Search Results (59)

The timely detection of delamination is essential for preventing catastrophic failures and extending the service life of carbon fiber-reinforced polymers (CFRP). Full wavefields in CFRP encapsulate extensive information on the interaction between guided waves and structural damage, making them a widely utilized tool for damage mapping. However, due to the multimodal and dispersive nature of guided waves, interpreting full wavefields remains a significant challenge. This study proposes an end-to-end delamination imaging approach based on UNet++ using 2D frequency domain spectra (FDS) derived from full wavefield data. The proposed method is validated through a self-constructed simulation dataset, experimental data collected using Scanning Laser Doppler Vibrometry, and a publicly available dataset created by Kudela and Ijjeh. The results on the simulated data show that UNet++, trained with multi-frequency FDS, can accurately predict the location, shape, and size of delamination while effectively handling frequency offsets and noise interference in the input FDS. Experimental results further indicate that the model, trained exclusively on simulated data, can be directly applied to real-world scenarios, delivering artifact-free delamination imaging. Full article

Graphite has great potential as a solid lubricant due to its low friction properties, but its poor adhesion to metal substrates limits its durability unless modified. This study explores the use of polydopamine (PDA), a bioinspired adhesive polymer, as an underlayer to enhance the adhesion and scratch resistance of graphite coatings applied to stainless steel (SS) substrates. Progressive load scratch tests were performed using a stainless steel ball counterface under normal loads ranging from 0.5 to 18 N. The PDA-modified coatings demonstrated significantly improved adhesion and durability, withstanding contact pressures up to 1.6 GPa without delamination or failure. In contrast, graphite-only coatings showed early coating loss, severe material transfer, and wide wear tracks. The PDA underlayer enhanced graphite flake compaction, reduced porosity, and preserved structural integrity under high contact stress. These findings demonstrate that PDA reinforcement enables robust, oil-free lubrication suitable for high-stress environments. Full article

Fault diagnosis based on the partial discharge (PD) recognition has been widely applied on a gas-insulated line breaker (GILB) and gas-insulated switchgear (GIS) as a reliable online condition monitoring method. This paper dealt with insulation defect diagnosis based on a Random Forest (RF) algorithm with an optimized feature selection method. Four different types of insulation defect models, such as the free-moving particle (FMP) defect, the protrusion-on-conductor (POC) defect, the protrusion-on-enclosure (POE) defect, and the delamination defect, were prepared to simulate representative PD single pulses and PRPD patterns generated from the GILB. The PD signals generated from defect models were detected using the PRPD sensor which can detect phase-synchronized PD signals with the applied high-voltage (HV) signals without the need for additional equipment. Various statistical PD features were extracted from PD single pulses and PRPD patterns according to four kinds of PD defect models, and optimized features were selected with respect to variance importance analysis. Two kinds of PD datasets were established using all statistical features and top-ranked features. From the experimental results, the RF algorithm achieved accuracy rates exceeding 92%, and the PD datasets using only half of the statistical PD features could reduce the computational times while maintaining the accuracy rates. Full article

Biodegradable films are a viable alternative to conventional plastics, thereby contributing to environmental pollution reduction. This study investigates the impact of substrate type on the properties of starch-based films produced using a plasticizer-assisted casting method. Four different substrates, namely, glass, copper, copper-free laminate, and Teflon^®, were evaluated, addressing a research gap in which previous studies primarily focused on film composition. The films were analyzed for color, tensile strength, surface free energy, and surface morphology using optical and electron microscopy. The results demonstrated a substrate-dependent impact on surface properties, particularly optical transparency, surface roughness, and adhesion. The films cast on glass and laminate exhibited higher transparency and lower roughness, while copper substrate induced micro-striations and strong adhesion. Teflon^® substrates replicated surface imperfections, which may be advantageous for optical applications, but caused film delamination. Tensile strength did not show statistically significant differences across substrates, although reduced elongation was observed for the films cast on Teflon^®. Water vapor permeability was also not significantly affected, indicating a dominant role of bulk material properties. It averaged 25 kg per day per square meter, which means high vapor permeability. Surface free energy analysis revealed marked variations between top and bottom layers, with values ranging from 35 to 70 mJ·m⁻² depending on the substrate. These findings confirm that the type of casting substrate plays a critical role in determining the surface and optical properties of starch-based films, even at the laboratory scale. This study provides new insights into substrate–film interactions and establishes a foundation for optimizing biodegradable film fabrication for industrial and application-specific needs. Full article

