EXPERIMENTAL-MEASUREMENT OF INTERNAL-STRESSES IN POLYPROPYLENE-INJECTED DISKS

Disks in polypropylene were injected in a mold with an unbalanced cool ing pattern to induce warpage. The internal stresses were determined u sing IR dichroism for molecular orientation measurement and an origina l method for thermal stress assessment, on the basis of the analysis o f the dilatometrical behavior of microtomed cuts removed from the part . From both experimental results and structural observations with an o ptical microscope, a simple model is proposed to describe the warpage due to the effect of unbalanced cooling. A constant deformation was ob served and cannot be described by our model, but calculated relative d eformations of the part geometry are in good agreement with experiment al results.