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Unformatted text preview: AAE352 1 AAE 352 Lecture 16 Material indices Choosing materials for different criteria, strength, buckling, bending Slides 1521 are taken from a presentation by Prof. Caceres at UCSD Optimizing a design requires answering a few questions Forming design requirements and identifying design variables AAE352 2 Constraints What essential loading conditions must be met ? Objectives What is the criterion of excellence ? Function What does the component do ? Free variables What can be varied ? Minimize Cost Weight Volume Ecoimpact Choice of material, thickness Design requirements are expressed as objectives and constraints AAE352 3 Summary Tensile strength with minimal weight AL weight = L A P stress = = yield P A = L P weight allowable = fracture P A = AAE352 4 Material 1 or Material 2? How much weight do we save? Compute relative weights for tension loads ( 29 1 1 1 weight PL = ( 29 2 2 2 weight PL = = = = 1 2 2 1 2 1 2 2 1 1 2 1 w w weight weight AAE352 5 Compute weight of an element with a rectangular cross section loaded by a constant bending moment fixed width, b, and variable thickness, t M max 2 6 max tensile stress My M I bt = =  = t b 12 bt I 3 = 2 t y = M AAE352 6 Let the allowable stress be equal to the max stress: compute the required minimum thickness...
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 Fall '08
 Chen

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