Search Results (12,995)

Coal gangue backfill serves as a primary supporting structure for overlying strata in mined-out areas, and its internal damage evolution is directly associated with the safety and stability of mining operations. Acoustic emission (AE) technology provides an effective approach for investigating damage evolution by capturing transient strain energy release events within materials in real time. However, conventional AE analysis methods predominantly rely on statistical interpretations of individual parameters, making them insufficient for revealing the underlying physical mechanisms governing the influence of fracture characteristics on energy evolution pathways. To address the aforementioned limitations, this paper proposes a fracture mode-informed physics-enhanced machine learning framework for predicting acoustic emission energy evolution in coal gangue backfill. First, based on the AE monitoring data of coal gangue backfill under uniaxial compression (a total of 18,992 valid AE events from three parallel specimens with identical mix proportion), the RA–AF parameters combined with the K-means unsupervised clustering algorithm were employed to automatically identify tensile and shear fracture modes, thereby constructing physically meaningful fracture mode labels. Second, the fracture mode information was integrated with AE statistical features, including rise time, duration, amplitude, counts, peak frequency, and center frequency. After selecting the most informative features using the minimum-redundancy, maximum-relevance (mRMR) algorithm, a Bayesian optimization-based support vector regression (BO-SVR) model was developed for AE energy prediction. The results demonstrated that after incorporating the fracture mode-based physical labels, the proposed model achieved a coefficient of determination (R²) of 0.9027 on the testing dataset, with an RMSE of 0.1562 and an MAE of 0.1204. Ablation experiments further confirmed that the introduction of fracture mode labels improved the R² value by approximately 3.4% compared with the model without physical constraints. Fivefold cross-validation yielded an average R² of 0.9460 with a standard deviation of 0.0023 for the SVR model. Furthermore, per-specimen independent holdout validation yielded an average R² of 0.9044 with a standard deviation of 0.0512 across three independent specimens, confirming the excellent stability and repeatability of the proposed framework. The original single-specimen results (4083 events, R² = 0.9727) are provided as a baseline reference. Mechanistic analysis revealed that the average energy release associated with shear fractures was approximately 739 times that of tensile fractures, demonstrating that fracture mode information provides physically consistent mechanical constraints for the machine learning model. This study provides an effective new method for the stability evaluation and intelligent monitoring of coal gangue filling materials. Full article

Protective gloves used by firefighters and other first responders may be stored for long periods in environments where radon and its decay products can accumulate. However, despite extensive research on the radiation ageing of elastomers, directly comparable data on the long-term response of finished nitrile rubber (NBR) and chloroprene rubber (CR) used as protective glove materials under radon chamber conditions remain limited. Accordingly, this study evaluated time-dependent changes in these two glove materials during up to six months of conditioning. The specimens were conditioned at an approximately constant ²²²Rn activity concentration of 540 kBq/m³, corresponding to a cumulative exposure of up to $2.35\times {10}^6$ kBq/m³. Changes were evaluated using microhardness measurements, mechanical testing, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). NBR exhibited a non-monotonic microhardness response, with an initial increase followed by a gradual decrease during further conditioning; after six months, the microhardness remained higher than that of the reference material. Isolated microcracks became visible after six months. In contrast, CR showed a general decrease in microhardness and earlier surface changes, including increased roughness and micropore formation. Its tensile strength decreased from approximately 1.2 MPa to 0.8 MPa after six months, corresponding to a reduction of about 33%, although force at break partially recovered during the later conditioning period. FTIR analysis revealed only limited chemical changes. Overall, the two materials exhibited distinct time-dependent responses, with NBR retaining greater mechanical and morphological stability than CR under the investigated conditions. Although barrier performance was not assessed directly, the observed defects may increase susceptibility to damage during use, highlighting the importance of appropriate storage, stock rotation, and pre-use inspection. Full article

