This article examined the influence of pulse current duty cycle at different pulse durations and frequencies on the ratio of thermal and true electroplastic effects (EPEs) during quasi-static tension testing of commercially pure Grade 2 titanium in a coarse-grained recrystallized state. Duty cycle values varied over a wide range corresponding to the minimum thermal effect of the current. Microstructural studies were performed using optical microscopy, microhardness analysis of various sections of the specimen, and scanning electron microscopy of the fracture surface. An increase in temperature, a decrease/increase in the amplitude of stress surges, a reduction in flow stress, ductility, and suppression of the twinning mechanism with a decrease in the duty cycle in the range of 1000-50,000 were demonstrated. In all cases, the failure mechanism remained ductile but changed from dimple type to predominantly cup type with a simultaneous increase in porosity. The use of the duty cycle parameter allows one to regulate the contribution of thermal and electroplastic effects, which can be useful both for modeling the EPE mechanism and for practical use in pressure processing of titanium alloys accompanied by current.
In this study, the individual effects of different modification strategies, namely 1% nano-bentonite and Bacillus subtilis (B. subtilis, 1.0 & times; 108 CFU/mL) combined with 0.3% polyacrylamide (PAM), were investigated to improve the water resistance and mechanical performance of rice husk ash (RHA)-based geopolymer slurry-infiltrated fiber concrete (SIFCON). Our objective of this study was to reduce water absorption through interfacial transition zone (ITZ) refinement and matrix densification without compromising the mechanical properties of the composite material. In addition to microstructural observations using scanning electron microscopy (SEM), an extensive experimental investigation was performed, including compressive strength, splitting tensile strength, flexural strength, and water absorption tests. Our results showed that nano-bentonite boosted matrix compactness and ITZ quality lead to higher compressive strengths, up to 51.7 MPa, and lower water absorption than untreated mixes. In contrast, B. subtilis combined with PAM increased the matrix density via bacterial action and internal curing. This combination yielded the best results: a compressive strength of 52.9 MPa, a flexural strength of 22.92 MPa, and least water absorption at 1.46%. The optimum bacteria-treated mixtures exhibited up to 35% lower water absorption than the corresponding untreated mixtures. SEM observations confirmed a denser microstructure, reduced microvoid content, and improved fiber-matrix bonding in the modified composites. The novelty of this study lies in the comparative evaluation of biological and nano-modification approaches as separate ITZ enhancement strategies for the sustainable RHA-based geopolymer SIFCON. These findings demonstrate the potential of these modification techniques for the development of durable and environmentally friendly geopolymer composites.
In this study, we proposed a data-driven approach integrating machine learning and experimental validation for the intelligent formula design of melt purification agents for recycled aluminum. Five machine learning algorithms, including random forest regression (RFR), gradient boosting regression (GBR), extreme GBR, polynomial kernel support vector regression, and radial basis function kernel support vector regression, were comprehensively evaluated in terms of root mean square error, mean absolute error, and coefficient of determination. RFR was selected as the optimal model. Combined with Pearson correlation matrix and SHapley Additive exPlanations (SHAP) interpretability analysis, the influence mechanism of each component on the hot-cracking susceptibility and ultimate tensile strength of recycled aluminum alloy was clarified. Multi-objective optimization was carried out to minimize hot-cracking susceptibility and maximize tensile strength, and a novel melt purification agent primarily based on CeF3 (NF-GX) was developed. The predicted values of hot-cracking susceptibility and tensile strength of NF-GX are 189.97 and 207.80 MPa, respectively, while the corresponding experimental measured values are 214.00 +/- 10.39 and 191.33 +/- 6.11 MPa, with relative errors of 11.23% and 8.61%. Comparative tests with three commercial purification agents show that NF-GX reduces the metal burn-off rate from 29.19 +/- 1.36% to 21.30 +/- 0.56%, and refines the average grain size from 191.64 +/- 1.98 to 106.36 +/- 0.92 mu m. Microstructural characterization confirms that the synergistic effect of multi-component fluorides in NF-GX can effectively remove oxide inclusions, break continuous grain boundary liquid films, and induce heterogeneous nucleation, thereby achieving microstructure densification and grain refinement. This study demonstrates that machine learning-driven formula design can break through the limitations of the traditional empirical trial-and-error method, providing a new idea and method for the customized development of high-performance melt purification agents for recycled aluminum.
