Search

Direct-write piezoelectric transducers are dedicatedly designed and fabricated to generate and detect both fundamental and second harmonic Rayleigh ultrasonic waves for evaluating overload-induced plastic deformation in aluminum (Al) alloy. The Rayleigh ultrasonic signals, generated by concentric focused direct-write transducers and propagating along the Al-alloy specimens, are measured either with other direct-write transducers or laser scanning vibrometer (LSV) to obtain the fundamental and second harmonic ultrasonic signals for analyzing the acoustic nonlinearity. The results show that the acoustic nonlinearity increases over 50% when the plastic strain reaches 7.8%. In comparison with LSV, the direct-write piezoelectric transducers exhibit substantially improved consistency and repeatability in the acoustic nonlinearity measurements. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are conducted to correlate micro-structural changes with the acoustic nonlinearity in the Al alloy. The results and analyses indicate that the direct-write piezoelectric transducers with the appropriate design have significant technical advantages for acoustic nonlinearity testing and yielding determination. [ABSTRACT FROM AUTHOR]

This paper develops an automatic and reliable nondestructive evaluation (NDE) technique that enables quantification of the width and depth of subsurface defects of metallic components simultaneously by using non-contact laser ultrasonic technique and identified machine learning (ML) algorithm. Twenty-two specimens with various subsurface defect dimensions are designed and fabricated for laser ultrasonic experiments, and a total of 220 labeled laser ultrasonic signals are obtained for training and verifying ML models. Twelve features, including four time-domain features (maximum, minimum, peak-to-peak, and |Neg|/Pos value of the laser generated Rayleigh ultrasonic waves) and eight wavelet energy features, are identified and extracted as sensitive feature vectors for establishing the dataset. The principal component analysis (PCA) is implemented as dimensionality reduction method of feature vectors to optimize the recognition algorithm and improve the detection accuracy. Three widely used ML models in NDE, adaptive boosting (Adaboost), extreme gradient boosting (XGBboost), and support vector machine (SVM), combined with the PCA are proposed and compared for detecting both the width and depth of subsurface defects. The PCA-XGBoost achieves the highest recognition rate of 98.48%, and is therefore identified as the most effective approach for analyzing laser-ultrasonic signals. Unlike published reports, the proposed model is trained and evaluated with experimental data covered various classification labels, which is more adaptive and reliable in practical application than the models established using simulated data or limited experimental data. In other applications, as long as sufficient laser ultrasonic data with regards to various defect properties (dimensions, orientations, locations, shapes, etc.) can be acquired, the developed approach can realize accurate detection of corresponding defects. [ABSTRACT FROM AUTHOR]

The determination of elastic constants of a transversely isotropic carbon fiber reinforced plastic (CFRP) composite is the prerequisite of mechanical strength calculation, material degradation evaluation, ultrasonic non-destructive testing for main load-bearing CFRP structures both after manufacturing and in service. Conventional ultrasonic methods request extra sample preparation, water immersion condition or special designed goniometric devices to rotate the test structures, making the elastic constants measurement expensive, inconvenient and not in situ. In this paper, a novel ultrasonic method that enables in situ determination of elastic constants via backwall reflection method (BRM) using a linear array probe is proposed. The BRM can achieve single sided measurement of ultrasonic travel times in various directions including the fiber direction using different pairs of transmitter and receiver array elements. Both quasi longitudinal and quasi shear waves are captured via the mode conversions from the multiple surface reflections. All elastic constants are determined through the particle swarm optimization by minimizing the sum of the squared deviations between the BRM measured and theoretically calculated multi-mode bulk wave travel times in the fiber orthogonal and parallel planes. This method is experimentally verified on a 4.45 mm thick unidirectional T700 carbon fiber/epoxy CFRP composite. The BRM measured Young's modulus in the fiber direction agrees well with that measured by tensile test, with a small deviation of −4.58%. This work proves that the proposed method is single sided, easy to operate, without the necessity of sample preparation, water immersion and extra rotation device, and can determine all elastic constants with high precision, which is therefore promising for in situ applications. [ABSTRACT FROM AUTHOR]