A signal-processing algorithm for the detailed determination of delamination in multilayer structures is proposed in this work. The algorithm is based on calculating the phase velocity of the Lamb wave A₀ mode and estimating this velocity dispersion. Both simulation and experimental studies were conducted to validate the proposed technique. The delamination having a diameter of 81 mm on the segment of a wind turbine blade (WTB) was used for verification of the proposed technique. Four cases were used in the simulation study: defect-free, delamination between the first and second layers, delamination between the second and third layers, and defect (hole). The calculated phase velocity variation in the A₀ mode was used to determine the location and edge coordinates of the delaminations and defects. It has been found that in order to estimate the depth at which the delamination is, it is appropriate to calculate the phase velocity dispersion curves. The difference in the reconstructed phase velocity dispersion curves between the layers simulated at different depths is estimated to be about 60 m/s. The phase velocity values were compared with the delamination of the second and third layers and a hole drilled at the corresponding depth. The obtained simulation results confirmed that the drilled hole can be used as a defect corresponding to delamination. The WTB sample with a drilled hole of 81 mm was used in the experimental study. Using the proposed algorithm, detailed defect parameters were obtained. The results obtained using simulated and experimental signals indicated that the proposed new algorithm is suitable for the determination of delamination parameters in a multilayer structure. Full article

In the space environment, the elastic vibrations of satellite solar panels are caused by various factors that disturb satellite missions. Therefore, we propose a multi-layered high-damping yoke structure based on a passive control method. To optimize the proposed yoke structure, we performed a free vibration test on various multi-layered blade specimens and designed a yoke structure with the maximum damping performance based on the test results. This high-damping yoke structure was mounted on a dummy solar panel with flexible mode (0.79 Hz) and basic characteristic tests were performed to validate the effectiveness of the solar panel vibration suppression. The test results demonstrated that the proposed multi-layered high-damping yoke is effective in suppressing the vibrations of the first and second modes. In addition, a thermal vacuum test was performed to investigate the delamination between multi-layered structures, and the test results proved the applicability of the proposed yoke structure in an actual space environment. Full article

Titanium alloys have a high cost of production and exhibit low resistance to abrasive wear. The objective of this work was to carry out diamond-like carbon (DLC) coating, with dissimilar thicknesses, on Ti-22Nb-6Zr titanium alloys produced by powder metallurgy, and to evaluate its microabrasive wear resistance. The samples were compacted, cold pressed, and sintered, producing substrates for coating. The DLC coatings were carried out by PECVD (plasma-enhanced chemical vapor deposition). Free sphere microabrasive wear tests were performed using alumina (Al₂O₃) abrasive suspension. The DLC-coated samples were characterized by scanning electron microscopy (SEM), Vickers microhardness, coatings adhesion tests, confocal laser microscopy, atomic force microscopy (AFM), and Raman spectroscopy. The coatings did not show peeling-off or delamination in adhesion tests. The PECVD deposition was effective, producing sp2 and sp3 mixed carbon compounds characteristic of diamond-like carbon. The coatings provided good structural quality, homogeneity in surface roughness, excellent coating-to-substrate adhesion, and good tribological performance in microabrasive wear tests. The low wear coefficients obtained in this work demonstrate the excellent potential of DLC coatings to improve the tribological behavior of biocompatible titanium alloy parts (Ti-22Nb-6Zr) produced with a low modulus of elasticity (closer to the bone) and with near net shape, given by powder metallurgy processing. Full article

This article concerns research into the influence of the energy dose distributed by UV lamps on selected parameters of varnish coatings formed during the varnishing process of lightweight cellular panels. The lightweight cellular board used in the study was made according to an innovative solution. The surface finishing of the boards was carried out using the roller method in combination with digital and analogue printing under industrial conditions. Contact angle measurements of the obtained varnish coatings were carried out, from which the surface free energy was calculated. In addition, interlayer adhesion was assessed by pull-off tests. Irrespective of the radiation dose, higher contact angle values (54.3–89.9°) were recorded for the last two applied layers (base coat 2 and base coat 3) than for the other coatings (39.6–64.1°). For all systems tested, the γs^p component showed lower values (2.25–28.99 mJ/m²) than γs^d (28.66–32.80 mJ/m²). The adhesion test results ranged from 0.5 to 0.9 MPa, although with varying types of delamination. Based on the test results, the most favourable variants from the furniture manufacturer’s point of view were selected that provided the desired level of adhesion, in which cohesive damage located within the substrate (A) predominated. Full article

