Chemistry for Engineering Logistics composite materials 1. Definition

1. Department “ORGANIC CHEMISRTY AND TECHNOLOGY” Chemistry for Engineering Logistics composite materials 1. Definition 2. Constituents of the Composite Materials 3. Classification of the Composite Materials Assoc. Pref. V. Grozev

2. 1. Definition Composites are materials made from two or more constituent materials with different physical and chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. The new material may be preferred for many reasons: common examples include materials which are stronger, lighter or less expensive when compared to traditional materials Example: concrete is a mixture of cement andaggregate, giving a robust, strong material.

3. 2. Constituents of the Composite Materials 2.1. Main Constituents of Composite Material The main constituents of composites are the matrix and the reinforcement materials. The matrix forms the volume of the composite material within which the reinforcingagent is imbedded. The matrix fit together all parts of the composite, while the reinforcements usually serve to strengthen the composite. • For the composite to operate effectively, the phases must bond where they join at the interface: Matrix Matrix Reinforcemet Interface

4. 2. Constituents of the Composite Materials 2.2. Functions of the matrix The matrix material can be polymer, metal or other unorganic substance. The Matrix Material: • Provides the bulk form of the part or product made of the composite material; • Holds the imbedded phase in place, usually enclosing and often concealing it; • When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent.

5. 2. Constituents of the Composite Materials 2.3. Reinforcing agents Function is to reinforce the matrix. Shape of Reinforcements Reinforcing agents are most commonly one of the following shapes: • Fibers (a); • Particles (b); • Flakes (c) • Textile materials, sheet of pater, folios.

6. 2. Constituents of the Composite Materials Materials for Fibers Fiber materials in fiber‑reinforced composites: • Glass – most widely used filament; • Carbon – high elastic modulus; • Boron – very high elastic modulus; • Polymers – Kevlar; • Ceramics – SiC and Al2O3 • Metals – steel. The most important commercial use of fibers is in polymer composites.

7. 2. Constituents of the Composite Materials Particles and Flakes A second common shape of imbedded phase are particles , ranging in size from microscopic to macroscopic. Flakes are basically two‑dimensional particles ‑ small flat platelets The distribution of particles in the composite matrix is random, and therefore strength and other properties of the composite material are usually isotropic. Strengthening mechanism depends on particle size.

8. 3. Classification of the Composite Materials After the kind of the matrix composites can be devided into three groups: • Metal Matrix Composites (MMCs) ‑ mixtures of ceramics and metals, such as cemented carbides and other cermets; • Ceramic Matrix Composites (CMCs) ‑ Al2O3 and SiC imbedded with fibers to improve properties, especially in high temperature applications; • Polymer Matrix Composites (PMCs) ‑ thermosetting resins are widely used in PMCs. Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders.

9. 3. Classification of the Composite Materials According to the type of reinforcing agents the composites can be classified:

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