Abstract
An ultrasonic bolt axial force inspection system is developed for the control of bolts used on turbine outercasings in a thermal power plant. The ultrasonic time of flight through the bolt under stress is analysed by using the acoustoelastic law. It turned out that the proportional constant, conventionally called the material constant, is determined by an acoustoelastic constant k and Young's modulus E as 1-kE. Measurements of k for some kinds of steel bolts revealed that k is approximately the same value (-1.1×1011 m2/N) without concerning heat treatment. Based on these results, an ultrasonic bolt axial force inspection system is developed. Applying this system to turbine bolts, it is found that the bolts could be controlled more precisely than ever.
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