Acoustic monitoring and structural damage evaluation of tensile fracture in various materials using optical fiber sensing

Acoustic emission (AE) technology is a crucial approach for ensuring the safe operation and maintenance of underground spaces. Traditional mechanical and piezoelectric AE sensors often fail to meet the monitoring requirements of complex underground environments. In this paper, a novel AE monitoring system based on a Michelson interferometer is designed and applied to monitor the tensile fracture processes of common materials (coal, concrete, quartzite, and granite) in various underground engineering projects. Signal noise reduction and feature parameter extraction of the waveform data collected by the optical fiber AE sensor are performed. The time series, frequency domain characteristics, and crack fracture modes of the optical fiber AE signals were analyzed, and the precursor characteristics of tensile fractures were extracted. The results indicate that the optical fiber AE system possesses high sensitivity, a wide frequency band response, and a large dynamic range, enabling it to effectively identify AE waveform characteristics and primary frequency differences generated in various rock fracture experiments. The AE count and energy evolution patterns are in good agreement with the material stress curves, effectively quantifying the material damage evolution processes. The proportional distribution of tensile and shear cracks in different materials was successfully classified using fiber AE waveforms. Based on the changing trends of the b-value, variance, and autocorrelation coefficient, a failure early warning mechanism was constructed, categorizing failure early warnings into three time levels: trend early warning, initial early warning, and critical early warning. This study provides a new and effective monitoring method for the safety development of deep engineering.