3D Shrinkage test adjusted mechanical properties (STAMP)

The Shrinkage test adjusted mechanical properties (STAMP) model [1] is a variant of the Uncorrected residual stress model. 3D analyses can use either model to predict warpage. The STAMP model uses measured shrinkage data to calibrate the modulus, Poisson's ratio and coefficient of thermal expansion. This provides you with more accurate shrinkage and warpage predictions than the Uncorrected residual stress model. You can only use the STAMP model for thermoplastic materials which have measured shrinkage data. The STAMP model works for both unfilled and filled polymer compounds.

The measurement procedure characterizes shrinkage in the flow and cross-flow directions of rectangular test plaques. These measurements of a highly aligned flow can capture the anisotropic shrinkage tendency of the material. This allows the STAMP model to calibrate the mechanical properties uniquely for each direction. Anisotropic mechanical properties allow for accurate prediction of anisotropic shrinkage. The STAMP model uses the same measured shrinkage data used to fit the CRIMS model for Midplane and Dual Domain warp analyses.

Once the STAMP model has calibrated the anisotropic mechanical properties, the calculation of molded-in initial stresses then follows the 3D residual stress model.

References

1. Costa, F.S., Bakharev, A., Yuan, Z., and Wang, J., Improved Injection Molding Warp Predictions by Characterization of Material Properties using Measured Shrinkage Data. Society of Plastic Engineers Annual Technical Conference (2023).