The assemblies had been produced domestically in a four cavity mold via an overmolding operation. Failures occurred within assemblies used in a transportation application. 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 this investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the failed components indicated that the cracking was the direct result of severe molecular degradation which occurred during the resin drying and molding operations, in conjunction with stresses induced through thermal shock testing of the parts. This paper reviews some of the testing performed to characterize the failure mode and identify the cause of the cracking while demonstrating the analytical procedure used in a failure investigation. The overmolding material was specified as Rynite (V 415HP, an impact modified 15% glass fiber reinforced poly(ethylene tereplithalate) (PET) resin from DuPont Engineering Polymers. Prior to molding, the virgin resin was dried in a hopper dryer set at 135 deg C. Occasionally, the pellets were dried overnight under these conditions. Following production, the assemblies underwent a series of design verification tests, which included a then-nal shock evaluation. The part failures were observed after 100 cycles of thermal shock testing. Non-failed, suspect assemblies were also evaluated which had been produced from the same lot of resin as the failed parts. Samples of molding resin, representing virgin and dried conditions, were also analyzed as part of the investigation.
Failure analysis of automotive assemblies (Part I)
Schadenanalyse von Fahrzeugbaukörpern (Teil I)
2002
6 Seiten, 8 Bilder, 3 Tabellen, 3 Quellen
Aufsatz (Konferenz)
Englisch
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