A reliable nondestructive evaluation technique that can effectively detect and quantify the internal defects of corner parts in complex-shaped carbon fiber reinforced plastic (CFRP) structures is highly demanded for assuring safety and reliability of safety-critical structures. The conventional methods generally utilize normal incidence ultrasound and suffer from poor image quality due to the unfocused beam. To produce a fully focused image of the CFRP corner part, the delay-and-sum total focusing method (TFM) is preferred. The prerequisite for TFM imaging is to calculate ultrasonic ray paths, which is challenged by the curved shape, elastic anisotropy and multilayered microstructure. In this paper, the complex ultrasonic ray paths transmitting through the corner parts of CFRP structures from the concave side are calculated for ultrasonic array imaging. A ray theory-based homogenization method is firstly proposed to describe the wave velocity distribution of corner parts, which is critically important to the subsequent ray tracing calculation. A ray tracing method based on Dijkstra's algorithm is further developed for rapid calculation of multiple ray paths between two specified points when the ultrasound is incident from the corner's concave surface. To demonstrate the validity of ray tracing method, the TFM images of an CFRP corner part with side drilled holes (SDH) at different depths obtained using three different types of ray paths, are compared and analyzed. Results show that TFM images using ray paths with the minimum or maximum ultrasonic travel time present unsatisfactory image quality due to the obvious structural noises from ply reflections. In contrast, the signal to noise ratio of the image is significantly improved when TFM uses the ray paths with the weakest refraction, and all SDHs are detected and accurately positioned. This paper proves that the proposed ray tracing method is an effective method for imaging the corner parts of CFRP structures. • Wave velocity distribution of CFRP corner part is described using a homogenization method. • Dijkstra's algorithm is used to calculate multiple ray paths through the corner's concave surface. • TFM images reconstruction using different ray paths are compared for CFRP corner part. [ABSTRACT FROM AUTHOR]

A multi-frequency ultrasonic method was proposed to detect and characterize delamination and rich resin in thick composites with waviness. Addressing the challenges for ultrasonic inspection caused by waviness, multi-layer structure, and multiple defect types, ultrasound propagation in thick wavy composite was investigated through a dedicated numerical model built in OnScale®. Key features of ultrasonic testing and composite sample, including water immersion environment, fiber waviness, uneven inter-ply resin distribution, and side-drilled hole (SDH)-simulated delamination, were embraced in the model. Via this model, waviness and thick resin layers were found to cause disturbance and wave vector deviation to inter-ply reflection signal and thus introduce difficulties for delamination detection based just on the signal to noise ratio. In addition, reflections from inter-ply resin and SDH were revealed with different reliance on probe frequencies. Using a 5 MHz probe with time corrected gain, ultrasonic testing in wavy composite was performed experimentally. Based on the reliance of defect characterization on frequency, SDHs and rich resin were differentiated experimentally in the B-scan images with various filtering frequencies, demonstrating the effectiveness of the proposed method for detection and characterization of delamination and rich resin in thick wavy composite structures. • A novel multi-frequency ultrasonic method to characterize delamination and rich resin in thick wavy composite. • A novel ultrasound model embracing multi-layer heterogeneous wavy composite with details. • A frequency-domain filtering method to allow for one-time test to detect delamination and rich resin in wavy composite. [ABSTRACT FROM AUTHOR]

