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Structural applications of composites
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- 2. A compositematerial 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. Different from mixtures and solid solutions.
- 3. Composite materials- two phases: i. Matrix ii. Fiber or dispersed phase Composite properties are a function of the properties of the constituent phases, their relative amounts, and the geometry of the dispersed phase. Dispersed phase geometry in this context means the shape of the particles and the particle size, distribution, and orientation
- 6. Particle reinforcedcomposite: Consist of particles of one material dispersed in a matrix of a second material. Fiber reinforced composite: Fibers of one material are surrounded by a matrix. Structural composite: Multi-layered and low density composite used in applications requiring structural integrity, ordinarily high tensile, compressive, and torsional strengths and stiffness. Nanocomposite: Multiphase solid material where at least one dimension of the reinforcing phase is in nanolevel (less than 100 nm).
- 7. Weight reduction Durability Low maintenance Design freedom
- 8. Concrete isa common large-particle composite in which both matrix and dispersed phases are ceramic materials. Concrete implies a composite material consisting of an aggregate of particles that are bound together in a solid body by some type of binding medium, that is, a cement. Portland and asphaltic cement concrete : Aggregate – gravel or sand Medium – Cement
- 9. The ingredientsfor this concrete are Portland cement, a fine aggregate (sand), a coarse aggregate (gravel), and water. Dense packing of the aggregate and good interfacial contact are achieved by having particles of two different sizes Can be poured in place and hardens at room temperature and even when submerged in water. Portland cement concrete is relatively weak and extremely brittle. Tensile strength is approximately one-fifteenth to one-tenth its compressive strength.
- 10. Large concretestructures can experience considerable thermal expansion and contraction with temperature fluctuations. Water penetrates into external pores, which can cause severe cracking in cold weather.
- 11. The strengthof Portland cement concrete may be increased by additional reinforcement. This is usually accomplished by means of steel rods, wires, bars, or mesh, which are embedded into the fresh and uncured concrete. Thus, the reinforcement renders the hardened structure capable of supporting greater tensile, compressive, and shear stresses. Coefficient of thermal expansion of steel is nearly the same as that of concrete – hence good reinforcement.
- 12. Steel isnot rapidly corroded in the cement environment. Another reinforcement method – pre-stressed concrete. This method uses one characteristic of brittle ceramics; that they are stronger in compression than in tension.
- 13. Glass Fiber–Reinforced Polymer(GFRP) Composites It is easily drawn into high-strength fibers from the molten state. When fiber is embedded in a plastic matrix, it produces a composite having a very high specific strength. It possesses a chemical inertness that renders the composite useful in a variety of corrosive environments. Carbon Fiber–Reinforced Polymer (CFRP) Composites Carbon fibers have high specific moduli and specific strengths. They retain their high tensile modulus and high strength at elevated temperatures. At room temperature, carbon fibers are not affected by moisture or a wide variety of solvents, acids, and bases.
- 14. Aramid Fiber–Reinforced Polymer(AFRP) Composites Aramid fibers - high strength and modulus. Outstanding strength-to-weight ratio, which is superior to that of metals. High toughness, impact resistance, and resistance to creep and fatigue failure. Resistant to combustion and stable to relatively high temperatures between -200°C and 200°C.
- 15. A structuralcomposite is a multi-layered and normally low-density composite used in applications requiring structural integrity, ordinarily high tensile, compressive, and torsional strengths and stiffness. The properties of these composites depend not only on the properties of the constituent materials, but also on the geometrical design of the structural elements. Laminar composites and sandwich panels are two of the most common structural composites
- 16. A laminarcomposite is composed of two-dimensional sheets or panels (lamina) bonded to one another. A multi layered structure such as this is termed a laminate In this regard, there are four classes of laminar composites: unidirectional, cross-ply, angle-ply and multidirectional. Most laminate fiber materials are carbon, glass, and aramid. Laminations may also be constructed using fabric material such as cotton, paper, or woven-glass fibers embedded in a plastic matrix.
- 18. A classof structural composites designed to be lightweight beams or panels having relatively high stiffness and strengths. Consists of two outer sheets or faces that are separated by and adhesively bonded to a thicker core. The core material is lightweight and normally has a low modulus of elasticity. Core materials typically fall within three categories: rigid polymeric foams, wood, and honeycombs.
- 20. Both thermoplasticand thermosetting polymers are used as rigid foam materials. Balsa wood as core : Low Density (0.10 to 0.25 g/𝑐𝑚3 ), Relatively inexpensive, Relatively high compression and shear strengths. Honeycomb structure: Tensile and compressive strengths are greatest in a direction parallel to the cell axis and shear strength is highest in the plane of the panel. Honeycomb structures also have excellent sound and vibration damping characteristics.