The Change in refractive index after warpage result displays the difference between the refractive index after warpage and the material's nominal refractive index as it appears in the material database.
This difference is a result of stresses within the part.
This result is a tensor value. You can change the way it is displayed by modifying the plot properties. To best view this result, select 
, select the Methods tab, and select Tensor as axes or Tensor as ellipsoids in the Selection box.
The Change in refractive index after warpage result is created at the end of a 3D Warp analysis.
Using this result
This result can be used qualitatively to detect changes in refractive index that are caused by stresses in the part after deformation. These stresses originate from the in-mold residual stresses that were not able to relax after ejection, or from stresses caused by the part cooling and deforming. A high value in this result may indicate that you need to move the injection location, alter processing conditions to reduce the stresses in the part (such as increasing the cooling time), or modify the geometry of the model so that stresses are concentrated to optically unimportant sections of the part.
Things to look for
Birefringence occurs when the change in refractive index tensor has different values in different principal directions (i.e., the result is displayed as ellipsoids). Birefringence has two visible effects, depending on the orientation of the tensor. Depending on the purpose of the part, one effect may be more important.
- Double images
- If the change in refractive index tensor has no axis along the direction of the incident light, then unpolarized light may appear as a double image when looking through the part.
- Polarization effects
- If one of the axes of the change in refractive index tensor is parallel to the incident light, no double image will appear, but instead the polarization of the light will change. The effect is proportional to the difference in the lengths of the two orthogonal components of the tensor. A change in polarization may be noticeable as colored bands like those that may be seen on the surface of a bubble.
If the change in refractive index tensors are symmetrical in each axis (i.e., the tensor is displayed as spheres) then birefringence cannot occur, though a lens effect is still possible if the magnitude of the tensor varies across the part.