The marine environment monitoring system is of considerable significance to the sea development. However, the power-supply issue of the sensor nodes in the system is a crucial consideration all the time. Here, a chaotic pendulum triboelectric-electromagnetic hybridized nanogenerator integrated with the power management circuit to power the wireless sensing nodes by scavenging wave energy has been proposed. The physical design of the harvester utilized the virtue of low working frequency and high electromechanical conversion efficiency characteristics of the chaotic pendulum. To verify the utility and applicability of the hybridized nanogenerators, several experimental scenarios were selected, the maximum output power of TENG can reach 15.21 μW and the EMG is up to 1.23 mW as triggered by the water wave. The hybridizied nanogenerator can light up about 100 LEDs. Moreover, the self-powered wireless sensing node distant transmission has been realized, and data transmission capability exceeds 300 m. This study provides a new direction of scavenging low-frequency vibrations from the environment of marine, also in the aerospace and industry. The chaotic pendulum triboelectric-electromagnetic hybridized nanogenerator has been utilized to scavenge the wave energy for powering the wireless sensing system. The physical design of the hybridized nanogenerator possess the virtue of low working frequency and high electromechanical conversion efficiency characteristics of the chaotic pendulum. This structure provides a new idea of scavenginglow-frequency vibrations from the environment of marine. Image 1 • A designed chaotic pendulum triboelectric-electromagnetic hybridized nanogenerator is proposed to scavenge the wave energy. • This communication provides a new way of harvesting low-frequency vibration from the environment of marine. • A chaotic pendulum hybridized nanogenerator possessing the merits of lower working frequency. • A low power consumption of power management circuit and wireless sensing node transmission is designed. [ABSTRACT FROM AUTHOR]

Novel direct-write ultrasonic transducers comprising piezoelectric poly(vinylidenefluoride/trifluoroethylene) [P(VDF/TrFE)] polymer coatings which were in-situ deposited, crystallized and patterned on pipe for structural health monitoring purpose. Lamb ultrasonic wave signals, generated and measured by the direct-write transducers and propagating along the pipe structure, were used to monitor the integrity of the pipe structure. The experimental measurements of the axial Lamb wave on pipe structure showed the substantial reduction in the ultrasonic signal by the defects. In addition, pipe thickness was accurately determined with the direct-write transducers to generate and detect the ultrasonic wave in the pipe thickness direction using pulse-echo mode. Our result and analyses suggest that implementation of the unique direct-write ultrasonic transducer technology is promising for realizing structural health monitoring for pipeline structures with improved consistency and reliability. [ABSTRACT FROM AUTHOR]

This paper describes the preparation of ferrocene-containing polymer brushes with different side chain lengths by surface-initiated atom transfer radical polymerization (SI-ATRP). The polymer brushes are characterized by cyclic voltammetry to determine the surface coverage of the ferrocene (Fc) units, their thickness in air by atomic force microscopy (AFM) and ellipsometry, and their mechanical properties by AFM-based nanoindentation. The results are compared against an ideal packing model and we conclude that brushes with short linkers between the Fc units and the polymer back bone are stiff and stand up in air up to 40 nm tall. In contrast, polymers with long linkers collapse and do not stand up in air. Our results indicate that the stiffness and packing structure of Fc-containing polymer brushes are affected by the length of the linkers between the Fc and polymer back bone. [ABSTRACT FROM AUTHOR]

• An improved variational mode decomposition strategy based on particle swarm optimization is proposed to enhance the signal-to-noise ratio. A fitness function based on permutation entropy and mutual information is developed to determine the optimized parameters in variational mode decomposition. • For the different excitation locations, the amplitude of the Rayleigh wave generated by laser irradiation on the defect is larger than on the small area around the defect, and the defect can be effectively detected using B-scans at elevated temperatures according to the abnormal evolution of Rayleigh waves. • For the same excitation locations, the amplitude of R waves gradually decreases at 100–300 °C and is consistent with the simulation, while it is opposite at 400–500 °C. Online monitoring is a critical issue for additive manufacturing components layer by layer to ensure the integrity of the structure. However, the rough surface and high temperature make it difficult to use conventional non-destructive testing methods to carry out. In this work, the laser ultrasonic technique, as a non-contact nondestructive testing method, is applied to detect defects in a 316L stainless steel specimen manufactured using selective laser melting at elevated temperatures. The unreported phenomenon of phase evolution of Rayleigh waves for different excitation locations and temperatures is observed and systematically explored using the finite element method and experiments. Furthermore, an improved variational mode decomposition strategy based on particle swarm optimization is proposed to enhance the signal-to-noise ratio. A fitness function based on permutation entropy and mutual information is developed to determine the optimized parameters in variational mode decomposition. The experimental results indicate that, for the different excitation locations, the amplitude of the Rayleigh wave generated by laser irradiation on the defect is larger than on the small area around the defect, and the defect can be effectively detected using B-scans at elevated temperatures according to the abnormal evolution of Rayleigh waves; for the fixed excitation locations, the amplitude and velocity of Rayleigh waves gradually decreases at 100–500 °C, which will provide a scientific basis for online monitoring and evaluation of additive manufacturing components. [ABSTRACT FROM AUTHOR]

