

ehaviour o

nt of view (

oftware),

xial tensile

st.

ng the ma

at both en

g machine

er, while th

lding of

d for avo

d buckling

obtained da

14).

were extr

ted) polyam

th on the

hape of the

with the d for the

F

s

an be draw

cs, extract

ding, the m

on than if t

ng, the max

on than if th

f the com

given the n

there wer

test, the e

terials' be

nds and lo

, until failu

he elongat

the resea

oiding the

g testing m

ata can be

racted sets

mide PA 6

direction o

e test sam

Fig. 14 The cfor test sa

silicone, withon the

wn after the

ted on the

maximal fo

the loading

ximal elon

he loading

A

posite ma

need to inp

re employ

equibiaxial

haviour is

oaded at a

re occurs.

ion (strain

arches, th

crushing

machine In

represente

s of five te

.6 fabric a

of the war

ples was t

characteristicamples that whout stress ce direction of

e experime

e direction

orce has

g is done o

gation has

is done on

bstract of the

terials rein

put the ma

yed some

tensile tes

the uniax

a speed th

The applie

) is measu

ere was

of the f

stron 5587

ed graphica

est sample

nd for poly

rp fibres a

the standa

c force-elongwere not coaoncentrator af the warp fib

ental uniax

of the wa

higher val

on the weft

s higher va

n the warp

e PhD thesis

nforced by

aterial data

types of

st, the Bias

xial tensile

hat can be

ed force is

ured using

used the

fibres, the

7 and the

ally directly

s for each

yamide PA

and on the

ard one for

gation curve ated with and loaded bres

xial tensile

arp or weft

ues if the

direction;

alues if the

direction;

s

y

a

f

s

e

e

s

g

e

e

e

y

h

A

e

r

e

t

e

e

used

sam

perfo

the p

com

unco

stres

the

perfo

failu

weft

sam

Fig. polyacon

the

decr

conc

optic

both

load

stret

emp

equi

Because

d for the m

e shape a

orations of

pyrotechni

parative st

oated, in t

ss concent

standard o

orated in i

re mode o

fibres, wh

ple.

15 Failure mamide PA 6.6ncentrator an

The conc

- at the u

value of

rease in

centrator;

- at the u

cally determ

h for the c

ed on the w

However

tching but

phasising t

biaxial loa

these com

manufactur

as deliver

f different d

cal cap etc

tudy betwe

the case w

trator does

one for th

its centre

of a test sa

hile figure

mode for a te6 coated with

nd loaded on weft fibres

clusions tha

uniaxial ten

the maxim

compariso

uniaxial te

mined she

oated sam

warp direc

, during

more to b

the behav

ading. For

mposite ma

ring of airb

red from w

diameters

c. Therefo

een the be

when there

s not exist

is type of

with a ho

ample with

16 presen

est sample wh silicone witthe direction

s

at can be d

nsile loadin

mal force

on with t

nsile loadi

earing angl

mples and

ction or on

their func

biaxial stre

viour of th

r this test,

16

aterials rei

bags, they

weaving m

needed fo

re, it has b

ehaviour of

e exists a

, respectiv

test, but,

le of diam

stress con

ts the valu

woven of th stress n of the w

drawn from

ng, for test

and the

the case

ng, for tes

les presen

for the un

the weft d

ctioning, a

etching. Th

he compos

, there wa

nforced by

y will not b

machines,

or the asse

been cons

f these ma

a stress co

vely. The s

suppleme

meter Φ 10

ncentrator,

ues of the

Fig. 16 Valsample wov

with silicone,on th

m these tes

t samples

value of t

of the t

st samples

t values s

ncoated on

irection;

airbags ar

herefore, a

site mater

as used a

A

y fabrics a

be found i

but will u

emblage, fo

idered as

aterials, co

oncentrato

shape of th

entary, eac

0 mm. Figu

loaded on

major stra

ues of the mven of polyam with stress c

he direction o

sts are as f

with stres

the corres

test samp

s with stre

pecific for

nes, but a

re not su

a specific s

rials reinfo

a testing i

bstract of the

re materia

n the airba

undergo a

or the intro

useful to c

oated with

r and whe

he test sam

ch test sa

ure 15 pre

n the direc

ain for the

major strain ε1

mide PA 6.6concentratorof the weft fib

follows:

ss concentr

sponding e

ples witho

ss concen

the shear

also for the

ubjected to

subchapter

orced by

nstallation

e PhD thesis

als that are

ags in the

series of

oduction of

carry out a

silicone or

en such a

mples was

ample was

esents the

ction of the

same test

1 for a test , uncoated r and loaded bres

rator, both

elongation

out stress

ntrator, the

ing stress,

e samples

o uniaxial

r aimed at

fabrics to

from the

s

e

e

f

f

a

r

a

s

s

e

e

t

h

n

s

e

,

s

l

t

o

e

endo

devi

syste

need

punc

of th

the

acqu

the

cons

dete

with

The

disp

could

strai

mea

depo

plain

FigAra

test

owment of

ce.

