Lecture 3.pptx
- 1. 201022 COMPOSITE MATERIALS AND STRUCTURES UNIT I MICROMECHANICS Department Aeronautical Engineering, PSNCET
- 2. Classifications of Composites Department Aeronautical Engineering, PSNCET More general classification
- 3. Classifications of Composites Department Aeronautical Engineering, PSNCET FIBER REINFORCED COMPOSITE MATERIALS Fibre - a filament with L/D very high • A composite with fibre-reinforcement is called Fibrous Composite • Fibers are the important class of reinforcements • Fibers very strong • Provide significant strength improvement to material Ex: fiber-glass • Continuous glass filaments in a polymer matrix • Strength due to fibers • Polymer simply holds them in place • The performance of a fiber composite is judged by its length, shape, orientation, and composition of the fibers and the mechanical properties of the matrix.
- 4. Classifications of Composites Department Aeronautical Engineering, PSNCET FIBER REINFORCED COMPOSITE MATERIALS
- 5. Classifications of Composites Department Aeronautical Engineering, PSNCET STRUCTURAL COMPOSITE A structural composite is normally composed of both homogeneous and composite materials. Layered composites Layer Lamina any of the term is used Ply • materials comprising of layers of materials bonded together • may be of several layers of two or more metal materials occurring alternately or in a determined order more than once, and in as many numbers as required for a specific purpose
- 6. Classifications of Composites Department Aeronautical Engineering, PSNCET Layered composites •Usual fiber orientations: 0, 90, +/-45. By combining these orientations, the desired strength and stiffness is achieved. Plane isotropy can be achieved. •Fiber layers arranged in a way so that strength is maximized and weight is minimized. •Laminated composites must always be symmetric with respect to their middle plane, and the must also be balanced to avoid irregular distortions in the structure •The strength and stiffness varies greatly with the orientation. •A piling of woven materials without any bonding does not have any structural use. Therefore a matrix is needed. •Exclusively unidirectional composites are never used.
- 7. Classifications of Composites Department Aeronautical Engineering, PSNCET Layered composites
- 8. Classifications of Composites Department Aeronautical Engineering, PSNCET Sandwich panels 2 external strong layers (face sheets) attached to a layer of less dense material (core) with low stiffness and low strength •Role of the face sheets they withstand most of the plane loads and transversal bending stresses •Face sheet material Al alloys, fiber-reinforced plastics, Ti, steel and plywood. •Core material separates both face sheets and resists deformations perpendicular to the face plane. Provide resistance to shear stress along the planes perpendicular to the face sheets
- 9. Classifications of Composites Department Aeronautical Engineering, PSNCET Sandwich panels Core materials may have different and have different structures: polymer foams, synthetic rubber, inorganic cement and balsa wood Typical core with honeycomb structure→ thin layers arranged in hexagonal cells.
- 10. Classifications of Composites Department Aeronautical Engineering, PSNCET Sandwich panels
- 11. Classifications of Composites Department Aeronautical Engineering, PSNCET
- 12. Classifications of Composites Department Aeronautical Engineering, PSNCET
- 13. Classifications of Composites Department Aeronautical Engineering, PSNCET
- 14. Classifications of Composites Department Aeronautical Engineering, PSNCET Thermoplastics have one- or two-dimensional molecular structure and they tend to at an elevated temperature and show exaggerated melting point. Another advantage is that the process of softening at elevated temperatures can reversed to regain its properties during cooling Types of Matrix Materials
- 15. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Matrix Materials
- 16. Classifications of Composites Department Aeronautical Engineering, PSNCET Thermosets have qualities such as a well-bonded three-dimensional molecular structure after curing. They decompose instead of melting on hardening. Types of Matrix Materials
- 17. Classifications of Composites Department Aeronautical Engineering, PSNCET THERMOSETS Types of Matrix Materials
- 18. Classifications of Composites Department Aeronautical Engineering, PSNCET THERMOSETS Types of Matrix Materials
- 19. Classifications of Composites Department Aeronautical Engineering, PSNCET THERMOSETS Types of Matrix Materials
- 20. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Matrix Materials
- 21. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Matrix Materials
- 22. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Matrix Materials
- 23. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Matrix Materials
- 24. Classifications of Composites Department Aeronautical Engineering, PSNCET
- 25. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 26. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 27. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 28. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 29. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 30. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 31. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 32. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 33. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 34. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 35. Classifications of Composites Department Aeronautical Engineering, PSNCET Cross Sectional Shapes of Fibres
- 36. Classifications of Composites Department Aeronautical Engineering, PSNCET Cross Sectional Shapes of Fibres
- 37. Classifications of Composites Department Aeronautical Engineering, PSNCET Types of Fibers
- 38. Classifications of Composites Department Aeronautical Engineering, PSNCET Properties of Fiber and Matrix Materials
- 39. Classifications of Composites Department Aeronautical Engineering, PSNCET Whisker Reinforced Composites A whisker has essentially the same near-crystal-sized diameter as a fiber but generally is very short and stubby, although the length-to diameter ratio can be in the hundreds. Whiskers have a preferred shape but are small both in diameter and length as compared to fibers. Single crystals grown with nearly zero defects are termed whiskers. They are usually discontinuous and short fibers of different cross sections made from several materials like graphite, silicon carbide, copper, iron etc. Typical lengths are in 3 to 55 N.M. ranges. Whiskers differ from particles in that, whiskers have a definite length to width ratio greater than one. Whiskers can have extraordinary strengths upto 7000 MPa.
