1 Reply Latest reply on Mar 18, 2009 1:07 PM by 1-DEXHLY

    Fatigue analysis

    Devi Prasad Samal
      Hi,

      I am very new to fatigue analysis. when applying fatigue curves, i have some doubt ..I have some fundamental questions...

      when to apply which interpolation method & how to consider reverse bias or zero bias. Although i find some data regarding interpolation & bias condition from help. but it doesnot satisfy my question.

      in help it will clarify only what are there defination. but if i want to apply a s-n curve for alloy steel, then how to find which interpolation method should b used.

      one more question when will i use the austenic curve data & carbon steel curve data. is there any theory or i can take whatever is required.

      if i dont have a s-n curve data for a specific material, how to do the fatigue analysis.

      Thanks in advance for the help....

      Devi Prasad Samal
        • Fatigue analysis
          Prasad,
          regarding the interpolation methods (Fatigue Loading)I suggest you to read as much as you can about this important phenomenon. As you know it is observed that repeated loading and unloading weakens objects over time. After a number of cycles, the object becomes so weak that it fails.
          Basically it is the way your load changes in amplitude over the time. Now you can have:
          1) Constant Amplitude Loading. It is fully defined by an alternating stress, mean stress, stress ratio and number of cycles.
          2) Variable Amplitude Loading. It is a load history record that defines the fluctuation history of a load. Usually it is loaded into Cosmos Works from a field test data acquisition system.

          S-N Curve is the behavior of a datum material characterized by the relation between the alternating stresses and the corresponding number of cycles to failure. This diagram is very important. You must pay attention on how the diagram was obtained. I mean this diagram depends of the material and the loading typology applied to obtain the data. For Low Cycle Fatigue (presents significant plastic deformations) I don't think Cosmom Simulation has the mathematical ability and the code to approach this class of problems.
          Regarding the High Cycle Fatigue you can use the formulation of Mischke with the equation of Mason-Coffin.
          A good approximation is given by Sf=1000N exp(-0.0738) where N is the number of cycle you want to calculate the Fatigue Limit at. So you could build a diagram (it is an approximation) for different number of cycles.
          Have you tried to check on this web site: Material Database

          Your last question.
          First of all you must calculate the Ultimate Limit Fatigue from Marin's equation and then you verify your results with Gerber, Goodman or ASME Elliptic criteria.

          Hope it is helpful.