PHYSICAL AGING IN POLYMERS AND POLYMER COMPOSITES - AN ANALYSIS AND METHOD FOR TIME-AGING TIME SUPERPOSITION

The ability to include the effects of physical aging is critical to th e design of engineering structures involving advanced polymers and pol ymer composites. Physical aging, a phenomenon caused by material evolu tion towards thermodynamic equilibrium, is typically described by redu cing short-term momentary compliance curves, via time-aging time super position, into a predictive reference curve and shift factor function. This paper presents an analytic method based on error minimization fo r this data reduction task, and introduces the concept of a total refe rence curve as an alternative to choosing a single momentary curve for the reference. Four different predictive approaches are considered to determine the efficacy of the total reference concept, and whether ve rtical shifting is beneficial. For most of the materials studied, the total reference using horizontal shifting alone is the recommended met hod; in the few remaining cases, the total reference procedure with bo th horizontal and vertical shifting resulted in the best outcome.