An effective nondestructive evaluation technique that enables the detection and quantification of subsurface defects is highly demanded for assuring safety and reliability of safety-critical structures. In this work, an improved genetic algorithm-back propagation neural network (GA-BPNN) model and non-contact laser ultrasonic technique are combined to quantify the width of subsurface defects. An experimentally validated numerical model that simulates the interaction of laser-generated Rayleigh ultrasonic waves with subsurface defects is firstly established, which is further utilized to generate a large number of labeled laser ultrasonic signals for training the GA-BPNN model. A total number of 189 data are obtained from simulation and experiments, with 173 simulated signals for training the GA-BPNN model and the remaining 13 simulated signals together with 3 experimental signals for verifying the performance of the trained GA-BPNN model. Five features including three time-domain features (maximum, minimum and peak-to-peak value of the Rayleigh ultrasonic waves) and two frequency-domain features (F c , BW -6dB), which are identified sensitive to the width of subsurface defects by both experiments and simulation, are extracted as inputs to train the machine learning algorithm. The result demonstrates that the GA-BPNN model trained with the combination of time and frequency features has the average error of 2.15%, which is substantially smaller than the errors obtained from the model trained with only time-domain features and frequency-domain features, with the average errors of 4.43% and 21.81%, respectively. This work proves the feasibility and reliability to quantify the width of subsurface defects in metallic structures using laser ultrasonic technique and the improved GA-BPNN algorithm. [ABSTRACT FROM AUTHOR]

• Phase evolution of Rayleigh ultrasonic waves is reported to detect subsurface defects. • The mechanisms of phase evolution with defect width and depth are intensively studied. • The relationships between phase evolution and defect width and depth are established. • A sensitive and robust parameter is proposed to detect and quantify subsurface defect. An unreported phenomenon of phase evolution of Rayleigh ultrasonic waves with subsurface defects is observed and systematically explored for detection of subsurface defects using non-contact line laser ultrasonic technique and numerical simulation. The mechanism of phase evolution of Rayleigh wave signals is explained by the interference of the reflected and direct Rayleigh wave, explored by finite element analysis. Both experiments and simulation show distinct peak evolution of the Rayleigh wave signals with the width and depth of subsurface defect. A dimensionless parameter (|Neg|/Pos), defined by the ratio of absolute negative peak to positive peak of Rayleigh wave, is proposed to evaluate the phase evolution of Rayleigh wave with defect width and depth, which is further used to quantify the subsurface defects. The phase evolution of Rayleigh waves can act as a robust and sensitive feature to detect subsurface defects using laser-generated ultrasound, which has promising applications in life prediction and health monitoring of various engineering structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanocomposite photoacoustic transducer utilized to modulate ultrasonic surface wave for acoustic nonlinearity evaluation. • A structural optimization method of photoacoustic transducer for minimizing unwanted components of surface wave. • High-intensity narrowband surface wave with pure fundamental component acquired with optimized design non-ablatively. • Fully non-destructive microscale fatigue crack localization is achieved by nonlinear wave mixing using optimized designs. Laser ultrasonics is a promising non-contact inspection technique but faces challenges of low signal-to-noise and low amplitude under non-destructive thermoelastic regime. In this paper, a laser ultrasonic surface acoustic wave (SAW) modulation method and photoacoustic transducer (PAT) are proposed and combined with nonlinear wave mixing technique to inspect microscale fatigue crack. PATs comprised of candle soot nanoparticles and polydimethylsiloxane are systematically optimized and combined with a line-arrayed laser source to generate desired high-amplitude and pure fundamental SAWs. Two modulated SAWs with frequencies of 2.1 and 2.9 MHz are excited on a fatigued aluminum plate to generate nonlinear mixed components, and the ultrasonic responses over the fatigue crack regions are acquired with a scanning laser Doppler vibrometer. The localization of fatigue crack with microscale is eventually achieved by mapping the nonlinear parameter of the mixed components, which proves it a reliable and non-destructive technique to inspect the fatigue crack. [ABSTRACT FROM AUTHOR]

