Search Results (2,991)

Hydric deformation can contribute to progressive damage in building stones, particularly when moisture-induced strains interact with pre-existing fabric anisotropy and thermally induced microstructural changes. Six Macigno sandstone prisms (20 mm × 20 mm × 200 mm), three with the longitudinal axis orthogonal to bedding (MTO) and three parallel to bedding (MTP), were examined after drying at 60 °C and after sequential thermal conditioning at 350 and 500 °C. At each stage, hydric deformation was continuously monitored during 8400 min of water immersion, and at the end of each test, water absorption and ultrasonic pulse velocity were measured on the samples. Mean final hydric deformation in the 60 °C reference state was 0.54 mm m⁻¹ for MTO and 0.44 mm m⁻¹ for MTP. Along the sequential conditioning path, it decreased to 0.18 and 0.10 mm m⁻¹, respectively, at 500 °C, whereas water absorption increased from about 0.42 to 0.58–0.59 wt.%. Ultrasonic pulse velocity decreased from 4347 to 3915 m s⁻¹ for MTO and from 4770 to 4437 m s⁻¹ for MTP. Bedding-related anisotropy persisted, while water absorption and hydric deformation followed divergent trends. Continuous acquisition further showed that the general temporal pattern of rapid initial deformation followed by a more gradual approach to a near-stable response was preserved after thermal conditioning, although the initial deformation rate decreased systematically. Full article

Degradation processes forming as a result of direct and indirect environmental interactions with soluble salts are important for the structural material of marble and in geotechnical applications. This is necessary, not only to identify the source and describe the material, but also to ensure the sustainability of artifacts and to be able to provide appropriate material for preservation and restoration. In this study, the durability of Afyon–İscehisar marbles (calcitic and dolomitic) to cyclic salt mist was investigated in a laboratory environment by considering weight, color, and ultrasonic pulse velocity values. Additionally, comprehensive experiments including mineralogical and petrographic investigations (polarizing microscope, X-ray diffractometry, scanning electron microscope (SEM/EDX), geochemical investigations, and physical and mechanical tests) were performed to evaluate the durability against the effect of salt mist. The results show that the calcite content in the calcitic marbles varied from 96% to 99%, while the dolomite content in the dolomitic marbles reached 64%–74%, in line with microscopic and semi-quantitative XRD analyses and geochemical investigations. The calcitic–dolomitic differentiation was tightly controlled by the magnesium (Mg) content. With the effect of salt mist, the samples had negligible weight changes (0.02% in the KH sample) and there was no significant material loss in any of the groups. For color analyses, total color differences (ΔE) in the KH and MN samples reached 4.39 and 4.06, respectively, and exceeded the human perception threshold. The dolomitic KS and PB samples and calcitic KP sample had increases identified for ultrasonic pulse velocity. Contrary to this, the GR (calcitic) sample was found to have a 15.15% reduction in ultrasonic pulse velocity. These findings provide critical selection, performance prediction and preservation criteria for Afyon–İscehisar marbles in both modern structural engineering applications and in archeological studies. Full article

Prolonged sitting and poor posture are linked to musculoskeletal discomfort, higher spinal loading, and lower study and work efficiency. An Arduino-based distributed system combining a multi-sensor was developed for low-cost, camera-free sitting posture monitoring. It comprises a wearable sensing board (WSB), a main control board (MCB), and a host computer. The WSB measures trunk inclination—that is, the forward pitch and lateral roll of the upper trunk relative to the upright reference—using an ADXL345 acceleration sensor, whereas the MCB measures the user-to-desk distance using a US-100 ultrasonic ranging unit; NRF24L01 Wireless Communication Units connect them. Rule-based thresholds classify six states: “normal”, “slouching”, “leaning left”, “leaning right”, “too close”, and “too far”. The Sound Audio Unit and Liquid Crystal Display Unit provide local voice alerts and visual feedback. Using a 4G Unit, the MCB uploads user ID, timestamp, ambient temperature, distance, and posture state to a cloud platform. Cloud-generated text files support host retrieval and display, with accounts for two users and one administrator. The system can determine sitting-distance states within a range of 40–2000 mm and output trunk inclination information over a range of 0–90°. Under the current test conditions, the wireless communication distance between the MCB and WSB exceeds 3 m. In addition, the auditory reminder, time and temperature display, and PC-side data retrieval functions all operate as intended. With a total hardware cost of USD 18.39, the system provides a viable prototype for low-cost, camera-free sitting posture monitoring and remote data management in educational and home settings. Full article

