Chapter 8 Slides

Chapter 8 Slides - Chapter 8 Failure Lectures begin Mar 27...

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1 Chapter 8 Chapter 8 - - Failure Failure Lectures begin Mar. 27 or Apr. 1, 08
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2 ISSUES TO ADDRESS... How do flaws in a material initiate failure? How is fracture resistance quantified; how do different material classes compare? How do we estimate the stress to fracture? How do loading rate, loading history, and temperature affect the failure stress? Welded ship fracture stress at low temperature Computer chip-cyclic thermal loading. Hip implant-cyclic loading from walking. Chapter 8: Failure Chapter 8: Failure
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3 Fracture mechanisms Fracture mechanisms Fracture – Ductile fracture Requires much plastic flow and energy dissipation – Brittle fracture Little or no plastic flow and often catastrophic failure Fracture under repetitive loading – Fatigue – Can be ductile and brittle, or just brittle Fracture under constant loading at high temperatures (>~0.6T M ) – Creep – At high temperature, thermal activation allows time- dependent plastic flow even at constant stress – ductile failure modes
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4 Very Ductile Moderately Ductile Brittle Fracture behavior: Large Moderate % AR or % EL Small Ductile: warning before fracture Brittle: No warning Ductile Ductile vs vs Brittle Failure Brittle Failure • Ductile fracture is usually desirable! • Classification:
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