Strain-based non-intrusive approaches for measuring the pressure of pipes have attracted widespread attention due to their great convenience and ability to avoid destroying the integrity of structures. However, the mentioned method usually measures the dynamic pressure based only on the static strain–pressure sensitivity coefficients (SSSCs) instead of the dynamic strain–pressure sensitivity coefficients (DSSCs) due to its complicated calibration, which will inevitably affect the accuracy significantly. To address this issue, a model-driven scheme with dual stages is proposed in the present study to compensate the dynamic pressure measurement. The DSSCs are analytically derived for the first time from the axial governing equations of the pipe, considering the general boundary conditions for the thin-walled and thick-walled pipes simultaneously. In the first stage, the physical parameters involved in the DSSCs are calibrated by minimizing the residual of the experimental results and the theoretical counterparts. In the second stage, the DSSCs calculated from the calibrated analytical model are utilized to compensate the dynamic pressure based on the relationship between the DSSCs and the SSSCs. The proposed method is applied to an industrial hydraulic pipe system, and the experimental results show that the relative error is reduced greatly after the compensation is implemented, demonstrating the validity of the proposed compensation method.

The small and light-weight pipeline is widely used in hydraulic system for aerospace engineering. The crack is one of the most common failures in the pipelines so that its incipient detection can further avoid the catastrophic damage of the piping system. The electrical and piezoelectric sensors are conventionally used for the structural health monitoring (SHM), while these are not suitable for the cascaded pipelines in harsh environment because the added mass will change the modal characteristics of the cascaded pipelines. The Fiber Bragg Grating (FBG) sensor with light-weight, multiplexed, and anti-electromagnetic interference properties, are employed to obtain the modal strain transmissibility with a novel diagram of the operational modal analysis (OMA). Based on the OMA an enhanced damage indicator is proposed to detect the crack. After going through analytical modeling, finite element modeling (FEM) and its corresponding experiments, it is concluded that the presented method is effective and accurate to detect and locate the crack.

Ensuring the safety and optimal performance of hydraulic pipelines, particularly in aircraft, is of paramount importance. The challenge of detecting incipient looseness in fasteners within a time-varying temperature environment has garnered widespread recognition, making it a focal point in the field of structural health monitoring. In this study, we propose an innovative solution—a smart clamp based on Fiber Bragg Grating (FBG). This clamp aims to detect incipient looseness in hydraulic pipe systems by measuring its macro strain. Notable advantages include its ability to avoid the chirping of the FBG, the ease of building a distributed sensing network, especially for the blind-hole connected structure, and its applicability for monitoring clamps connected with small-diameter bolt. The analytical model of the clamp under the preload of the connected bolt, along with the unique condition for the measurement, is provided. Demonstrating a force resolution 0 . 1 kN , the clamp exhibits a strong capability in detecting incipient looseness. Furthermore, environmental temperature interference is mitigated by configuring two FBGs. Conducting application experiments in a hydraulic system, the results indicate that the proposed clamp can effectively detect the loosening and tightening processes in real time, even under the time-varying temperature environment.

This article presents the design, modeling, and application of a miniature tri-axis tip force sensor with fiber Bragg grating (FBG) for cardiac ablation. A compliant mechanism (CM) composed of thin-walled beams is designed to convert the distal forces applied at the tip of the sensor to the variations of the wavelengths of the FBGs. The CM design reserves the middle channel for an optical fiber used in laser ablation (LA). The differential principle is utilized to eliminate the impact of the environmental temperature on orthogonal forces (${{f}_x},\ {{f}_y}$, and ${{f}_z}$). The uniqueness condition for the measurement of forces and temperature is established. To enable rapid iteration of sensor design, an accurate and efficient reduced-order global transfer matrix method is proposed to develop the unified statics/dynamics model of the sensor. Static calibration experiments reveal resolutions of $11.6{\rm{\ mN}}$, $4.7{\rm{\ mN}}$ and $6.2{\rm{\ mN}}$ for $ - x$, $ - y$, and $ - z$ axes, respectively. The force ranges are $0--2\mathrm{N}$ and $ - 1\sim 1\mathrm{N}$ for axial and flexural directions. Modal test shows the 1^st natural frequency of 1071.6 Hz. Linearity, repeatability, and hysteresis errors are below $5.3{\rm{\% FS}}$. A novel application involving LA with the designed sensor on an ex vivo tissue from a pig heart was conducted to help understand the thermomechanical interaction between the laser and the tissue.