Frequency Response analysis Vs Durability analysis 1

[ninjaz]

Does Validating a sheet metal supporting bracket on a moving vehicle , using dynamic Frequency response analysis and modal analysis will come under the category of Durability analysis? or fatigue analysis?
The validating parameter would be obviously ,the allowable stress limit of the sheet metal.
Any comments on this will be really appreciated.

 

[bxtsafe]

Ninjaz, both nomenclature can be used to describe this type of analysis. The nomenclature "fatigue analysis" appeared first and is used both in academic and industrial environment. The term "durability analysis" was created by the market department of the FE-Based Fatigue Softwares (e.g.: nCode Design Life, fe-safe, Nastran Embedded Fatigue, FEMFAT, Fatiga, etc) and mean exactly the same as "fatigue analysis".

It's important to mention one thing: Consider a component subjected to constant amplitude stresses. It's almost certain that a fatigue analysis assessment (by hand calculation or numerical one) will certainly be different from experimental results (when there are few samples). It's very normal because fatigue assessment has a large standard deviation, because each step of the the fatigue assessment theory (found in fatigue books of standards) is an approximate method to assess the life. For example: (1) the reliability factor is used to explain (and account) the scattering; (2) each modifing factor has an uncertain intrisic; (3) the Palmgren-Miner method is not an exact method and contain uncertainties, (4) there are a lot of approximation and uncertainties in the method used in fatigue from random loads (for example, the load must be an ergodic, stationary and Gaussian random process).