Search Results (119)

As research on fiber-reinforced concrete progresses, investigating the enhancement effect of hybrid fiber-reinforced concrete becomes increasingly crucial. In the present research, the contents of steel fiber (SF) and polypropylene fiber (PP) were set as variable parameters to study the mechanical performance of steel-polypropylene hybrid fiber-reinforced concrete (SPFRC). Mechanical performance tests were undertaken on 16 groups of standard specimens. The failure modes were observed, the strength variation patterns were analyzed, and both a strength prediction equation and a complete stress–strain curve equation were established. Research results indicated that the specimen containing 1.5% SF and 0.25% PP exhibited the maximum strength enhancement compared with plain concrete: cube compressive strength improved by 27.78%, and splitting tensile strength surged by 41.18%. When the SF content was 1.5% and that of PP was 0.5%, the specimen’s elastic modulus experienced the greatest enhancement, reaching 58.59%. Hybrid fibers significantly enhanced the mechanical performance of SPFRC, simultaneously exerting strengthening, crack-resistance, and toughening effects. The research findings offer both experimental evidence and theoretical support for promoting research and engineering applications of SPFRC. Full article

Overhead transmission lines have long relied on cross-linked polyethylene (XLPE) insulation. The production of XLPE insulation requires silane cross-linking, which generates by-products, consumes high energy, and results in poor recyclability-retired XLPE insulation can only be disposed of through incineration or landfilling. Additionally, its high density leads to increased cable weight and sag, reducing the service life of the cables. Therefore, there is an urgent need to develop recyclable and lightweight insulation materials. In this study, recyclable polypropylene (PP) was used as a substitute for XLPE. Hollow glass microspheres (HGM) were incorporated to reduce weight, and hydrogenated styrene-ethylene-butylene-styrene block copolymer (SEBS) was added for toughening, thereby constructing a PP/HGM/SEBS ternary composite system. The results show that the introduction of HGM into the PP matrix effectively reduces the material density, decreasing from 0.890 g/cm³ (pure PP) to 0.757 g/cm³—a reduction of 15%. With the addition of SEBS, the mechanical properties of the composite are significantly improved: the tensile strength increases from 14.94 MPa (PP/HGM) to 32.40 MPa, and the elongation at break jumps sharply from 72.02% to 671.22%, achieving the synergistic optimization of “weight reduction” and “strengthening-toughening”. Electrical performance tests indicate that the PP/HGM/SEBS composite exhibits a volume resistivity of 1.66 × 10¹² Ω·m, a characteristic breakdown strength of 108.6 kV/mm, a low dielectric loss tangent of 2.76 × 10⁻⁴, and a dielectric constant of 2.24. It achieves density reduction while maintaining low dielectric loss and high insulation strength, verifying its feasibility for application in lightweight insulation scenarios of overhead transmission lines. Full article

This study explores the fabrication and characterization of hybrid aluminum matrix composites reinforced with boron carbide (B₄C) and microsilica, produced via ultrasonically assisted stir casting followed by T6 heat treatment. Pure aluminum was selected as the base matrix to evaluate the combined effects of B₄C and microsilica reinforcements. Microstructural analyses showed that ultrasonic treatment effectively dispersed nanoparticles, reduced agglomeration, and enhanced particle–matrix interfacial bonding. T6 heat treatment further refined the grain structure through Zener pinning and promoted the formation of reaction layers at particle interfaces. Mechanical testing revealed that Al/B₄C composites provided the highest strength and hardness, while Al/microsilica systems retained superior ductility. The hybrid Al/B₄C/microsilica composites demonstrated a balanced combination of yield strength (38.6 MPa), ultimate tensile strength (82.6 MPa), and elongation (35.2%), confirming a synergistic strengthening–toughening effect. These results highlight the potential of Al/B₄C/microsilica hybrid reinforcements to optimize the trade-off between strength and ductility in aluminum-based composites. Full article

