This paper reviews recent advances in sensor technologies for non-destructive testing (NDT) and structural health monitoring (SHM) of civil structures. The article is motivated by the rapid developments in sensor technologies and data analytics leading to ever-advancing systems for assessing and monitoring structures. Conventional and advanced sensor technologies are systematically reviewed and evaluated in the context of providing input parameters for NDT and SHM systems and for their suitability to determine the health state of structures. The presented sensing technologies and monitoring systems are selected based on their capabilities, reliability, maturity, affordability, popularity, ease of use, resilience, and innovation. A significant focus is placed on evaluating the selected technologies and associated data analytics, highlighting limitations, advantages, and disadvantages. The paper presents sensing techniques such as fiber optics, laser vibrometry, acoustic emission, ultrasonics, thermography, drones, microelectromechanical systems (MEMS), magnetostrictive sensors, and next-generation technologies.

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A Systematic Review of Advanced Sensor Technologies for Non-Destructive Testing and Structural Health Monitoring

Experiments and modelling of ultrasonic waves in composite plates under varying temperature

• SHM system, based on guided waves, is investigated under an operating load; • Failure is introduced through a low velocity impact in a real composite structure; • Different FE models are proposed to study different/combined states of the structure; • FE models are assessed against experiments through GW dispersion curves. • The damage sensitivity of the SHM system decreases when the structure is preloaded. Guided wave-based methods for damage detection have been widely investigated as techniques to identify damages and their dimensions in structures. Most of the research activities presented in literature have been performed focusing on simple case studies in a laboratory environment, whereas Structural Health Monitoring systems should be investigated under operational loading conditions. When subjected to an operational load, propagation mechanisms can change, suffering from the interaction between propagating signal and scattered waves due to an initial stress-strain state, and so leading to errors in damage sites estimation. In this work, a numerical model, based on Finite Element approach, is proposed to investigate the effects of an initial stress-strain state, induced by a quasi-static load, on guided-wave propagation mechanisms. The case study consists of a real structure, a blended winglet of a general aviation aircraft. The methodology was assessed with reference to different scenarios. 

A modelling technique to investigate the effects of quasi-static loads on guided-wave based structural health monitoring systems

Ultrasonic guided waves as an indicator for the state-of-charge of Li-ion batteries

Fe analyses for the assessment of the coverage area of a guided waves SHM system

Among the Structural Health Monitoring (SHM) systems, Guided Waves (GW) based ones have been increasingly investigated by both research community and industry since their reliability in damage detection, requirement of a lower power consumption and capability in the monitoring of extended areas with a reduced number of transducers. However, their use in real applications is still challenging. Among the critical aspects that can compromise the effectiveness of such SHM systems in the identification of structural anomalies, the operating conditions (temperature, loads, vibration, corrosion, etc.) require a particular attention. Damage detection algorithms and methods are thought mainly by referring to lower Technology Readiness Levels, typical of laboratory conditions where real scenarios cannot be easily reproduced. For this purpose, the Finite Element (FE) models find a key role for the understanding of the physics of governing phenomena driving the GW also in scenarios closer to the real one. In this paper, an experimentally validated FE model has been used to investigate on the effects of GW propagation mechanisms in a composite plate at 65 ℃. The effects of this in-service temperature have been highlighted by comparing GW dispersive behavior as well as polar plots with respect to the room temperature (20 ℃). According to the results, it has been observed a decrease of GW propagation velocity at 65 ℃. 

Pete Atherton

Papers

Experiments and modelling of ultrasonic waves in composite plates under varying temperature

Simulation of Guided Waves in a CFRP Plate at a Specific Temperature