Chapter8_comp

Chapter8_comp - Chapter 8 Composite Materials for Aero...

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Chapter 8 Composite Materials for Aero p Applications
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eading Material Reading Material allister p. 578 15 (607- 10 will be covered Callister p. 578 615 (607 610 will be covered later)
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Composite Materials A composite material satisfies the following conditions: –It is manufactured; i.e., artificial rather than natural –It consists of 2 or more physically and/or chemically distinct, suitably arranged phases with an interface separating them pp g –It has characteristics not displayed by the omponents in isolation components in isolation
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omposites atrix + reinforcement Composites – matrix + reinforcement The matrix; e.g.,epoxy and the reinforcement; e.g., glass fibres, are the two essential components in any composite. h ti t h ti h The matrix is the continuous phase. The reinforcement is the dispersed phase.
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Matrix The matrix is the material in which the reinforcement is embedded. It provides the bond between the reinforcement materials and protects them and impedes fracture. In aerospace applications, composites are ased on polymer ceramic or metal matrices These based on polymer, ceramic or metal matrices. These are called MC olymer matrix composites: PMC polymer matrix composites: • CMC – ceramic matrix composites: MC etal matrix composites: MMC metal matrix composites:
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Reinforcing materials can be in the form of particles, flakes, whiskers, discontinuous fibers, continuous fibers or sheets. It is these materials which carry up to 0% of the load (transferred from the matrix ) 90% of the load (transferred from the matrix.) Typically these are classified as: particle, fibre (US - fiber) or structural Orientations: • Particulate (uniform) - isotropic • Randomly oriented short fibres - isotropic • Unidirectional short fibres- anisotropic • Laminar (ply layers) - anisotropic • Nb: fibres can also be woven (cloth or tape), 3-D or raid braid
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Fig 16. 8 p 547, fibre reinforced mposites composites The most effective strengthening and stiffening requires a critical fibre length lc. This is about 1 mm for many glass and carbon fibres. lc is dependent on the fibre diameter d, its strength σ f * and on the fibre-matrix bond (or the shear strength of the matrix, whichever is smaller) τ c . lc = σ f * d/ 2 τ c a. Continuous and aligned fibres, continuous fibres have l >> lc,
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Shorter, thicker fibre onger thinner fibre σ (x) σ (x) Longer, thinner fibre Poorer fibre efficiency Better fibre efficiency Normally, many small d, long fibres are best. Smaller d fibres have a lower probability of defects (higher fraction of theoretical rength) Many smaller fibres provide a larger interfacial area strength). Many smaller fibres provide a larger interfacial area reducing shear stresses which develop. Note: for MMCs it's better to have maximum interfibre spacing so that the crack blunting ability of metals can be exploited.
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Typical Benefits PMCs have enhanced E, TS, creep performance CMCs have enhanced K c MMCs have enhanced σ y , TS, creep performance CMCs: Increased toughness PMCs: Increased E/ ρ 0 3 ceramics Force E(GPa) 10 2
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This note was uploaded on 11/13/2011 for the course CIVE 2*** taught by Professor - during the Spring '11 term at Carleton CA.

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Chapter8_comp - Chapter 8 Composite Materials for Aero...

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