fracture of components |
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failure analysis, failure causes, failure probability, causes breakage components, fatigue, creep, corrosion, erosion, cracks |
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Fracture |
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| Definition of fracture: the irregular surface produced when a piece of metal is broken. See also crystalline fracture, fibrous fracture, granular fracture, intergranular fracture, silky fracture, and transgranular fracture. Other types of fractures are: > ductile fracture > brittle fracture > fatigue fracture Ductile fracture results from the application of an excessive force to a metal that has the ability to deform permanently, or plastically, prior to fracture. Thus, the property of ductility is simply the ability of the material to flow or deform, which may or may not lead to fracture, depending upon the magnitude of the force applied. The property of ductility is somewhat related to the property of toughness, although the latter is usually measured in the presence of a notch or other stress concentration. The Charpy V-notch impact test is commonly used as a measure of toughness. Ductile fracture has characteristics that are different from those of brittle fractures. However, it must be recognized that many fractures contain some of the characteristics of both types. The classic example of a ductile fracture is a tensile specimen that has "necked down," or deformed to form a "wasp waist" prior to fracture. A typical fracture of this type is the socalled cup-and-cone fracture characteristic of ductile metals pulled in tension. Brittle fracture is fracture that involves little or no plastic, or permanent, deformation. Many nonmetals lack ductility and normally are subject to brittle fracture; examples are chalk, rock, brick, and - under normal conditions of use - glass. Brittle fracture of normally ductile steels has occurred primarily in large, continuous, box-like structures such as box beams, pressure vessels, tanks, pipes, ships, bridges, and other restrained structures, frequently joined with welded construction. Brittle fractures that occur in service are invariably initiated by defects that are initially present in the manufactured product or fabricated structure or by defects that develop during service. Fatigue fractures are generally considered the most serious type of fracture in machinery parts simply because fatigue fractures can and do occur in normal service, without excessive overloads, and under normal operating conditions. Fatigue fractures are serious because they are insidious. |
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