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One noteworthy event in which the failure was a result of LCF was the 1994 Northridge earthquake. Many buildings and bridges collapsed, and as a result over 9,000 people were injured. [ 6 ] Researchers at the University of Southern California analyzed the main areas of a ten-story building that were subjected to low-cycle fatigue.
[2] [3] The law provides a mathematical model to predict the number of cycles to failure (N) based on the applied stress amplitude (). A High Cycle Fatigue Test is used to determine material behaviour under repetitive cyclic loads. This test aims to establish the stress-cycles-to-failure characteristics of materials, primarily utilising an ...
Also, in the presence of a steady stress superimposed on the cyclic loading, the Goodman relation can be used to estimate a failure condition. It plots stress amplitude against mean stress with the fatigue limit and the ultimate tensile strength of the material as the two extremes. Alternative failure criteria include Soderberg and Gerber. [36]
When cyclic stresses are applied to a material, even though the stresses do not cause plastic deformation, the material may fail due to fatigue. Fatigue failure is typically modeled by decomposing cyclic stresses into mean and alternating components. Mean stress is the time average of the principal stress.
Modern procedures for critical plane analysis trace back to research published in 1973 in which M. W. Brown and K. J. Miller observed that fatigue life under multiaxial conditions is governed by the experience of the plane receiving the most damage, and that both tension and shear loads on the critical plane must be considered.
A crack growth equation is used for calculating the size of a fatigue crack growing from cyclic loads. The growth of a fatigue crack can result in catastrophic failure, particularly in the case of aircraft. When many growing fatigue cracks interact with one another it is known as widespread fatigue damage. A crack growth equation can be used to ...
Here ∆ε ⁄ 2 represents the elastic-plastic cyclic strain range, E represents elastic modulus, σ m represents means stress, and N f represents cycles to failure. The remaining variables, namely σ f , ε' f , b ,and c are fatigue coefficients and exponents representing material model constants.
When the amplitude of cyclic stresses exceed the elastic limit, the plastic deformation that occurs keep accumulating paving way for a catastrophic failure of the structure. Nonlinear kinematic hardening, which occurs when the stress state reaches the yield surface, is considered as the main mechanism behind ratcheting. [5]