Abstract The detection of fatigue cracks around fastener holes in riveted structures is important to ensure the safety of the structures and to prevent major structural failure. However, due to the complex structure around the fastener holes, the existing non-destructive methods are not effective to address this challenge. Here, we demonstrate a directed acoustic shearography system using a ring-shaped phased array transducer for crack imaging around fastener holes in thick aluminum plates. Supported by numerical simulations, a 16-element ring-shaped phased array transducer was designed, fabricated and tested. The 16-element phased array transducer was excited by an in-house developed phased array drive circuit to control the directions of acoustic waves. Directed acoustic shearography testing with the ring-shaped phased array transducer showed that by controlling the direction of acoustic waves, the imaging contrast of the defects could be significantly improved. Directed acoustic shearography was able to detect subsurface crack which was not detectable by conventional acoustic shearography excited at the same voltage and frequency. This work demonstrates a promising practical NDT tool for fast and full-field detection of surface and subsurface defects with significantly enhanced sensitivity. [ABSTRACT FROM AUTHOR]

A reliable non-destructive evaluation technique that accurately assesses the wall thickness and slag inclusions of ductile iron pipes prior to annealing is crucial to reducing costs in subsequent operations. The rough outer layer of the produced ductile iron pipes leads to considerable background noise, limiting the probability of detection of laser ultrasonic testing equipment. In this study, an improved variational mode decomposition approach based on particle swarm optimization is suggested initially to increase the signal-to-noise ratio. This technique develops a fitness function suitable for processing ultrasound signals. A scanning laser ultrasound technique is designed for simultaneous measuring wall thickness and finding slag inclusions in ductile iron pipes based on excitation locations and flight time. A finite element analysis simulation model is established to assess the feasibility of this scanning method. This experiment is conducted on a 4.2 mm thick sample with slag inclusion defects and a 6.2 mm thick sample without slag inclusion flaws. Experimental results demonstrate that the developed denoising technique may enhance the average signal-to-noise ratio from 34.83 dB to 43.15 dB; the accuracies of thicknesses measurement for two ductile iron pipes are 96.90% and 99.52%, respectively, and the slag inclusion defects can be recognized by ultrasonic amplitude or energy distribution in different B-scan images. It has potential implications for in-service inspection of ductile iron pipe structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fully noncontact LU-based method is developed for fast and high-resolution visualization of defects. • A strategy adopted for fast defect localization using Rayleigh waves with circular scans. • High-resolution 3D imaging performed focusing around the located defect areas to quantify defects. • Various defect locations, depths, and sizes in AM parts are analyzed to verify the feasibility of the method. Additive manufacturing (AM) is an emerging technique for efficient fabrication of individually tailored and complex geometry parts. The fabrication process is prone to induce various defects that can have detrimental effects on the AM components. Therefore, a reliable technique that enables monitoring the integrity of AM components and in return helping to optimize the fabrication parameters in mission-critical structures is highly demanded. This work presents a fast and high-resolution damage visualization method using laser-ultrasonic (LU) imaging technique for accurately detecting and quantifying the subsurface defects in printed AM components. Specifically, a fully noncontact LU scanning system is implemented to generate and detect high signal-to-noise ratio laser ultrasonic waves using a pulsed laser and laser Doppler vibrometer, respectively. A strategy for fast defect localization using Rayleigh waves with circular scans is firstly proposed. The high-resolution 3D synthetic aperture focusing technique (SAFT) imaging with raster scans is subsequently performed focusing around the located damage areas to stereoscopically visualize and quantify the subsurface defects. The reconstructed images are further processed and improved using Gaussian filter algorithm to obtain accurate defect shapes, sizes, and positions. The feasibility of the proposed method is eventually verified on AlSi10Mg and stainless steel (316L) components containing subsurface defects with various types and dimensions. The measured sizes are well consistent with the designed values, suggesting that it is a reliable inspection method for AM parts to ensure quality control and feedback. [ABSTRACT FROM AUTHOR]

