6 Replies Latest reply on Nov 4, 2015 6:37 AM by Hampus Johansson

    How does COSMOS define compressive strength

    James Canney
      I have done an analysis using COSMOSWorks on a steel structure we are designing.

      One of my colleuges has asked how COSMOS defines compressive strength of the material when it is not defined in the material properties.

      The material we are using is AISI 304, from the COSMOSWorks material library. My VAR has been unable to help with this.

      Any assistance or advise would be very much appreciated.
        • How does COSMOS define compressive strength
          Vince Adams
          Hi James, a quick review of basic FEA might help here. COSMOSWorks doesn't define or even require "strength" information in a linear analysis and only requires Yield Strength in a nonlinear plasticity analysis. A Static analysis only requires Young's Modulus and Poisson's Ratio to complete the stress/deflection calculations. The failure strengths, Tensile & Compressive, are listed in the database only as a reference to you. The solver doesn't look at them.

          So... in answer to your question, COSMOSWorks doesn't define Compressive Strength because it doesn't really care what it is to do its job. That said, 304 is an extremely ductile SS at room temps and ductile materials tend to have the same compressive properties as tensile properties (a characteristic called 'symmetry') While the data gnome who typed all these properties in many many years ago may simply have neglected to enter a compressive strength, it is equally likely that he assumed compressive strength was equal and opposite to tensile and left it blank intentionally. I opened 2 references I keep on my desk and neither list a compressive strength for 304.

          Make sense?

          Vince
            • How does COSMOS define compressive strength
              Ranga Narasimhan
              Vince,

              Thats was really helpful literature on COSMOSWorks.. Well.. where can i get docs on stuff which tells how COSMOSWorks correlates with Strength of materials.. Because, i thought CW makes use of SOM props.. but your
              last msg enlightened me..

              thanks
                • How does COSMOS define compressive strength
                  Vince Adams
                  FEA is just another method of calculating response. If used and interpreted similarly, it correlates to other methods well. When presented with a case where FEA doesn't compare to hand calcs or test well, I can usually show that we weren't comparing "apples to apples."

                  I've attached a couple of slides from a presentation on "Why Analyze?" comparing COSMOSWorks results to standard hand calcs where I made sure all the assumptions were identical. You can see the correlation was excellent. As problems become more real-world, identifying the variation between test and analysis starts to become more difficult. I guess that's where the"art" of analysis meets up with the science of engineering.

                  Vince
              • How does COSMOS define compressive strength
                Andrew Hallas
                In any static linear analysis performed in a FEA program the program calculates deformation results first based on the applied loads and boundary conditions. Once knowing the deformed and undeformed shapes, strain is calculated and once knowing the strain results, stress results are calculated. In calculating the stress values based on the strain results only Young's Modulus (E) and Poisson's ratio are used. Yield stress values are only used in factor of safety's calculations when performing linear analysis problems.
                • Re: How does COSMOS define compressive strength
                  Hampus Johansson

                  Bump/borrow this thread :-)
                  Im currently facing a problem with high compressive loads on a plastic part between two metal sheets in a stone crusher machine. In order to get results that in some way close to reality I guess I can't go with only the E-modulus and poissons ratio since all loads will be compressive and for polymers the tensile modulus and compression modulus do differ quite a bit.
                  So wouldn't Cosmos / SW need a compression modulus to give a more accurate answer in this case?

                  Vince Adams