General Mechanical

General Mechanical

Load in micro-strain

    • masud407
      Subscriber

      How can I apply compressive load in the form of micro-strain (for example 3000 μ epsilon) in ANSYS workbench?


      epsilon means strain here.

    • SaiD
      Ansys Employee

      Hi,


      In Workbench, go to the top tab --> Units --> Unit Systems. The Unit system number 9 has length in micrometers. So activate it under columns B and C and hit Close. If you check Units again, this unit system should be selected and you can apply Displacement boundary conditions in micrometers.


      Hope this helps,


      Sai


       

    • masud407
      Subscriber

      Hello Sai,


       


      Thanks for your reply. I understand the point regarding unit systems. However, is the application of displacement as the boundary condition similar as the application of strain?

    • SaiD
      Ansys Employee

      Hi,


      You cannot apply Strain as a boundary condition. What you would do is convert that strain to displacement (based on the geometry dimensions) and apply the Displacement boundary conditions. E.g. if you have a cylindrical bar of length 10 m and you want to apply a strain of 10%, you would apply a displacement boundary condition of 0.1*10= 1m. But this analytical conversion of strain to displacement assumes that strain is uniform everywhere which might be a valid assumption if you have a simple geometry, but may not hold if the geometry is complicated.


      Hope this helps,


      Sai

    • masud407
      Subscriber

      Hello Sai,


       


      My geometry is a kind of elliptical shape. The paper that I am following mentioned that they applied  3000 μ epsilon (Where epsilon is strain). You gave an example of a 10% strain, but how should I consider for  3000 μ epsilon case?

    • SaiD
      Ansys Employee

      Hi,


      Strain and stress are outputs in any finite element analysis. If it's a Static Structural system, the solver solves the equation [K]{u}={F}. So on the boundary you can either define u i.e. displacements or F i.e. force (which can be derived from force or pressure boundary conditions). So I am not sure how they applied a strain boundary condition without converting the strain to an equivalent displacement on the boundary. The only way I can think of is applying a displacement, checking the output strains and increasing or decreasing the displacement applied till the desirable strain output is achieved.


      You mentioned "applied 3000 μ epsilon". What does the "μ" stand for? May be that could be a clue?


       

    • masud407
      Subscriber

      Hello Sai,


      The point that you mentioned in the first paragraph is totally understandable. It was mentioned that a compressive


      uni-axial load of 3,000-microstrain was applied. The term 3000 microstrains confused me and I don't know how to apply it in ANSYS workbench


      Here, 3000 μ epsilon means 3000-microstrains.


       

    • SaiD
      Ansys Employee

      Hi,


      Looks like microstrain just means 1*10^-6 strain. So the paper applies a strain of 3000*10^-6 i.e. strain = 0.003. My guess is they calculated the approximate displacement of the top surface based on the geometry and linear assumption (strain=(L-L0)/L0) and applied the displacement boundary condition.

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