Explicit bond-slip modeling for glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) members is computationally inefficient for structural-scale parametric analyses. This study develops a calibrated equivalent finite-element (FE) framework for GFRP-RC isolated footings on Winkler foundations. A GFRP-RC two-way slab test was used for calibration. After boundary correction, a tensile stress-scaling factor was introduced into the concrete tensile model to compensate for stiffness overestimation caused by the embedded-reinforcement assumption. The calibrated model was then transferred to a full-scale isolated footing, and the effects of subgrade modulus, bar diameter, reinforcement spacing, and footing thickness were examined. The results show that the footing response is governed mainly by settlement development, concrete cracking, and stiffness degradation, while the GFRP stress remains far below its tensile strength. Footing thickness is the most effective structural parameter for improving stiffness and reducing damage, whereas increasing bar diameter provides limited improvement despite higher reinforcement consumption. Reducing reinforcement spacing mainly improves tensile-demand distribution and damage control. The proposed calibrated equivalent FE framework provides an efficient numerical approach for comparative deformation- and damage-based assessment of GFRP-RC isolated footings within the investigated parameter range. Full article

This study investigates the possibility of producing complex metal matrix composites (CMMCs) via powder metallurgy. Two types of powders, a mixture of core–shell Cu@Ag+W@Ag powder and dual core–shell W@(Cu@Ag) powder, have been successfully sintered using spark plasma sintering at 700 °C/5 min, forming Ag–(W+Cu) and Ag–(W@Cu) CMMCs, respectively. Scanning electron microscopy study revealed that both Ag–(W@Cu) and Ag–(W+Cu) CMMCs are characterized by a complex microstructure consisting of Ag matrix reinforced with W@Cu core–shell and a mixture of Cu+W particulates, respectively. The compression tests showed that Ag–(W@Cu) CMMC is characterized by the highest compression yield strength (CYS, 201 MPa) compared to pure Ag (27 MPa) or other counterparts (such as Ag–W, Ag–Cu). On the other hand, Ag–(W+Cu) CMMC exhibits a lower CYS value (150 MPa) by approximately 25% compared to Ag–(W@Cu) CMMC; while its tensile yield strength (TYS) reaches 99 MPa, which is 98% higher than the TYS of pure Ag (50 MPa). Full article

In this study, we identified the stiffness, natural frequency, and damping properties of a metallic mesh fabric applied to spaceborne antennas and proposed finite element models (FEMs) based on static and dynamic property tests. Tensile tests along the course and wale directions were performed to analyze the static characteristics of the metallic mesh fabric, and dynamic property tests were conducted to evaluate natural frequencies and damping properties under pre−tensions. By applying pre−tensions of 1, 3, and 5 N to each edge of the mesh fabric, the 1st natural frequencies were derived as approximately 35, 50, and 60 Hz. Furthermore, by applying direct dynamic loads to the fabric, high damping properties (ζ ≈ 1.0) were confirmed. FEMs of the mesh fabric were developed using a 1D beam−based detailed model and a 2D shell−based simplified model. The effectiveness of both models was validated by comparing numerical results with experimental data, showing discrepancies below 5% for static stiffness in the linear elastic region and within 5.4% for the 1st natural frequency. To evaluate dynamic behavior under an agile attitude maneuver, the simplified mesh model was applied to a 4 m deployable antenna model. Under the maneuver profile, dynamic responses rapidly attenuated due to high damping, with residual vibrations showing peak displacements below 0.02 mm decaying to the origin within 0.2 s. For the proposed 4 m deployable antenna with the SUS316L Atlas−Atlas mesh, the post−disturbance dynamic influence was confirmed to be negligible, indicating that post−maneuver residual vibrations do not cause surface accuracy distortions or degradation in the antenna’s electrical RF performance in orbit. Full article