Hydrotalcite exhibits the capability to adsorb CO₂ at elevated temperatures. High surface area and favorable coating properties are essential to harness its potential for practical applications. Stable alcohol-based dispersions are needed for thin film applications of mixed membranes containing hydrotalcite. Currently, producing such dispersions without the need for delamination and dispersing agents is a challenging task. This work introduces, for the first time, a manufacturing approach to overcoming the drawbacks mentioned above. It includes a synthesis of hydrotalcite nanoparticles, followed by agent-free delamination of their layers and final dispersion into alcohol without dispersing agents. Further, the hydrotalcite-derived sorption agent is dispersed in a matrix based on organo-silica gels derived from 1,2-bis(triethoxysilyl)ethane (BTESE). The analytical results indicate that the interconnection between hydrotalcite and BTESE-derived gel occurs via forming a strong hydrogen bonding system between the interlayer species (OH groups, CO₃²⁻) of hydrotalcite and oxygen and silanol active gel centers. These findings lay the foundation for applications involving incorporating hydrotalcite-like compounds into silica matrices, ultimately enabling the development of materials with exceptional mass transfer properties. In part 2 of this study, the gas separation performance of the organo-silica and the hydrotalcite-like materials and their combined form will be investigated. Full article

Boeing and Airbus developed a special testing procedure to investigate the compressive response of laminates that have been impacted (following standards ASTM D 7137 and DIN 65561). This study focuses on both experimental and numerical analysis of Kevlar plates subjected to compression after impact. To ensure high quality and appropriate mechanical properties, the composite plates were manufactured using autoclaving. The DIN 65561 protocol was followed for all three test systems. Initially, ultrasonic C-scanning was performed on all plates before testing to confirm they were free of any significant defects arising from the manufacturing process. Subsequently, low-energy impact testing was conducted at levels ranging from 0 to 8 Joules. Three specimens were tested at each energy level. After the impact, all specimens underwent ultrasonic C-scanning again to assess the internal delamination damage caused by the impactor. Finally, both pristine and impacted specimens were subjected to compressive testing using the special jig specified in DIN 65561. The compressive impact strength results obtained from these tests were plotted against the delamination area measured by C-scanning. These data were then compared to the results obtained from specimens with artificial damage. Semi-empirical equations were used to fit both sets of curves. The same procedure (impact testing, C-scanning, and data analysis) was repeated to investigate the relationship between impact energy and total delamination area. Lastly, finite element modeling was employed to predict the buckling stresses that develop under compression in the impacted systems studied. These modeling approaches have demonstrated good accuracy in reproducing experimental results for CAI tests. Full article

The aim of this study is to investigate the antibacterial capabilities of different coating durations of three nanoparticle (NP) coatings: molybdenum (Mo), tantalum (Ta), and zinc oxide (ZnO), and their effects on the surface characteristics of 316L stainless steel (SS). The coated substrates underwent characterization utilizing field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffractometer (XRD) techniques. The antibacterial efficacy of NPs was evaluated using the agar diffusion method. The FE-SEM and EDX images confirmed the presence of nano-sized particles of Mo, Ta, and ZnO on the surface of the substrates with perfectly symmetrical spheres and a uniform distribution of the NPs. All groups demonstrated antibacterial activity, and the ability to inhibit the growth of Streptococcus mutans and Lactobacillus acidophilus bacteria. The ZnO group had the most potent antibacterial effect, followed by the Mo group, while the Ta group had the least effect. A direct-current (DC) plasma sputtering system was used to produce nano-coatings of high purity that were homogeneous, crack-free and showed no sign of delamination. Bacterial strains exposed to Mo, Ta, and ZnO coated surfaces exhibited a significant loss of viability in a time-dependent manner. The optimum sputtering time to ensure the best antibacterial properties and preserve the resources was 1 hour (h) for Mo, 3 h for Ta and 6 h for ZnO. Full article

One of the useful features of 3D-printed specimens of recycled polyethylene terephthalate glycol (R-PETG) is the ability to repetitively develop free recovery as well as the work-generating, shape-memory effect. This behavior is enabled by the R-PETG’s capacity to stiffen during cooling, thus allowing for a new temporary shape to be induced. Aiming to devise an explanation for the polymer’s stiffening, in this study, the variation in some of the R-PETG’s parameters during cooling are emphasized and discussed. The evolution of an R-PETG filament’s shape was monitored during room-temperature-bending heating–cooling cycles. Straight-shape recovery and the complete loss of stiffness were observed at the start and the end of heating, respectively, followed by the forced straightening of the filament, performed by the operator, around 40 °C, during cooling. The tests performed by dynamic mechanical analysis disclosed the rise of the storage modulus (E’) after 100 °C heating followed by either liquid-nitrogen- or air-cooling to room temperature, in such a way that E’ was always larger after cooling than initially. Static tests emphasized a peculiar stress variation during a heating–cooling cycle applied in air, within the heating chamber of the tensile testing machine. Tensile-failure tests were performed at −10 °C at a rate of 100 mm/min, with specimens printed at various deposition directions between 10 and 40° to the transversal direction. The specimens printed at 40°, which had the largest ultimate strains, were broken with tensile rates between 100 and 500 mm/min. Deformation rate increase favored the shift from crazing to delamination failure modes. The correlation between the structural changes, the sharp E’ increase on heating, and the stiffening induced by cooling represents a novel approach that enables the use of 3D-printed R-PETG for the fabrication of the active parts of low-priced lightweight resettable actuators. Full article

