Uniformity of Deterioration and Virtual Human Visual Evaluation
As shown in Fig. 10, the cracked sealant surfaces display the least surface uniformity. Specimens with severe dirt pick-up rated lower than the cracked specimen in surface uniformity, but higher than other samples with less dirt pick-up. It is obvious that the retained dirt particles render nonuniformity. It should be noted that this analysis yields different ratings than the overall surface texture discussed earlier.
The perceptual biases and limitations inherent in evaluations conducted by the unaided human eye may be overcome through the use of optical imaging and software analysis technologies that are available today. The application of such technologies can provide improved accuracy and objectivity in evaluation results across the entire field of visual evaluation. The current study of weathered sealant samples that had been exposed for a relatively long period of time (6.8 years in Japan) showed that an Optical Imaging/Image Analysis System, Atlas VIEEW™, is capable of quantifying four distinct surface defects in the samples. These surface detects are cracking (crazing), visual color change, spatial uniformity of deterioration (due to dirt pick-up and uneven color changes, or both), and overall surface texture. Chalking and dirt pick-up, as rated visually prior to this evaluation, could not be accurately assessed with the digital imaging technique.
The analysis shows that surface cracking and crazing generally can be well characterized using the automated VIEEW™ system. The study also confirms that judging color changes visually is problematic, since cracking and crazing interferes with color judgment. Further investigations are needed to develop an automated surface characterization method for sealants.