processing-induced properties in strongglassystrong polymers application.pdf

Processing-Induced Properties in Glassy Polymers:Application of Structural Relaxation to Yield StressDevelopmentTOM A. P. ENGELS, LEON E. GOVAERT, GERRIT W. M. PETERS, HAN E. H. MEIJERDutch Polymer Institute (DPI), Section Materials Technology (MaTe), Eindhoven University of Technology,NL-5600 MB, Eindhoven, herlandsReceived 27 October 2005; revised 18 January 2006; accepted 19 January 2006DOI: online in Wiley InterScience (.com).ABSTRACT:A method is presented to predict the yield stress distribution throughoutan injection-molded product of an amorphous polymer as it results from processingconditions. The method employs the concept of structural bined with a?ctive temperature, following the Tool–Narayanaswamy–Moynihan formalism. Thethermal history, as it is experienced by the material during processing, is obtained bymeans of numerical simulation of the injection molding process. The resulting predic-tions of yield stress distributions are shown to be in excellent agreement with experi-mental ?ndings, both for different mold temperatures and for different part thick- Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1212–1225, 2006Keywords:glassy polymers; physical aging; yield stressINTRODUCTIONIn the current engineering practice there is agreat variety of numerical tools available todesign polymer products. Examples -mercial codes that aid the optimization process intool design. In the ?eld of injection molding, thesecodes (for example, Moldex3D, Mold?ow) not onlyallow the analysis of mold ?lling, but in the caseof glassy polymers, also give access to numericalevaluation of residual stresses and dimensionalstability (shrinkage, warpage).1–3However, infor-mation concerning mechanical properties, suchas the yield stress distribution in a product ortime-to-failure when placed under a static load, isnot provided by these codes. Nevertheless, theseare of high interest for the use of polymers instructural, load bearing a