Polyester-based materials are widely used in insulation systems due to their low cost and relatively low thermal conductivity; however, further reduction in heat transfer is desirable for building envelope components exposed to elevated surface temperatures. In this study, polyester-silica aerogel composite insulation tiles were fabricated and systematically evaluated to identify the filler concentration that minimizes thermal conductivity while maintaining practical curing integrity. Silica aerogel powder was incorporated into unsaturated polyester resin at 1-5 wt.% (relative to resin mass) using methyl ethyl ketone peroxide (MEKP) as the hardener and cobalt naphthenate as the accelerator, and glass-fiber reinforcement was applied as a constant layup to enhance structural integrity. Curing was performed at 120 degrees C. The resulting composites were characterized using Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and steady-state thermal conductivity measurement suing a guarded heat flow meter, indicating retention of the polyester chemical structure, predominantly amorphous composite formation, and improved high temperature thermal resistance with increasing silica content. The monotonic reduction in thermal conductivity was consistent with interruption of continuous matrix conduction pathways and increased thermal boundary resistance introduced by dispersed, ultra-low-conductivity aerogel domains within the polyester matrix. Thermal conductivity was measured under steady-state conditions at 55 degrees C using a guarded heat flow meter in triplicate (N = 3). The thermal conductivity decreased from 0.2800 +/- 0.0030 W m-1 K-1 at 1 wt.% SiO2 to 0.2300 +/- 0.0036 W m-1 K-1 at 5 wt.% SiO2, corresponding to an overall reduction of 0.0500 W m-1 K-1 (17.9%) within the investigated range. TGA results further indicated a major decomposition event over approximately 390-500 degrees C, with composition-dependent residues increasing with silica loading, consistent with enhanced thermal resistance at elevated temperatures. Overall, 5 wt.% silica aerogel provides the lowest measured thermal conductivity among the tested formulations and supports the potential of these polyester-based composites for rigid insulation tile applications with practical curing feasibility for roof and building-envelope use.
Red clay exhibits unfavorable engineering properties that limit its direct use as subgrade fill material. This study investigated the stabilization of red clay using cement, fly ash, silica fume, and brick powder. Uniaxial compression tests were conducted on single-stabilizer and multi-component mixtures to evaluate their mechanical behavior. Results show that cement provides the highest strength improvement, followed by silica fume, fly ash, and brick powder. Multi-component mixtures with cement as the primary binder, combined with silica fume and fly ash, achieved the highest strengths from 2.0 to 2.4 MPa, representing a 40% increase over single-stabilizer treatments. Three distinct failure modes were identified: ductile fragmentation, X-shaped conjugate shear bands, and single-plane brittle shear. Their evolution is governed by the dominant stabilization mechanism. Range analysis revealed the influence weights of the four stabilizers on strength development as 0.594 for cement, 0.183 for silica fume, 0.135 for fly ash, and 0.088 for brick powder. A predictive model based on a comprehensive strengthening coefficient was proposed and validated against experimental data. The findings demonstrate that the synergistic use of cement and multi-source solid waste provides an effective approach for red clay improvement.
The growing clinical demand for antimicrobial textiles requires ensuring that their performance remains stable after sterilization, a critical condition for medical-grade materials. Silver nanoparticles (Ag NPs) are widely used for their antimicrobial properties. However, autoclave sterilization can induce morphological and physicochemical changes due to wet steam and high-pressure conditions, potentially compromising their antibacterial performance. The specific behavior of polyvinylpyrrolidone (PVP)-stabilized Ag NPs immobilized on cellulosic fibers under clinically relevant sterilization conditions remains poorly understood. This study evaluated the antibacterial performance of Ag/PVP-coated cotton gauzes subjected to a standard clinical sterilization protocol consisting of autoclaving at 121 degrees C for 35 min followed by dry heating. The non-woven cotton gauzes were in situ impregnated with Ag/PVP nanoparticles under different synthesis conditions, with varying impregnation time and substrate alkalinity, with an emphasis on sonication as the dispersion method. The textiles were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), while colloidal solutions were analyzed by ultraviolet-visible spectroscopy (UV-Vis). Water absorption, water vapor permeability, and tensile properties were also evaluated. Quantitative evaluation of the antimicrobial effect of Ag/PVP nanoparticle-impregnated gauzes before and after the autoclaving process was performed according to ASTM E-2149 and correlated with nanoparticle size changes. Additionally, cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Antibacterial testing according to ASTM E-2149 showed reductions of approximately 95% against Staphylococcus aureus and 99% against Escherichia coli, which were maintained after autoclave sterilization. MTT results showed acceptable cell viability at 24 h, followed by a decrease at 48 h, indicating a time-dependent cytotoxic effect. The release study further revealed that an additional 24 h of static impregnation significantly improves nanoparticle homogeneity and release control. Overall, this work provides practical guidelines for the rational design of clinically compatible antimicrobial textiles with predictable post-sterilization behavior.
