The word “composite” in composite material signifies that two or more materials are combined on a macroscopic scale to form a useful material. The key is the macroscopic examination of material different materials can be combined on a microscopic scale, such as in alloying, but the resulting material is macroscopically homogenous. The advantage of composites is that they usually exhibit the best qualities of there constituents and often some qualities that neither constituent possesses. The properties that can be improved by forming a composite material include.
3. corrosion resistance
4. wear resistance
7. fatigue life
8. temperature dependant behavior
9. thermal insulation
10. acoustical insulation
Naturally not all of the above properties are improved at the same time nor is there usually any requirement to do so.
CLASSIFICATION OF COMPOSITE MATERIALS
There are three commonly accepted types of composite materials
1 fibrous composite which consist of fibers in a matrix
2 laminated composites which consist of layer of various materials 3 particulate composites which are composite of particles in matrix
1 FIBROUS COMPOSITES
Long fibers in various forms are inherently much stiffer and stronger than the same material in bulk form. For example ordinary plate glass fractures at stresses of only a few thousand PSI yet glass fibers have strengths of 400000 to 700000 PSI in commercially available forms and about 1000000 PSI in laboratory prepared forms. Obviously, then the geometry of a fiber is somehow crucial to the evaluation of its strength and must be considered in structural applications. More properly, the paradox of a fiber having different properties from the bulk form is due to the more perfect structure of a fiber. The crystals are aligned in the fiber along the fibers axis. Moreover, there are fewer internal defects in fibers than in bulk material. For example, in materials that have dislocations, the fiber form has fewer dislocations than the bulk form.
PROPERTIES OF FIBERS
A fiber is characterized geometrically not only by its very high length to diameter ratio by its near crystal sized diameter. Strength and stiffnesses of a few selected fiber materials are shown in the following table
|Fiber or wire |Density,ρ |Tensile strength S|S/ρ |Tensile stiffness,E |E/ρ | | |Lb/in3 | |105 in. |106 lb/in2 |107 in. | | | |Lb/in2 | | | | |Aluminum |.097 |90 |9 |10.6 |11 | |Titanium |.170 |280 |16 |16.7 |10 | |Steel |.282 |600 |21 |30 |11 | |E-glass |.092 |500 |54 |10.5 |11 | |S-glass |.090 |700 |78 |12.5 |14 | |Carbon |.051 |250 |49 |27 |53 | |Beryllium |.067 |250 |37 |44 |66 | |Boron |.093 |500 |54 |60 |65 | |Graphite |.051 |250 |49 |37 |72 |
PROPERTIES OF MATRICES
Naturally , fibers are of little use unless they are bounded together to take the form of structural elements which can take loads .the binder materials is usually...