For the e

em are loa

ded for the

ch are real

he research

force-disp

uisition sys

pressure

stant speed

ermine the

silicone a

obtained

lacement.

By coupl

d be deter

ns and the

In order

asurement

osition, on

nt layer app

. 17 The expamis optical m

the equ

There we

samples w

f the ”Lucia

equibiaxia

aded by m

e material

lised by tw

hes descri

placement

stem and t

is transfo

d and acqu

point pairs

nd uncoate

data can

ing the tes

rmined als

e size of th

to be a

system

their surfa

plied previo

perimental insmeasuremenuibiaxial tens

ere carried

without stre

an Blaga”

l tensile te

means of a

's fastenin

wo distinct h

bed in this

curve fo

the Matlab

rmed into

uiring on a

s force – d

ed, with st

be repre

sting instal

o the princ

e cap form

able to d

(fig. 17),

ace, of fine

ously.

stallation witnt system usesile tests

d out tests

ess concen

17

University

esting, the

a punch w

ng and the

hydraulic c

s thesis, the

r the pun

b software

electrical

nother cha

displaceme

tress conce

esented gr

lation with

cipal strain

med prior to

etermine

the test

e droplets

th the ed for

F

c

on test sa

ntrator, coa

y of Sibiu,

e test sam

with hemis

e active fo

circuits. Of

e area of i

nch. Using

package

voltage a

annel the v

ent for four

entrator an

raphically

h the optica

ns, the sec

o failure.

the strain

samples

of black p

Fig. 18 The vwoven test soated with s

subjec

amples wit

ated with s

A

along with

mples faste

spherical h

orce neede

f course, fr

nterest wa

g pressur

(also pres

and then

variable tim

r types of t

nd without

directly in

al measure

condary st

ns using

were pre

paint applie

values of the sample madeilicone, withocted to equib

th stress c

silicone or

bstract of the

h the Aram

ened in a

head. Both

ed for act

rom the po

as the dete

re sensors

sented in c

into force

me, it was p

test sample

stress con

n coordina

ement sys

rains, the

the Aram

epared thr

ed on a w

principal strae of polyamidout stress cobiaxial stretch

oncentrato

uncoated.

e PhD thesis

mis optical

fastening

the force

uating the

oint of view

ermining of

s, a data

chapter 5),

. Using a

possible to

es: coated

ncentrator.

ates force-

tem, there

equivalent

mis optical

rough the

white matte

ain ε1 for a de PA 6.6 ncentrator,

hing

ors and on

Figure 18

s

l

g

e

e

w

f

a

,

a

o

d

-

e

t

l

e

e

n

8

show

witho

equi

sam

with

occu

obta

to a

is th

sam

cour

is a

sam

The

using

this

at al

in fig

test

Fcom

ws the var

out stress

biaxial ten

- at the e

ple and th

silicone;

- at the e

ur on the

ained also o

- at the e

decrease

Another c

he Bias te

ples, nam

rse at the s

tensile tes

ple was ex

test is sim

g special t

test type is

ll homogen

gure 19. F

sample co

Fig. 19 The smposite test s

The main

riation of

concentra

sile test ar

equibiaxial

e maxima

equibiaxia

direction

on the dire

quibiaxial t

of the stre

consecrate

st. The na

mely at an

same angl

st too, but

xtracted, th

mpler than

testing inst

s the fact t

neous and

Figure 20 p

oated with s

strain areas tsamples with

Bias test

n conclusio

the princip

ator. The m

re:

tensile loa

l height of

l tensile lo

of the we

ection of th

tensile loa

ngth by 45

ed test app

ame of th

angle of

e from the

which can

he shear b

other tests

tallations,

hat the loc

there are

presents th

silicone an

hat appear otextile suppot

ons that ca

18

pal strain

main conc

ading, both

the cap a

oading, the

eft fibres, b

e warp fibr

ding, the p

5% and of t

plied to the

is test com

450 from

e direction

n emphasi

behaviour o

s specific f

but only o

cal strains

different a

he values

nd subjecte

on the ort at the

n be drawn

for a test

lusions tha

h the force

re larger in

e maximal

but values

res;

presence o

the elonga

e composite

mes from

the directi

of the wef

se, due to

of the com

for shearin

of classical

on the surf

areas on th

of the Von

ed to the B

Fig. 20 Vastrain εVM foPA 6.6 coa

concen

n after the

A

sample c

at can be

e needed f

n the case

values of

s that are

of the stres

ation by 24

e materials

the mann

ion of the

ft fibres. A

o the mann

posite mat

ng because

testing ma

rface of the

he sample'

n Mises eq

ias test.

