Public concern over blast-induced CRACKING has led to the search for a radically new approach to vibration control. The present system, while scientifically correct, is cumbersome to explain. Historically the potential for blast-induced cracking has come to be described through velocity time histories, which are correlated with observation of crack extension under controlled experimental conditions. Unfortunately time histories are simply too difficult for jurors and village or county regulatory boards to understand. Furthermore these arbiters must accept on faith that the observers were unbiased. Since these public bodies control the manner in which blasting activity is adjudicated and regulated, information must be presented in a form they can understand and that is not subject to second-guessing.Automatic, micro-inch measurement of changes in crack width offers an alternative approach to vibration control. This approach directly measures response of that which concerns the public, the CRACKS themselves. When presented in conjunction with environmental effects, changes in crack width presents a direct comparison of blast- with environmentally induced crack response. This direct comparison avoids both the necessity to understand the complexity of particle velocity time histories and believe past correlations of velocity and cracking.This paper describes an experimental system to measure changes in crack width for comparison with blast- and environmentally induced disturbances. Results of the use of the experimental system will also be presented. Micro-inch changes in crack widths are measured with a proximity measurement system that has been developed in conjunction with computerized, numerically controlled (CNC) manufacturing. The robustness of these systems, necessary to survive the manufacturing floor, is more than sufficient for use in homes adjacent to blasting. These proximity devices are able to respond dynamically as well as statically. Thus the same gauge is able to measure the micro-inch changes in crack width produced by long-term in temperature and humidity as well as the dynamic blast induced excitation.
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