Lec 13 - ENGR ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 ENGR 4250 – dvanced Materials Engineering Advanced Materials Engineering cture 13 Lecture 13 COMPOSITES idterm Midterm
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Classification Scheme for omposite Materials Composite Materials 1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, such as cemented carbides and other cermets 2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC imbedded with fibers to improve properties, especially in high temperature applications he least common composite matrix (RC?) The least common composite matrix (RC?) 3. Polymer Matrix Composites (PMCs) - thermosetting resins are widely used in MCs PMCs – Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders
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Composite Survey Composites Particle-reinforced Fiber-reinforced Structural Large- particle Dispersion- strengthened Continuous (aligned) ligned andomly Discontinuous (short) Laminates Sandwich panels Aligned Randomly oriented
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Composite Survey: Particle-III lastic modulus of composites: Particle-reinforced Fiber-reinforced Structural Elastic modulus , E c , of composites: -- two approaches. cm m upper limit: E = VE + V p E p “rule of mixtures” Pa) Adapted from Fig. 16.3, Callister 7e . (Fig. 16.3 is from R.H. Krock, ASTM Proc , Vol. 63, 1963.) lower limit: 1 = V m + V p Data: Cu matrix w/tungsten 250 300 350 E (GPa) E c E m E p particles 02 0 4 0 6 0 8 0 1 0 0 150 200 vol% tungsten (Cu) (W) Read section 16.2
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Fiber Alignment Adapted from Fig. 16.8, Callister 7e . ligned ligned random aligned continuous aligned discontinuous
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Composite Survey: Fiber-IV Critical fiber length for effective stiffening & strengthening: Particle-reinforced Fiber-reinforced Structural f d σ > 15 length fiber fiber diameter shear strength of fiber strength in tension Ex: For fiberglass, fiber length > 15 mm needed c τ fiber-matrix interface hy? Longer fibers carry stress more efficiently! Why? Longer fibers carry stress more efficiently! Shorter, thicker fiber: c f d τ σ < 15 length fiber Longer, thinner fiber: c f d τ σ > 15 length fiber ) Adapted from Fig. 16.7, Callister 7e . σ (x) σ (x) Poorer fiber efficiency Better fiber efficiency
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Composite Strength: Longitudinal Loading Continuous fibers - Estimate fiber-reinforced composite strength for long continuous fibers in a matrix Longitudinal deformation σ c = σ m V m + σ f V f but ε c = ε m = ε f volume fraction isostrain E ce = E m V m + E f V f longitudinal (extensional) modulus m m f f m f V E V E F F = f = fiber m = matrix Read section 16.5
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Modulus of Elasticity Cont. Fibers
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Composite Strength: ransverse Loading Transverse Loading • In transverse loading the fibers carry less of the load - isostress σ c = σ m = σ f = σ ε c = ε m V m + ε f V f f m V V + = 1 transverse modulus f m ct E E E Read the entire section 16.5 And solved examples
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Modulus of Elasticity Cont. Fibers
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Composite Strength • Estimate of nd S r discontinuous fibers: Particle-reinforced Fiber-reinforced Structural
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Lec 13 - ENGR ENGR 4250 Advanced Materials Engineering...

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