Laser ultrasonic technique has been increasingly implemented for nondestructive testing and structural health monitoring. However, the poor signal-to-noise ratio (SNR) and low amplitude of laser generated ultrasonic signals under thermoelastic regime severely restrict its applications. In this paper, we propose a method for fabricating flexible, high-intensity and readily transplantable photoacoustic transducer (PAT) comprised of candle soot nanoparticles (CSNPs) and polydimethylsiloxane (PDMS), and utilize it to generate high SNR and amplitude ultrasonic signals for inspecting thick structures. A robotic-arm based layer-by-layer automatic scanning strategy is developed to realize candle soot nanoparticles (CSNPs) deposition with excellent homogeneity and thickness controllability, and the optimal thickness of PDMS/CSNPs nanocomposite layer to achieve high SNR and amplitude ultrasonic signal is obtained. In addition, a novel method for optimizing the PAT's structure to generate distinguishable and pure longitudinal ultrasonic signals is proposed, with amplitude over 100 times, and with center frequency (13.5 MHz) and −6 dB bandwidth (20.1 MHz) 29.8% and 35.8% higher than those generated without PAT. The optimized PAT is eventually combined with laser ultrasonic technique to successfully inspect and visualize the internal defects with various sizes (4, 2, 0.8 mm in diameter) of an aluminum component with thickness of 50 mm. With the merits of flexible and high-intensity nanocomposite PAT, the laser ultrasonics can be promisingly implemented for inspecting structure with large thickness and complex geometry under thermo-elastic mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

A reliable non-destructive testing technique that enables effective detection and quantification of defects within safety-critical curved structures is highly demanded both in manufacture and service. Conventional Ultrasonic Testing (UT) methods usually adopt planar ultrasonic probes and it is preferable to adjust the probe axis direction perpendicular to the curved surface, because both the transmitting and receiving sensitivities in the probe axis direction are the highest. This paper proposes a new UT method using a hemispherical-omnidirectional ultrasonic probe. This probe has an omnidirectional directivity pattern and can cover curved surfaces with normal incident ultrasounds at different scan positions without the necessity of adjusting the probe attitude and position to follow the curved surface profiles. A surface reconstruction algorithm is firstly proposed to estimate curved surface profiles, which is based on a fast-imaging algorithm for ultra-wideband radar called the Shape Estimation Algorithm based on the Boundary scattering transform and Extraction of Directly scattered waves (SEABED). This method only uses surface reflection echoes, and thus can inspect curved structures without knowing the surface profiles a prior. Further, the Synthetic Aperture Focusing Technique (SAFT) is implemented to generate a focused image of internal defects by performing delay-and-sum beamforming on defect echoes based on the reconstructed surface profile. The proposed UT method is eventually experimentally verified on a curved plexiglass specimen with 29.4 mm surface curvature radius containing three Ø 3.5 mm Side Drilled Holes (SDHs) at different depths. Results show that compared with the planar ultrasonic probe, the reconstructed surface profile via SEABED is much wider and accurate with a relative error ≤ 0.47%. All SDHs are not only clearly positioned with relative errors ≤ 7.43%, but also can be accurately quantified from the curvature radius of SDH indications in the SAFT images with relative errors ≤ 8.60%. This work proves that the UT method based on the hemispherical-omnidirectional ultrasonic probe can emerge as a promising technique to inspect curved structures with high efficiency and accuracy, which has great potential in practical applications. • A hemispherical-omnidirectional ultrasonic probe is presented for NDT purposes. • Curved structure is inspected by probe linear scanning with fixed attitude. • Surface profile is reconstructed from surface echo travel times with SEABED. • SAFT is used to generate a focused image with high accuracy. [ABSTRACT FROM AUTHOR]

