24 July 2001 Effect of bending on ultrasonic preload measurements in bolts
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An ultrasonic pulse/echo technique is used to measure tensile preload on the umbilical flange joint bolts of the space shuttle orbiter. The ultrasonic instrument measures the round trip pulse travel time through the length of bolt. The pulse travel time increases with the applied load. The umbilical bolts experience bending loads in addition to the tensile load. The bending load affects the preload readings. The paper provides simplified theoretical derivations to explain the effect of bending on ultrasonic measurements. The bending loads cause rotation and translation of the ultrasonic pulse reflecting face. The bending also causes stress gradient in bolts. These effects cause phase gradient and physical shift in the received ultrasonic beam across the face of transducer, distorting the ultrasonic signal and introducing errors in the preload readings. A number of experiments were performed on the bolt to study the effect of bending combined with variation in transducers, bolt end designs and configurations. The bolt end design of the operational bolts was modified to reduce error in the readings. The paper provides explanation of the effect of bending in ultrasonic preload measurements and suggests approaches to minimize their effect.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ajay M. Koshti, Ajay M. Koshti, } "Effect of bending on ultrasonic preload measurements in bolts", Proc. SPIE 4335, Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring, (24 July 2001); doi: 10.1117/12.434168; https://doi.org/10.1117/12.434168

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