Copper is an important engineering material for precision micro-devices, due to its superior electrical/thermal conductivity and ductility. However, its high plasticity and toughness introduce significant challenges in traditional milling, including work hardening, tool adhesion, burr accumulation, and poor surface finish, which limit further improvement of machined surface quality. Ultrasonic vibration-assisted machining (UVAM) can improve surface integrity of difficult-to-machine materials by introducing high-frequency intermittent cutting, which reduces cutting force, heat accumulation, and tool wear. Compared with one-dimensional longitudinal or two-dimensional longitudinal-torsional vibration, the longitudinal-bending composite vibration enables independent adjustment of amplitude and phase via two separate ultrasonic signals, thus offering greater flexibility under varying machining conditions. Nevertheless, the research on longitudinal-bending UVAM of copper remains scarce. In this study, we experimentally investigated longitudinal-bending composite vibration-assisted milling (LBVAM) of copper. Burr morphology, surface roughness, and microstructure were systematically compared among conventional milling, longitudinal vibration-assisted milling, and LBVAM. The influences of vibration amplitude and spindle speed on surface quality were also examined. Experiments were conducted using a 1 mm diameter four-edge tungsten steel micro-milling cutter, with amplitudes ranging from 1 to 5 mu m and spindle speeds of 1000-3000 r/min. Our results showed that longitudinal-bending composite vibration significantly suppresses burr formation and reduces surface roughness by 40.27% compared to conventional milling, and by 23.44% compared to single longitudinal vibration-assisted milling. Furthermore, surface roughness further decreases with increased amplitude, reaching a minimum of 129 nm at 5 mu m, accompanied by a uniform "fish-scale" microstructure. The best surface quality was achieved at 2000 r/min, whereas speeds that were too high or too low caused disordered surface texture or secondary damage. This work confirms the feasibility and advantages of longitudinal-bending UVAM in enhancing machined surface quality of copper, thus providing valuable processing support for the microfabrication of high-precision copper components in precision electronic applications.
The incorporation of natural fibers into composite materials has attracted growing interest due to their low cost, regional availability, and reduced environmental impact. However, their adoption in industrial applications remains limited by the absence of reliable predictive models linking constituent properties with the laminate's macroscopic behavior. In this context, this work developed and validated a multiscale predictive model to estimate the tensile behavior of laminates reinforced with fique fiber. The approach first evaluates classical micromechanical predictions (Chamis model) against experimentally characterized ply properties, demonstrating that idealized analytical formulations fail to capture the structural heterogeneity of twisted natural fibers. Consequently, experimentally obtained ply data were used as direct inputs for classical laminate theory (CLT) and finite element method (FEM) simulations to ensure accurate laminate-level predictions. The predictions were experimentally validated according to ASTM D3039 in [0 degrees/90 degrees/0 degrees], [90 degrees/0 degrees/90 degrees], and [90 degrees/0 degrees/45 degrees] configurations. The results showed that the Chamis model systematically underestimates longitudinal strength and overestimates transverse stiffness due to assumptions that do not accurately represent natural fibers. In contrast, when both CLT and FEM were informed by the experimental properties of the unidirectional ply, they achieved predictions consistent with the tests: the combined coefficient of determination of 0.69 for CLT and 0.70 for FEM, with mean absolute errors of 16.65 and 16.04 MPa, respectively.
