The maximum delamination force at different types of composite structures.

Sabau, Emilia ; Iancau, Horatiu ; Hancu, Liana 等

1. INTRODUCTION

The composite materials represent arrangements of reinforce materials in continuous or discontinuous fibers, covered by a matrix having a lower mechanical resistance, (Zgura & Moga, 1999). From technical point of view, the notion of composite materials reports to materials which possess the following properties:

--they are created artificial, through the combination of different components;

--represent a combination of at least two special materials from chemical point of view, between which exists a distinct separation surface;

--presents properties which no other component taken separately could have.

The interface includes the contact surface between matrix and surfaces of the fibers, as well as the next area. The nature and the interfacial force connection depend on the structure, on the surface characteristics of the fibers (roughness, determined surface, porosity, crystal dimension, the presence of functional classifications chemical active) and on structural characteristics of the matrix (chemical composition, macromolecules conformation). The maximum performances of the composite materials are obtained in the case of realization o optimum adhesion between matrix and fibers, (Misca, 2001), (Iancau & Nemes, 2005). Shocks, impact, loadings or repeated cyclic stresses can cause the laminate to separate at the interface between two layers, a condition known as delamination. This phenomenon can be produced locally or can cover a large area which leads in the end at the breaking up of the composite structure, (Sabau, 2006). Delamination is interlaminar damage; it is the separation on a certain length of the sheets from the interior composite material, (Kachanov, 1990). Delamination can be produced during production or exploitation of the composite structure and can have a great variety of causes (the unsuitable choice of the component materials, technological imperfections, stress solicitation, and so on).

2. EXPERIMENTAL INSTALLATION

For the "delamination" test we realized an installation, which has the components represented in figure 1.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The components of installation are: composite sample (1), guiding columns (2), guiding socket (3), clamping screw (4), knife holder (5), slice knife--role of sample slicing (composite structure) (6); sample holder--fixes the sample (7); holder fixes the sample holder (8), foot plate (9).

The experimental installation is actuated with the help of the Instron 1196 pressing machine, figure 2. The method consists of a force application along the main axle of the sample, with a constant speed, until the delamination sample. The operation is realized through the drop displacement on the vertical direction until the knife is penetrating the sample, moment that the delamination takes place. The sample is fixed on the holder (7) through the agency of the clamping screw. The values of the forces can be read on the diagrams delivered of the press.

3. THE DELAMINATION TEST AT DIFFERENT TYPES OF SAMPLES

The used samples are of three types:

A: Mat 270 g/[m.sup.2], 60% reinforcing grade, with polyester resin Lerpol TIX 3603/R type, 4 layers;

B: Fibers glass tissue 450 g/[m.sup.2], 60% reinforcing grade, with polyester resin Lerpol TIX 3603/R type, 4 layers;

C: Cotton tissue, 60% reinforcing grade, with epoxy resin Ephiphen RE 4020/DE 420 type, 4 layers.

Five test pieces have been taken from each plate, by cutting out with a cutter. The first phase consists in the sample penetration by the knife. The speed of application was of 10 mm/s. For the determining of the specific force we related the maximum delamination force of the test piece that's been arisen at the strained area.

[F.sub.spf] = [F.sub.del] / S (1)

S = b x h (2)

The average of the experimentally obtained results were processed and inserted in table 1.

We can notice that the maximum delamination force for cotton tissue is more resistant then glass or Mat tissue. Diagrams were assigned to each test pieces depending on the maximum delamination force, figure3, 4 and 5. The mechanical behavior of polymeric composite materials depends in principal on nature and architecture of the reinforced material, reinforced grade and the technological process. The architecture of the reinforced grade influence meaningful the mechanical characteristics.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The specific force gives as indications about strength and quality of the realized composite structure. This installation is precise because of guiding columns and of possibility to obtain diagrams where we can read the forces that actuate on the sample and the moment of the sample delamination.

4. CONCLUSION

The mechanical behavior of polymeric composite materials depends in principal on the nature and the architecture of the reinforced material, reinforced grade and the technological process. The degree of reinforcement also depends by the used fiber.

Delamination is interlaminar damage and can be produced during production or exploitation of the composite structure and can have a great variety of causes. It is very important in industrial practice to know the principal causes of delamination appearance, to can be eliminated.

This installation is precise because of guiding columns and of possibility to obtain diagrams where we can read the forces that actuate on the sample and the moment of the sample delamination.

The specific force gives as indications about strength and quality of the realized composite structure.

In the future, we will have in view, the extension of the experimental investigations with the help of suggested installation and verification in the practice of mathematical model.

5. REFERENCES

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

Kachanov, L.M. (1990), Delamination Buckling of Composite Materials, Library of Congress in Publication Data, ISBN 90-247-3770-2, Brookline, Massachusetts, USA

Misca, B.R.H. (2001), Materiale compozite polimerice, Polymer Composite Materials, Presa Universitara Clujeana, ISBN 973-8095-13-1, Cluj-Napoca, Romania

Sabau, E; Iancau, H. &. Crai, A. (2006), Experimental researches regarding the delaminating process at composite materials with organic matrix, Mechanical Engineering 2006, The 10th international conference, pag. 612-616, ISBN 80-227-2513-7, Bratislava, Slovakia

Zgura, G. & Moga, V. (1999), Bazele proiectarii materialelor composite, Designing basements of composite materials, Ed. BREN, ISBN 973-9493-01-7, Bucuresti, Romania

Tab. 1. The experimental results

Cr. no. Samples Maximum Specific force
 Delamination [N/[m.sup.2]]
 Force
 [N]

 1. A 1 21277
 2. B 2.4 79365
 3. C 4.56 86805