Low-temperature magnetic pyrolysis (LMP) of municipal solid waste (MSW) was conducted in a pilot scale continuous reactor to investigate the distribution and transformation of heavy metals (HMs) in biochar. Environmental safety was evaluated by the risk assessment code (RAC) and the modified potential ecological risk index (MRI). Statistical analyses of HMs revealed that the total concentrations of HMs in biochar was higher than that in MSW and the exchangeable fraction of Cd in biochar under 200 °C and 250 °C were at high risk levels. Temperature increment indicates an increase in regular steps not only migrated more HMs into biochar, but also broke the immobilization of HMs, so resulted in higher environmental risks. The lowest direct toxicity to the environment was obtained by LMP at 200 °C. In light of the residual fraction and the high concentration of HMs in biochar produced in this work, it should be mixed with other uncontaminated plant waste for further application in agriculture. The results of economic assessment reveal that the value of net present value (NPV) and the internal rate of return (IRR) can be positive if high quality bio-products are produced with low operating costs. Optimized design of operation, feedstock and the investment are the key factors to improve the economic feasibility of LMP. [Display omitted] • MSW can be converted to biochars by low-temperature magnetic pyrolysis. • LMP enriched the heavy metals in biochar at high reaction temperature. • The immobilization of HMs was broken with the reaction temperature increase. • The RAC and MRI of heavy metals shown relative low and considerable environmental risk at 200 °C. [ABSTRACT FROM AUTHOR]

A laser ultrasonic based non-contact detection method combined with support vector regression (SVR) was proposed for the first time for in-situ predicting the volume fraction of α-phase in titanium alloy (Ti-10V-2Fe-3Al). The alloy specimens were heated with incremental temperatures from 820 to 1100 °C to obtain different microstructures and volume fraction of α-phase, and the nonlinear relationship between the parameter of Rayleigh ultrasonic wave (velocity, amplitude and peak frequency) and the volume fraction of α-phase was established and analyzed by the combination of laser ultrasonic experiment and metallographic analysis. The SVR, with ultrasonic parameters and heat treatment parameters (heating and cooling rate, holding time and holding temperature) as input features, was implemented to predict the volume fraction of α-phase, achieving a relative mean error less than 5%. The results indicate that the SVR-based laser ultrasonic technique can be applied as a reliable and effective method for in-situ characterization of volume fraction of α-phase in titanium alloy. [ABSTRACT FROM AUTHOR]

The main components of municipal solid waste (MSW) include food waste (FW) and polyvinyl chloride (PVC), which present an opportunity to convert energy or value-added products through low-temperature synergetic pyrolysis. In this study, the characteristics of char and bio-oil derived from MSW, FW and PVC feedstocks via pyrolysis at relatively low temperatures (200–300 °C) for 60 min were investigated. The results revealed that the transformation of PVC to HCl gas production started at a temperature of ＞ 200 °C. The oxygenated carbon groups on the char surface were decomposed at elevated reaction temperatures. The relative molecular mass of bio-oil derived from FW increased when PVC-derived char was used as a catalyst at 250 °C. In addition, active functional groups and pore structures were formed through synergistic pyrolysis. This work provides information regarding the possible route underlying the network of char and bio-oil production from the synergistic conversion of FW and PVC-derived char. Image 1 • Low temperature pyrolysis of municipal solid waste (MSW), food waste (FW), and polyvinyl chloride (PVC) were compared. • Bio-oil and gas yield decreased at lower interaction temperature with PVC. • PVC-derived char additives promote the upgrading of bio-oil derived from food waste. • Activity functional groups and pore structure were formed through synergistic pyrolysis. • A possible route is provided for char and bio-oil production from the synergistic conversion. [ABSTRACT FROM AUTHOR]

