Static_Failure_1 - Static Failure Theories Stress and...

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Unformatted text preview: Static Failure Theories Stress and Strain • Given: • Stress-strain data for simple uniaxial tension • Find: • When failure occurs for general state of stress 1-Why do materials fail? Stress and Strain 2- What kind of stresses cause the material to fail? Depends of the material Ductile: Significant plastic deformation before fracture Brittle: yield ~fracture Depends on the loading Static: Constant load, no motion Dynamic; Time varying (No inertia effects) Failure Two primary theories for static ductile failure The Von Mises Theory ( Distortion-energy Theory ) Maximum Shear Stress Theory Three primary theories for static brittle failure Maximum Normal Stress (MNS) Coulomb-Mohr Theory Modified-Mohr Theory Von Mises Theory Yielding? • Relative sliding of materials atoms due to dislocations motion. • Dislocations move under the effect of shear stress (sliding=shearing). • Stored energy in the part is an indicator of the shear stress present. Total Strain Energy? ) ( 2 1 2 1 3 3 2 2 1 1 U U 2 1 3 3 3 1 2 2 3 2 1 1 1 1 1 E E E...
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This note was uploaded on 10/31/2009 for the course MECH 420 taught by Professor M.s during the Spring '09 term at American University of Beirut.

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Static_Failure_1 - Static Failure Theories Stress and...

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