1.3 Composite materials: matrix, interface, combination

KM represent a heterogeneous system of two or more components (phases) with the preservation of identity of each individual component.

KM – are materials consisting of two or more components (phases) and having specific properties different from average properties of their constituents. In KM is the matrix, inclusion and interphase boundary.

A matrix is called a component that has continuity throughout the volume KM.

The inclusion is divided into a volume component, it can be reinforcing or reinforcing.

The interfacial boundary is the boundary between the matrix and the inclusion with properties different from the properties of matrix and inclusion.

The purpose of KM is the Union of similar or dissimilar components to obtain a material with new desired properties and characteristics different from the properties and characteristics of the original components. With the advent of such materials raises the possibility of selective selection properties of the composites necessary for the needs of each specific application.

1. The combination of these substances remains today one of the ways of creating new materials.

2. Most modern structural materials are the compositions, which allow technical products to possess a specific combination of performance properties, such as reinforced concrete structures, fiberglass pressure cylinders, automotive tyres etc.

3. In all cases it is the system of different materials, each of which has its specific purpose in relation to this finished product.

4. Neither the rubber nor the cord automobile tire can not perform its functions independently, they are used together and should be treated as a single composition.

5. Collaboration of dissimilar materials in the composite gives the effect equivalent to the creation of a new material whose properties are quantitatively and qualitatively different from the properties of its components.

For KM, characterized by the following signs:

1. The composition and shape of the component determined in advance.

2. Components are present in amounts that provide the desired properties of the material.

3. KM is uniform in a macro scale and heterogeneous at the microscale.

4. Components vary in properties.

5. Between the components there is a clear boundary.

The properties of KM cannot be determined only by the properties of the components without considering their interaction.

KM are of two types: 1) hardened; 2) with special physical properties, which sometimes have no natural materials.

Depending on the kind of the reinforcing component composites can be divided into 3 main groups: dispersion-strengthened (DCM), fiber (ECM) and eutectic (EKM), which differ in structure, mechanism of formation of high strength, anisotropy, etc.

The matrix materials can be metals and their alloys, organic and inorganic substances, polymers, ceramics and other substances (carbon, wax). Sometimes the matrix does not consist of one but of two dissimilar materials, the so-called polimetrica KM. Reinforcing, or reinforcing, components are often fine powdery particles or fibrous materials of various breeds.

Table 1 – Material classification

Сomposite materials
Group			Composition
dispersion strengthened	Fibrous	Eutectic	Inclusions: organic glass, metal, Me-con- United 1-2-3 substances	Matrix: organic Nick plastmas- sy, coal, less Tall, ceramics, 1-2-3 substances

The directional character properties of KM, of course, assumes that along with the high mechanical characteristics in some areas they are low in others.

The most important advantage of composites is the ability to create elements of structures with predetermined properties, most suitable for the nature and conditions of work. The diversity of fibers and matrix materials and reinforcement pattern when creating composites, directionally allows you to adjust the strength, rigidity, service temperature and other properties through selection of composition, the change ratio of the components and microstructure of the composites.

Fibrous reinforcement (figure 2) allows the use of new design principles and manufacturing products based on that material and the product are generated simultaneously within the same process.

a) chaotic reinforcement; b) reinforcement of one-dimensional; c) two-dimensional reinforcement; d – dimensional reinforced structure (PAS)

Figure 2 – Classification of composites according to the design feature

As a result of combining the reinforcing elements and the matrix is formed a set of properties of the composite, not only reflecting the source characteristics of its components, but also includes properties that do not have isolated components. In particular, the appearance of new properties in the composites is due to the heterogeneous structure, determining the presence of a large interface between fiber and matrix. Thus, the presence of the interface significantly increases the fracture toughness of the material.

The stability of any solid to crack propagation is determined by the mechanism of energy absorption at the vertex of a growing crack.

In composites transverse tensile stresses at the end of the growing cracks can cause delamination of the fibers from the matrix, and shear stresses at the interface – distribution plots of the delaminated along the grain. While exfoliation requires energy because the fibers must be moved relative to the matrix. In addition, upon further loading to failure of the fibres can rupture in the matrix away from the plane of propagating cracks. Therefore, for reinforced materials characterized by such mechanisms of increasing fracture toughness, which are not homogeneous materials.

In composites an important element is a matrix which:

1) ensure the solidity of the composite;

2) fixes the form of the product;

3) fixes the placement of reinforcing fibers;

4) distributes the operating voltage according to the amount of material, providing a uniform load on the fiber and its redistribution in the destruction of part of the fibers;

5) defines a method of manufacturing products from composite materials;

6) determines the possibility of executing design dimensions;

7) determine the parameters of technological processes, etc.

Thus, the requirements matrix can be divided into operational and technological.

Operational requirements. These include requirements related to mechanical and physical-chemical properties of the matrix material. They provide the performance of the composition by the action of various operating factors:

1. The mechanical properties of the matrix must work together reinforcing fibers or particles under various types of loads.

2. Strength characteristics of the material of the matrix are decisive for the shear loads, the loading of the composite in directions different from the orientation of the fibers, as well as under cyclic loading.

3. The nature of the matrix determines the level of operating temperatures of the composite nature of changing properties when exposed to atmospheric and other factors. With increasing temperature the strength and other characteristics of the matrix materials as well as the strength of their connections with many types of fibers is reduced. The matrix material also characterizes the resistance of the composite to the external environment, chemical resistance, partially thermophysical, electrical and other properties.

The technological requirements for the matrix are determined usually simultaneously occurring processes of a composite material and articles thereof, i.e. the process of combining reinforcing fibers with a matrix and final forming of the product. The purpose of technological operations is:

1) provision of uniform (without touching each other) the distribution of fibers in the matrix given their volumetric content;

2) the maximum preservation of the strength properties of the fibers;

3) create a strong enough interaction on the border of the fiber – matrix.

Figure 3 – Spatial schem reinforcement

Thus, the material of the matrix have the following requirements:

1) good wettability of the fibers;

2) pre-production of semi-products with the subsequent manufacturing of these products;

3) quality connection of several layers of composites during the molding process;

4) low values of the shaping parameters (e.g., temperature, pressure, etc.).