Carbon Fiber Reinforced Polymers (CFRPs) have become an essential part of designing and engineering lightweight rigid bodies, predominantly in the aerospace and automotive industries. Typical epoxy based CFRPs exhibit virtually no plasticity with minimal strain to failure. Although CFRPs have high specific strengths and elastic moduli, the brittle fracture mechanism presents unique challenges in failure detection for the US Army’s vertical lift vehicle components since failure can occur catastrophically. The Army currently uses a “safe-life” interval-based service methodology where components are replaced with regards to a usage spectrum rather than the component’s actual state of structural health. This paper explores a method for solving this problem by investigating the possibility of embedding Terfenol-D particles (∼100 microns in diameter), a magnetostrictive material, into the CFRP’s ply interphase for embedded non-contact, real-time, structural health monitoring. For baseline results, the change in localized (32 mm 2 field of view) magnetic flux was only 0.02% for an applied load of 0–100% of the material’s ultimate tensile strength (UTS). For quasi-static testing procedure on specimen 5714 (15 wt.% Terfenol-D embedded CFRP) on a 0–40% loading interval of the material’s UTS, there was an observed localized (32 mm 2 field of view) magnetic flux gradient of more than 5 mT (4%) with a reversible flux of 100%. For quasi-static testing procedure on specimen 5714 (15 wt.% Terfenol-D embedded CFRP) on a 0–70% loading interval of the material’s UTS, there was an observed localized (32 mm 2 field of view) magnetic flux gradient of more than 3 mT (2%) with a reversible flux of only 25%. Terfenol-D embedded CRFPs have shown promising results for detecting instantaneous strain and degradation levels. Acoustic emission (AE) and X-ray computed tomography (CT) scanning were used to validate the observed results.

As the field of Structural Health Monitoring (SHM) expands to spacecraft applications, the understanding of environmental effects on various SHM techniques becomes paramount. In January of 2013, an SHM payload produced by New Mexico Tech was sent on a high altitude balloon flight to a full altitude of 102,000 ft. The payload contained various SHM experiments including impedance measurements, passive detection (acoustic emission), active interrogation (guided waves), and wireless strain/temperature sensing. The focus of this paper is the effect of altitude on the active SHM experiments. The active experiment utilized a commercial SHM product for generation and reception of elastic waves that enabled wavespeed measurements, loose bolt detection, and crack detection through the full profile of the flight. Definite deviations were observed in the data through the stages of the flight which included a ground, ascent, float, and descent phases. Several elements of the high altitude environment can have an effect on the measurement such as temperature and pressure. The flight data was compared against a ground altitude baseline and heavy emphasis is placed on comparing changes in the data with the temperature profile of the flight. Conclusions are drawn on the effect of altitude on wavespeed of elastic waves, crack detection, and the sensing of a loose bolt.

Filament wound composite pressure vessel with thin-wall alloy liner might exist local buckling during manufacture and in service, this phenomenon have great influence on the security and service lifetime of pressure vessel. AE (acoustic emission) technique is employed to monitor the damage progression of the vessel during hydraulic pressure experiment. Two sensors of acoustic emission (AE) were attached to front dome and cylinder to monitoring the behavior of the vessel bearing maximum 4.5MPa water pressure during loading, keeping load and unloading. Meanwhile ten strain gauges were bonded to front dome, equator and cylinder of the outer surface by meridian and hoop direction respectively in order to monitor the vessel deformation characters. Analysis show that strain gauges is suitable for evaluate deformation character of the outer surface of the vessel. Analysis indicated AE is more suitable to monitoring the damage propagation of the vessel. AE analysis explained the local buckling of inner thin-wall liner.

Advanced signal processing approaches such time-frequency analysis are widely used for online evaluation, damage detection, and wear state classification. The idea of this paper is to introduce a new methodology for online examination of wear phenomena in metallic structure by means of acoustic emission (AE), Short-Time Fourier Transform (STFT) and Wavelet Transform (WT). The proposed novel low-cost system is developed for analyzing and monitoring specific signals indicating tribological effects with focus on field programmable gate array (FPGA) implementation of discrete WT (DWT). In addition, experimental results obtained from each approach are given showing the success of the introduced approach.

Monitoring of fatigue cracking in steel bridge structures using a combined passive and active scheme has been approached by the authors. Passive acoustic emission (AE) monitoring is able to detect crack growth behavior by picking up the stress waves resulting from the breathing of cracks while active ultrasonic pulsing can quantitatively assess structural defect by sensing out an interrogating pulse and receiving the structural reflections. The dual-mode sensing functionality is pursued by using the R15I ultrasonic transducers. In the paper, we presented the subject dual-mode sensing on steel compact tension (CT) specimens in a laboratory setup. Passive AE sensing was performed during fatigue loading and showed its capability to detect crack growth and location. At selected intervals of loading cycles, the test was paused to allow for active sensing by pulsing the transducers in a round-robin pattern. Plate waves were excited, propagated and interacted within the structure. Several approaches were proposed to analyze the interrogation data and to correlate the data features with crack growth. Root means square deviation (RMSD) damage index (DI) was found as a good indicator for indicating the overall crack development. Short time Fourier transform (STFT) provided both time and frequency information at the same time. Moreover, wave velocity analysis showed interesting results when crack developed across the transmitter-receiver path.

