Define the Material Properties

We now assign the material properties to the six parts. First, we create a custom units system to suit the units in which the material properties are specified. Watts (Joules/second) are commonly used in the electronics industry, for both English and metric designs. Therefore, we define a custom unit system based on English inch conventions, but substitute J for the in·lbf thermal energy units.

  1. Right-click the Units Systems heading in the browser (tree view) and click New. The Unit System dialog box appears.
    1. Click in the cell where English (in) is currently shown. This is the model units system and therefore the default display units system. A down-arrow appears at the right end of the cell.
    2. Click the down-arrow and select Custom from the drop-down list.
    3. Click in the Thermal Energy input cell (which currently shows in·lbf). A down-arrow appears at the right end of the cell.
    4. Click the down-arrow and select J from the drop-down list.
    5. Type English (in s F J) in the Description field to identify the custom unit system.
    6. Click OK. The newly created unit system becomes the current Display Units system.
  2. Double-click the Material heading for Part 1 in the browser. The Element Material Selection dialog box appears.
    1. Click Edit Properties. The Element Material Specification dialog box appears.
      Note: The mass density and specific heat values are not needed for a steady-state heat transfer analysis. The values that are currently in these fields are the default steel properties assigned by SimStudio Tools (where the CAD model originated). These values are incorrect for the circuit board parts. Therefore, enter zero in these two fields. Of course, the actual values can be entered if they are known, but they have no effect on the results for a steady-state thermal analysis.
      1. Type 0 in the Mass Density field.
      2. Type 0.549 in the Thermal conductivity field.
      3. Type 0 in the Specific Heat field.
      4. Click OK to accept these properties.
    2. Click OK to exit the Element Material Selection dialog box.
  3. Double-click the Material heading for Part 2 in the browser.
    1. Select Silicon, Si from the Other Nonmetals folder of the Autodesk Simulation Material Library.
    2. Click OK.
    3. Click Yes if prompted to confirm replacement of the current material.
  4. Select the Material heading under Part 3 in the browser.
    • Hold down the Ctrl key and also select the Material headings for Part 4, Part 5, and Part 6. Four Material headings should now be selected.
  5. Right-click one of the four selected headings and choose Edit Material.
    1. Click Edit Properties.
      1. Type 0 in the Mass Density field.
      2. Type 0.544 in the Thermal conductivity field.
      3. Type 0 in the Specific Heat field.
      4. Click OK to accept these properties.
    2. Click OK to exit the Element Material Selection dialog box.

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Parent topic: Circuit Board Steady-State Heat Transfer Analysis