Machine Design_slide 7

Machine Design_slide 7 - Machine Design ENGR 3220U UOIT,...

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Unformatted text preview: Machine Design ENGR 3220U UOIT, 2011, Winter Failures Failure can mean a part has separated into two or more pieces; has permanently distorted, thus ruining its geometry; has had its reliability downgraded; or has had its function compromised. A designer speaking of failure can mean any or all of these possibilities. Impact failure of a lawn- mower blade driver hub. The blade impacted a surveying pipe marker. (left top) Valve-spring failure caused by spring surge in an over sped engine (left bottom) Ductile and Brittle Materials Ductile Materials Brittle Materials ) ( 05 . cases most S S S y yc yt f = = 05 . < f Where f is true strain of fracture Failure Theories Ductile Materials (yield criteria) Maximum shear stress Distortion energy Ductile Coulomb-Mohr Brittle Materials (fracture criteria) Maximum normal stress Brittle Coulomb-Mohr Modified Mohr Maximum-Shear-Stress Theory The maximum-shear-stress (MSS) theory predicts that yielding beings whenever the maximum shear stress in any element equals or exceeds the maximum shear stress in a tension-test specimen of the same material when that specimen begins to yield....
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This note was uploaded on 04/16/2011 for the course ENGR 3220 taught by Professor Turro during the Spring '11 term at UOIT.

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Machine Design_slide 7 - Machine Design ENGR 3220U UOIT,...

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