Topic 4_Fracture and Fatigue_s

Topic 4_Fracture and Fatigue_s - Topic 4: Fracture and...

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1 1 Topic 4: Fracture and Fatigue MATE 210 Introduction to Materials Engineering 2 Topic 4 Outline Topic 4 Outline Composition Structure Performance Processing
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2 3 Why we study material fracture? A structure which is properly designed to avoid both excessive elastic and plastic deformation, may still fail in a catastrophic way by fracture. Consequences of catastrophic fracture: 4 Causes of Fracture The causes of fracture include: The engineer’s job is to anticipate failure and design to avoid them, and if necessary analyze failures and redesign to compensate.
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3 5 Application: Pressure Vessels Nuclear reactor containment dome 6 Pressure Vessel Failures Explosion video
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4 7 Boeing 737 Aloha Airlines Failure (1987) The aluminum skin of the aircraft failed due to a combination of corrosion (reaction to environment) and fatigue (reaction to stress). 1 person died. Please leave your seatbelts fastened until the captain has turned off the seatbelt sign! 8 Pressure Vessel Loading Cylindrical pressure vessels have two dominant loading modes: –Hoop stresses (wrap around the tube) –Longitudinal stresses (run along the length of the tube) Hoop Stress Longitudinal Stress
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5 9 Pressure vessel failure modes In general, hoop stresses are twice as high as longitudinal stresses: ½ inch thick stainless steel superheater tube Longitudinal crack propagates perpendicular to the maximum stress Clearly whatever material is used for a pressure vessel must be able to resist the propagation of a crack. 10 Fracture and Fatigue Composition Structure Performance Processing
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6 11 Strength vs. Toughness Strength: Ability of a material to resist the onset and continuation of plastic deformation Toughness: Ability of a material to absorb mechanical energy up to the point of fracture (area under entire curve).
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This note was uploaded on 04/02/2008 for the course MATE 210 taught by Professor Niebuhr during the Winter '05 term at Cal Poly.

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Topic 4_Fracture and Fatigue_s - Topic 4: Fracture and...

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