Phenyl silicone rubber is widely used in aircraft seals for its high- and low-temperature tolerance and chemical stability. However, intense UV radiation and elevated ozone at high altitudes accelerate aging, threatening seal reliability. The accelerated aging tests of phenyl silicone rubber seals have been carried out under UV and ozone to examine their mechanical, microstructural, and chemical evolution. Then, a finite element contact model of phenyl silicone rubber seals was developed considering the influence of UV and ozone aging. Both conditions increased hardness and elastic modulus but reduced tensile strength and elongation at break, with UV degradation markedly more severe. UV exposure caused a 29% maximum loss in elongation (compared to 16% under ozone) and a hardness rise of 2.30 HA, roughly 1.7 times that of ozone aging (1.35 HA). The contact pressure increases by approximately 15.2% and 10.7%. These findings provide a theoretical basis for performance evaluation and service-life prediction of these seals in high-altitude environments. Full article

Gas carburization is widely used to improve the surface durability of load-bearing steels, yet alloy-dependent thermodynamic and kinetic effects often cause large variability in case development and component life. This study presents a physics-guided comparison of carburization behavior in EN3, 20MnCr5, and EN353 steels by integrating hardness profiles, mechanical and wear testing, and thermodynamic–diffusion analysis. Under an identical boost–diffuse–equalize cycle at 930 °C, distinct surface carbon levels of 0.764 wt.% (EN3), 0.792 wt.% (20MnCr5), and 0.822 wt.% (EN353) were obtained. These corresponded to effective case depths of ~1 mm in EN3 and ~2 mm in 20MnCr5 and EN353. Near-surface hardness reached ~12–13 HRC in EN3, ~33 HRC in 20MnCr5, and ~35–36 HRC in EN353. Ultimate tensile strength increased from ~620 MPa (EN3) to ~870 MPa (EN353), while wear mass loss decreased from ~28 mg to ~21 mg. Thermodynamic interpretation showed alloy-dependent moderation of carbon activity and sustained chemical-potential gradients, promoting deeper diffusion. Reconstructed carbon profiles confirmed diffusion-controlled case growth. By enabling longer service life and reduced material replacement, the results support durability-oriented and resource-efficient surface engineering for engineering steels. Full article

Five pectin-rich mucilage fractions from yellow passion-fruit peel, extracted using 0–10.0% (w/v) citric acid, were evaluated in separate films and sunflower-oil emulsions. The 0.086% fraction gave the highest mean tensile strength and Young’s modulus (31.26 and 468.9 MPa), while 0.086–0.50% produced the lowest water-vapor permeability (1.70–1.82 × 10⁻¹⁰ g m m⁻² s⁻¹ Pa⁻¹). The 0.50% fraction produced the smallest initial and day 21 emulsion droplets (1.72 and 1.81 µm) and the lowest day 21 creaming (2.0%). At 10.0% acid, film strength decreased to 3.34 MPa, while emulsion droplets reached 5.31 µm and creaming reached 28.1%, despite the most negative ζ-potential (−56.0 mV). These responses are consistent with reduced molecular integrity under severe extraction and indicate that charge alone does not determine performance. Under the tested formulations, mild extraction at 0.086–0.50% citric acid provided the most favorable combination of film and emulsion properties. Full article

