indication of impending materials state changes than what is provided by knowledge of the instantaneous condition.

However, in general, the nature of materials degradation is such that localization is more problematic than more extensive overall degradation. For example, corrosion resulting in a pit might be more problematic than uniform metal loss due to stress concentration caused by the localized loss of metal in the pit.

Efforts of the author and others to develop methods to detect and track material degradation preceding detectable crack formation, as well as variations in material condition associated with precipitation hardening, include early work to monitor the influence of mobile dislocation populations on ultrasonic attenuation; efforts to use continuous monitoring of changes in ultrasonic attenuation to detect degradation preceding crack formation during cyclic loading of 7075 Al; combined continuous monitoring of changes in ultrasonic attenuation and acoustic emission for the early detection of life-limiting fatigue damage; continuous monitoring of ultrasonic plate waves to track damage development in fiber-reinforced laminated composite materials; and practical limitations with using nonlinear ultrasonic response to monitor precursor fatigue damage in metal alloys. The issue of measurement scale and critical flaw size is discussed in this context.

In addition, the potential of electromagnetic, mechanical, and thermal assessment of surface and near-surface condition is discussed with regard to point and multipoint (array) measurements for assessing work hardening, alloy variation, nonuniform cyclic, residual stress mapping, and alloy variation.

Finally, the notion of developing components from sensible material “particles” that facilitate state awareness polling or reporting is proposed as a way to overcome practical physical measurement limitations on the atomic scale. The importance of sustainable design in this context is emphasized.



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