| While polymer based materials offer many beneficial properties, they are inherently susceptible to environmental degradation over time. This type of degradation, especially for thermal oxidative aging, occurs predominantly within a thin surface layer often less than 200 mum thick. A nondestructive technique for characterizing this layer has been developed that uses high resolution laser detection of displacements generated by a surface traveling ultrasonic Rayleigh wave. This research evaluates the potential of the technique to quantify the degree and depth of surface degradation caused by thermal aging. Rayleigh surface waves are useful because the measurement parameters depend directly on the mechanical properties of the degraded material, and the frequency of operation determines the ultrasonic depth of penetration. The measurements show sensitivity to polymeric thermal degradation, and feasibility is demonstrated for measuring surface layer depth with a frequency sweep. This research establishes the fundamental relationships between the developed ultrasonic procedures and its potential applications to thermal oxidative polymeric aging through finite element simulation, a representative aging experiment, and appropriate data analyses. |
