The influence of the manufacturing process on the mechanical characteristics of composite materials reinforced with fiber.

Berf, Paul ; Iancau, Horatiu ; Crai, Alina 等

Abstract: In the present paper we propose the study of several production processes of composite materials reinforced with fiber. We developed a comparative study of the mechanical characteristics obtained through different technologies. The paper describes the results obtained from tensile strain to planes studied from the perspective of different technologies. At the end of paper we give experimental results.

Key words: fiber of glass tissue; polyester resin; epoxy resin, composite materials reinforced with short fibers.

1. INTRODUCTION

In this paper we shall study the different technologies of composite materials (MC) reinforced with fiber, as well as the influence of the mechanical characteristics of the materials obtained. The specialty literature presents different technologies, but the obtained results do not refer strictly to the material or fiber types, tissue types and neither the architecture of the reinforced material, nor its position in the composite material are clearly specified (Gay, 1991). The study presented below is based on the comparative analysis of the technology of plane obtainment as well as its mechanical characteristics.

These technologies are: hand lay up molding, hand molding and pressing and manufacturing vacuum.

For the future, we propose to obtain a specific database for each material, to be of use within the industry.

2. TECHNOLOGIES OF PLANE OBTAINMENT FROM USED COMPOSITE MATERIALS

The planes were obtained practically inside the composite material laboratory of the Technical University from Cluj-Napoca, (Iancau, 2003). The materials which were used are fibers glass tissue type normal 500 g/[m.sup.2] and polyester resin Norpol 440-M 750 types and a epoxy resin Epiphen RE 4020/DE 420 type, according to table 1.

3. ANALYSIS OF THE OBTAINED PLANES

The obtained characteristics of composite material planes are presented in table 2.

The plane with the label P1 was made of spun glass fiber of 500 g/[m.sup.2], tough tissue, with the eyeholes between the filaments of great dimensions, a rare tissue which realized a higher degree of reinforcement.

The planes with the P2 label on which stress had been applied on a surface of 19, 37 Pa (N/[m.sup.2]) obtained a reinforcement degree of 68 %. Thus, we may deduce that applying pressure on the composite surface during the polymerization process results in the removal of some part of the resin, while the degree of reinforcement increases. From the point of view of coat thickness, this results in a decrease of 0.15 mm/coat at the give pressure-level.

The plane labeled with P3 makes the passing to a newer technology, namely to the technology of obtaining composites in bags under vacuum. In order to obtain planes with higher mechanical characteristics, with a higher compaction degree, on which we eliminate the contaminants and the tumbling resin, we used the vacuum procedure of planes. On this plane we obtained a reinforcement degree of 90%. We can observe that we obtain a higher degree of reinforcement if we use hard fibers tissue (500 g/[m.sup.2]), the eyeholes of which permit a good impregnation and also extract a surplus of the resin. From the point of view of layer thickness, we can notice that the thickness decreases from 0,6 mm to 0,43 mm. We observe a strong compaction of material which resulted in a decrease of layer thickness.

In the case of the vacuum planes we can observe a decrease of layers thickness, because of the material compaction. This thickness depends on the type of the material as well as on the architecture of the material.

4. THE TENSION TEST OF THE OBTAINED PLANES

The tension test is executed by applying an ascending axial force to a tensile test piece and recording his length variation. This action is repeated until the tensile piece has been broken. Both, the data regarding the test actions, as well as the size of the pieces are standard, by STAS 11268-70, STAS 9140-80, ASTM D3039-76.

Five test pieces have been taken from each plane, by cutting out with a cutter. For the tension test we used a hydraulic tensile test-machine with an acquisition data plate. The chosen travel was of 0.2 mm/s. For the determination of the breaking strength we related the maximum breakage force of the test piece that's been arisen at the strained area, (Isaac, 1994).

For the planes labeled with P1, P2, P3, made of fibers glasses to polyester matrix we realized a comparative study on the influence of the reinforcement degree on the mechanical composite behavior.

Thus, by using different technological molding procedures of the planes, different reinforcement degrees were obtained for the same type of material. Hence, the degree of reinforcement has increased from 64% in the case of planes obtained through hand lay up molding process, up to 90% using the molding procedure in manufacturing to vacuum.

