Assemblies produced in an impact-modified PET polyester with 15% glass fiber reinforcement had been evaluated by a variety of analytical techniques. The cracking was observed in a relatively high number of parts immediately after cyclic thermal shock testing of the components. The cracking was found at several locations within the overmolded resin in areas immediately adjacent to underlying metal components. The focus of the investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the field samples indicated that the cracking was the direct result of molecular degradation that occurred during resin drying and molding operations, in conjunction with stresses induced through thermal shock testing of the parts. This part of the paper reviews the various methods that were used to evaluate viscosity changes in the material during drying and molding. This study illustrates the various strengths and weaknesses of the methods available to determine the molecular weight of a polymer. Since polymer degradation is frequently observed in the melt processing of PET polyesters, retained molecular weight of the material was assessed as part of the evaluation. For samples of dried and undried raw material, where sufficient samples were available, this was carried out using melt flow rate. A corroborating evaluation designed to eliminate the contribution of the filler was conducted using intrinsic viscosity, a solution technique that removes the glass fiber and considers only effects on the polymer. Typically, there is a correlation between these two methods, although quantitatively they will provide different values because of the effect that glass fiber length has on the melt flow determinations. However, in this case the results gave conflicting results. The melt flow rate test documented a significant decline in viscosity that pointed to the strong possibility of polymer degradation.


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    Titel :

    Failure analysis of automotive assemblies (Part II)


    Weitere Titelangaben:

    Schadenanalyse von Fahrzeugbaukörpern (Teil II)


    Beteiligte:
    Sepe, M.P. (Autor:in) / Jansen, J.A. (Autor:in) / Kosarzycki, M.K. (Autor:in)


    Erscheinungsdatum :

    2002


    Format / Umfang :

    4 Seiten, 3 Bilder, 1 Tabelle, 4 Quellen




    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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