Predicting residual stresses due to solidification in cast plastic plates

Thermal processing is an economical and efficient way of manufacturing poly meric products. However, it suffers from an important side effect that may considerably affect product performance: during non-uniform cooling to mom temperature, strains become 'frozen in' the material. These frozen in strai ns lead to undesirable distortions and residual stresses within the final p roduct. This work is concerned with cast filled PMMA plates for domestic ap plications. In a typical casting process, the material is first polymerised at a high temperature and then cooled to the ambient temperature. After co oling, the plate has distorted to an extent dependent on the cooling condit ions. A method has been developed for quantitative prediction of the distor tions and consequent residual stresses caused by non-uniform solidification . A 'residual' temperature held is introduced, which provides the relations hip between the thermal history and frozen in strains. When applied as an a ctual temperature distribution, it results in distortions and residual stre sses. Laboratory tests indicative of the actual casting process validated t he frozen in strain model. Preheated plates were cooled in a controlled env ironment while temperatures were recorded at a number of locations on the p late surfaces. The measured temperature histories were then used in the num erical prediction of the residual temperature field. Experimental and numer ically predicted distorted shapes agree very well.