Learning Forum

[Brian Schlagenhaft]

For injeciton molded plastic components, the CTE value typically isn't isotropic, it usually depends on the flow direction of the material.  For my material specifically, the CTE values provided by the manufacturer are in the flow direction and transverse to the flow direction.  Is there a way to define CTE's based on flow direction, or is my only option to define them using the XYZ coordinates within the orthotropic CTE property?

[peteroznewman]

One way I can think of doing this would be a huge amount of work. First you would simulate the mold flow to get the flow directions. Then you would use the flow direction data to create a local coordinate system for each element in the mesh. Then you would assign the orthotropic CTE on an element-by-element basis. You would need a significant amount of MAPDL code to achieve this. 

Other properties, such as Young's modulus might also depend on the mold flow direction. That is certianly the case for glass fiber reinforces plastics.

How much does the CTE change between the flow direction and orthogonal to that?  Compare that with the CTE of steel. While it would not be as accurate, running a model with an isotropic value of CTE is so much simpler and you could run with the high and low values to see how sensitive the solution is to that variation.