Structural Crack Detection Using DPP-BOTDA and Crack-Induced Features of the Brillouin Gain Spectrum

Abstract

Structural damage generally initiates in the form of structural cracks. Thus, developing efficient crack detection techniques is of great importance for the structural health monitoring. In this paper, a new crack identification method is proposed, which is based on the differential pulse-width pair Brillouin optical time domain analysis (DPP-BOTDA) technology and the irregular features of Brillouin gain spectrum (BGS) in the fiber due to structural cracks. The proposed method provides a new way to detect and quantify structural cracks without knowing the strain in the structure. First, the working mechanism of DPP-BOTDA is introduced to illustrate the reason that the DPP-BOTDA, compared to traditional BOTDA technique, can significantly improve the spatial resolution of distributed strain sensing, which is critical for structural crack detection. Then, the BGSs in the fiber with the presence of structural cracks, measured by the DPP-BOTDA, are numerically simulated, from which the crack-induced irregular features of the BGS are summarized. Based these irregular features, new structural crack detection and quantification methods are proposed, which are found to be independent of structural stain. Finally, an experiment is conducted on a simple supported reinforced concrete (RC) beam. The results demonstrate that by using the BGS measured by the DPP-BOTDA, the proposed structural crack identification method successfully detects the occurrence of structural cracks and relatively accurately predicts the crack widths.

FPGA-based fast pulse coding and decoding technique for Brillouin optical time domain analyzer

“…Among them, Brillouin optical time-domain analyzers (BOTDA) can be used for distributed measurements of temperature and strain. Compared with the Brillouin optical time-domain reflectometer (BOTDR) and the Raman optical time-domain reflectometer (ROTDR), BOTDA has an advantage on long distance sensing, and is widely used in the field of structure monitoring 1 , construction monitoring 2 , disaster warning 3 , geological measurement 4 and so on.…”

Characterization of OFDR distributed optical fiber for crack monitoring considering fiber-coating interfacial slip

“…Reinforced concrete (RC) structures usually experience various types of cracking during their service lives due to either material or structural causes, such as early stage cracking from concrete shrinkage, 1 service stage cracking induced by overloading, 2 thermal expansion and contraction, 3 freezing and thawing, 4 uneven settlement, 5 and corrosion of steel reinforcement. 6,7 Crack reflects the integrity of RC structures and is an indication of structural health condition.…”

“…18 Other techniques such as differential pulse-width pair BOTDA (DPP-BOTDA), which uses the differential Brillouin gain of two pump pulse lights, was also utilized to detect structural cracks. 2 In contrast to BOCDA and BOTDA, which are based on Brillouin backscattering, frequency domain systems based optical frequency domain reflectometry (OFDR) provide high spatial resolution in the order of submillimeter. For this reason, OFDR has received more attention in structural heath monitoring applications compared with time domain based counterparts.…”

Application of Dual-Frequency Self-Injection Locked DFB Laser for Brillouin Optical Time Domain Analysis

“…Unlike single-point optical fiber sensors [ 2 , 3 ], distributed optical fiber sensors can interrogate and spatially resolve measurands along an optical fiber due to their specific sensing mechanisms [ 4 , 5 , 6 , 7 ]. Among them, Brillouin-based distributed sensors [ 8 , 9 , 10 ] have attracted immense interest in recent years in fields such as the health monitoring of large structures in oil and gas pipelines [ 11 ], railways and high-voltage transmission lines [ 12 ], high-temperature distributed measurement in industrial applications [ 13 ], distributed strain measurement for cracks detection [ 14 ], and structural health monitoring [ 15 ]. The conventional distributed Brillouin optical fiber sensing is based on the backward-stimulated Brillouin scattering, where the strain or temperature is a linear function of the Brillouin frequency shift (BFS) and so can be recovered from the distribution of Brillouin gain spectra (BGS) along the sensing fiber [ 16 , 17 ].…”