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Bulletin UASVM, Horticulture 67(2)2010 Print ISSN 1843-5254; Electronic ISSN 1843-5394

Modification of The Mechanical Behaviour of Fiber Reinforced Composite

Materials under the Action of the Ad Type Bio-Phyto-Modulators

Anton HADĂR1), Horia GHEORGHIU1), Florin BACIU1), Ancu DINCA2), Daniela Ioana TUDOR1)

1) University “Politehnica” of Bucharest, Department of Strength of Materials,

313 Splaiul Independentei, 060042, Bucharest, Romania; [email protected] 2) Center of Biosynergetic Studies and Researches Dincă Ancu Bucharest, 17th Manastirea Putna

street, sector 1, Bucharest, Romania; www.viatasienergie.ro, [email protected]

Abstract: The paper investigates the influence of the AD type bio-phyto-modulators on the mechanical behavior of certain anisotropic materials. The specimens were manufactured from layered composite materials which were subjected to the action of the modulators for a certain amount of time and then loaded in traction. The modifications of the Young’s modulus, maximum tensile elongation, yield limit and ultimate tensile strength were examined. The results show that, for a certain exposure time, composite materials exhibit a decrease of tensile strength and maximum tensile elongation and an increase of the Young’s modulus. For small exposure time, the considered material behaved as the isotropic plastic materials, that is Young’s modulus decreased and the ultimate tensile strength increases with a small amount. Keywords: bio-phyto-modulators, glass fibers, carbon fibers, asbestos fibers, silica fibers, quartz fibers

INTRODUCTION

In order to emphasize the effects of the bio-phyto-modulators on composite materials,

a layered fiber reinforced composite material was investigated. Such materials, increasingly used for manufacturing strength structures, are made of a matrix (polymer) and reinforcement, chosen depending on the characteristics and service conditions of the designed product.

For the matrix one uses polyesters, acrylates, polyamides, etc. Such materials have to fulfill several conditions in order to be able to replace metals in strength structures: high mechanical strength and stiffness, stability, resistance to high temperatures, thermal stability, resistance to corrosion, humidity and chemical factors, high dielectric resistance, resistance to flaming arc, etc.

Fibers or other reinforcements are introduced in the matrix to obtain materials with better mechanical properties, compared to the base material. The influence of the reinforcements on the plastic material differs as a function of the material, the arrangement, proportions, and the possibility of obtaining a good adherence between the polymer and the reinforcement. The choice of the reinforcement is made based on the knowledge of the conditions that the material should fulfill: ultimate tensile, bending and shock strength and Young’s modulus higher than those of the matrix, chemical resistance with respect to the matrix, shape according to the functional role and surface with good adherence with the matrix.

Materials most used for reinforcement are: glass fibers, carbon fibers, asbestos fibers, silica fibers, quartz fibers, boron fibers, graphite fibers [1].

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Layered fiber reinforced composites are the most used worldwide. Owing to their configuration and the reduced number of elastic constants necessary for their characterization, the analysis of structures made of such materials can be made with high precision. Such materials are among the very few for which strength calculations can be made regardless the complexity of the structure. The fibers can be: continuous (uni- or bi-directional, woven, and multi-directional) or discontinuous (uni-directional or randomly oriented). A layered fiber reinforced composite is obtained by gluing several laminae (layers) with different fiber orientations. If two or more laminae have the same orientation, a group of laminae is formed.

The disposal of the fibers in laminae or groups of laminae is made depending on the necessary mechanical performances for the designed structure. The layered composite is characterized by the number of laminae and the orientation angle θ of the fiber in the lamina. Each lamina has assigned a local system of axes Olt, in which the axis Ol is parallel to the direction of fibers, and the axis Ot is normal to the direction of fibers and in the plane of the lamina [2].

h/2

l

x

1

2

3

y

z

t

Θ>0

Fig. 1 Layered fiber reinforced composite

Each lamina is characterized by the angle θ between the direction of fibers (axis Ol)

and the axis Ox). The setting of the laminae can be described starting from the surface of the material, located at z = - h/2 and ending at z = h/2. For a group of laminae, a subscript denoting the number of laminae in the group is used. A layered [0/903/0/45] contains six laminae with fibers oriented at 0°, 90° and 45° with respect to Ox, the 90° laminae being three. A layered composite has mirror symmetry if identical laminae (as type and orientation) are symmetrical with respect to the xOy plane. An example is the composite [90/02/-45/45]S, made of 10 laminae symmetrically disposed with respect to the middle plane (see subscript S). The fibers are oriented as follows with respect to the Ox axes: 90° (two laminae), 0° (four laminae), −45° (two laminae) and 45° (two laminae). The study of a certain structure made of layered fiber reinforced composites should consider five elastic constants [3]: - El - elastic modulus of the lamina on the fiber direction (direction of Ol axis); - Et - elastic modulus of the lamina on a direction normal to the fiber (direction of Ot axis); - Glt - shear modulus of the lamina (in the Olt plane); - νlt – Poisson’s ratio in the Olt plane;

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- νtz - Poisson’s ratio in the Otz plane. If the structure is made of a plane layered composite, only four constants are necessary: El, Et, Glt and νlt. They can be approximately calculated either using mathematical relationships or (much better) by experimental determinations.