Due to the high abrasiveness and anisotropic nature of composites, along with the need to machine different materials at the same time, drilling multi-materials is a difficult task, and usually results in material damage, such as uncut fibres and delamination, hindering hole functionality and reliability. Image processing and analysis algorithms can be developed to effectively assess such damage, allowing for the calculation of delamination factors essential to the quality control of hole inspection in composite materials. In this study, a digital image processing and analysis algorithm was developed in Python to perform the delamination evaluation of drilled holes on a carbon fibre reinforced polymer (CFRP) and aluminium (Al) multi-material. This algorithm was designed to overcome several limitations often found in other algorithms developed with similar purposes, which frequently lead to user mistakes and incorrect results. The new algorithm is easy to use and, without requiring manual pre-editing of the input images, is fully automatic, provides more complete and reliable results (such as the delamination factor), and is a free-of-charge software. For example, the delamination factors of two drilled holes were calculated using the new algorithm and one previously developed in Matlab. Using the previous Matlab algorithm, the delamination factors of the two holes were 1.380 and 2.563, respectively, and using the new Python algorithm, the results were equal to 3.957 and 3.383, respectively. The Python results were more trustworthy, as the first hole had a higher delamination area, so its factor should be higher than that of the second one. Full article

A heightened interest in developing MXene (Ti₃C₂T_x) for energy storage is evident in binder-free MXene ink being directly applied to current collector Ni-foam. Moreover, 2D titanium carbide MXene, with a few layers of nanostructure, has been prepared for symmetric supercapacitor device applications. As-prepared MXene nanosheets exist in two forms: dried powder and ink, achieved through wet-chemical etching and dimethyl sulfoxide delamination from the MAX (Ti₃AlC₂) phase. This comparative study of electrode devices involves (i) MX-dry powder with binder/additive electrodes and (ii) binder-free MXene inks with directly applied MX-conductive inks. The surface morphological images of pure MX-powder/ink display few layers, and material analysis reveals the good crystalline nature of delaminated MXene (Ti₃C₂T_x) inks. The electrochemical symmetric supercapacitor device performances of pure MXene powder and binder-free directly applied/coated MXene (Ti₃C₂Tx) ink, in terms of cyclic voltammetry (CV) and impedance spectroscopy (EIS), exhibit galvanostatic charge–discharge (GCD) curves that show high specific capacitance (Csp) at 105.75 F/g at a current density of 1 A/g. A comparison of active material electrodes demonstrated excellent cycle stability. Hence, in this work, we confirmed the superior capacitive behavior of binder-free MXene ink (MX-I) compared to conductive additives with polymeric binders included in MXene electrodes. Full article

Magnesium (Mg) and graphene in alloy formulations are of paramount importance for lightweight engineering applications. In the present study, ZE10 Mg-alloy-based nanocomposites reinforced with graphene nanoplatelets (GNPs) having a thickness of 10–20 nm were fabricated via ultrasound-assisted stir casting. The effect of GNP contents (0.25, 0.5, and 1.0 wt.%) on the microstructure, Vickers hardness, and tensile properties of nanocomposites was investigated. Further, tribological studies were performed under a ball-on-disc sliding wear configuration against a bearing ball counterbody, at room and elevated temperatures of 100 °C and 200 °C, to comprehend temperature-induced wear mechanisms and friction evolution. It was revealed that the GNP addition resulted in grain coarsening and increased porosity rate of the Mg alloy. While the composites exhibited improved hardness by 20–35% at room temperature and 100 °C, a minor change was observed in their hardness and tensile yield strength values at 200 °C with respect to the GNP-free alloy. A notable improvement in lowering and stabilizing friction (coefficient of friction at 200 °C~0.25) and wear values was seen for the self-lubricating GNP-added composites at all sliding temperatures. The worn surface morphology indicated a simultaneous occurrence of abrasive and adhesive wear mode in all samples at room temperature and 100 °C, while delamination and smearing along with debris compaction (tribolayer protection) were the dominant mechanisms of wear at 200 °C. Inclusively, the results advocate steady frictional conditions, improved wear resistance, and favorable wear-protective mechanisms for the Mg alloy–GNP nanocomposites at room and elevated temperatures. Full article