module 1.pptx. composite material notes for ktu notes is uploaded b y this
- 1. Historical Perspective • 4000 B.C. Fibrous composites were used in Egypt in making laminated writing materials • 1300 BC: “You are no longer to supply the people with straw for making bricks; let them go and gather their own straw” - Exodus 5.7. • 1700 AD: French Scientist, Reumer talked about potential of glass fibers
- 2. Historical Perspectives (continued) • 1939: Glass fiber manufactured commercially for high temperature electrical applications • 1950s: Boron and carbon fibers were produced to make ropes. • 1960s: Matrix added to make polymeric matrix composites
- 3. Historical Perspectives (continued) • 1970s: Cold war forces development of metal matrix composites for military aircrafts and missile guidance systems • 1990s: High temperature ceramic matrix composites are being aggressively researched for use in next generation aircraft engines and power plant turbines
- 4. Are Composites Important? • Considered as one of the ten outstanding achievements of 1964-1989
- 5. From constituents to application
- 6. Advantages of Composites • Specific Strength and Stiffness • Tailored Design • Fatigue Life • Dimensional Stability • Corrosion Resistance • Cost-Effective Fabrication • High creep resistance • Low coefficient of thermal expansion • Low density • Low thermal conductivity • Better wear resistance • Better temperature dependent behavior
- 7. • Lightweight • Easily moldable to complex (net) shapes • Part consolidation leading to lower overall system cost • Easily bondable • Good damping • Crash worthiness • Internal energy storage and release • Stealth (low radar visibility) • Thermal transport (carbon fiber only) Advantages of Composites (continued)
- 8. Drawbacks of Composites • High cost of fabrication of composites • Complex mechanical characterization • Complicated repair of composite structures • High combination of all required properties may not be available • Lack of well-proven design rules • Long development time • Metal and composite designs are seldom directly interchangeable
- 9. • Manufacturing difficulties (manual, slow, environmentally problematic, poor reliability) • Fasteners • Low ductility (joints inefficient, stress risers more critical than in metals) • Hidden damage • EMI shielding sometimes required • Solvent/moisture attack • Temperature limits • Damage susceptibility Drawbacks of Composites (continued)
- 10. Classification Based on the type of matrix material Polymer Matrix Composites (PMCs) Metal Matrix Composites (MMCs) Ceramic Matrix Composites (CMCs) Carbon/Carbon Composites (C/Cs) Based on the geometry of reinforcement Particulate reinforced Composites Whisker/Flakes reinforced composites Fiber reinforced composites Hybrid: A composite laminate comprising of laminae of two or more composite material systems or a combination of two or more different fibers such as C and glass or C and aramid into a structure Classification of Composites
- 11. Relationships of the tensile strength of fiber, matrix, and composite
- 12. What are smart materials? • Smart materials are materials that have one or more properties that can be significantly altered in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields.
- 13. Smart materials Smart materials have appropriate responses Photochromic glass Darkens in bright light Low melting point wax in a fire sprinkler Blocks the nozzle until it gets hot Acoustic emission Sounds emitted under high stress Embedded optical fibres Broken ends reflect light back Microporous breathable fabrics
- 14. Smart-fabric • pine-cone model • adapts to changing temperatures by opening when warm or shutting tight if cold
- 15. Biomimetics • Lotus effect self-cleaning surfaces • surface of leaf water droplet on leaf • Image from http://library.thinkquest.org/27468/e/lotus.htm
- 16. Biomimetics • Lotus effect self-cleaning surfaces • surface of leaf water droplet on leaf • Image from http://library.thinkquest.org/27468/e/lotus.htm
- 17. Biomimetics: Lotus effect • most efficient self-cleaning plant = great sacred lotus (Nelumbo nucifera) • mimicked in paints and other surface coatings • pipe cleaning in oil refineries Images from
- 18. QTC (Quantum Tunneling Composites ) • Quantum Tunneling Composites (or QTCs) are composite materials of metals and non-conducting elastomeric binder, used as pressure sensors. • As the name implies, they operate using quantum tunneling: without pressure, the conductive elements are too far apart to conduct electricity; when pressure is applied, they move closer and electrons can tunnel through the insulator. • QTCs were discovered in 1996 and PeraTech Ltd was established to investigate them further.
