With the widespread application of FRP (Fiber Reinforced Plastics) materials in fields such as wind turbine blades and ships, the safety performance of these materials during their service life has garnered signification attention. This study employs the fiber Bragg grating (FBG) sensor to monitor damage of the FRP materials. An FRP plate embedded with six FBGs was fabricated, and different degrees of damage were induced in the FRP plate. The six FBGs measured the damage information of the FRP plate under impulse and continuous sinusoidal vibration loads. The results demonstrate that both the strain information and the frequency shift information measured by the FBG sensors can effectively and sensitively identify damage in the FRP plate.

Leveraging the sensitivity of long-period fiber grating (LPFG) to changes in the environmental refractive index, an LPFG-based seawater concentration monitoring sensor is proposed. Considering the highly saltine and alkali characteristics of the sensor’s operating environment, the proposed sensor is packaged by basalt fiber-reinforced polymer (BFRP), and the sensor’s sensitivities were studied by sodium chloride and calcium chloride solution concentration experiments and one real-time sodium chloride solution concentration monitoring experiment. The test results show the wavelength of LPFG, a 3 dB bandwidth and a peak loss of LPFG’s spectrogram change with changes in the concentration of sodium chloride or calcium chloride solutions, but only the wavelength has a good linear relationship with the change in solution concentration, and the sensing coefficient is −0.160 nm/% in the sodium chloride solution and −0.225 nm/% in the calcium chloride solution. The real-time monitoring test further verified the sensor’s sensing performance, with an absolute measurement error of less than 1.8%. The BFRP packaged sensor has good corrosion resistance and a simple structure, and it has a certain application value in the monitoring of salinity in the marine environment and coastal soil.

The overlying rock layers in a mining area may collapse or settle, subjecting pipelines to uneven forces that can lead to deformation or even fracture. This paper proposes a pipeline safety monitoring method that combines fiberoptic vibration and strain sensing to detect vibrations and deformations caused by rock layer collapse in mining zones. First, pipeline deformation monitoring under unknown force directions was investigated using fiber Bragg grating (FBG) sensing technology. Second, we constructed a mining area pipeline model and conducted vibration/deformation monitoring tests employing FBG sensors, distributed Brillouin strain sensing, and distributed fiberoptic vibration sensing technologies. The experimental results demonstrate that FBG sensor arrays deployed at 90-degree intervals can effectively identify the pipeline’s primary force direction and maximum strain, with direction angle errors of less than 5.2%. The integrated analysis of vibration and strain data enables accurate identification and measurement of extended vibration responses and pipeline deformations in open-air zones. This study establishes a comprehensive monitoring framework for ensuring pipeline safety in mining areas.

To resolve the discrepancy between the measured strain and the actual surface strain of wind turbine blades when using rubber-encapsulated fiber Bragg grating (FBG) sensors for strain monitoring, this study establishes a surface-bonded strain transfer model for such sensors. The total strain transfer efficiency of the sensor is decomposed into two components: the strain transfer efficiency from the rubber substrate to the FBG core (encapsulated grating strain transfer efficiency) and that from the wind turbine blade to the rubber substrate (strain transfer efficiency between the rubber substrate and the blade). Based on the theory of mechanics of materials, the strain transfer equation is derived, and the key factors influencing strain transfer efficiency—FBG bonding length and rubber substrate thickness—are analyzed via the control variable method. Three ethylene propylene diene monomer (EPDM)-encapsulated FBG sensors with rubber substrate thicknesses of 3 mm, 4 mm, and 6 mm were fabricated. Tensile strain transfer tests were conducted using fiber-reinforced plastic (FRP) strips to simulate the material properties of wind turbine blades, so as to validate the effectiveness of the proposed model. The experimental results demonstrate that the strain transfer efficiency of the sensor increases with the extension of FBG bonding length and decreases with the increase in rubber substrate thickness, with 4 mm determined as the optimal substrate thickness for EPDM-encapsulated FBG sensors. On the basis of the aforementioned findings, an EPDM-encapsulated FBG strain rosette sensor was developed, which can effectively measure the complex stress of a wind turbine blade model. This study provides a theoretical foundation for the structural design and engineering application of rubber-encapsulated FBG sensors in the strain monitoring of wind turbine blades.

Subgrade deformation under load is accumulated from the local compressive strain of each layer. Solely relying on the overall settlement monitoring at the top surface makes it difficult to reveal the internal strain distribution and the evolutionary characteristics of early damage. Therefore, acquiring the local compressive strain field along the depth direction is of great engineering significance for subgrade condition assessment and safety early warning. In this paper, a vertically installed FBG sensor (VI-FBG) with GFRP packaging suitable for layered strain measurement of subgrade is developed. The effectiveness of the sensor is verified by direct compression tests and compressive strain tests with the sensor embedded in concrete. Furthermore, the sensor was buried in the subgrade of a high-speed railway to carry out strain monitoring. The test results show that the sensor has favorable sensing performance, with a strain sensitivity of 1.2 pm/με and a temperature sensitivity of 16.84 pm/°C. The measured compressive strain of concrete is in good agreement with the theoretical value, and the relative error is less than 8%. The field monitoring data can truly reflect the vertical compressive strain during subgrade filling. The measured time-history curve exhibits good consistency with the displacement time-history curve obtained by the adjacent FBG settlement sensor. This study verifies that the sensor is applicable to the monitoring of local vertical compressive deformation of subgrade, and its GFRP encapsulation endows it with good engineering applicability.

Wind turbine blades serve as the core components of wind energy conversion systems, and their safe and stable operation is pivotal to the operational efficiency and reliability of wind farms. However, prolonged operation in harsh environmental conditions such as strong winds, heavy rainfall, ultraviolet radiation, and temperature fluctuations renders wind turbine blades susceptible to fatigue damage and structural failure. Aiming at the drawbacks of traditional electromagnetic sensors, including their vulnerability to lightning strikes and poor corrosion resistance, as well as the elastic modulus mismatch between existing fiber Bragg grating (FBG)-encapsulated sensors and wind turbine blade structures, this study selects the ethylene–propylene–diene monomer (EPDM) as the encapsulation material to develop EPDM-FBG strain sensors. The effectiveness of the proposed sensor in blade strain monitoring is ultimately verified via static load model tests on small-scale wind turbine blades. Test results demonstrate that the EPDM-FBG strain sensor exhibits excellent static strain sensing performance, with its test results being highly consistent with those of bare FBG sensors and a relative error of less than 5%, which can fully meet the practical requirements of static strain monitoring for wind turbine blades. This research provides a novel and reliable monitoring method for the health monitoring of wind turbine blades.