With the ever-increasing importance of nanoscale deformation phenomena in contemporary technologies, basic understanding of material behavior at the nanoscale has become of critical importance. Especially, nanomechanical testing that provides the capability to study fundamental nanoscale deformation and phase change phenomena in real time and under controlled loading conditions is essential for nanomaterial research. In this study, acoustic emission (AE) was used in situ to characterize nanoindentation-induced deformation, microfracture, and phase transformation processes intrinsic of bulk single-crystal MgO and polycrystalline Al, thin films of polycrystalline SiC, and thick films of austenitic TiNi shape-memory alloy. Scale-dependent plastic deformation and microfracture affected by the indenter tip radius and the applied normal load are interpreted in terms of the type and intensity of AE events revealed by abrupt displacement excursions in the loading response of the indented materials. The amplitudes of AE waveforms are used to examine characteristic deformation, microfracture, and phase change mechanisms in the time domain. Fast Fourier transformation and short-time Fourier transformation analyses provide further insight into the material behavior and structural changes due to indentation loading in the frequency and time-frequency domain, respectively. The methodology developed in this study represents an effective approach for nanomechanical testing and in situ characterization of nanoscale deformation, microfracture, and phase transformation phenomena.

Plastic deformation of micron-scale crystalline materials differs considerably from bulk samples as it is characterized by stochastic strain bursts. To obtain a detailed picture of the intermittent deformation phenomena, numerous micron-sized specimens must be fabricated and tested. An improved focused ion beam fabrication method is proposed to prepare non-tapered micropillars with excellent control over their shape. Moreover, the fabrication time is less compared with other methods. The in situ compression device developed in our laboratory allows high-accuracy sample positioning and force/displacement measurements with high data sampling rates. The collective avalanche-like motion of the dislocations is observed as stress decreases on the stress–strain curves. An acoustic emission (AE) technique was employed for the first time to study the deformation behavior of micropillars. The AE technique provides important additional in situ information about the underlying processes during plastic deformation and is especially sensitive to the collective avalanche-like motion of the dislocations observed as the stress decreases on the deformation curves.

A micro-indentation system integrated with an acoustic emission (AE) sensor is used as a damage test method for crack detection of the specimen during the indentation loading–unloading cycle. The specimens investigated are the Si die, and various stacked structures of metallization (Al or Cu) deposited over the dielectric layers (SiO2 or Si3N4) on the Si substrate. The 1st AE event detected during the loading stage corresponded to the ‘pop-in’ observation in the force–displacement curve, which was related to the brittle cracking in the dielectric or Si substrate. However, during unloading, a 2nd AE event was detected, but no “pop-out” was observed, which was mainly due to the delamination between the dielectric and Si substrate. It was also found that for Si die, “pop-out” was observed without any AE event during the unloading stage, which was related to the Si phase transformation. This observation is unique to sharp indenter tip but not for a blunt indenter tip.

The exploitation of cyclostationarity properties of vibratory signals is now more widelyused for monitoring rotating machinery and especially for diagnosing bearing defects. Theacoustic emission (AE) technology has also emerged as a reliable tool for preventivemaintenance of rotating machines. In this study, we propose an experimental study thatcharacterizes the cyclostationary aspect of acoustic emission (AE) signals recorded from adefective bearing (40 μm on the outer race) to see its efficiency to detecta defect at its very early stage of degradation. An industrial sensor (UE10 000) is used.An electrical circuit converts the high frequency signal into an audible signal byheterodyning. The cyclic spectral density, which is a tool dedicated that put intoevidence the presence of cyclostationarity, is used for characterizing thecyclostationary. Two new indicators based on this cyclostationary technique are proposedand compared for early detection of defective bearings.

Anelastic recovery of pure magnesium was monitored quantitatively by means of acoustic emission (AE) in cyclic compression–quick unloading–recovery process. The influences of grain size, strain rate, and the strain-controlled cyclic process on anelastic recovery were analyzed in details. A detwinning model in anelastic recovery process was proposed, and the results showed good agreement with the experimental data. Three stages of anelastic recovery behavior as a function of strain were observed: stages I and III were considered to be dominated by various detwinning processes and stage II was dominated by thermal motion of dislocation. A quantitative relationship between anelastic recovery strain and AE signals was obtained, and from which the anelastic recovery strains from dislocation motion and detwinning were separated for the first time. In the strain-controlled cyclic process, both the amount of AE signals and the anelastic recovery strain were observed to decrease while the fraction of anelastic recovery strain from dislocation motions was observed to decrease more rapidly than that from detwinning with increasing cyclic number.

