6 Replies Latest reply on Apr 12, 2017 10:11 PM by Richard King

    Failure stress

    Sivateja Kasireddy

      while calculating S-N curve we consider max and minimum stress. may I know what is the maximum stress ? and among s,y and Z dirextions which direction stress do i need to consider?

       

      can I use von mises stress as my max stress in calculating fatigue life ?

        • Re: Failure stress
          Shaodun Lin

          It depends on different material type.

          Steel ? Aluminum ?

          • Re: Failure stress
            Richard King

            Hi Sivateka, in an S/N curve, your are applying a cyclic load to your material. The maximum stress is the max stress in your model when the load is at its maximum, and the min stress is the value at the same point when the load is at its minimum.

             

            When the stress is not uniaxial, it's a bit tricky. This is discussed in "mutliaxial fatigue" in my favorite fatigue book, below. I'm assuming your material is a metal. Maximum principal stress, max shear stress (Tresca), and Von Mises stress are all commonly used. There are more complicated shear stress based models like Fuch's model

             

            rich

             

            Bannantine, J, Comber, J, and Handrock, J, Fundamentals of Metal Fatigue, Prentice-Hall, 1990.