Seminar On Composite Materials PPT Report PDF Download
What Is Composites: ?
A composite material (also called a composition material) is a material made from two or more constituent materials with significantly different physical or 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.
Typical engineered composite materials include:
- Composite building materials, such as cements, concrete
- Reinforced plastics, such as fiber-reinforced polymer
- Metal composites
- Ceramic composites (composite ceramic and metal matrices)
Composite materials are generally used for buildings, bridges, and structures such as boat hulls, swimming pool panels, race car bodies, shower stalls, bathtubs, storage tanks, imitation granite and cultured marble sinks and countertops. The most advanced examples perform routinely on spacecraft and aircraft in demanding environments.
Classification of Composites
Composite materials are commonly classified at following two distinct levels:
• The first levelof classification is usually made with respect to the matrix constituent. The major composite classes include Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs) and Ceramic Matrix Composites (CMCs). The term organic matrix composite is generally assumed to include two classes of composites, namely Polymer Matrix Composites (PMCs) and carbon matrix composites commonly referred to as carbon-carbon composites.
• The second level of classification refers to the reinforcement form – fibre reinforced composites, laminar composites and particulate composites. Fibre Reinforced composites (FRP) can be further divided into those containing discontinuous or continuous fibres.
• Fibre Reinforced Composites are composed of fibres embedded in matrix material. Such a composite is considered to be a discontinuous fibre or short fibre composite if its properties vary with fibre length. On the other hand, when the length of the fibre is such that any further increase in length does not further increase, the elastic modulus of the composite, the composite is considered to be continuous fibre reinforced. Fibres are small in diameter and when pushed axially, they bend easily although they have very good tensile properties. These fibres must be supported to keep individual fibres from bending and buckling.
• Laminar Composites are composed of layers of materials held together by matrix. Sandwich structures fall under this category.
• Particulate Composites are composed of particles distributed or embedded in a matrix body. The particles may be flakes or in powder form. Concrete and wood particle boards are examples of this category.
Examples for composite materials:
1. Fibre reinforced plastics:
A. Classified by type of fiber:
- Wood (cellulose fibers in a lignin and hemicellulose matrix)
- Carbon-fibre reinforced plastic (CRP)
- Glass-fibre reinforced plastic (GRP) (informally, “fiberglass”)
B. Classified by matrix:
- Thermoplastic Composites
- short fiber thermoplastics
- long fiber thermoplastics or long fiber reinforced thermoplastics
- glass mat thermoplastics
- continuous fiber reinforced thermoplastics
C. Thermoset Composites
2. Reinforced carbon-carbon (carbon fibre in a graphite matrix)
3. Metal matrix composites (MMCs):
- White cast iron
- Hardmetal (carbide in metal matrix)
- Metal-intermetallic laminate
4. Ceramic matrix composites:
- Bone (hydroxyapatite reinforced with collagen fibers)
- Cermet (ceramic and metal)
5. Organic matrix/ceramic aggregate composites
- Asphalt concrete
- Dental composite
- Syntactic foam
- Mother of Pearl
6. Chobham armour (see composite armour)
7. Engineered wood
- Oriented strand board
- Wood plastic composite (recycled wood fiber in polyethylene matrix)
- Pykrete (sawdust in ice matrix)
Advantages of Composites
Summary of the advantages exhibited by composite materials, which are of significant use in aerospace industry are as follows:
• High resistance to fatigue and corrosion degradation.
• High ‘strength or stiffness to weight’ ratio. As enumerated above, weight savings are significant ranging from 25-45% of the weight of conventional metallic designs.
• Due to greater reliability, there are fewer inspections and structural repairs.
• Directional tailoring capabilities to meet the design requirements. The fibre pattern can be laid in a manner that will tailor the structure to efficiently sustain the applied loads.
• Fibre to fibre redundant load path.
• Improved dent resistance is normally achieved. Composite panels do not sustain damage as easily as thin gage sheet metals.
Limitations of Composites
Some of the associated disadvantages of advanced composites are as follows:
• High cost of raw materials and fabrication.
• Composites are more brittle than wrought metals and thus are more easily damaged.
• Transverse properties may be weak.
• Matrix is weak, therefore, low toughness.
• Reuse and disposal may be difficult.
• Difficult to attach.
• Repair introduces new problems, for the following reasons:
- Materials require refrigerated transport and storage and have limited shelf life.
- Hot curing is necessary in many cases requiring special tooling.
- Hot or cold curing takes time.
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