alues of the Vor a test samated with silictrator, subjec

Bias test a

bstract of the

coated with

drawn foll

for breakin

e of the fab

f the princ

close to

s concentr

%.

s that cont

ner of extr

warp fibr

ctually, the

ner in whic

terial or of

e it does n

achines. S

e test samp

's surface,

quivalent s

Von Misses emple made ofcone and witcted to the B are as follo

e PhD thesis

h silicone,

lowing the

ng the test

bric coated

cipal strain

these are

rator leads

ain fabrics

racting the

res and of

e Bias test

ch the test

the fabric.

not require

Specific for

ple are not

as shown

strain for a

equivalent f polyamide hout stress

Bias test

ows:

s

,

e

t

d

n

e

s

s

e

f

t

t

e

r

t

n

a

case

case

com

expe

(fast

test

subje

dete

simp

trans

Figs

silico

with

be n

max

of th

coat

bein

repla

ages

temp

whic

- the high

e of the fab

- the elon

e of the fab

The test

posite ma

erimental in

tened to th

sample th

ected to s

ermining a

ple calcula

sformed in

. 21 The chahearing anglone, without

As in the

stress con

noticed tha

ximal value

he sample

ted with sil

g obtained

It can be

ace silicon

s and, wh

peratures

ch it is used

her values

brics coate

ngation co

brics coate

that is the

aterials is

nstallation

he mobile b

hat is fas

shear. The

curve form

ations, bas

to a curve

aracteristic cue for test samstress concethe shearing

e case of t

ncentrator

at the pre

e of the she

e without s

icone and

d for the co

e noticed

ne at the m

hen subje

or low tem

d. The new

of the ma

d with silic

orrespondin

d with silic

e most use

the fram

. This insta

beam of th

tened by

e acquisiti

med of poi

sed on trig

in coordin

urve shearinmples coatedentrator, subg test

he other e

and witho

esence of

earing forc

stress con

the uncoa

oated ones

that lately

manufactur

ected for

mperatures

west resea

19

aximal forc

cone, as co

ng to the

cone that in

ed for emp

me test. T

allation is b

he testing m

means of

on device

int pair’s d

gonometric

nates shea

g force - d with

bjected to

experiment

out stress c

the stress

ce with stre

ncentrator.

ated ones

s.

y, at world

ring of airb

longer pe

s) it loses

arches in th

ce that occ

ompared to

maximal f

n the case

phasising

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21

7. FINAL CONCLUSIONS. THE MAIN ORIGINAL CONTRIBUTIONS

OF THE THESIS Through the current thesis there have been brought a series of original

contributions with regard to the mechanical behaviour of the composite materials with

textile support coated with silicone or other types of oxides, contributions published

by the author in Romania and abroad or to be published soon, as follows:

From a theoretical point of view:

- there have been synthesised as a bibliographical study, most of the scientific and

technical results published with regard to the composite materials reinforced by

fabrics;

- there has been elaborated an original classification of the textile materials that

compose the composite materials;

- there have been identified the forming mechanisms of the composite materials

reinforced by fabrics (weavings or knitting’s);

- the state of the art with regard to methods and techniques used in the numerical

simulation of composite materials reinforced by weavings or knitting’s has been

determined;

- there has been synthesised the state of the art of the experimental researches for

these types of materials, identifying the types of loads and implicitly the

mechanical tests to which these materials can be subjected;

- a study has been elaborated regarding the modelling of the mechanical haviour of

the composite materials reinforced by fabrics, emphasising the representative

mechanical models of unit cells;

- there have been realised three dimensional geometrical models for four types of

fabric (plain, satin, basket and twill weaving) in order to export these models

into a software for analysis through the finite element method;

- there have been realised numerical simulations through the finite element method in

linear domain, at mesoscopic level, for four types of weavings, targeting the

determination of the von Mises equivalent stress, of the equivalent strain and of the

nodal displacements for the four types of weavings. Based on these numerical

simulations there have been realised a comparative study regarding the behaviour

of the various types of weavings at the uniaxial and biaxial tensile tests;

- an explicit dynamic analysis through the finite element method in the nonlinear

domain has been realised, at macroscopic level, in order to identify the

mechanical behaviour at the uniaxial tensile test of the composite materials that

comprise fabrics;


