Improving sensitivity and coverage of structural health monitoring using bulk ultrasonic waves

Abstract

Practical ultrasonic structural health monitoring systems must be able to deal with temperature changes and some signal amplitude/phase drift over time; these issues have been investigated extensively with low-frequency-guided wave systems but much less work has been done on bulk wave systems operating in the megahertz frequency range. Temperature and signal drift compensation have been investigated on a thick copper block specimen instrumented with a lead zirconate titanate disc excited at a centre frequency of 2 MHz, both in the laboratory at ambient temperature and in an environmental chamber over multiple 20°C–70°C temperature cycles. It has been shown that the location-specific temperature compensation scheme originally developed for guided wave inspection significantly out-performs the conventional combined optimum baseline selection and baseline signal stretch method. The test setup was deliberately not optimised, and the signal amplitude and phase were shown to drift with time as the system was temperature cycled in the environmental chamber. It was shown that the ratio of successive back wall reflections at a given temperature was much more stable with time than the amplitude of a single reflection and that this ratio can be used to track changes in the reflection coefficient from the back wall with time. It was also shown that the location-specific temperature compensation method can be used to compensate for changes in the back wall reflection ratio with temperature. Clear changes in back wall reflection ratio were produced by the shadow effect of simulated damage in the form of 1-mm diameter flat-bottomed holes, and the signal-to-noise ratio was such that much smaller defects would be detectable.

Strain‐Responsive Persistent Room‐Temperature Phosphorescence from Halogen‐Free Polymers for Early Damage Reporting through Phosphorescence Lifetime and Image Analysis

“…While the phosphorescence peaks with vibrational structures are from localized excited triplet ( 3 LE) state. [12] It is noteworthy that a moderate energy gap of 0.4 eV between 1 CT and 3 CT states is observed, which enables intersystem crossing (ISC) from 1 CT to 3 CT (Figure 2c and Figure S15 and Table S2, Supporting Information). The energy of 3 CT state is transferred to ( 3 LE) state through triplet-triplet energy transfer, [12] followed by decaying to ground state (S 0 ) through radiative pathway, giving rise to RTP.…”

“…Early damage reporting of materials is of great importance for preventing major fatal catastrophes in engineering and military fields such as transportation, aircraft, and submarine. [1] The advances in design and synthesis of mechanochromic materials, they suffer from some inherent shortcomings such as subtle signals and requirements for strong external force stimuli. Possible reason is that emission intensity and color are dependent on couples of external factors such as excitation intensity and wavelength, chromophore concentration, distance between excitation source and samples, and are also interfered by autofluorescence from substrates and background light.…”

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common methods for damage monitoring are ultrasonic wave and X-ray imaging, which suffer from bulky and expensive instruments as well as low sensitivity. [1,2] Early damage reporting of materials in a facile manner with high sensitivity still remains a great challenge.Mechanically responsive materials (MRMs), featured remarkable changes in optical property under external mechanical stimuli, have attracted tremendous interest due to their potential applications in deformation sensing, information storage, optical devices, and anticounterfeiting. [3] Among them, mechanochromic (or piezochromic) materials have been widely reported in the literature.

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Ultrasonic Guided-Waves Sensors and Integrated Structural Health Monitoring Systems for Impact Detection and Localization: A Review

“…This approach is also rather simple to implement in sensors with on board embedded processing, but it suffers from the sensitivity to environmental and operational conditions, mainly temperature variations. Recently, Mariani et al [ 45 , 46 ] have proposed a method for the compensation of this detrimental phenomenon. For the electro-mechanical-impedance (EMI) method, the temperature compensation was achieved with some benefits by using artificial neural network (ANN) as reported by Sepehry et al [ 47 ].…”

A Development Strategy for Structural Health Monitoring Applications

“…In some systems, it is possible to employ signal processing methods that eliminate the effect of drift, one example being a bulk wave ultrasound test in which the amplitude of the echo from the back face of the test piece is monitored. In this case, Mariani et al [51] used a method first proposed by Achenbach et al [52] in which instead of using the amplitude of the back wall echo as the measure of structural health, the ratio between successive back wall echoes is employed; the ratio is much less sensitive to drift. However, this technique is only applicable in a limited number of cases, so more research is needed on the problem of sensor drift.…”