Topic 3b_Manipulating Strength and PD_s

Topic 3b_Manipulating Strength and PD_s - Topic 3b:...

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1 1 Topic 3b: Manipulating Strength and Phase Diagrams MATE 210 Introduction to Engineering Materials 2 Topic 3b Outline Topic 3b Outline Composition Structure Performance Processing Plastic Mechanical Heat Treatment
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2 3 Application: Strong, Inexpensive Bicycle Frames 4 Frame Stiffness • The stiffness (or elastic modulus) of the material determines the “ride” of the bike frame. • This is why carbon fiber frames are an attractive option. Out-of-plane deflection
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3 5 Density (kg/m^3) 2000 3000 4000 5000 6000 7000 8000 9000 10000 Young's modulus (GPa) 50 100 200 Cast Magensium Carbon Fiber Heat Treatable Aluminum Non Heat Treatable Aluminum Titanium Low alloy steel Steel Stiffness vs. Density Observations? 6 Frame Strength • Frame durability is related to the material’s strength. • For a metal, strength is directly related to dislocation motion. • Can this be manipulated? FEA showing frame stresses
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4 7 Strength vs. Density Observations? Density (kg/m^3) 1000 2000 5000 10000 20000 Yield strength (elastic limit) (MPa) 50 100 200 500 1000 Carbon Fiber Cast Magnesium Non Heat Treatable Aluminum Heat Treatable Aluminum Titanium Low alloy steel Steel 8 Strength vs. Cost Cost per unit weight 5000 10000 20000 50000 100000 200000 500000 50 100 200 500 1000 Titanium Carbon Fiber Non Heat Treatable Aluminum Cast Magnesium Heat Treatable Aluminum Low alloy steel Steel Observations?
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5 9 Crystal Defects Composition Structure Performance Processing Crystalline Defects 10 Crystalline Defects Defects in crystals are generally categorized by their dimensionality: Dimensionality Defect Zero One Line defects (dislocations) Two Three Bulk defects (cracks, inclusions, phases)
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6 11 Vacancies • Vacancies: Not the same as an interstitial! • Vacancies form during solidification and from normal vibrations of atoms within the crystal. 12 Impurities A truly pure material does not really exist. For example: In 1 oz. (~28g) of Si that is 99.9999999% pure (the best we have) there are still 10 trillion impurity atoms in that 1 oz. of silicon.
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7 13 Dislocation Types Edge Dislocation Screw Dislocation Mixed Dislocation 14 Surface Defects: Grain Boundaries and Interfaces An interface is a boundary between two different crystal structures, or phases. It can also be a boundary between materials that are amorphous. Exposed surfaces (such as between a metal and the surrounding air) is also a surface defect.
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8 15 Controlling Strength Through Microstructure Composition Structure Performance Processing Crystalline Defects 16 Strengthening Mechanism #1: Strain Hardening
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9 17 Dislocations and the σ - ε curve Without dislocation motion there can be no plastic deformation. So if yield strength is the measure of plastic deformation, stopping dislocations will always make a metal stronger! Strain Stress Yield strength: measurable plastic deformation 18 Strain Hardening Strain True Stress Engineering Stress Strain Hardening : when a metal is plastically deformed, it becomes stronger.
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This note was uploaded on 04/02/2008 for the course MATE 210 taught by Professor Niebuhr during the Winter '05 term at Cal Poly.

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Topic 3b_Manipulating Strength and PD_s - Topic 3b:...

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