Laser powder bed fusion (LPBF) enables the fabrication of complex metallic components, yet processing dissimilar systems such as copper and 316L stainless steel presents severe challenges due to mismatched physical and thermal properties. This study provides new insights into the role of atomized spheroidal TiC reinforcement in controlling densification, microstructure, and localized deformation mechanisms in LPBF-fabricated Cu- and 316L-based composites and their multi-material joints. Spheroidal TiC particles were introduced at 2 and 4 wt.% into copper and 316L powders via V-type rotary mixing. The microstructural and mechanical response was evaluated through quantitative porosity analysis, Vickers microhardness testing, uniaxial tensile testing, and digital image correlation (DIC) strain mapping. In the copper matrix, adding 2% wt. TiC effectively reduced porosity from 0.83% to 0.44%, yielding an ultimate tensile strength of Rm ≈ 190 MPa and total elongation of 26% compared to 110 MPa and lower ductility for unreinforced LPBF copper. Increasing the TiC content to 4% wt. enhanced strength to Rm ≈ 250 MPa (Rp0.2 ≈ 180 MPa), although elongation decreased to 16%. In the 316L matrix, TiC addition progressively increased mean microhardness from 175.00 to over 322.25 HV0.1; however, 4% wt. TiC induced severe lack-of-fusion defect formation, resulting in a critical porosity of 10.59% and reduced ductility (12%). A DIC strain field analysis demonstrated that 2% wt. TiC promotes uniform strain distribution prior to necking, delaying localized failure. For Cu–316L multi-material joints, reinforcing the copper zone with 2% wt. TiC improved joint integrity, increasing tensile strength from ~110 MPa to ~190 MPa with a maximum elongation of 26%. These findings explicitly demonstrate that tailoring reinforcement concentration is vital to optimizing densification and mitigating strain localization in LPBF multi-material structures. Full article

Ferritic–martensitic EP-450 steel has been widely used for fast-reactor fuel assembly wrappers because of its high resistance to irradiation-induced swelling; however, its radiation-hardened state formed under low-temperature, high-dose neutron exposure may evolve during subsequent thermal exposure. This study examines the time dependence of post-irradiation thermal softening in EP-450 steel taken from two BN-350 spent fuel assembly wrappers irradiated at approximately 351 °C to 61 and 71 dpa. Samples were annealed in static argon at 470 °C for cumulative durations of 10, 30, and 100 h. Vickers hardness was measured for both wrappers, while miniature tensile tests were performed for the 71 dpa material. The initial hardness values were similar, 356 and 360 HV0.2, but the thermal response differed markedly: after 100 h, hardness decreased by 10.2% and 17.9%, respectively. For the 71 dpa material, the 0.2% proof stress decreased from 815 to 752 MPa between 10 and 100 h, while total and localized strains increased from 15.33% to 17.94% and from 8.84% to 11.45%, respectively. These results demonstrate a gradual, time-dependent reduction of irradiation hardening at 470 °C and reveal that materials with similar initial hardness can exhibit substantially different thermal stability. Full article

Polymer concretes with fiber reinforcement have many desirable properties when compared to cementitious concretes, including rapid development of mechanical properties, excellent bond to concrete and other substrates, high tensile strength, and resistance to abrasion and aggressive chemical environments. However, their use as a structural material has been limited, in part, by temperature-dependent mechanical properties, affecting bond and development of steel reinforcement, deformation of structural elements, and section capacity of structural members. This research investigated the development of mechanical properties for a commercially available polymer concrete with fiber reinforcement to determine the effects of temperature on compressive strength, elastic modulus, modulus of rupture, and pull-out bond strength. The compressive, flexural, and bond strengths of the tested polymer concrete with fiber reinforcement were over 70% of their 7 d values within 4 h after mixing when cured at laboratory temperature, demonstrating the rapid development of mechanical properties that is possible with polymer binders. The average 7 d compressive strength across the experimental program was 62.2 MPa at 25 °C, with the measured elastic modulus and modulus of rupture roughly half and three times that of estimated values using established code relationships and the measured compressive strength, respectively. The pull-out bond strength at 25 °C was found to be similar to non-proprietary ultra-high performance and polymethyl methacrylate concretes, and the variation in mechanical properties with temperature was roughly linear and independent of the mechanical property tested when normalized by the value at laboratory temperature. This limited test series supports the structural use of polymer concrete with fiber reinforcement, when in-service temperature is expressly considered in the design process, although further testing is needed to develop rational design procedures. Full article