22

- an explicit dynamic analysis through the finite element method in the nonlinear domain

has been realised, at macroscopic level, in order to identify the mechanical

behaviour at the Bias test of the composite materials that comprise fabrics;

- there has been realised a model of an explicit dynamic simulation, parameterised from

the point of view of the material data, for the equibiaxial tensile test;

- an explicit dynamic analysis through the finite element method in the nonlinear domain

has been realised, at macroscopic level, in order to identify the mechanical

behaviour at the equibiaxial tensile test of the composite materials that comprise

fabrics;

- an inverse analysis has been elaborated, based on the simulation in the dynamic

domain of the equibiaxial tensile test, by means of which it was possible to identify

with a high degree of accuracy, the material data that contribute to defining the

mechanical behaviour of the composite materials that comprise fabrics;

From the experimental point of view:

The experimental researches were channelled on two directions: one for

determining the real material characteristics for the polyamide PA 6.6 fibres used for

the numerical simulation (analysis through the finite element method) and one for

determining the mechanical behaviour of the polyamide PA 6.6 fabrics uncoated or

coated with silicone or other oxides that have been introduced more recently in the

textile industry.

The experimental researches related to determining the the real material

characteristics for the polyamide PA 6.6 fibres comprised following original

contributions:

- in a first phase, based on well determined experimental plans, there have been

carried out tensile tests for three different testing temperatures and with three

different testing speeds;

- an experimental programme has been designed for realising the tensile tests on the

polyamide 6.6 fibres;

- the author has elaborated, in the Visual C++ software, a software product that would

allow the determining of all data types needed for the tests that can be carried out

on the testing machine;

- there has been carried out a statistical processing of the experimental data by

applying the Student, Cochran and Fisher-Snedecor tests.

The experimental researches related to determining the mechanical behaviour

of the polyamide PA 6.6 fabrics uncoated or coated with silicone or other oxides, with

or without stress concentrators comprised following activities:

- there have been elaborated experimenting strategies for each of the experimental

research directions taken into account;


23

- there have been realised two experimental installations, one for realising the

uniaxial tensile tests and the Bias test and one for determining the shearing

behaviour, both installations being conceived so that they can be fastened on

the tensile testing machine from the endowment of the Faculty of Engineering;

- there has been adapted an installation from the endowment of the Faculty of

Engineering, used for determining the forming limit curves, so that there can be

realised on it equibiaxial tensile tests for the composite materials that have as

support fabrics made of polyamide 6.6;

- the pressure transducer was calibrated to be used to determine the force at the

equibiaxial tensile test;

- there have been realised two virtual instruments in the Matlab software, one for the

signal acquisition and one for filtering the signal for determining the force at the

equibiaxial tensile test;

- there have been realised experimental researches for determining the behaviour of

materials woven with polyamide 6.6 coated or uncoated with silicone, with or

without stress concentrators, at the uniaxial tensile test for test samples

extracted on the direction of the warp fibres and on the direction of the weft

fibres;

- there have been carried out experimental researches for determining the behaviour

of the materials woven with polyamide 6.6 coated or uncoated with silicone, with

or without stress concentrators at the Bias test;



or without stress concentrators at the shearing test;



or without stress concentrators at the equibiaxial tensile test;

- there have been realised analyses using a SEM microscope for fabrics made of

polyamide 6.6 impregnated with various oxides;


of the materials woven with polyamide 6.6 coated with other oxides, without

stress concentrators at the uniaxial tensile test;

- - there have been carried out experimental researches for determining the

behaviour of the materials woven with polyamide 6.6 coated with other oxides,

without stress concentrators at the equibiaxial tensile test;

Future research directions

The topic tackled in the current Ph.D. thesis contributes to a better knowledge

of the mechanical behaviour of the composite materials that comprise in their


24

structure fabrics. Taking into account the current trends at world level in the area of

composite materials, there can be predicted new preoccupations related to these

materials, there still remaining open for tackling research directions such as:

- replacing polyamide as base material for the fabrics with other polymeric materials;

- modifying the fabric type (plain weaving) with other fabric types;

- studying the influence of other oxides used as coating materials not only on the

mechanical behaviour, but also on the thermal behaviour of these materials,

especially since the usage of silicone appears to become uncertain due to the

fact that the coating procedures are not ecological;

- elaborating mathematical models that are closer to the real behaviour of these

materials than the ones currently in existence;

- realising specific material subroutines for each type of weaving and of coating, that

would take into account all stresses to which these materials are subjected;

- realising rheological studies that would emphasise the friction behaviour of these

materials.

Documents

Eng. Mihaela Emilia OLEKSIK