Multichannel acoustic emission (AE) measurements by four laser interferometers were developed and applied during a plasma-spray coating process that is known as being a high-temperature process and an extremely noisy environment in both mechanical and electrical domains. The AE signals could be successfully detected during the cooling period after the deposition, and it was clearly indicated that a higher preheating temperature resulted in the improvement of bonding between splats and/or at the interface of the coating and the substrate. The maximum principal stress generated during the deposition process was calculated by the transient heat and stress analysis and the obtained AE events. The critical stress for crack initiation of the alumina coating on a steel substrate with an NiCr bond coat layer was estimated as 30∼45 MPa. The developed techniques were shown to be a potential tool for in situ monitoring of the thermal spray process, by which an increase in the reliability of thermal spray coatings can be expected.

Cro/CrOx-doped hybrid glasses are designed to develop novel laser device materials by inserting alkylene spacers between inorganic oxides. In TEM images, morphology of the organically modified hybrid glasses reveals highly arranged nano-periodic patterns. The nano-patterns observed from the hybrid glass based on alkylene-bridged xerogel are sustained over substantial domains and appears to arise from modified glassy lattice fringes. In electron diffraction pattern, it also shows the circled diffraction patterns arise from Cro/CrOx. In laser experiments, the hybrid glass shows a new optical property, which generates a huge acoustic wave; the diffraction efficiency (45 %) of the modified glass is higher than that of methanol (25 %); it means that the compressibility of the solid type of glass is as effective as the liquid. The hybrid glass shows a new optical property that hitherto hasn’t been found and could be useful for developing diffraction beam modulators.

Tin-dioxide (SnO2) ultra-small nanorods (UNR) have been successfully synthesized using the novel micellar technique. From transmission electron microscopy, the average diameter and length of the UNRs are estimated to be 1.3 nm and 5.0 nm, respectively. The crystal structure of the SnO2 UNRs was found to be tetragonal from the glazing incidence x-ray diffraction. The optical band gap estimated from the absorption spectrum is blue-shifted by 1 eV from that of bulk (3.64 eV). The photoluminescence spectrum shows two groups of peaks each with several fine peaks, one in the wavelength range of 270 – 370 nm and the other in the range of 380 – 500 nm which are due to the strong quantum confinement effect.

Acoustic emission (AE) signals were continuously recorded and their intrinsic frequency characteristics examined in order to evaluate the mechanical performance of cementitious wasteform with encapsulated Al waste. The primary frequency in the power spectrum and its range of intensity for the detected acoustic waves were potentially related with appearance of different micromechanical events caused by Al corrosion within the encapsulating cement system. In addition the process of cement matrix hardening has been shown as a source of AE signals characterised with essentially higher primary frequency (above 2 MHz) compared with those due to Al corrosion development (below 40 kHz) and cement cracking (above 100 kHz).

Nous présentons dans cet article une étude expérimentale de l'influence de la qualité de l'interface fibre/matrice sur le comportement en traction et en fluage jusqu'à rupture d'un polypropylène renforcé de 40 % en masse de fibres de verre courtes (soit 18,85 % de fraction volumique de fibres). Les essais de traction avec des taux de fibre de 20 et 30 % en masse montrent l'existence d'un plateau pour le matériau avec fibres non-traitées (absence d'ensimage) qui disparaît pour le taux de 40 % en masse. Également, ces essais de traction montrent, pour chaque type d'interface, l'existence de trois zones de comportement pour chaque matériau. La mesure de l'émission acoustique permet de quantifier les différents mécanismes d'endommagement et montre qu'il y a plus d'événements acoustiques pour le matériau avec fibres traitées. Des essais de fluage jusqu'à rupture sont entrepris avec la mesure de l'émission acoustique pour un taux de fibre de 40 % et montrent également plus d'événements acoustiques pour le matériau avec fibres traitées. Finalement on observe, à partir des résultats de l'émission acoustique, l'influence de la nature de la sollicitation sur les mécanismes d'endommagement et on constate qu'il y a plus d'événement lors des essais de fluage jusqu'à rupture.

Laboratory scale unit for registration of acoustic emission (AE) signals was used for integrity control of glass granules and ceramic bodies. AE waveform recorded in course of the temperature changes has been shown to allow for an unambiguous interpretation and may be used for nondestructive quality control of glass and ceramics bodies.

Acoustic emission (AE) is used as a means to anticipate the mechanical failure of critical materials and structures by detecting the release of energy caused by material rearrangement at the microlevel. Optical-fiber sensors have potential advantages over conventional tuned piezoelectric transducers and signal-processing methods for the detection of such types of ultrasonic acoustic wave events. A number of fiber Bragg grating techniques are presented, which in particular offer the potential to provide the high-speed signal processing and ability to multiplex numbers of AE sensors necessary to detect, quantify, and locate AE sources and thereby determine material properties and damage.