A series of TiB₂-Ni multilayer films with different Ni layer thicknesses was prepared by magnetron sputtering technology. The effect of Ni layer thickness on the microstructure and mechanical properties of the multilayer films was investigated, and the deformation and fracture mechanisms underlying the observed behavior were analyzed in detail. The results show that all multilayer films exhibit a well-defined layered architecture with sharp interfacial boundaries. Specifically, the Ni layers grow as columnar grains with an average diameter of approximately 10 nm, while the TiB₂ layers form a very fine acicular nanocolumnar structure. With the increase in Ni layer thickness, the hardness of the multilayer films shows a decreasing trend, gradually decreasing from 27.3 GPa at a 4 nm Ni thickness to 19.3 GPa at 50 nm. In contrast, the fracture toughness increases gradually from 1.54 MPa·m^1/2 to 2.73 MPa·m^1/2. This enhancement in toughness is primarily attributed to a transition in the deformation and fracture mechanism. With the increase in Ni layer thickness, the crack propagation mode in the multilayer films gradually changes from the integral propagation penetrating the film layers to the crack deflection propagation within the layers. This transformation is the result of the combined effect of the stress state of each layer and the crack energy dissipation. Full article

In response to the issues of microcrack susceptibility, high brittleness, and unstable mechanical properties of desert sand recycled aggregate concrete (DSRAC), this study experimentally investigated the mechanical performance of DSRAC reinforced with hybrid steel–FERRO fibers. By testing macroscopic properties (compressive, splitting tensile, and flexural strengths) under different desert sand replacement ratios and fiber dosages, combined with microscopic analysis, the fiber-matrix interfacial behavior and toughening mechanism were clarified. The results showed that (1) DSRAC achieved optimal compressive strength when desert sand replaced 30% natural sand, with an obvious early strength enhancement; (2) both steel fibers and FERRO fibers independently improved DSRAC’s mechanical properties, while their hybrid combination (especially F0.15-S0.5 group) exhibited a superior synergistic strengthening effect, significantly outperforming single-fiber groups; (3) the established constitutive model accurately described the stress–strain response of hybrid fiber-reinforced DSRAC; (4) microscopic observations confirmed fibers inhibited crack propagation via bridging and stress dispersion, with hybrid fibers exerting multi-scale synergistic effects. This study provided theoretical–technical support for resource utilization of desert sand and recycled aggregates, and offered practical references for localized infrastructure materials (e.g., rural road subgrades and small-span culverts) in desert-rich regions and high-value reuse of construction waste in prefabricated components, advancing eco-friendly concrete in sustainable construction. Full article

Eutectic high-entropy alloys (EHEAs) combine the casting advantages of eutectic alloys with the comprehensive properties of high-entropy alloys, making them a research hotspot in the field of metallic materials. Among them, the AlCoCrFeNi_2.1 EHEA has attracted significant attention due to its excellent strength–toughness balance characteristics. In this study, alloy samples of AlCoCrFeNi_2.1Si_x (x = 0, 0.1, 0.2, 0.3) were prepared to investigate the regulatory effects of trace Si on its phase composition, microstructure, and mechanical properties. The results show that the base alloy AlCoCrFeNi_2.1 is composed of an FCC and BCC phase composition. With the increase in the Si content to x = 0.3, the CrSi₂ phase gradually precipitates in the alloy, and its microscopic morphology transforms from the regular lamellar to the dendrite and network structure. The introduction of Si significantly enhances the room-temperature microhardness, wear resistance, and yield strength of the alloy through the mechanisms of solid solution strengthening and second phase strengthening. However, an excessive addition leads to a decrease in ductility and toughness. This study reveals the role of Si in phase control and the strengthening and toughening mechanism of eutectic high-entropy alloys, providing experimental evidence and a theoretical reference for the design of high-performance silicon-modified high-entropy alloys. Full article

This study was focused on addressing the performance degradation in core microstructures of ultra-heavy steel plates (thickness ≥ 50 mm) caused by non-uniform cooling during thermo-mechanical controlled processing. Using microalloyed DH36 steel as the research subject, we systematically investigated the effects of cooling rate on the nucleation and growth of acicular ferrite and its consequent microstructure-property relationships through an integrated approach combining in situ observation via high-temperature laser scanning confocal microscopy with multiscale characterization techniques. Results demonstrate that the cooling rate significantly affects acicular ferrite formation, with the range of 3–7 °C/s being most conducive to acicular ferrite formation. At 5 °C/s, the acicular ferrite volume fraction reached a maximum of 74% with an optimal aspect ratio (5.97). Characterization confirmed that TiOx-Al₂O₃·SiO₂-MnO-MnS complex inclusions act as effective nucleation sites for acicular ferrite, where the MnS outer layer plays a key role in reducing interfacial energy and promoting acicular ferrite radial growth. Furthermore, the interlocking acicular ferrite structure was shown to enhance microhardness by 14% (HV0.1 = 212.5) compared to conventional ferrite through grain refinement strengthening and dislocation strengthening (with a dislocation density of 2 × 10⁸ dislocations/mm²). These results provide crucial theoretical insights and a practical processing window for strengthening-toughening control of heavy plate core microstructures, offering a viable pathway for improving the comprehensive performance of ultra-heavy plates. Full article