- 40. Classifications of Composites Department Aeronautical Engineering, PSNCET Whisker Reinforced Composites Metal-whisker combination, strengthening the system at high temperatures, has been demonstrated at the laboratory level. But whiskers are fine, small sized materials not easy to handle and this comes in the way of incorporating them into engineering materials to come out with a superior quality composite system. Early research has shown that whisker strength varies inversely with effective diameter. When whiskers were embedded in matrices, whiskers of diameter upto 2 to 10μm yielded fairly good composites. Ceramic material’s whiskers have high moduli, useful strengths and low densities. Specific strength and specific modulus are very high and this makes ceramic whiskers suitable for low weight structure composites.
- 41. Classifications of Composites Department Aeronautical Engineering, PSNCET Whisker Reinforced Composites They also resist temperature, mechanical damage and oxidation more responsively than metallic whiskers, which are denser than ceramic whiskers. However, they are not commercially viable because they are damaged while handling.
- 42. Classifications of Composites Department Aeronautical Engineering, PSNCET Flakes Reinforced Composites Flake composites consist of flat reinforcements of matrices. Typical flake materials are glass, mica, aluminum, and silver. Flake composites provide advantages such as high out-of-plane flexural modulus, higher strength, and low cost. Flakes cannot be oriented easily and only a limited number of materials are available for use. Flakes are often used in place of fibers as can be densely packed. Metal flakes that are in close contact with each other in polymer matrices can conduct electricity or heat, while mica flakes and glass can resist both. Flakes are not expensive to produce and usually cost less than fibers.
- 43. Classifications of Composites Department Aeronautical Engineering, PSNCET Flakes Reinforced Composites But they fall short of expectations in aspects like control of size, shape and show defects in the end product. Glass flakes tend to have notches or cracks around the edges, which weaken the final product. They are also resistant to be lined up parallel to each other in a matrix, causing uneven strength. They are usually set in matrices, or more simply, held together by a matrix with a glue- type binder. Depending on the end-use of the product, flakes are present in small quantities or occupy the whole composite. Flakes have various advantages over fibers in structural applications. Parallel flakes filled composites provide uniform mechanical properties in the same plane as the flakes.
- 44. Classifications of Composites Department Aeronautical Engineering, PSNCET Flakes Reinforced Composites While angle-plying is difficult in continuous fibers which need to approach isotropic properties, it is not so in flakes. Flake composites have a higher theoretical modulus of elasticity than fiber reinforced composites. They are relatively cheaper to produce and be handled in small quantities.
- 45. Classifications of Composites Department Aeronautical Engineering, PSNCET Particulate Reinforced Composites Particulate composites consist of particles immersed in matrices such as alloys and ceramics. They are usually isotropic because the particles are added randomly. Microstructures of metal and ceramics composites, which show particles of one phase strewn in the other, are known as particle reinforced composites. Square, triangular and round shapes of reinforcement are known, but the dimensions of all their sides are observed to be more or less equal. Various geometrical shapes (cubes, spheres, flakes, etc.) Various materials (rubber, metal, plastics, etc.) Have generally low strength.
- 46. Classifications of Composites Department Aeronautical Engineering, PSNCET Particulate Reinforced Composites The dispersed size in particulate composites is of the order of a few microns and volume concentration is greater than 28%. Particulate composites have advantages such as improved strength, increased operating temperature, oxidation resistance, etc. Typical examples include use of aluminum particles in rubber; silicon carbide particles in aluminum; and gravel, sand, and cement to make concrete.