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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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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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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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.

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