Environmental concerns over plastic waste have increased the demand for sustainable materials in additive manufacturing. Polylactic acid (PLA), a biodegradable polymer, is widely used in 3D printing but is limited by poor thermal and ultraviolet (UV) durability. This study explored the development of PLA composite filaments for fused filament fabrication (FFF) by combining virgin PLA (vPLA), reprocessed PLA (rPLA), and titanium dioxide (TiO2) nanoparticles at 0.25 and 0.5 wt.% for 3D-printing material. Six PLA-TiO2-based formulations were melt-extruded into filaments using a single-screw laboratory extruder, with processing adjusted to the TiO2 content to ensure filament quality. The resulting filaments were then used to fabricate 3D-printed specimens for subsequent mechanical, thermal, and structural characterization. Results show that incorporation of TiO2 nanoparticles improves the thermal stability and mechanical performance affected by the recycling process. Fourier transform infrared spectroscopy (FTIR) analysis confirmed chemical integrity, and thermogravimetric analysis (TGA) and tensile testing showed increased stiffness and thermal resistance. Additionally, rPLA accelerates biodegradation in compost due to its reduced structural integrity and increased hydrophilicity, while TiO2 nanoparticles can slightly mitigate this effect in higher concentrations.
Thermal fatigue is a dominant failure mechanism in aluminum piston alloys exposed to repeated heating and cooling in internal combustion engines. In this study, the thermal fatigue behavior of cast aluminum 4032 alloy (Al4032) was investigated using a custom-built test rig that combines external electrical heating with internal water cooling to generate severe cyclic thermal gradients in wedge-shaped specimens. The specimen-tip temperature was cycled between 75 and 270 degrees C with 10 s heating and 10 s cooling per cycle, and crack initiation and growth were monitored by optical microscopy. Thermal fatigue started cracking at approximately 3000 cycles, predominantly near the internally cooled region where the thermal gradient and associated stresses are highest. After initiation, crack length increased rapidly during intermediate cycles and then stabilized, with crack growth approaching saturation at approximately 15,000 cycles under the tested conditions. These results demonstrate that gradient-driven cyclic thermal stresses govern crack nucleation sites and subsequent propagation behavior in Al4032 and provide service-representative experimental evidence relevant to piston regions influenced by internal cooling.
Microalloying elements (<1 wt%) are widely used in the steel industry, but their effect on AgAu alloys is still unclear. Therefore, this paper uses first-principles calculations and experimental verification to explore this topic. For first-principles calculations, the formation enthalpy, elastic constants, and mechanical properties of AgAu alloys and microalloyed AgAu systems (doped with Pd, Pt, Ni, Cu, Zn, Ti, Y, Be, Mg, Al, Sr) were calculated. The results show that the AgAu alloys and AgAu-Malloys have thermodynamic and mechanical stability. Doping elements increase the hardness, shear modulus, and Young's modulus of the alloys to varying degrees. Except for Be, other doping elements all reduce the elastic anisotropy index of the alloys to varying degrees. Experimentally, an Ag-16wt%Au-0.5wt%Al alloy was prepared, and the alloy contained Ag, Au, AlAu, and trace amounts of AlAu2 phases. The experimental hardness value was slightly lower than the calculated value. Energy-dispersive spectrometer (EDS) results proved that the alloy matrix was an Ag(Au, Al) solid solution and the intermetallic phase AlAu was distributed in the matrix. Additionally, trace amounts of the AlAu2 may be interspersed within the Ag(Au, Al) solid solution. There is a certain mutual verification between the calculation results and experimental results in this article. Therefore, this study provides a new approach to improving the performance of AgAu alloys by doping with microalloying elements.
The effects of Cr and Er microalloying on the microstructural evolution and mechanical properties of high-pressure die-cast hypereutectic Al-Si-Ni alloys were systematically investigated. The morphology and distribution of primary Si were quantitatively analyzed using optical microscopy and Image) software, and the tensile properties were evaluated at room temperature and 350 degrees C. The results indicate that Cr addition promotes the formation of CrSi2 phases, which act as heterogeneous nucleation sites, increasing the nucleation rate and suppressing the growth of primary Si. Er addition refines primary Si through interfacial segregation and the modification of growth kinetics; however, excessive Er leads to the precipitation of Al3Er and weakens the refinement effect. As a result of the refined and more homogeneous distribution of primary Si, both Cr-and Er-containing alloys exhibited enhanced tensile strength and ductility at room temperature and 350 degrees C. The 0.4Cr alloy showed the best mechanical performance among the investigated compositions, and the optimal Er addition was identified to be approximately 0.2 wt.%. This work provides guidance for the microalloying design of hypereutectic Al-Si-Ni alloys with improved high-temperature mechanical performance.
