MIT 16 01 - Block 3 –Materials/Structural Integrity (50 pages)

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Block 3 –Materials/Structural Integrity



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Block 3 –Materials/Structural Integrity

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Lecture Notes


Pages:
50
School:
Massachusetts Institute of Technology
Course:
16 01 - Unified Engineering I, II, III, & IV
Unified Engineering I, II, III, & IV Documents

Unformatted text preview:

Block 3 Materials Structural Integrity Three purposes to this block of lectures 1 To allow you to understand limits on stresses that a structure can carry 1 D and multiaxial in order to design 2 To allow you to understand the origins and limits of the strength in the different classes of material identifying unobtainium origins and limitations on models for strength 3 To allow you to select materials for specific functions understand design process Note Failure occurs when a structure cannot meet its design requirements Does not necessarily correspond to material failure e g buckling We will focus on material aspects here Materials can behave in a variety of ways according to the loading Examples 1 a piece of metal wire paper clip Can twang it elastic deformation Bend it leading to permanent deformation Cyclic loading rupture into two pieces fatigue 2 A piece of aluminum foil Load it up and it necks down before fracture Put a notch in it and it tears 3 A balloon pressurized aircraft fuselage Stick a pin in it and it explodes catastrophic failure 4 e g piece of solder wire with a weight hanging from it under a bright light creep We will examine four types of failure in Unified Yield ductile failure Fracture brittle failure Fatigue cyclic loading and creep time temperature dependent failure necessarily brief Read Ashby and Jones for more details M15 Yielding and Plasticity Reading Ashby and Jones ch 8 11 Characteristic stress strain curve and material response for a ductile metal under uniaxial loading Load extension curve for a bar of ductile metal e g annealed copper pulled in tension F Tension F Slope E A F F F F F Ao F 0 F 0 I0 u F 0 u F 0 Image adapted from Ashby M F and D R H Jones Engineering Materials 1 Pergamon Press 1980 Unloading and reloading is elastic permanent strain F Reversible elastic deformation u Permanent plastic deformation Image adapted from Ashby M F and D R H Jones Engineering Materials 1 Pergamon Press 1980 Most engineering alloys have an



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