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1 April 2019 Rockbolt monitoring by means of guided waves
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Abstract
In this paper we present principles of NDE and structural health monitoring (SHM) of rockbolts using ultrasonic guided waves. Specialized techniques and instruments are presented that apply low frequency ultrasound to investigate bolts status, especially its load imposed by movements of the surrounding rock. Guided waves (GW) that propagate in real rockbolts are dispersive and multimodal. The technique based on the use of modal resonances in bolts is presented. In this technique an application tailored ultrasound probe is employed that transmits the high-energy, low frequency (below 100kHz) guided waves and is capable of receiving weak echoes reflected from the bolt-end. The received end-echoes are amplified and sent back in the sing-around mode. The echo, related to the selected guided wave mode, will generate resonant oscillations with frequency that depends on the velocity of that wave mode, bolt's length and also, in result of the acoustoelastic effect, its load. The latter effect can be used for the evaluation of the load imposed on the bolt by means of the sing-around setup that converts wave velocity to the frequency of self-oscillations. In practical applications the frequency band has to be limited by a suitable band-pass filter to avoid frequency jumps due to the presence of resonances generated by other wave modes. Simulation results are presented that facilitate the choice of the frequency band where the acoustoelastic effect is significant and the frequency jumps can be minimized.
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© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Tadeusz Stepinski "Rockbolt monitoring by means of guided waves", Proc. SPIE 10972, Health Monitoring of Structural and Biological Systems XIII, 109721C (1 April 2019); https://doi.org/10.1117/12.2513807
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