Fatigue analysis from market data

[chandran]

I am working on a project for a company to analyse the fatigue life of a component. There is an existing component that the company
manufactures and the component fails by fatigue on the average 540 days. The component is a tube made of low carbon steel of yield 260N/sqmm and ultimate of 340N/sqmm. But the company gives a guarantee of 700 days to the customers. How can i simulate
by theory the fatigue life of 540 days for that component.

 

[minger]

What exactly do you mean by "simulate by theory?" I'm a little lost at that phrase.

 

[chandran]

Yes. Simulate by basic theory.

 

[Clausius2]

What exactly do you mean by "simulate by theory?" I'm a little lost at that phrase.

I recall there are two ways:

-Using Paris equation, which is equated with experimental coefficients.

-Using FEM.

For a rapid calculation see first case.

 

[PerennialII]

Would also consider how you define "fatigue life" of the component, i.e. whether it consists of crack initiation and/or propagation, if only the latter then Paris law is the best way to go, if former is included methods of "classical" fatigue analysis come into play. Depending on the complexity of your component I think you can have decent enough estimates using "desktop" solutions, such as the IIW rules and there are some general lower bounds for Paris law coefficients (or Nasgro if a more general form of FCP law is required) depending on type of material and under what conditions the fatigue occurs.

 

[chandran]

can anyone help with classical fatigue analysis

 

[PerennialII]

Found these general intros to different aspects of fatigue analysis - one by D. Socie and another lecture paper:

http://www.mie.uiuc.edu/content/files/FCP%202001%20Basic%20Short%20Course/4%20Analysis.pdf
http://www.engr.ku.edu/~rhale/ae510/fatigue.pdf

... good starts in familiarizing the different approaches and concepts, I think a classical 'stress - life' / S-N approach might do it in this case (?).