The objective of this research program is to explore the possible use of the Positron Annihilator Spectroscopy (PAS) technique for mapping the three-dimensional defect distribution surrounding an extending crack in brittle materials, such as concrete and structural ceramics. PAS is a non-destructive and an in-situ method for quantifying hidden surfaces and defects as small as one angstrom (1/10,000,000,000 meter) in porous media. The proposer, Dr. Chong, and his collaborator, Dr. Cheng, feel that PAS can also be used to measure much larger defects of the orders of micron (1/1,000,000 meter) in dense ceramics and millimeter (1/1,000 meter) in concrete. Neither the X-ray nor the ultrasonic techniques, which are currently under development, provide adequate resolution for such nondestructive inspection (NDI). Large defects ahead of the crack tip in a brittle material will decrease its toughness but clouds of small defects surrounding and behind the crack tip will increase its toughness. Since such controlled defects increase the toughness of a brittle material, it is imperative that the size and location of these defect be known. The PAS technique may provide us with a NDI procedure for this purpose. Dr. Chong, University of Wyoming, is well known for his expertise in rock and concrete fracture and Dr. Cheng, University of Missouri, is well known for his work in PAS. The cooperative research between these two faculty members provide an optimum arrangement for this exploratory study.
