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Study Concerning the Mechanical Tests of MAT&ROVING
Fiber Reinforced Laminated Composites
STANCIU A.1, COTOROS D.
1
Department of Mechanics 1 Transilvania University of Brasov
Brasov, 29 Eroilor St.
ROMANIA
ancastanciu77@yahoo.com , dcotoros@yahoo.com
http://www.unitbv.ro
Abstract: - The glass fibres used in reinforcing thermo-plastic thermo-rigid resins are obtained from the so called
textile glass consisting of yarn and ply. The assessment of the tensile behaviour for a polymeric composite part is a
more difficult issue than for example the assessment of a metal part in the same conditions, especially due to the
accentuated dependence of the polymeric composite materials of some influences like temperature, test duration,
sample humidity, sample cross-section, etc. The manual or contact method for obtaining plate type specimens for
mechanical tests is presented in a dedicated standard STAS 9140-79. Inside a composite material the fibre shaped
materials take over the tensions acting directly upon the matrix, which presents less stiffness than the fibres.
Key-Words: - specimens, tension, stiffness, Young's module, mat, roving.
1 Introduction The mechanical tests methods for layered reinforced
polymeric composite materials should be adequate to the
type of the analyzed composite material and also to the
product structure that will be manufactured of these
materials.
For the layered polymeric composites there are a series
of rules at the level of national standards (SR ISO, SR
EU, STAS, BS, ANSI/ASTM, ISO, GOST) or internal
regulations at the level of manufacturing companies.
For any polymeric composite material we consider a
minimum number of tests based on which we are able to
characterize the respective material.
The main objective of the paper is to provide contributions
to the modeling of the fiber reinforced composite structures,
in order to achieve a correct approach both of the structure
itself and of the manufacturing processes of these materials.
For this purpose we need to find ways of determining the
continuity and the reproduction of the preformed parts
properties in order to improve the manufacturing process.
The scientific and technical objective is represented by
the research, fundamenting and ellaboration of some
new, performing methods meant to determine the
mechanical properties of the composite materials. This
area of research is between the boundaries of several
domains like: applied mechanics, strength of materials,
finite element method, homogenization method and
materials science.
2 Mechanical tests of the glass fibers
reinforced laminated composites For the tensile test we respect the regulations of the
standard STAS 11 268-79, which recommends the
application of a progressive tensile along the specimen
longitudinal axis, allowing the data gathering concerning
the following quantities: elasticity modulus, maximum
tensile (breaking point), elongation for maximum force
(fracture elongation).
The tensile intensity represents the traction force which
loads the specimen at every moment during testing over
the area unit of the initial cross section of the specimen
calibrated part.
][MPabh
F=σ (1)
The elongation represents the increase of the distance
between two reference points, marked on the specimen
calibrated part, which is produced by the tensile and
expresses in percent part of the initial distance between
the reference points.
[%]100o
r
RL
ZA = (2)
The elasticity modulus is the ratio of the tensile intensity
and the corresponding deformation within the limits of
the maximum tensile intensity that can be born by the
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ISSN: 1790-2769 154 ISBN: 978-960-474-140-3
material without exceeding the tensile – deformation
proportionality.
The elasticity modulus tangent to the origin represents
the slope of the tangent to the origin form the tensile
intensity – relative deformation diagram.
][1
1 MPaZ
F
A
RLE
o
oT
∆
∆×= (3)
The secant elasticity modulus for a certain elongation,
representing the slope of the line passing through the
tensile intensity – relative deformation diagram origin
and also through the point corresponding to a certain
relative elongation from the same diagram.
][MPaZ
F
A
RLE
x
x
o
ox
∆
∆×= (4)
The bending properties can be used only in engineering
studies, for materials having a linear stress – strain
behaviour.
We are going to represent the determination methods for
the bending characteristics of glass fibre reinforced
materials, cut out of plates.