In this paper, an experimental study on the static strength and fatigue of carbon fiber-reinforced polymer (CFRP) laminates with ply angles of 0°, ±15° and ±45° and single-walled carbon nanotubes (SWCNTs) of 3% mass fraction in epoxy matrix has been presented to systematically demonstrate the SWCNT-modified effect on the static tensile properties and fatigue behavior of the CFRP laminates. The results of pseudo-static tensile tests show that the addition of SWCNTs increases the tensile strength of the three laminates by 37%, 43%, and 34%, respectively, and the elastic modulus by 5%, 62%, and 35%, respectively. The S-N curves obtained by the fatigue tests at various stress levels under graded tension–tension cyclic loads demonstrate that the SWCNT-modified laminates sustain higher stress levels than those without SWCNTs at the same fatigue cycles, and with the most obvious improvement of ±15° laminates. The fracture surface observations of the laminates indicate that the enhanced performance is attributed to the synergistic effects of matrix modification, interfacial bonding improvement and crack bridging by SWCNTs. Therefore, moderate addition of SWCNTs in the epoxy matrix of CFRP laminates is an effective approach for improving both the static strength and fatigue performance of the laminates. Full article

PETG composite filaments containing 1 wt%, 3 wt%, and 5 wt% hexagonal boron nitride (h-BN) were produced. The produced filaments were transformed into test specimens using the fused deposition modeling (FDM) technique. The tensile, compression, and wear behaviors of the composite polymer test specimens produced by the FDM method were investigated. The wear characteristic was measured using a ball-on-flat tribometer under normal loads of 5, 10, and 15 N. The worn surfaces were characterized by profilometer, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). PETG/1hBN showed the lowest coefficient of friction (COF) at all tested loads and provided a 40–46% reduction compared to neat PETG. In addition, it was observed to have the wear track with the lowest depth and the smoothest surface. Furthermore, the highest compressive yield strength among the investigated compositions was reached in these specimens. For specimens containing higher h-BN contents, a proportional improvement could not be achieved, and this was interpreted as being due to the agglomeration of the filler material reducing its effectiveness in the transfer film layer. These results show that the addition of a low amount of h-BN to PETG is an effective and easily processable method for improving the wear resistance of the PETG matrix. Full article

This paper is intended to study the fatigue behaviour of low-carbon steel DD11 with the combined effect of pre-strain and notch geometry, which are important in components working under cyclic loading in service. To this end, experimental fatigue tests were performed on specimens with different configurations: (i) specimens pre-strained to 24% (beyond the tensile strength point), (ii) specimens combining pre-strain and notch effects, and (iii) double-notched specimens, which feature a higher stress concentration factor. The experiments were complemented by numerical simulations and analytical formulations, and fracture surfaces were examined to support the interpretation of the results. The main results show that the applied pre-strain (24%) reduces the fatigue limit by 8.5% when compared to the un-notched case. However, when pre-strain and notch effects are combined, no significant additional influence on the fatigue limit is observed. In the double-notched configuration, a higher stress concentration factor is found compared to previous studies by the authors, leading to a reduction in the fatigue limit, with localised plasticisation similar to that observed in the compared scenario. Full article

High-density polyethylene (HDPE) has attracted attention as an alternative material for marine structures because of its chemical resistance, processability, and recyclability. However, internal pores formed during extrusion welding can reduce weld quality and mechanical performance. This study investigated pore formation mechanisms in HDPE extrusion welds by considering material throughput, filler wire storage condition, and artificial defect volume fraction. Porosity increased from 0.06% to 0.37% as material throughput increased from 0.96 to 2.00 kg/h and slightly decreased to 0.33% at 2.60 kg/h. Under these process conditions, tensile strength changed within approximately 1.49%, whereas elongation decreased more clearly with increasing porosity. In contrast, residual surface moisture on the filler wire caused severe pore formation and reduced tensile strength by approximately 55.53%. Artificial defect tests also confirmed that increasing internal defect volume directly reduced tensile strength. Overall, controlling material throughput and removing surface moisture are essential for improving HDPE extrusion weld quality. Full article