Because of high specific strength and many other benefits, the use of composites for the large lightweight structures such as modern aircrafts and wind turbines are increasing. However, one of the serious drawbacks of composites is that the structural failure occurs in complex patterns without yielding. Therefore, structural health monitoring has been intensively investigated for the early detection of any problems in structural integrity. One of the promising sensors for this purpose is fiber Bragg grating (FBG) sensor. They can be easily inserted into the layered-structure of the composite materials due to their small size. The excellent multiplexing capability enables measurement to be taken at multiple points along a single sensor line. As well as damage detection, the structural shape measurement also draws attention. Particularly for structures experiencing aerodynamic forces such as wind turbines or helicopter blades, the structural shape itself is important because the applied aerodynamic forces are affected by structural shape deflections. Therefore, the authors have conducted a series of studies on the structural shape estimation of various structures. We have also developed a wavelength division multiplexing (WDM) Bragg grating sensing system for high speed strain sensing as well as low frequency dynamic strains. In the case of high-speed sensing, the interrogator allows a sampling ratio of over 40 kHz for six linearly arrayed FBG sensors per channel. Utilizing the developed interrogator, this paper presents some experimental results for simultaneous measurement of deformation and fracture signals of composite structures. An array of FBG sensors were installed onto composite beam specimens and the acoustic emission (AE) signals due to structural failure was continuously monitored while the overall structural deflection shape was monitored in real time. The reconstructed shapes of the specimens were in good agreement with the shapes captured from photographs taken with a high-speed camera. In summary, it was demonstrated that both fracture signals and the overall deformation shape of composite structures could be simultaneously monitored.

Structural systems that autonomously repair damage have the potential for enhanced longevities and performance envelopes. This paper addresses the issue of autonomously sensing and controlling self-repair processes in structural systems. Such an approach has the potential to expand upon self healing materials technology to the development of engineered smart self-healing structural systems. This involves coordinating damage-sensing capabilities with control of the healing processes. Much of the conceptual underpinning of this work comes from biological systems that routinely combine sensing with healing actions that span multiple spatial and temporal scales. The specific details and modalities of the response depend on the extent and vital threat of the damage. Coordination of antagonistic repair and material remodeling processes with a self-aware sense of health is an essential part of the process. This paper describes the results of experimental and system development efforts that attempt to mimic some aspects of coordinated self-healing in structural systems. This research expands and demonstrates the enhancement of autonomous repair techniques through the coordinated damage sensing and directed repair activities with test bed pressure vessels and structural panels that have been damaged by puncture and drilling of holes. Acoustic emission, embedded optical and capacitance sensors detect the damage. Thermoplastic repair techniques are initiated upon repair detection and localization of damage. Autonomous leak repair in pneumatic pressure vessels and panels with perforations up to 3 mm upon detection and localization of the damage are demonstrated.

The aim of this study is to investigate fully reversed electric fatigue behavior of a piezoelectric composite actuator (PCA). For that purpose, fatigue tests with different loading conditions have been conducted and the performance degradation has been monitored. During a preset number of loading cycles, non-destructive acoustic emission (AE) tests were used for monitoring the damage evolution in real time. The displacement-cycle curves were obtained in fully reversed cyclic bending loading. The microstructures and fracture surfaces of PCA were examined to reveal their fatigue damage mechanism. The results indicated that the AE technique was applicable to fatigue damage assessment in the piezoelectric composite actuator. It was shown that the initial damage mechanism of PCAs under fully reversed electric cyclic loading originated from the transgranular fracture in the PZT ceramic layer; with increasing cycles, local intergranular cracking initiated and the either developed onto the surface of the PZT ceramic layer or propagated into the internal layer, which were some different depending on the drive frequencies and the lay-up sequence of the PCA.

Composite structural self-diagnostic (CSSD) technology has been tested to detect the mechanical damages in carbon-fiber reinforced polymer-matrix composites. In order to characterize the self-sensing technique for damage detection, discrete electrodes were mounted on Double-Cantilever-Beam (DCB). Results on mechanical properties with corresponding electrical resistance changes of the CFRC specimens are presented in this paper. The lay-up configuration of the composite specimens is [0 6 /Teflon/0 6 ] T . In addition, acoustic emission was also used to corroborate the CSSD results.