chem_note3 - Eg Fishing Pole(1 Resilience(elasticity...

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A modern fishing rod – a complex composite of fibre glass weaves, parallel carbon fibres and wound filaments of carbon fibre tape. E.g. • The fibre glass/epoxy weave provides resilience •The parallel fibres orientated along the axis of the backbone provide great bending strength and elasticity to the rod •The outer carbon fibre weave reduces torsional strains and helps provide extra sensitivity (Source: Advanced materials for sports equipment, K.E. Easterling) Eg) Fishing Pole (1) Resilience (elasticity, toughness (2) (Minimum) vibration (3) Lightness (4) Sensitivity depends on the rod’s backbone 74 75 Carbon fibre reinforced polymer A 6 μ m diameter carbon filament compared to a human hair. Carbon Fibre Watch Strap Composites 76 Carbon Fibre Steering Wheel Carbon Fibre Bicycle Frame Models Triathlon Composites 77 ‘The stronger the material, the lower its critical crack size’ Cracking and Fracture Crack originated at the circumferential fatigue crack (lower right) and propagated toward the left in this view. Note that this crack quickly changes to a plane approximately 45 degrees from the metal surface. Consider a metal alloy or a wood, once a crack is opened up (takes a certain amount of energy!), it cannot be stopped. The problem of cracking/fracture cannot be solved merely by using a stronger material! When crack size exceeds the critical crack size, the structure can be assumed to have fatigue failure. 78 Now consider carbon-fibre reinforced epoxy composites. The The fibres fibres absorb cracks absorb cracks by allowing the crack to spread between the fibre and the epoxy glue. Composites have this great advantage – crack-stopping effect . Eg) A wooden squash racket vs a carbon-fibre-reinforced epoxy squash racket Composites A growing crack in a fibre composite is effectively stopped by the fibres. The secondary cracks along the fibres are relatively harmless. 79 Raw Materials in Composites: Fibres and Binders Main types of fibres used in sport equipment: Carbon (most common) , glass, aramid or Kevlar, polyurethane (PU) and boron. Ceramic (silicon carbide or aluminium oxide) fibres are also used in certain applications. Fibres Property Kevlar E-glass Carbon SiC Polyethylene Mean fibre diameter / mm 2 x 10 -4 2 x 10 -4 1 x 10 -4 1.4 x 10 -4 5 x 10 -6 Density / Mgm -3 1.44 2.54 1.8 3.0 0.97 Young’s modulus / MNm -2 1.24 x 10 5 7.2 x 10 4 2.2 x 10 5 4.0 x 10 4 1.2 x 10 5 Tensile strength / MNm -2 2760 3450 2070 4830 2590 Elongation to fracture / % 2.4 4.8 1.2 3.8 High-grade glass Very high-stiffness fibres (Source: Advanced materials for sports equipment, K.E. Easterling)
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This note was uploaded on 12/01/2010 for the course CHEM yscn0027 taught by Professor Drtong during the Spring '10 term at HKU.

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chem_note3 - Eg Fishing Pole(1 Resilience(elasticity...

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