University of Connecticut |
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IMS Associates Program Annual Meeting - May 17, 2006The IMS Associates Program Annual Meeting will be held on Wednesday, May 17, 2006. Representatives from all member companies and invited guests are encouraged to attend. Associates Program Annual Meeting
Wednesday, May 17, 2006 Unexpected and unusual failures are presented in five categories: 1. Production or processing of polymers 2. Assembly of polymers into products 3. Unauthorized or unexpected change in composition 4. Service conditions 5. Synergistic effect of two stresses acting simultaneously Failures can occur for practically any polymeric material in various ways and at various stages of manufacture, assembly and service. A risk/benefit assessment including worst case possibilities might prevent some failures. Unexpected and unusual failures will continue to surprise and plague us, such as the disintegration of a polyethylene liquid waste container. One person put toluene in and another nitric acid unbeknownst to each other. Over time nitrotoluenes that formed exploded. We can learn from failures to be alert to similar situations of composition, service conditions and all factors that together may make for success or failure with plastics and rubbers. Interfaces between components in composite materials are often sites for defects formed during and after materials processing. "Unexpected" product failures can be minimized by using fundamental principles of polymer science to anticipate how the materials will respond to the stresses of processing and service conditions. The potential for brittle failure of particulate rubber-toughened nylon composites will be anticipated by examining how their morphology might affect the formation and propagation of stress cracks and then quantifying the material properties and processing conditions necessary to minimize the potential for catastrophic failure. A second example, the determination of material properties required for maximizing the reliability of heat-welded polymeric joints, will be analyzed by relating the molecular dynamics of interface formation to material properties that might lead to a weak interface. The so-called Arrhenius theory, which derives from the concept of an energy barrier in a chemical reaction pathway, has been applied widely to polymer aging problems. Over a temperature range free of 1st-order transitions in the polymer, it is extremely difficult to gather data that is sufficient to reject this simple hypothesis. However, a recently completed fifteen-year project supported by the Electric Power Research Institute has resulted in what appears to be compelling evidence that the laboratory aging of certain elastomeric materials cannot be used to predict the aging rate under actual application conditions. The only way to gain sufficient precision for hugely scattered natural aging data was to ratio two properties of the material and follow this ratio as the materials aged.
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