By means of the following tests we are able to determine
the following characteristics: bending load and fracture
deflection of the materials breaking before or during
reaching the conventional deflection; bending load for
maximum load for materials reaching the maximum
bending before reaching the conventional deflection;
fracture bending load or for maximum load when the
conventional deflection is overcome or if this is required
by the material specification; apparent bending
elasticity modulus.
The bending load fσ for a certain load F is calculated
in Mega Pascal using the following formula:
W
Mf =σ (5)
Where M is the bending moment of the force F given by
4
LFM
⋅= (6)
W is the inertia modulus of the straight cross section in
cubic mm given by
6
2hb
W⋅
= (7)
In the previous formulae F is an applied force expressed
in Newton, L the distance between the supports,
expressed in mm, b and h the width and the thickness of
the section, both expressed in mm.
It comes out that the bending load is given by the
following relation:
22
3
hb
LFf
⋅
⋅=σ (8)
In order to determine the flexural elasticity modulus we
use:
d
F
bh
LEb
∆
∆=
2
3
2 (9)
F∆ - Force variation on the initial rectilinear side of the
force – deflection curve;
d∆ - deflection variation which corresponds to the
force variation F∆
The equipment we used is a testing machine with
constant traction speed, consisting of a fixed part
provided with specimen fixing clamps and a moving part
also with fixing clamps, driving mechanism.
The testing machine type LS100 is manufactured by
Lloyd’s Instruments, Great Britain and is presented in
fig.1.
Fig.1 Tensile testing machine
In this paper we will present the study of a tank made of
MAT + roving composite material (fig.2).
The following materials have been used:
• MAT 600 - fibreglass composite (short wires) in the
matrix of epoxy resin with specific weight 2x600g / m2,
2-2, 6 mm thick;
• RT 800 - fibreglass composite (fabric) in the matrix of
epoxy resin with specific weight of 4x 800g / m2,
thickness 3,2-3,6 mm;
• MAT 450 - fibreglass composite (short wires) in the
matrix of epoxy resin with specific weight 2x450g / m2,
1.6-2mm thick.
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ISSN: 1790-2769 155 ISBN: 978-960-474-140-3
The tank has a 2000mm diameter and 3800mm height,
consisting of the body, bottom, cover, connecting and
reinforcing layers, manhole (fig.2).
Fig.2 Preformed tank made of MAT&roving
Due to the very different components and manufacturing
methods, the classification of the used materials proves
to be a difficult issue.
The manufacturing of the material called MAT is done
by help of the following materials: non woven glass
fiber impregnated with non-saturated orto-phtalic
polyesteric resin.
3 Tests results The glass fibers used for reinforcing thermo-plastic and
thermo-rigid resins are obtained of textile glass
consisting of yarns and plies. The most used textile glass
for reinforcing composite materials is type E glass, non-
alkaline. For special use there is also type R and C glass.
The short fibers material (fig. 3) – represents the most
used form of reinforcing material and consists of a layer
of fibers with the length between 3,2 and 50 mm
randomly oriented and joined by help of a light binding
agent.
Continuous roving (fig. 4) – is a collection of fibers or
parallel filaments joined without a purposeful torsion.
+ Fig.3 Roving Fig.4 MAT
The specimens (fig.5) were cut out of an 8mm thick
plate whose upper side was painted with a white gelcoat
layer. They were polymerized for 24 hours at a
temperature of approx. 20°C.
Fig.5 Specimens 1-8 after tensile test
In table 1 we presented the values of the specimen
parameters, subjected to tensile testing.
Table 1 Values of testing parameters
The diagrams presented in fig. 6 and 7 are the results of
tensile testing for specimen 5 and respectively 8,
performed on the tensile testing machine with an
attached PC.
The diagrams and all the results of the tensile testing are
automatically presented by help of a machine dedicated
software.
