material-selection-w-solutions

material-selection-w-solutions - ME250 Design and...

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ME250 Design and Manufacturing I Materials selection
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Outline What? Why? Material properties Major classes of materials Material selection Summary 2
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What? Given: Basic shape and function of parts Find: Best materials for manufacturing parts considering properties eight Weight Static load resistance Impact resistance Service life Temperature resistance orrosion resistance Corrosion resistance Cost Compatible manufacturing processes 3 etc. .
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What? Various materials and processes used in tractor 4
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Why? 5
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Why? There are many materials with varying properties, cost, and compatible mfg processes 6
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Why? Material-property compatibility (more later) aterial trength rming orrosion oloring cycle ining onductor? material strength /weight forming corrosion resistance coloring recycle joining conductor? Metals ++ +++ + + +++ +++ either Ceramics +++ + +++ + + + no Glasses +++ +++ +++ +++ +++ + no Polymers + +++ + +++ ++ ++ no Composites +++ + depends + + + either 7
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Why? Process-material compatibility (more later) 8
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Why? Shape-process compatibility (more later) 9
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Why? Similar shape can be made with different mfg processes (more later) casting forging extrusion machining assembling 10
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Why? Design, material selection, process selection are dependent to each other ypically proceed with iteration process Typically proceed with iteration process eeds Needs unction esign aterial selection Function Design Material selection 11 Process selection
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Material properties Mechanical properties Stiffness [Force/area] Strength [Force/area] Fatigue [force/area that survives 10 6 cycles] Fracture toughness [Force/area * length^0.5] 12
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Material properties Physical properties Density [mass/volume] Thermal expansion [length/length/deg] Melting temperature [deg] Specific heat [energy/mass/deg] Thermal conductivity [energy/time/length/deg] Electrical resistance [voltage/current] Corrosion resistance 13
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Material properties Stiffness and strength (informal definitions) aterials deforms and eventually breaks Materials deforms and eventually breaks under force Stress = force/area applied to material iece piece Strain = displacement/length under stress Yield strength = stress at which material stops to spring back Ultimate strength = stress at which material breaks Stiffness and strength are defined in stress-strain curve obtained by tensile 14 test
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Material properties Tensile test machine 15 http://www.youtube.com/watch?v=5QaqwmZ7Sic
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Material properties Stress-strain relationship (tensile test) ltimate) yield strength: S y racture (ultimate) tensile strength: S ut Fracture strength: S f 16
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Material properties Tensile test results Brittle material Ductile material 17
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Material properties Engineering stress 0 eng P A A 0 = cross sectional area before loading Why “engineering”? True stress = P / A > eng A is hard to measure during tests Typically given in MPa (Mega = 10 6 ) or psi 18
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Material properties Engineering tensile strain ll 0 0 t e l l 0 = length before loading Unitless or given in % 19
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Material properties Young’s modules ue ot engineering) stress during lastic deformation t E e = true (not engineering) stress during elastic deformation
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material-selection-w-solutions - ME250 Design and...

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