Development of 3D Knitted Fabrics for Advanced Composite Materials

Luminita Ciobanu, Ph. D., Eng.

„Gheorghe Asachi" Technical University of Iasi

Romania

1. Introduction

Generally, a composite material is made of distinct materials, that together act in a different way than when considered separately. There are a lot of examples of composite materials, both natural and synthetic, from the human body, to buildings, airplanes and so on.

Most comprehensive definition of the composite materials that characterises their nature is given by P. Mallick. According to Mallick (1997), a composite is a combination of two or more chemically different materials, with an interface between them. The constituent materials maintain their identity in the composite material (at least at macroscopic level), but their combination gives the system properties and characteristics different from those of each component. One material is called matrix and is defined as the continuous phase. The other element is called reinforcement and is added to the matrix in order to improve or modify its properties. The reinforcement represents the discontinuous phase, distributed evenly in the matrix volume.

There are several options for reinforcement and matrix, as illustrated in Fig.1, that are taken into consideration based on the mechanical requirements specific to the application.

COMPOSITE MATERIALS

Подпись: REINFORCEMENTTextile Reinforced

Development of 3D Knitted Fabrics for Advanced Composite Materials Подпись: CONCRETE/ Подпись: METALL C

Composites

CEMENT

Подпись: FIBRE S/YARNSThermoset resins

Thermoplast resins

[Advancelnomposite^l

Fig. 1. Structure of composite materials

ensemble strength, while the matrix ensures the composite unity and transmits the strains. The advantages of the textile reinforced composites are:

• controlled anisotropy of the textiles which means that their structure materials can be designed so that the fibres are placed on preferential directions, according to the maximum strain;

• the use of textile reinforcements allows to obtain a better weigh/ strength ratio compared with the classic materials, such as steel;

• textile materials maintain their integrity and behaviour under extreme conditions – for example, they do not corrode in a outdoor environment, nor vary their dimensions when there are significant temperature variations, nor are they sensible to electro­magnetic fields;

• TRCs present an improved fatigue life.

The aeronautic industry was the first that used TRCs for airplanes. Currently, there is a high diversity of TRCs applications, with high economic impact (Mouritz, 1999). Composite materials can be found in all fields of technical textiles. Industrial applications of the composites include tanks, storage structures, pipes, hoses, etc. The automotive industry uses TRCs for car frames and other machine parts (manifold, wheels), while in aeronautics the composites developed from 1st level applications to 2nd level that refers to resistance elements in an airplane structure and the future trend is building one exclusively with composites. The composite materials also replaced traditional ones for the rotor blades of helicopters, increasing their life span and their resistance to wear (Mallick, 1997). One field of great interest for textile reinforced composites is the wind energy management – these materials are used to build wind mills. The TRCs are also used to produce sport equipment – tennis rackets, bicycles and motorcycles, etc.

An interesting application is in buildings, where composites (the so called Textile Reinforced Concrete) are used to reinforce walls (cement/concrete matrix), increasing their strength and reducing their thickness and subsequently production costs.