- 19. QTC
- 20. QTC
- 21. Properties of Composites Properties depend on: • ● constituent phases • ● relative amounts • ● geometry of dispersed phase • ● shape of particles • ● particle size • ● particle distribution • ● particle orientation
- 22. Composites Offer High Strength Light Weight Design Flexibility Consolidation of Parts Net Shape Manufacturing
- 23. A nanocomposite is as a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm) NANOCOMPOSITES
- 24. In mechanical terms, nanocomposites differ from conventional composite materials *Exceptionally high surface to volume ratio of the reinforcing phase and/or its exceptionally high aspect ratio. The reinforcing material can be made up of particles (e.g. minerals), sheets (e.g. exfoliated clay stacks) or fibres (e.g. carbon nanotubes or electrospun fibres). The area of the interface between the matrix and reinforcement phase(s) is typically an order of magnitude greater than for conventional composite materials. Nanocomposite VS Composite
- 25. Nano composites are found in nature also. It is found in abalone (small or very large-sized edible sea snail) and bones. Advantage of using the nanocomposites: • Greater tensile /flexural strength • Reduced weight for the same performance • Flame retardant properties • Improved mechanical strength • Higher electrical conductivity • Higher chemical resistance
- 26. Matrix Reinforcements Gives shape to the composite part Give strength, stiffness, and other mechanical properties to the composite Protects the reinforcements from the environment Dominate other properties such as the coefficient of thermal expansion, conductivity, and thermal transport Transfers loads to the reinforcements Contributes to properties that depend upon both the matrix and the reinforcements, such as toughness Roles of the matrix and reinforcement in a composite
- 27. RULE OF MIXTURES For particulate composites, the rule of mixtures predicts the density of the composite as well as other properties (although other properties may vary depending on how the dispersed phase is arranged) Density, r, is given as a fraction, f, as: f f m m c f f Where the subscripts m and f refer to the matrix and fiber. f m f f 1 that Note
- 28. RULE OF MIXTURES For fiber reinforced composites, the rule of mixtures predicts the density of the composite as well as electrical and thermal conductivity along the direction of the fibers if they are continuous and unidirectional. Density, r, is given as a fraction, f, as: f f m m c f f Thermal and electrical energy can be transferred through the composite at a rate that is proportional to the volume fraction, f of the conductive material f m f f 1 that Note f f m m c K f K f K f f m m c f f For thermal conductivity: For electrical conductivity:
- 29. RULE OF MIXTURES The rule of mixtures can also be used to predict the modulus of elasticity when the fibers are continuous and unidirectional. Parallel to the fibers, the modulus of elasticity may be as high as: f f m m c E f E f E f f c E f E However, when the applied load is very large, the matrix begins to deform and the stress-strain curve is no longer linear. Since the matrix now contributes little to the stiffness, the modulus is approximated by:
- 30. FIBER REINFORCED COMPOSITES Fiber reinforced composites provide improved strength, fatigue resistance, Young’s modulus and strength to weight ratio over the constituent materials. This is achieved by incorporating strong, stiff, yet brittle fibers into a more ductile matrix. Generally speaking the fiber supplies the strength and stiffness while the matrix binds the fibers together and provides a means of transferring the load between fibers The matrix also provides protection for the fibers
- 31. CHARACTERISTICS OF FIBER REINFORCED COMPOSITES Many factors must be considered when designing a fiber- reinforced composite including the length, diameter, orientation, amount and properties of the constituents, and the bonding between them. The method used to produce the final product is also very important as it dictates the type of properties just mentioned as well as the quality of the product.
- 32. CHARACTERISTICS OF FIBER REINFORCED COMPOSITES Fiber length and diameter: Fiber dimensions are characterized by their aspect ratio l/d where l is the fiber length and d is the diameter. The strength improves when the aspect ratio is large. Typical fiber diameters are from 10 mm to 150 mm. Fibers often fracture because of surface imperfections. Making the diameter small reduces its surface area, which has fewer flaws. Long fibers are preferred because the ends of the fiber carry less of the load. Thus the longer the fiber, the fewer the ends and the higher the load carrying capacity of the fibers.
- 33. CHARACTERISTICS OF FIBER REINFORCED COMPOSITES As can be seen from this plot, the strength of the composite increases as the fiber length increases (this is a chopped E-glass- epoxy composite)
- 34. COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Random mat and woven fabric (glass fibers)
- 35. Three different conditions of wetting
- 38. Young’s equation, obtained by resolving forces horizontally where ˠ is the specific surface energy, and the subscripts SV, LS, and LV represent solid/vapor, liquid/solid, and liquid/vapor interfaces ˠSV = ˠLS + ˠLVCosθ
- 39. Effect of Surface Roughness
- 40. Types of Bonding at the Interface • Mechanical bonding • Physical bonding • Chemical bonding • Dissolution bonding • Reaction bonding
- 41. Interface bonds formed by molecular entanglement
- 43. by interdiffusion of elements
- 44. by chemical reaction between groups A on one surface and groups B on the other surface
- 45. by chemical reaction following forming of a new compound(s), particularly in MMCs
- 47. Mechanical or Frictional bond
- 48. Fig. (a) Good mechanical bond. (b) Lack of wettability can make a liquid polymer or metal unable to penetrate the asperities on the fiber surface, leading to interfacial voids
- 49. Physical Bonding Any bonding involving weak, secondary or van der Waals forces, dipolar interactions, and hydrogen bonding can be classified as physical bonding. The bond energy in such physical bonding is very low, approximately 8–16 kJ/mol.
- 50. Chemical Bonding 1. Dissolution bonding Interaction between components occurs at an electronic scale. 2. Reaction bonding Two polymer surfaces may form a bond owing to the diffusion of matrix molecules to the molecular network of the fiber, thus forming tangled molecular bonds at the interface.
- 51. Defects in Composites •Cracks •Voids •Debonding •Delamination •Variations in fiber alignment.
- 53. (a) fiber break and local debonding; (b) matrix cracking; (c) deflection of the principal crack along a weak fiber/ matrix interface
- 54. Fig. Fracture models: (a) interface delamination where the composite acts as a fiber bundle, (b) first fiber fracture turns into a complete fracture, (c) cumulative damage
- 57. Measurements of interface/interlaminar properties Single fiber compression test loading eventually causes the debond crack to initiate from these regions due to the interface shear stress concentration
- 59. Creep test
- 61. Short beam shear test
- 64. Fig (a) Dog-bone shape fiber fragmentation test specimen; (b) fiber fragmentation under progressively increasing load from (i) to (iii) with corresponding fiber axial stress
- 65. Schematic presentation of a multi-fiber pull-out specimen
- 67. Delamination Fig. Modes of interlaminar crack propagation: (a) Mode I opening mode; (b) Mode II sliding shear mode; (c) Mode III tearing mode.
- 68. Interface zone in a metal matrix composite showing solid solution and intermetallic compound Formation