In reality the breakage strength has increased from 246 MPa in case of the hand lay up molding planes to 352 MPa in case of the P2 plane, which the obtained reinforcement degree was of 68%. In case of the P3 plane, where the obtained reinforcement degree was of 90%, the breaking strength had decreased till 234 MPa. By comparison, the resulting value is inferior to the value obtained in the case of plane P1, which was obtained by hand lay up molding.

Diagrams were assigned to each test pieces depending on the maximum race and maximum force, (Bere, 2006). A diagram was elaborated for the five test pieces pertaining to the same plane, which diagrams were superimposed on a single diagram in order to make the comparative study possible between the test pieces that pertain to the same plane.

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5. CONCLUSIONS

We can notice a decrease of the final thickness depending on the production process in use. This doesn't have the total value of the coats, the value being lower than that.

The degree of reinforcement is closely related to the pressure applied on the composite surface. The more this value grows the higher reinforcement degree we obtain. The degree of reinforcement also depends by the used fiber. The firmer it is, the higher the degree of reinforcement grows.

A depreciation of mechanical characteristics to superior reinforcement degrees can be noticed. In this case the matrix was absorbed by the vacuum pump, and we observe a matrix insufficiency in composite that leads to depreciation.

The matrix is insufficient for conveying stresses to filaments, which aren't being bound up between each other with the matrix, and that is the reason for the composite depreciation.

With the hand lay up molding procedure we obtain pieces with a low reinforcement degree, nearly 50% or even 30% in case of the use of layered-coats, which structure is in homogeneously distributed. With this procedure pieces are obtained easily, the necessary investments and personal competence being minimal. The procedure may be improved through the cold molding procedure after pressing and inserting in stove.

Theoretically the molding procedure in bag under vacuum is a simple procedure. This procedure requires the use of auxiliary materials necessary for vacuum process which results in the increase of the price of the final product. By this procedure we obtain homogeneous composite structures, well-condensed and with a higher degree of reinforcement.

6. REFERENCES

Gay, D.,(1991), Materiaux composites,(Composite Materials 3e Edition), Hermes, ISBN 2-86601-268-2 Paris

Bere, P. (2006), Cercetari experimentale privind fabricatia tuburilor din materiale compozite, (Experimental Research on the Manufacturing and Mechanical Behavior of Composite Materials Tubes), reference III, Cluj-Napoca

Iancau, H. & Nemes, O. (2003), Materiale Compozite. Conceptie si fabricatie, (Composite materials. Manufacture and conception).Ed. Mediamira, ISBN 973-9357-24-5, Cluj-Napoca, Romania

Isaac, M.D. &, Ishai, O. (1994), Engineering Mechanics of Composite Materials, Oxford University Press, New York, 1994

Table 1. The materials and the technologies used

Notation Plane 1 P1
Type of reinforced material Fibers glass tissue 500 g/[m.sup.2]
Matrices types Polyester resin
Number of layers 2
Technology Hand lay up

Notation Plane 2 P2
Type of reinforced material Fibers glass tissue 500 g/[m.sup.2]
Matrices types Polyester resin
Number of layers 2
Technology Hand lay molding and pressing

Notation Plane 3 P3
Type of reinforced material Fibers glass tissue 500 g/[m.sup.2]
Matrices types Epoxy resin
Number of layers 3
Technology Vacuum manufacturing

Table 2. Characteristics of composite materials planes

Characteristics of MC P1 P2 P3

Grades of reinforcement (%) 64.51 68.18 90
Thickness of reinforcing layer (mm) 0.6 0.6 0.6
Final thickness of the composite 1.1 1.3 1.3
 material (mm)

Table 3. The experimental results

 Average
 Breakage Breakage
Cr. Test piece Maximum Strength Strength
no. Code Force [Kn] [MPa] [MPa]

1 P1 P11 5.197 233.89 245.41
2 P12 5.425 246.22
3 P13 4.493 200.22
4 P14 5.337 242.24
5 P15 6.211 304.46
6 P2 P21 8.391 292.37 288.33
7 P22 5.299 185.54
8 P23 9.589 349.90
9 P24 8.052 299.75
10 P25 8.481 314.11
11 P3 P31 6.529 226.39 215.47
12 P32 4.261 137.90
13 P33 6.577 250.46
14 P44 6.117 232.94
15 P55 6.001 239.66