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Fatigue cracks can grow from material or manufacturing defects from as small as 10 μm. When the rate of growth becomes large enough, fatigue striations can be seen on the fracture surface. Striations mark the position of the crack tip and the width of each striation represents the growth from one loading cycle.
Static fatigue tests can be used to determine the lifespan of a material with different loads and environmental conditions. [ 13 ] [ 14 ] However, accurately assessing a material's true static fatigue life presents challenges, as these tests often require an extended duration and there is significant variability in the results.
Widespread fatigue caused the in-flight failure of the fuselage on Aloha Airlines Flight 243. Widespread fatigue damage (WFD) in a structure is characterised by the simultaneous presence of fatigue cracks at multiple points that are of sufficient size and density that while individually they may be acceptable, link-up of the cracks could suddenly occur and the structure could fail. [1]
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Low cycle fatigue (LCF) has two fundamental characteristics: plastic deformation in each cycle; and low cycle phenomenon, in which the materials have finite endurance for this type of load. The term cycle refers to repeated applications of stress that lead to eventual fatigue and failure; low-cycle pertains to a long period between applications.
Vibration fatigue is a mechanical engineering term describing material fatigue, caused by forced vibration of random nature. An excited structure responds according to its natural-dynamics modes, which results in a dynamic stress load in the material points. [ 1 ]
Curve A shows the fatigue behavior of a material tested in air. A fatigue threshold (or limit) is seen in curve A, corresponding to the horizontal part of the curve. Curves B and C represent the fatigue behavior of the same material in two corrosive environments. In curve B, the fatigue failure at high stress levels is retarded, and the fatigue ...
The difference between pitting and micropitting is the size of the pits after surface fatigue. Pits formed by micropitting are approximately 10–20 μm in depth, and to the unaided eye, micropitting appears dull, etched or stained, with patches of gray. [2] Normal pitting creates larger and more visible pits.