1 Reply Latest reply on Feb 1, 2007 2:02 PM by SolidWorks Corp

    Design Check Wizard Using Mohr-Coulomb

    Patrick Meyer
      Hello:

      I have recently been using CosmosWorks to analyze stress the in aceramic component of an assembly.  When I walk through thedesign check wizard I initially select the Mohr-Coulomb stress andthe part I am concerned with.  In the next step (2 of 3) Iselect the units; then select the ultimate strength for the tensileand compressive stress limits.  The ultimate tensile strengthfor my material is 520 psi and the ultimate compressive strength is1200 psi, which shows up in the lower windowcalled  Material involved.  The next window down is Max stress in the model.  In it, the first principlestress is shown to be 407.2 psi and the 2nd principle stress isshown to be 1024 psi.  When I check the 1st principle stressin the model it gives me a max of 192 psi and -407.2 psi. When I check the 3rd principle stress in the model it givesme a max of -92 psi and min of -1024 psi.  Then in step 3 of 3the factor of safety is shown to be 0.366683, not good.  Ibelieve there is some error in cosmos or in what I am doing thatdoesn't account for compressive stress in the model.  Ibelieve that the model is primarily compressed, I verified thiswith a check of stress directions on elements by using the vonmises stress and tensor option in the display type for the stressplot.  all looked to be compressive.  Anyway I believethe value for the max first principle stress should be 192 psi andthe value for the min 2nd principle stress should be -1024 psi. According to that, the part doesn't fail because itstensile stress never goes over 520 psi and its compressive stressnever goes below 1200 psi.  Can someone tell me what I amdoing wrong?
        • Design Check Wizard Using Mohr-Coulomb
          SolidWorks Corp
          Hi Patrick, VMS has no direction or sign (tension / compression) so this isn't the best tool to evaluate the compressive nature of the results. A P1 or P3 plot will tell you this ("-" stresses are compressive) To check the C-M results, note the equation at the beginning of the Design Check Wizard, then note the areas of low SF. Create a P1 & P3 plot and Probe the stress in the areas of low SF. Plug these numbers in the equation and see if you get the same results. If not, can you send me the model?

          Thanks!