Brillouin scattering-based distributed fiber optic sensing (Brillouin-DFOS) technology is widely used in health monitoring of large-scale structures with the aim to provide early warning of structural degradation and timely maintenance and renewal. Material cracking is one of the key mechanisms that contribute to structural failure. However, the conventional strain measurement using the Brillouin-DFOS system has a decimeter-order spatial resolution, and therefore it is difficult to measure the highly localized strain generated by a sub-millimeter crack. In this study, a new crack analysis method based on Brillouin scattering spectrum (BSS) data is proposed to overcome this spatial resolution-induced measurement limitation. By taking the derivative of the BSS data and tracking their local minimums, the method can extract the maximum strain within the spatial resolution around the measurement points. By comparing the variation of the maximum strain within the spatial resolution around different measurement points along the fiber, cracks can be located. The performance of the method is demonstrated and verified by locating and quantifying a small gap created between two wood boards when one of the wood boards is pushed away from the other. The test result verifies the accuracy of the crack strain quantification of the method and proves its capability to measure a sub-millimeter crack. The method is also applied to a thin bonded concrete overlay of asphalt pavement field experiment, in which the growth of a transverse joint penetrating through the concrete–asphalt interface was monitored. The method successfully locates the position, traces the strain variation, and estimates the width of a crack less than $0.1 \hspace{0.17em}\text{mm}$ wide using a Brillouin-DFOS system with $750 \hspace{0.17em}\text{mm}$ spatial resolution.

基于布里渊散射的分布式光纤传感（Brillouin-DFOS）技术广泛应用于大型结构的健康监测，旨在提供结构退化的预警和及时的维护和更新。材料开裂是导致结构失效的关键机制之一。然而，使用布里渊-DFOS 系统的常规应变测量具有分米级空间分辨率，因此难以测量亚毫米裂纹产生的高度局部化应变。在这项研究中，提出了一种基于布里渊散射光谱 (BSS) 数据的新裂纹分析方法，以克服这种空间分辨率引起的测量限制。通过获取 BSS 数据的导数并跟踪它们的局部最小值，该方法可以提取测量点周围空间分辨率内的最大应变。通过比较光纤上不同测量点周围空间分辨率内最大应变的变化，可以定位裂纹。该方法的性能通过定位和量化当一个木板被推离另一个木板时在两个木板之间产生的小间隙来证明和验证。测试结果验证了该方法裂纹应变量化的准确性，证明了其测量亚毫米裂纹的能力。该方法还应用于沥青路面现场试验的薄粘结混凝土覆盖层，其中监测穿过混凝土-沥青界面的横向接缝的生长。该方法成功定位位置，$0.1 \hspace{0.17em}\text{毫米}$ 使用 Brillouin-DFOS 系统 $750 \hspace{0.17em}\text{毫米}$ 空间分辨率。