Fatigue is the strength of a component at alternating stresses. Here, stress amplitudes and medium stress position are the determining factors and not maximum stresses verified by structural analysis. Proof can be provided either by finite life for a given number of load cycles or fatigue strength. Fluctuating or changing loads with constant amplitude loading are special cases.
Among others, surface roughness, size of components, temperature, supporting effects etc. are influencing factors for fatigue strength. Generally, stress amplitudes are determined by FE computations and evaluated with special software tools such as FEMFAT.
Under changing amplitude loading and frequencies, cumulative damage calculation can be performed resulting in a certain utilization ratio. With a utilization ratio of > 1, the component fails computationally. Generally, no failures will occur with the loads assumed if fatigue proof can be provided. Then, construction design is “safe”.
The reverse, that a construction fails at reaching exactly a utilization ratio of 1, is not allowed, as these a conservative methods. Complexity ranges from constant, uniaxial amplitude loading to consideration of multiaxial stress conditions with measured load time series.
Complexity ranges from constant, uniaxial amplitude loading to consideration of multiaxial stress conditions with measured load time series.
Proof of fatigue strength and fatigue strength for finite life of housings:
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