2 Replies Latest reply on Nov 18, 2008 6:39 PM by Bill McEachern

    Problems with Hertz contacts.

    Jose Antonio Vazquez Ares

      Hello everybody,

      I had a problem with the stress calculation of a hydrodynamicbearing shell. I tried to obtain the stress in the supporting shelland contact pressure distribution over the antifriction surface ina static study (were I supposed the bearing supporting only theweight of the shaft) but I obtained two different results for thiscalculation. One of them (that I expected to be the good one) givethe contact pressure distribution with a maximum in the contactline between the shaft and the bearing surface, and the other givesthe maximum in other point of the bearing (were initially there wasno contact). I obtained randomly this two kinds of results (I saythat because I obtained the two results by running the study 4 or 5times changing only the position of the shaft in the assembly toleft it as there was initially) using the SW2007 OfficeProfessional 32 bit running in a P4 @ 3.0 GHz and I don't know why,but the worst come right now because we change the computer (as itwas very slow) to a Pentium Core 2 Quad 6600 with the Windows XPx64 to use the SW2007 64 bit also and I couldn't obtain "thegood result" again.

      Could anybody tell me if COSMOS have any limitation in thestudies using Hertz contacts? Does the COSMOS solver support thiskind of contacts? Why I can't reach "the good result"again with the 64 bit edition?

      Any suggestion will be well received.

      Best Regards

      P.D.- I attach some pictures of the result so you can see theexplained problem better.

        • Problems with Hertz contacts.
          Leonardo Pinhel
          Hi Jose, I do Herz contact with some frequency. Here is what I do, First of all, contacts must be set for start, what means to adjust bearing and shaft to be tangent, having the load normal to the contact. The contact between them must be surface to surface, with a good degree of refinement. The Stress results are structural stresses, from the boundary to inside the model, so you can see the compression distribution locally, even the beautiful maximum stress just at converging point somewhere beneath the surface, plus the stretch at plus/minus 90deg from the contact, where the bearing is being pushed (in my cases).

          The hertz contact is a surface or contact characteristic and you can see it plotting contact pressure instead of tensions (defined as one kind of stress plot, just change the type).

          now, about the same study returning different results, did you sent it to your reseller to forwward as Service request? I mean, that dismiss completely confidence on the program...
          • Problems with Hertz contacts.
            Bill McEachern
            Attached are 1 an image of a contact problem and 2 the associated files withthe problem set up in SWX 2009 format. My hand calcs for hetz contact problems - this case is pretty easy to run a hand calc on - pretty much nails the 67ksi peak shown inthe curve plot. The maximum would typically have some noise associated with it. Not sure why this is but probably due the specifics of the contact formulation, mesh, etc. I put a small .001" gap prior to startinghte analysis and I also use an elastic support to provide initial stiffnes. Hope this helps.