Evaluation of Bolt-Nut Fastening Condition Using Nonlinear Ultrasonic Components

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This study examines the use of ultrasonic second harmonic components in the quality control of bolt-fastened structures. An improved method for detecting the second harmonic components, from a bolt fastened with a nut, using the transmission method is constructed. A hexagon head iron bolt was used in the experiments. The bolt was fastened using a digital torque wrench. The second harmonic component increased by approximately 10 dB before and after the bolt was fastened. The sources of second harmonic components were contact acoustic nonlinearity in the screw thread interfaces of the bolt-nut and were the plastic deformation in the bolt with fastening bolt. This result was almost same compared with previous our method. Moreover, increase values of second harmonic components are changed at the normal axial force. Consequently, usefulness of the novel method for detecting second harmonic ultrasonic components generated from fastened bolt was confirmed.