Digital fabrication with concrete enables manufacturing of geometrically complex and individualized elements, increasing the need for scalable non-destructive quality-control methods. This study is a preliminary investigation of the ultrasonic pulse velocity (UPV) use for shotcrete 3D-printed (SC3DP) concrete, with a particular focus on material variability caused by changes in the key manufacturing parameters, i.e., nozzle traverse speed and distance, as well as air volume flow and concrete pump speed. A series of small SC3DP specimens was produced using different manufacturing parameters settings. UPV was first measured transversely, across a single layer. Cores were then extracted, and UPV was measured axially through multiple layers before compression testing. The results showed a good correlation between UPV and bulk density but only a weak relationship between UPV and compressive strength. Pulse velocities measured across a single layer were lower than those measured through multiple layers, indicating direction-dependent wave propagation different to what is known from extrusion-based concrete 3D printing. Subsequently, UPV measurements were performed on two full-scale wall elements. The wall elements exhibited very low spatial variability in UPV, although their absolute velocities were lower than those measured for the small specimens. Overall, UPV appears promising for relative quality and homogeneity assessment of SC3DP elements, but further systematic research is required to clarify its relationships with microstructure and mechanical properties imposed by variation of manufacturing parameters. Full article

The conservation of the UNESCO World Heritage site of the Sassi di Matera requires an evaluation of consolidation strategies for Gravina calcarenite, a highly porous calcareous stone extensively used in the historic built environment. The pore system, characterized by a predominance of macropores combined with a significant microporous fraction, plays a key role in the performance and long-term behaviour of consolidating agents. Although consolidation treatments have been widely investigated for carbonate stones, studies specifically addressing Gravina calcarenite remain relatively limited. This study presents a comparative assessment of the performance and durability of four commercially available strengthening agents: an ethyl silicate-based product, two nanolime formulations, and a nanosilica-based treatment. The products were applied to Gravina calcarenite and evaluated using a multi-analytical approach integrating mercury intrusion porosimetry, water absorption assessed by the contact sponge method, ultrasonic pulse velocity (UPV), colorimetric measurements, and artificial aging tests. The results reveal distinct performance trends: the ethyl silicate-based product shows the most pronounced immediate reduction in water absorption, together with a consistent increase in UPV, although these effects are not retained after aging. The more concentrated suspension of Ca(OH)₂ nanoparticles (50–250 nm) exhibits a moderate reduction in water absorption with limited chromatic impact, although a decrease in effectiveness emerges after aging. In contrast, the Ca(OH)₂ nanoparticle suspension (100–300 nm), dispersed in isopropanol at a concentration of 5 g/L, shows more limited and variable changes across the investigated parameters. The nanosilica-based treatment shows a reduction in water absorption and the largest mean increase in UPV after application, although with greater variability among specimens, together with modifications in the finer and intermediate pore fractions. None of the investigated products provided a uniform and persistent improvement across all evaluated parameters. Overall, the evaluation of the investigated properties provides a basis for assessing treatment performance and supporting informed conservation strategies. Full article

Elevated salinity can significantly affect the rheological behavior, consistency development, and early strength development of API Class G cement slurries. This study experimentally investigated the effect of NaCl additions of 0, 4, and 8 wt.% BWOC on cement slurries with densities of 1.5 and 1.9 g/cm³ at temperatures of 25, 50, 75, and 90 °C. Rheological parameters, the times required to attain selected UCA-estimated compressive strength thresholds, and the ultrasonic cement analyzer (UCA)-estimated compressive strength after 12 and 24 h were evaluated. The results indicated that the effect of NaCl was not proportional to its concentration but varied with temperature, slurry formulation, and the property being evaluated. NaCl generally reduced plastic viscosity and yield stress, whereas gel strength exhibited a non-uniform response with a pronounced dependence on temperature. Its influence on atmospheric consistency development and early strength development was likewise non-monotonic. Under certain test conditions, higher NaCl concentrations accelerated the attainment of the initial strength thresholds; however, they did not consistently increase the UCA-estimated compressive strength after 24 h or improve all evaluated operational properties. Among the three investigated NaCl concentrations, the 4 wt.% formulation frequently exhibited favorable responses across several evaluated parameters; however, no single NaCl concentration consistently provided the most favorable response for every property or under all investigated conditions. The findings provide a basis for the further optimization of cement slurry formulations intended for use in high-salinity environments. Since the experimental program did not include independent repetitions, the observed differences should be interpreted as descriptive trends that require statistical validation in future studies. Full article