MATERIAL AND METHODS

In order to quantify the influence of bio-phyto-modulators on the fiber reinforced composites, standardized specimens were manufactured (Fig. 2). They were treated with AD modulators in order to emphasize the effect on the characteristic curve of the material. In order to have more precise results, several tests were undertaken using an INSTRON 8801 testing machine (Fig. 3). The tests were made using controlled force with a low velocity (static test, [4]) In order to determine the elastic modulus El and yield limit, displacements were measured with a mechanical extensometer with a measurement base of 50 mm.

The considered material was a layered composite with four MAT layers, each one having 450g/m2. The layers are impregnated with orthophthalic polyester resin. The fibers are glued with powder textile glue.

Fig. 2. Standardized specimens

Fig. 3. The INSTRON 8801testing machine

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The first set of three specimens, which were not subjected to the influence of modulators, were tested in order to obtain the characteristic curve of the material and the mechanical characteristics.

In order to quantify the influence of the bio-phyto-modulators on the mechanical characteristics of composite materials, the specimens were tested after being put in contact with the modulators for 50 hours (two specimens), 91 hours (four specimens), 139 hours (four specimens) and 312 hours (three specimens).

RESULTS AND DISCUSSION

The characteristic curves of the materials are shown in Figs. 4 to 8.

0

20

40

60

80

100

120

140

0 1 2 3

Tensile stress (MPa)

Tensile strain (%)

Specimen 1 to 3

Specimen #

123

Fig. 4. Characteristic curves of the composite material without the influence of modulators

0

20

40

60

80

100

120

140

0 1 2 3


Tensile strain (%)

Specimen 1 to 3

Specimen #

123

Fig. 5. Characteristic curves of the composite material influenced by modulators for 50 hours

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0

20

40

60

80

100

120

140

0 1 2 3


Tensile strain (%)

Specimen 1 to 4

Specimen #

1234


0

20

40

60

80

100

120

140

0 1 2 3


Tensile strain (%)

Specimen 1 to 4

Specimen #

1234


0

20

40

60

80

100

120

140

0 1 2 3


Tensile strain (%)

Specimen 1 to 3

Specimen #

123


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For a bird’s eye view and a comparative study about the influence of the modulators on the elastic constants and mechanical characteristics of composites, graphs from Figs. 9-12 were plotted. In these plots, the characteristics are represented as a function of the number of hours in contact with the modulator.

Fig. 9. Variation of the maximum Fig. 10. Variation of the yield limit

tensile elongation

Fig. 11. Variation of the elastic Fig. 12. Variation of the ultimate

modulus El tensile strength

Some conclusions can be drawn from the graphs, as follows: - a significant influence of the modulators on the four considered elastic constants and mechanical characteristics can be noticed; - the influence depends on the time span in which the material is in contact with the modulators; - the time span of contact with the modulators should be strictly controlled.

Compared to the behavior of plastic materials subjected to the action of modulators, a composite material show a decrease of the ultimate tensile strength and maximum tensile elongation, and an increase of the elastic modulus El [5]. For small exposure time, the considered material behaved as the isotropic plastic materials, that is Young’s modulus decreases and the ultimate tensile strength increases with a small amount.

Timp de contact cu modulatorul

[h]


[h]


[h]


[h]

511

CONCLUSIONS

The abovementioned behavior can be explained by: - the anisotropy of the material, that is modulators have different influence on the materials from which the composite is manufactured; - the fact that the fibers have micrometric dimensions and are flawless, with high tensile strength, and the influence of the modulators is insignificant; - the appearance and favoring of the debonding fiber-matrix phenomena, following the action of the modulators, due to the influence of the modulators on matrix (practically, the modulators modify only the characteristics of the plastic material); - following a higher exposure time in the field generated by the modulators, the material becomes more fragile, losing the elasticity given by the matrix; this can be explained by the fact that the adherence fiber-matrix decreased and the material did not behave as a composite, the fibers being those that make resistance. In order to clarify the complexity of phenomena both at the interface fiber-matrix and in the bulk of the material, a microscopic experimental study should be undertaken.

BIBLIOGRAPHY

1. Gheorghiu, H., A. Hadăr and N. Constantin (1998). Analiza structurilor din materiale izotrope şi anizotrope, Printech Publishing House, Bucharest.

2. Gay, D. (1991). Matériaux composites. Ed. Hermes, Paris. 3. Hadăr, A. (2002). Structuri din compozite stratificate Publishing House of the Romanian

Academy and AGIR, Bucharest. 4. Constantinescu, I. N., C. Picu, A. Hadăr and H. Gheorghiu (2006). Rezistenţa materialelor

pentru ingineria mecanică. BREN Publishing House, Bucharest. 5. Hadăr, A., Fl. Baciu, H. Gheorghiu and A. Dincă (2010). Influenţa modulatorilor bio-fito-

dinamici de tip AD asupra caracteristicilor mecanice ale unor materiale plastice. The Informative Bulletin of the Center of Biosynergetic Studies and Researches Dincă Ancu Bucharest, Ed.Tipolex.

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