The document discusses composites materials and their properties. Composites consist of fibers and a matrix bonded together to form a strong material. The properties of composites depend on the fiber type, fiber orientation, fiber length, fiber content, and the matrix used. Natural fibers have advantages over glass fibers in terms of cost, density and sustainability, but also have limitations like moisture absorption. Proper treatment of fibers can improve adhesion between the fiber and matrix. Different manufacturing techniques like hand layup, filament winding, pultrusion are used to produce composites depending on the end application.

1. COMPOSITES: A WONDER MATERIAL FOR THE FUTURE Sreekumar P.A

4. Composite materials Fibre reinforced composites Particle reinforced composites Single layer Multi layered Composites (Angle ply) Laminate Hybrid Continuous fibre Discontinuous fibre Unidirectional Bi-directional Random orientation Preferred Orientation Random Preferred

5. Fibre Natural Man Made Regenerated Synthetic Mineral Plant Animal Leaf Bast Fruit Wool Mohair Silk

6. Natural fiber classification

11. Factors influencing the mechanical properties of the composite Critical Fiber Length The minimum length per given fiber diameter essential for high tensile fracture stress.When the length of the fibre is below critical fibre length, the maximum fibre stress may never reach the ultimate fiber strength  f l l< l c l = l c l > l c

12. How to calculate critical fibre length? Consider an infinitesimal length distance dx at a distance x form one of the fibre ends the force equilibrium for this length is (  /4.d 2 f ) (  f + d  f ) – (  /4. d 2 f  f ) -  d f dx.  = 0 (1) Which on simplification gives d  f /dx = 4  / d f (2) Where  f = longitudinal stress in the fibre at a distance x from one of its ends.  = Shear stress at the fibre/matrix interface. d f = Fibre diameter. Factors influencing the mechanical properties of the composite

13. Assuming no stress transfer at the fibre ends, i.e  f =0 at x=0, and integrating equation (2) the normal stress distribution in the fibre ends as  f For simple analysis, it is assumed that interfacial strength is constant. Then equation becomes  f = (4  I / d f ) x Where = interfacial shear stress. The maximum fibre stress that can be achieved at a given load is (  f ) max = 2  I (l t / d f ) Where x= l t /2 = load transfer length at each fibre end . Factors influencing the mechanical properties of the composite 3 4 5

16. How to calculate fibre content and composite density? Factors influencing the mechanical properties of the composite Where R is the resin content in composite, r is the sisal fibre vol%, D is the density of the resin d is the density of sisal fibre. T d =100/(R/D + r/d) V f = W f /  f W f /  f + (1-W f ) /  m Where W f is the fibre weight fraction ( 1-W f ) is the matrix weight fraction  m is the resin density  f is the fibre density

17. Interfacial Adhesion How to improve interfacial adhesion? By Chemical Methods By Physical methods By using Coupling agents Factors influencing the mechanical properties of the composite fibre matrix interface

24. Continuous and aligned fibre composites Longitudinal loading There are composites in which the fibers are aligned in the direction of applied stress.Assume that all the filaments are perfectly bonded to the matrix. Where  c = composite strain  f = fibre strain  m = Matrix strain Factors influencing the mechanical properties of the composite  f =  m =  c The total tensile force applied on the composite lamina is hared by the fiber and matrix P =P f +P m Since load = stress x area: then

25. Rule of mixtures Factors influencing the mechanical properties of the composite  c . A c =  f . A f +  m . A m  c . =  f (A f /A c ) +  m (A m /A c ) Where  c . = Average tensile strength A f = Area of the fibre A m = Area of the matrix A c = A f + A m Since V f = A f /A c and V m = Am/A c  c . =  f V f +  m V m This equation is known as rule of mixtures

26. For transverse loading In this type the load is applied at 90 0 angle. Under this situation Stress to both phases are exposed in the same time E c = E m .E f /V m .E f + V f . E m Factors influencing the mechanical properties of the composite E c = elastic moduli of the composite E f = elastic moduli of the fibre E m = elastic moduli of the matrix V f = elastic moduli of the fibre V M = elastic moduli of the matrix

27. For randomly oriented fibre composites are composed short and discontinuous fibre. Under these circumstance the expression for the elastic modulus K= Fibre efficiency parameter which value is lees than unity Modified rule of mixture Factors influencing the mechanical properties of the composite E c = KE f V f +E m V m

33. COMPRESSION MOULDING Moulding through the force of compression is another very common industrial process. The materials used are melamine, phenol and urea formaldehyde, Polyesters etc. Process Description The mould is held between the heated platens. A 'slug' or piece of the plastic is placed into the mould . The hydraulic press closes with sufficient pressure. The Compound softens and flows to shape. If necessary cooling is done. The press is opened and the moulding removed

34. Classification of Moulds Positive Mould Semi-positive mould Flash Moul d

36. The filament winding process was originally invented to produce missile casings, nose cones and fuselage structures, but with the passage of time industries other than defense and aerospace have discovered the strength and versatility of filament winding. Picture

41. Polar The fibre passes tangentially in the polar opening at one end of the chamber.Reverses direction, and passes tangentially to the opposite side of the polar.It is simple and winding speed can be maintained Hoop patterns High angle helical winding that approaches an angle of 90 o. They are generally combined with longitudinal windings to produce a balance structure

47. Preform Tool Injection Cure Demould SCHEMATIC REPRESENTATION

50. Is fibre washing is related to injection pressure ? How? Fibre washing increases when pressure is increased

52. Schematic diagram of edge flow

53. Factors governing the edge flow? Injection pressure Only a marginal increase for mould filling at the edge with increasing edge pressure

62. INJECTION MOULDING It involves forcing or injecting a fluid plastic material into a closed mould where it solidifies to give the product Two basic categories: Thermoplastic; Thermosetting In former material is melted and force through an orifice or gate into a cool mould . In later a reacting material is injected into a warm mould in which the material further polymerizes into a solid part

63. Schematic Diagram

65. Screw move back and check valve opens Stage 4 Stage 1 Stage 3 Stage 2 Mould open Mould clamped cavities filling with melt. Mould clamped cavities full, melt freezing. Screw almost stationary Screw move forward and check valve closed Reservoir full Frozen moulding in clamped mould. MOULDING STAGES

66. EXTRUSION MOULDING

68. Rotational Moulding It is used t o produce small to large hollow items with very uniform wall thickness Heating while rotating Cooling while rotating Part removal

70. Rotational Moulding Three arm indexing machine

73. A sheet of plastic (for example, compressed polystyrene) is clamped in position above the mould. The heater is then turned on and the plastic slowly becomes soft and pliable as it heats up. The plastic can be seen to 'warp' and 'distort' as the surface expands . After a few minutes the plastic is ready for ‘ forming’ as it becomes very flexible.

74. The heater is turned off and the mould is moved upwards by lifting the lever until it locks in position. The 'vacuum' is turned on and this pumps out all the air beneath the plastic sheet. Atmospheric pressure above the plastic sheet pushes it down on the mould. At this stage the shape of the mould can be clearly seen through the plastic sheet. When the plastic has cooled sufficiently the vacuum pump is switched off.