Ultra-high-performance concrete (UHPC) is characterized by exceptional compressive strength; however, its structural performance is primarily governed by tensile behavior, fracture resistance, and energy dissipation. This study presents a comprehensive mechanical characterization of a steel fiber-reinforced UHPC incorporating a slag–limestone powder-based binder system with a low water-to-binder ratio of 0.15 and steam curing at 90 °C for 48 h. The experimental program comprised compressive strength, flexural behavior, split and direct tensile response, impact energy absorption, ultrasonic pulse velocity, and an assessment of specimen size and geometry effects. The UHPC achieved mean compressive strengths of approximately 209 and 218 MPa at 7 and 28 days, respectively, in 75 × 150 mm cylindrical specimens, indicating only modest strength development after the initial steam-curing period. Smaller cube specimens exhibited higher nominal compressive strengths, reaching approximately 221 and 227 MPa at 7 and 28 days, respectively, demonstrating a measurable but limited specimen-size effect. Flexural testing produced an average strength of 33.1 MPa and a stable post-peak response, although no strain hardening in bending was observed. Split tensile strength reached approximately 16.1 MPa, exceeding that of conventional normal-strength concrete by more than four times. Direct tensile tests demonstrated an intrinsically ductile response, with tensile strengths above 10.9 MPa and strain capacities of 0.25–0.30%, including a pronounced strain-hardening regime. Under drop-weight impact loading, specimens absorbed more than 40 J of energy without catastrophic fragmentation. Ultrasonic pulse velocity averaged 5344 m/s, indicating a dense and well-integrated microstructure. Overall, the results confirm that the investigated UHPC functions as a fracture-resistant structural composite in which tensile capacity, fiber-controlled crack bridging, and energy dissipation govern performance across multiple loading modes. Full article

Drainage pipeline environments are typically characterized by darkness, high humidity, water accumulation, sediment deposition, reflective surfaces, and severe occlusions. These challenging conditions make conventional single-sensor inspection methods highly susceptible to environmental interference, resulting in false detections, missed defects, and insufficient reliability in defect confirmation. To address these challenges, this paper proposes a vision–LiDAR–ultrasonic multi-sensor fusion method for defect confirmation in drainage pipeline inspection. The three sensing streams are processed in parallel rather than using visual detection as the exclusive trigger: the vision branch performs high-recall screening of apparent defects, the LiDAR branch continuously evaluates geometric anomalies in spatially indexed point-cloud segments, and the ultrasonic branch independently evaluates wall-thickness and echo anomalies along the valid probe-contact path. Candidate regions proposed by any branch are merged through timestamp-, odometry-, and coverage-aware spatial association, after which all available visual, geometric, and acoustic evidence at each union candidate is mapped to basic probability assignments and fused using reliability-constrained Dempster–Shafer evidence theory. The five-run evaluation on the fixed 105-group test subset (18 defects and 87 non-defects) gives the proposed method an Accuracy of 97.7 ± 0.5%, Precision of 93.4 ± 2.2%, Recall of 93.3 ± 2.5%, F1-score of 93.3 ± 1.5%, and false-alarm rate of 1.4 ± 0.5%. Under the same test protocol, the vision-only baseline gives an F1-score of 81.1 ± 2.4% and a false-alarm rate of 3.9 ± 0.6%. These results are calculated from the measured per-group predictions obtained in the experiments. Full article

We investigated the possibility of developing super austenitic stainless steel Avesta SMO 254 X1NiCrMoCuN20-18-7 (EN 10088-4) and austenitic stainless steel X15CrNiSi25-21 (EN 10095) coated with SiC, resulting in the obtainment of a Metal Matrix Composite (MMC) by additive manufacturing (AM) for the upgrade of nozzles for sulfur recovery thermal reactors. One layer of the MMC targets the outer surface of the part that is in constant contact with the flame and the area is subjected to high friction erosion. The Directed Energy Deposition Laser (DED-LB) method has made it possible to produce a high strength-to-weight ratio. The aim is to engage lower-cost material with similar thermal stability and durability in extreme conditions. The robotic unit used for the application allowed for computer control of the positioning, feeding of the SiC particles inside the shielding gas and deposition in the molten pool. After the solidification process, visual testing (VT) and ultrasonic testing (UT) were applied for non-destructive evaluation, checking for disbonding and subsurface imperfections. Then, samples were tested with microhardness measurements, bond strength, microcracking detection, porosity, interface zone assessments and microstructural analysis. The process achieved 0.4 to 0.7 KJ mm⁻¹ heat input with no defects and the intended nozzle surface passed UT and VT. Controlled parameters provided strong metallurgical bonding. Full article

