General Mechanical

General Mechanical

Making a material that does not revert in properties after passing a threshold

    • Zhi Wei Ang

      Case 1

      I'm currently conducting a transient thermal analysis which includes a material that changes in thermal conductivity and specific heat capacity that changes after a certain threshold of 120°C.
      I will be referring to the thermal conductivity as "W/mK" as "Wm^-1K^-1".

      Therefore in regards to the situation, is it possible to assign a material a thermal conductivity of the following scenario:
      Initially, the temperature and the thermal conductivity would be the following as the temperature rises:
      22°C, 2Wm^-1K^-1
      120°C, 2Wm^-1K^-1
      150°C, 0.05Wm^-1K^-1
      1100°C, 0.05Wm^-1K^-1

      However, I would like to assign that the material remains at 0.05Wm^-1K^-1 after the temperature of 150°C, even after it rises to 1100°C, and after it drops back to 22°C it will remain at 0.05Wm^-1K^-1 instead of returning to 2Wm^-1K^-1.

      What was describes means, afterwards as the material decreases in temperature, it would be like this:
      1100°C, 0.05Wm^-1K^-1
      150°C, 0.05Wm^-1K^-1
      120°C, 0.05Wm^-1K^-1
      22°C, 0.05Wm^-1K^-1

      In this case, I would like for a property of the material to continue to stay at a certain value after passing a threshold.

      Is there any way to achieve this?

      Case 2

      The shape of the curve is as shown below, from Engineering Data when editing the heat capacity of a material. This is for purpose for simulating the change in property as it gets burnt.

      As there is a huge change in the material property across a small amount of temperature change, would this cause problems in the simulation such as non-convergence when solving? If so, are there any ways to solve it? Is changing the 2 sharp points at 120°C and 150°C to smoother curves better?

      Note, I am using Ansys Workbench 2021R2.

      Thank you so much everyone!

      Ang Zhi Wei

    • Ashish Khemka
      Ansys Employee

      Hi Zhi,

      For case one - the properties will remain the same as the nearest defined input properties.

      For case 2 - try running the model, there may not be any issues. But please comment if you get any error.



      Ashish Khemka

    • peteroznewman


      Hello Zhi,

      In this transient thermal model, you have a temperature-dependent thermal conductivity material and you want that material property to permanently change on an element-by-element basis after the element crosses the 150 C threshold.

      I’m not an expert at APDL, but I believe code could be written that executes after each time step to change the material assignment of any element whose current temperature was above 150 C to a different material that has a constant value of thermal conductivity.  MPCHG is an APDL command to change material. You need code to select the elements to apply that change to. A simple loop through every element with a simple IF statement that checks if the temperature is > 150 then changes material would do it. Maybe there is a command to get all elements that meet that condition without needing a loop.

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