Large-area, lightweight and flexible sensing networks are highly demanded in complex (either in structural topology or material property) structural health monitoring (SHM) applications. Development of piezopolymer offers a feasible solution. In pursuit of maximum exploitation of their functionality, the optimal fabrication technique requires to be investigated first. In this study, PVDF-TrFE coatings were in-situ fabricated and directly functionalized on structural surfaces in the consecutive processing steps as spray, thermal annealing, and corona poling. The processing conditions, including annealing temperature/time and poling voltage/duration, were correlated with their crystallinity, ferroelectric phase, morphology, polarization, and final piezoelectricity, through a systematic study. With the help of various characterization methods, the conditions of optimal functional performance were identified and rationalized. To study the feasibility of thus-prepared functional coatings in transducing guided waves, the host structures with sensors made of such coatings were interrogated by passive acoustic emission and active ultrasonic transmission to validate the sensing and actuation capability, respectively. The developed piezopolymer coatings possess excellent performance as a novel configuration of sensing networks, with lightweight, ultrathin, flexible, rapid-prototyping and adhesive-free features, manifesting high adaptability, high consistency, negligible inter-path interference, and minimal extra penalty for a robust SHM system. Unlabelled Image • In-situ fabrication and functionalization of piezopolymer coatings. • Optimized crystallization and piezoelectricity by annealing and corona poling. • Light, thin, flexible, consistent, rapid-prototyping and adhesive-free sensing networks. • High adaptive, high consistent performance of actuation and sensing guided waves with negligible inter-path interference. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are inherently complex and potentially span a vast composition space, making their research and discovery challenging. In the present study, high-throughput synthesis of an Al x (CoCrFeNi) 100- x combinatorial material library covering x = 4.5–40 atomic percent Al is achieved, using magnetron co-sputtering. The effects of Al on the microstructure and corrosion behavior are investigated. With the increased amount of Al, crystal-structures of thin films transform from face-centered cubic (FCC) to body-centered cubic (BCC). Both the FCC and BCC thin films demonstrate a uniform elemental distribution. Corrosion characteristics of combinatorial samples immersed in the 3.5 wt% (wt%) NaCl solution are evaluated via electrochemical tests. Complementary X-ray photoelectron spectroscopy analysis reveals the compositional variation of passivated films formed on the sample surface after immersion. The results show that the Al x (CoCrFeNi) 100- x HEA thin films possess outstanding corrosion-resistant properties, but the resistance diminishes with the increasing Al content. The decreased corrosion resistance is revealed to be directly related to the constituents of passivated films. Unlabelled Image • High-throughput synthesis of Al x (CoCrFeNi) 100- x high-entropy alloys is achieved. • The influences of Al on the microstructure and corrosion behavior are evaluated. • Al x (CoCrFeNi) 100- x thin films possess outstanding corrosion-resistant properties. [ABSTRACT FROM AUTHOR]

With a combination of the improved ultrasonic measurement model (IUMM) and support vector machines (SVM), a novel method to identify inclusions and cavities in metallic materials using scanning acoustic microscopy is proposed. In the IUMM, a hybrid model of Born approximation and Kirchhoff approximation is developed to calculate the far-field scattering amplitude of cavities, which improves the accuracy in phase and amplitude of the predicted pulse-echo signals of defects. The SVM classifier, with the amplitude and peak frequency of the predicted echo signals as major features, is applied to distinguish inclusions and cavities. The experimental result shows that the echo signals predicted by the proposed IUMM are more accurate than conventional UMM in amplitude and frequency. The SVM classifier, with the predicted signals as the training set, enables the identification of inclusions and cavities in metallic materials successfully. This work improves the performance of SAM in the identification of internal defects in metallic materials and realizes the intelligent analysis of ultrasonic signals. [ABSTRACT FROM AUTHOR]