Ultrasonic bonding offers a promising alternative to traditional sewing and other plastic bonding techniques, with several potential advantages. This paper comprehensively analyzes ultrasonic bond characteristics in PVC-coated hybrid textiles, prevalent in awnings and camping tents. Untreated samples were used as controls to compare the effects of ultrasonic bonding on various characteristics. Developed experimental designs were applied using a 12 mm welding width in a lapped seam, with carefully selected parametric levels to achieve higher bond strength based on preliminary test results. Mechanical properties (tensile, cyclic, and tear strength, including thickness reduction) were thoroughly examined to assess ultrasonic bond seam efficiency. The analysis covered thermal, chemical, morphological, and weight loss aspects before and after ultrasonic welding. Results showed that the weld seam tensile efficiency ranged from 68.27% to 96.13%, indicating enhanced durability. Cyclic efficiency exceeded 95%, tear efficiency surpassed 70%, and both treated and untreated samples showed strengths above standard thresholds. Thermal findings indicated a 3% increase in crystallinity after ultrasonic treatment, enhancing thermal stability with lower weight loss and causing shifts in glass transition and melting temperatures. FTIR spectra revealed that ultrasonic bonding had no significant impact on the material’s chemical properties. Morphological analysis identified pre-existing microvoids, with no significant increase in their number and/or size following ultrasonic treatment. Overall, the study demonstrates the efficacy of ultrasonic welding in improving the mechanical, chemical, and thermal properties of PVC-coated hybrid textiles, providing valuable insights for applications like awnings, camping tents, and roofing materials for short- and long-term use. Full article

Non-destructive evaluation (NDE) methods are widely used to assess concrete quality, but their interpretation in reinforced concrete members remains challenging because measured responses may be influenced by reinforcement layout, casting and surface conditions, and testing configuration. This study investigates the effects of longitudinal reinforcement type, stirrup spacing, and stirrup material on Schmidt rebound hammer (SRH) and ultrasonic pulse velocity (UPV) responses of concrete beams. Nine beams were cast from the same concrete batch: one plain concrete reference beam, steel-reinforced beams, GFRP-reinforced beams, and hybrid steel–GFRP-reinforced beams. Two stirrup spacings, 100 and 200 mm, and two stirrup materials, steel and GFRP, were considered. In total, 1044 rebound readings and 162 UPV measurements were collected, with UPV testing performed using Right–Left direct, longitudinal direct, and Right–Left indirect configurations. Compared with the plain reference beam, the mean rebound number (RN) increased by up to 21.5% in steel-reinforced beams and 23.2% in hybrid beams, whereas the GFRP-reinforced beam with wider stirrup spacing showed a slight reduction of about 0.8%. UPV differences were more moderate, with a maximum increase of approximately 10% relative to the plain beam. Rebound results also showed a clear face effect, with the bottom face producing the highest values and the top face the lowest. The dense spatial mapping captured local variability within each beam; however, because one beam represented each configuration, the comparisons are interpreted as descriptive specimen-level trends rather than generalized reinforcement effects. Single-pair spacing comparisons indicated larger and more variable differences in RN than in UPV between the 100 and 200 mm specimens. These findings demonstrate the importance of documenting casting face, reinforcement proximity, measurement location, and transmission path when interpreting NDE results in hybrid-reinforced concrete members. Full article

Continuous monitoring of gas-induced changes in coal is important for carbon dioxide storage, coalbed methane recovery, and underground mine safety. Conventional ultrasonic monitoring primarily relies on direct-wave velocities, which may exhibit limited sensitivity to subtle, distributed changes within the coal microstructure. This study evaluates coda wave interferometry (CWI) for monitoring the response of an anthracite coal specimen to helium (He) and carbon dioxide (CO₂) injection under controlled triaxial loading with an axial-to-confining stress ratio of 2:1, with confining stress held 1.0 MPa above the gas pressure in every test so that the effective confining stress was constant at 1.0 MPa and the stages differ only in the gas present. Gas was introduced at nominal injection pressures of 2.5, 5.5, and 12.5 MPa. Ultrasonic waveforms were recorded continuously for 5 h during the CO₂ experiments and 7 h during the He experiments. P- and S-wave velocities, and their fractional changes (dv/v), were calculated from Akaike Information Criterion-based arrival picks, while coda-derived relative velocity changes (δv/v) were estimated by the CWI stretching method over a 300–600 µs coda window. All six gas–pressure conditions were imposed sequentially on a single specimen, which was vented, degassed, and reconditioned between successive runs. CO₂ exhibited slower upstream-pressure dissipation than He, a response consistent with sorptive retention and adsorption-induced modification of the coal pore structure. Direct-wave velocities captured pronounced mechanical changes at low and intermediate injection pressures but showed limited sensitivity during the 12.5 MPa CO₂ experiment. In contrast, CWI detected a persistent negative δv/v trend at 5.5 MPa and a progressive negative trend at 12.5 MPa. Although adsorption was not measured independently, the contrasting He and CO₂ responses demonstrate that CWI can complement direct-wave analysis by detecting subtle, distributed changes associated with coupled mechanical and gas–coal interactions. Full article

