ch9.1-S09 - Chapter 9: Failure structure processing...

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MY2100 – Ch 9, Part 1, Slide 1 Chapter 9: Failure structure processing properties Performance 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?
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MY2100 – Ch 9, Part 1, Slide 2 What is failure? Failure can mean many things. A part has failed if it loses its shape, for example. This means it exceeded its yield strength. A part can fail by corrosion, or wear, etc. Parts can functionally fail by losing electrical properties, chemical properties, bio-compatibility, etc. In this chapter, when we say failure we mean fracture. Due to defects or fatigue, parts can fracture at stresses significantly below the yield strength! These are the failures that drive design engineers crazy, and keep lawyers in Mercedes-Benz vehicles.
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MY2100 – Ch 9, Part 1, Slide 3 Ductile fracture The simplest kind of fracture is ductile failure , for example when a specimen finally breaks after a tensile test. This is easily predictable, because the part has substantially exceeded its yield strength and deformed plastically. example: failure of a pipe Ductile failure: --one piece --large deformation cup-and-cone fracture
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MY2100 – Ch 9, Part 1, Slide 4 Brittle fracture Ceramics, along with some polymers and metals, have little ductility. They fail in a brittle manner, even in tension tests. This can happen to steels at low temperatures. example: failure of a pipe Brittle fracture in a mild steel • Brittle failure: --many pieces --small deformation
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MY2100 – Ch 9, Part 1, Slide 5 Ductile vs brittle behavior • Classification: Very Ductile Moderately Ductile Brittle Fracture behavior: Large Moderate % AR or % EL Small Ductile fracture is usually more desirable than brittle fracture! Ductile: Warning before fracture Brittle: No warning We can assess the fracture behavior of materials using tensile tests.
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MY2100 – Ch 9, Part 1, Slide 6 Fracture Mechanics Parts which contain notches, holes (such as bolt holes), or defects can be analyzed by the principles of fracture mechanics. Fracture mechanics analyzes the stresses ahead of notches or
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ch9.1-S09 - Chapter 9: Failure structure processing...

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