Strain Monitoring

Abstract

This chapter provides an overview of the use of strain sensors for structural health monitoring. Compared to acceleration-based sensors, strain sensors can measure the deformation of a structure at very low frequencies (up to DC) and enable the measurement of ultrasonic responses. Many existing SHM methods make use of strain measurement data. Furthermore, strain sensors can be easily integrated in (aircraft) structures. This chapter discusses the working principle of traditional strain gauges (Sect. 8.1) and different types of optical fiber sensors (Sect. 8.2). The installation requirements of strain sensors and the required hardware for reading out sensors are provided. We will also give an overview of the advantages and the limitations of commonly used strain sensors. Finally, we will present an overview of the applications of strain sensors for structural health monitoring in the aeronautics field.

Characterization of Biocomposites and Glass Fiber Epoxy Composites Based on Acoustic Emission Signals, Deep Feature Extraction, and Machine Learning

“…Sensors 2022, 22, x FOR PEER REVIEW 6 of 17 the acoustic wave through the optical sensor, the vibration is transferred to the sensing mandrel and then to the coiled fiber around it. The resulting interferometric signal is transferred to the OptimAE readout box for signal acquisition, demodulation of the acoustic emission (AE) signal, and communication to a computer with OptimAE software for acoustic event detection and further processing [22]. The threshold for signal acquisition was set to 0,6 nm to avoid noise at low temperatures.…”

“…They have some limitations that narrow down their application in harsh environments. FOS in comparison to conventional piezoelectric sensors offers simplified integration with little interference into a wide variety of structures of different materials, resistance to electromagnetic interference, lower weight, and broader sensing capabilities, such as strain, pressure, and temperature in addition to AE [21][22][23]. The components of optical fiber systems are optical sources, i.e., laser, laser diode or LED, optical fibers, that sense elements to transduce the measurement to an optical signal, an optical detector, and a processing unit in the form of an oscilloscope or optical analyzer [24].…”

Temperature compensated strain sensor in fused silica by femtosecond laser inscription

“…The wings of aeroplanes endure significant stress and strain during flight, especially during take-off and landing. [6][7][8] Apart from the condition monitoring, as mentioned above, strain information can provide insight into the behaviour of the wing, which can be helpful in the design phase of an aeroplane. A different field where strain sensing provides significant added value is in process monitoring and quality control.…”

Piezoresistive Fibers with Large Working Factors for Strain Sensing Applications

“…Essentially, W relates to the low strain piezoresistive linear relationship for nanocomposites undergoing uniaxial tensile deformation. − Such linearity is well demonstrated in conventional metallic strain gauges . This has allowed their easy installation as strain sensors to determine magnitudes of principal surface strains and residual stresses in rigid mechanical structures. , However, metallic strain gauges show extreme stiffness of ∼3 GPa, , low values of G ∼ 2–4, and small values of W ∼ 0.04 . This renders it difficult for these devices to be applied as strain sensors for wearable technology where compliance and flexibility are vital requirements …”