We notice that specimen no.5 has the following
characteristics: Stiffness (N/m) 25899466.9; Young's
E1 E2 E3 E4 E5 E6 E7 E8 E9 E 10 E 11 E 12
Cali-
brated
part
length
[mm]
50 50 50 50 50 50 50 50 50 50 50 50
Load
speed
[mm /
min]
1
1
1
1
1
1
1
1
1
1
1
1
Test-
piece
width
[mm]
10 9,5 9,3 9 9,5 9,5 9,2 9,2 9,8 9,2 9,5 9
Test-
piece
thick-
ness
[mm]
7 7,2 7,6 7,1 7,2 7,1 7 7,8 7 7,1 7,3 7,5
Area
[mm2]
70 68,4 70,7 63,9 68,4 67,5 64,4 71,8 68,6 65,3 69,4 67,5
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ISSN: 1790-2769 156 ISBN: 978-960-474-140-3
Modulus (MPa) 18932.3589; Load at Maximum Load
(kN) 13.5078689; Stress at Maximum Extension (MPa)
110.288943; etc.
Stress (MPa)
0
50
100
150
200
Strain0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08
BreakGreatest Slope Point #2
Greatest Slope Point #1
Graph 5
Fig.6 Force – tensile displacement diagram for no.5
Following the traction, specimen no.8 has the following
characteristics: Stiffness (N/m) 15530004.4; Young's
Modulus (MPa) 10820.7946; Load at Maximum Load
(kN) 13.3924207; Stress at Maximum Extension (MPa)
181.028712; etc.
Stress (MPa)
0
50
100
150
200
Strain-0,05 0,00 0,05 0,10
Break
Greatest Slope Point #2
Greatest Slope Point #1
Graph 8
Fig.7 Force – tensile displacement diagram for no.8
Table 2 Average values of the tensile mechanical
characteristics
Stiffness [N/m] 20019000
Young’s modulus [MPa] 14572
Tensile Strength [MPa] 202,26
Extension from preload at
Minimum Extension [mm] -0,0026504
Strain at Maximum Extension 0.090161
Work to Minimum Extension
[Nmm] -9726
Load at Minimum Extension
[kN] 2,2202
Stress at Minimum Extension
[MPa] 33,935
Elongation at Fracture [mm] 1,1406
4 Conclusion For the reinforcing materials the results of the tensile
tests depend essentially on the size of the used specimen.
Test results are strongly influenced by test speed, which
is chosen to provide an elongation of about 1 ... 2% /
min. Results of the matrices tests are quite largely
spread, requiring a relatively large number of tests for a
reasonable confidence coefficient and however the
conclusions are limited.
The reinforcing fibres generally behave in a linear-
elastic way for high values of the tension.
We notice that the composite material presents little
changes with reference to the values coming out of the
tests and keeps within a certain range of values.
We can not match a composite material with a regular
one, it is much more resistant, elastic, easier to
manufacture, cheaper, lighter and keeps its properties in
time.
References:
[1] Purcarea R., Stanciu A., Munteanu V., Guiman V.,
Vasii M., Theoretical Approach of an Ultra-Lightweight
Sandwich Composite Structure, Advenced Composite
Materials Engineering, COMAT 2006, 19-22 October
2006, ISBN 973 635 821 8,ISBN 973 635 821 -0,
Brasov.
[2] H. Teodorescu, A. Stanciu(Patranescu), V.
Munteanu, D. Rosu, Computing Model To Determine
The Homogenized Coefficients Of A Smc Composite
Material Using The Homogenization Method, 2nd
International Conference “From Scientific Computing
To Computational Engineering”, 2nd
Ic-Scce, Athens, 5-
8 July, 2006.
[3] Stanciu A., Teodorescu Draghicescu H., Candea I.,
Munteanu V., Guman V., Experimental Aproaches
Regarding the Elastic Properties of a Composite
Laminate Subjected to Static Loads, The 3rd
International Conference on International Conference
Computational Mechanics and Virtual Engineering
COMEC 2009, 29 – 30 October 2009, Brasov, Romania.
RECENT ADVANCES in APPLIED and THEORETICAL MECHANICS
ISSN: 1790-2769 157 ISBN: 978-960-474-140-3
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