High-precision manufacturing in unstructured factories imposes stringent requirements on real-time scene perception and end-effector positioning accuracy. Traditional single-sensor solutions suffer from perception blind spots in human-robot mixed environments with complex lighting, while chassis cumulative error often leads to rigid collisions during end-effector operations. To address this, this paper proposes and evaluates a decision-level multi-sensor coordination mechanism for robust navigation and high-precision planar positioning of industrial mobile robots. The mechanism assigns explicit sensor roles, distance-dependent trigger conditions, and deterministic safety priorities. At the navigation and obstacle avoidance level, a sequential decision policy is constructed: macroscopically, a lightweight You Only Look Once version 5 small (YOLOv5s) is utilized for the early detection of dynamic objects, providing bounding-box coordinates to trigger preemptive deceleration, while LiDAR independently provides geometric ranging for ROS local-costmap updating and detour replanning; microscopically, a low-level hardware interrupt strategy triggered by ultrasonic sensors is proposed to mitigate near-field blind spots and reduce communication latency. At the end-effector positioning level, under illumination conditions ranging from 200 to 1000 lux, an adaptive alignment algorithm combining hue-saturation-value color-space morphological processing and Kalman filtering is proposed to suppress measurement noise caused by illumination variations and mechanical vibrations. Experiments in the tested dynamic human-robot mixed scenarios showed no rigid collisions for the proposed system and an emergency response time of approximately 50 ms against sudden blind-spot intrusions. Simultaneously, the system achieves a 95% reliability rate in controlling the end-effector 2D planar positioning error (X-Y plane) within a ±2 mm tolerance under complex illumination interference. These results demonstrate improved navigation safety and planar-positioning reliability under the tested flexible-manufacturing conditions. Full article

Owing to their exceptional thermal insulation and protective capabilities, thermal barrier coatings (TBCs) are widely applied to critical hot-section components of aero-engines. However, under increasingly harsh service environments, internal defects such as delamination tend to form within the coatings, posing a severe threat to engine operational safety and service life. To effectively evaluate delamination defects in TBCs, this study employs the immersion ultrasonic pulse-echo technique to inspect specimens subjected to various thermal cycling treatments. Four specimens, subjected respectively to 21, 32, 43, and 54 thermal cycles at 1200 °C, were tested. Ultrasonic response data were systematically acquired via normal incidence scanning from both the superalloy substrate side and the ceramic top coat side. Combining Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT) based on the generalized Morse wavelet, Wavelet Packet Energy Entropy (WPEE), and peak-to-peak amplitude variations of the second echo, multi-dimensional features were extracted from ultrasonic signals across the frequency domain, joint time-frequency domain, and energy distribution profiles. Through comparative analysis, ultrasonic waveform and time-frequency characteristics representing defect evolution were obtained. A significant monotonically decreasing trend of WPEE with the aggravation of interfacial delamination was established, characterizing the acoustic energy confinement process induced by interfacial damage. Furthermore, a multilayer finite element (FE) model reasonably reproduced dynamic acoustic wave propagation; numerical results are in agreement with experimental data, validating the feasibility of the proposed detection method. The detection and evaluation framework established in this study provides a reference for safety monitoring and lifespan prediction of aero-engine TBCs. Full article

The article examines the use of pozzolanic cement and ground glass waste in mortar and their influence on physical and mechanical properties and resistance to the alkali–silica reaction (ASR). The materials used and the research methods used to determine the main properties of mortar are described. CEM II/A-P 52.5 N pozzolanic cement with ash additive, 0/4 fraction sand, and ground glass waste was used for the tests. The resistance of mortar to the ASR was determined according to the developments using the RILEM AAR-2 methodology. Seven mortar compositions were studied, in which cement was replaced with glass processing waste in the amounts of 5, 10, 15, 20, 25 and 30% of the cement mass. The effect of the amount of pozzolanic cement and glass waste on the following mortar properties was studied: density, ultrasonic pulse propagation velocity, compressive and flexural strengths, and ASR. A comparison of the physical and mechanical properties of mortar before and after ASR tests was performed. It was found that by modifying mortar with ground glass, i.e., by replacing pozzolanic cement with 5% to 10% ground glass waste, it is possible to reduce the amount of cement in the mortar, increase resistance to the alkali–silica reaction, and at the same time reduce CO₂ emissions associated with cement production and reuse ground glass waste. Full article