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It is important to determine and control the clamping force of a bolted joint. Due to its simple setup, the torque control method is typically used to control the clamping force when tightening bolts. After tightening, hammer tests, ultrasonic techniques and methods employing sheet materials as sensors are often used. Many methods have been proposed, but using them to determine and control the clamping force during or after tightening bolts is labor intensive or expensive. Here we conduct impact tests with an impulse hammer combined with experimental modal analysis to determine the clamping force by interpreting the change in the local mode frequency of a bolt head in the high frequency region as a function of the clamping force. To demonstrate the applicability of our method, we also investigate its limits with regard to bolt sizes. Keywords Vibration • Non-destructive testing • Clamping force • Bolted joint • Experimental modal analysis IntroductionMultiple bolts are often used to join or restrain the components of a structure. Because loosening of these bolts may damage the structure, it is important to be able to monitor and control the clamping force of bolted joints [1]. Methods Naoki Hosoya B

The authors have proposed an analyzing method for vibration testing based on impulse excitation by laser ablation in order to experimentally identify dynamic characteristics of micro devices such as HDD head actuators or MEMS that have in the high frequency region the natural frequencies of a few tens of kilohertz. This paper proposes a method that makes it possible to analyze FRF by only measuring the output (acceleration response) in a laser excitation experiment.This enables the measurement of the force input sensorless. First, the laser excitation force is normalized by Newton's second law using a rigid block. Next, the laser excitation experiment with an object structure having a natural frequency within the high frequency region is conducted. Complex Fourier spectrum obtained by Fourier transforming the measured response is divided by the estimated laser excitation force. Finally, since the trigger position of the response and the time the impulse input is actually applied have errors, phase characteristics of the force-regulated complex Fourier transform is modified by taking the dead time included in the response into account, resulting in the FRF of the structure. The effectiveness of the proposed method is demonstrated by the vibration test with an aluminum block as object structure.

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