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URGENT HELP Why does the stress increase for lower temperature loads ??

    • Jpret99
      Subscriber

      Hi all, i need urgent help as the results for my dissertation due very soon make no sense. I have conducted CFX analyses to obtain accurate pressure and temperature loads subject to a gas turbine blade, which i am now analysing in a static structural analysis. I noticed that for tests with thicker thermal coatings, the body temperature of the blade decreases by a relatively small amount. However, the corresponding stress due to LOWER temperatures INCREASES which makes no logical sense to me. To see if it was an issue with my CFX results, i made new models where i simply applied a uniform thermal condition of 500 degrees C and 600 degrees C to separate models which are ramped from 21 degrees to their final value in 1 second. There is also a rotational velocity ramped from 0-3000 rpm in 1 second. The same issue occurred here where the maximum stress for the 500- and 600-degree conditions are 600 MPa and 533 MPa respectively. This does not make sense as all theory suggests higher temperature induce higher thermal stresses.

      On closer inspection, the maximum stress overtime for both cases are relatively similar, however, their charts are slightly different. I don’t know how to properly comprehend the chart behaviour to explain why my results are behaving the way they are, so I have attached each graph below.

      I have also used IN-625 from the additive manufacturing materials list from Ansys engineering data but I am not sure if this is part of the reason. The bilinear hardening graph shows that the yield strength gradually decreases at higher temperatures. Additionally, with an increase temperature, the young’s modulus decreases, poisons ratio increases, thermal expansion coefficient increases, and density remains constant.

      I am in need of desperate help, so any suggestions on this matter would be greatly appreciated !

      500 degrees condition stress plot

    • peteroznewman
      Subscriber
      Did you use the command ERESX,NO in your analysis?
      That prevents stress computed at the Gauss points from being extrapolated to the nodes and simply copies the stress to the nodes. This is often helpful when elements experience plasticity because using extrapolation can create a high stress artifact in the results.
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