Concrete materials undergo a series of physical and chemical changes under high temperature, leading to the degradation of mechanical properties. This study investigates basalt fiber-reinforced concrete (BFRC) through high-temperature testing using the split Hopkinson pressure bar (SHPB) apparatus. Impact compression tests were conducted on specimens after exposure to elevated temperatures to analyze the effects of varying fiber content, temperature levels, and impact rates on the mechanical behaviors of BFRC. Based on fractional calculus theory, a dynamic constitutive equation was established to characterize the viscoelastic properties and high-temperature damage of BFRC. The results indicate that the dynamic compressive strength of BFRC decreases significantly with increasing temperature but increases gradually with higher impact rates, demonstrating fiber-toughening effects, thermal degradation effects, and strain rate strengthening effects. The proposed constitutive model aligns well with the experimental data, effectively capturing the dynamic mechanical behaviors of BFRC after high-temperature exposure, including its transitional mechanical characteristics across elastic, viscoelastic, and viscous states. The viscoelastic behaviors of BFRC are fundamentally attributed to the synergistic response of its multi-phase composite system across different scales. Basalt fibers enhance the material’s elastic properties by improving the stress transfer mechanism, while high-temperature exposure amplifies its viscous characteristics through microstructural deterioration, chemical transformations, and associated thermal damage. Full article

This study investigates H13 steel through Q-P-T (quenching–partitioning–tempering) heat treatment experiments, focusing on the effects of quenching and tempering temperatures on its microstructure and mechanical properties. Experimental results demonstrate that elevated heat treatment temperatures induce grain coarsening and increased hardness. Under the optimized thermal processing parameters of 1020 °C quenching followed by 530 °C tempering, H13 steel achieves an optimal balance between strength and toughness. This balanced performance effectively addresses the issue of insufficient toughness and susceptibility to fracturing when H13 steel is utilized as shank material. Full article

Biodegradable zinc alloys for orthopedic implants must balance mechanical strength and plasticity, yet current as-cast alloys struggle to meet this dual requirement. In this study, a Zn-3Cu-1Mg-0.3Nd alloy was designed, and the influence of room-temperature rolling at four reduction levels (50%, 60%, 70%, and 80%) on its microstructure and mechanical properties was systematically investigated. Results indicate that as the reduction increases, the CuZn₅ phase elongated along the rolling direction, and the η-Zn+Mg₂Zn₁₁ eutectic structure was progressively fragmented. The average grain size of the η-Zn matrix decreased significantly from 18.9 μm (50% reduction) to 1.71 μm (80% reduction). A distinct bimodal heterogeneous microstructure (coarse/fine grains) was formed at 60% and 70% reductions, while a predominantly fine-grained structure (91.3% fine grains) was achieved at 80% reduction. Furthermore, cracks initiated in the NdZn₁₁ phase due to stress concentration during rolling. As the rolling reduction increases, the alloy’s ultimate tensile strengths (UTS) initially rose and then declined (peaking at 417 ± 5 MPa at 60% reduction), while its elongation (EL) consistently improved. At 80% reduction, the alloy exhibited optimal mechanical properties, achieving a tensile strength of 406 ± 4 MPa and an EL of 16.4 ± 0.3%, both significantly higher than those of the as-cast alloy (126 MPa, 4.4%). The enhancement in strength is attributed to a multi-scale synergistic mechanism involving grain refinement and back stress strengthening induced by heterogeneous microstructures. The continuous improvement in plasticity results from grain refinement, texture weakening, and the activation of non-basal <c+a> slip systems. Notably, cracks within the NdZn₁₁ phase were confined by its high-binding-strength interface, preventing detrimental propagation into the matrix. This study elucidates the strengthening and toughening mechanisms in zinc alloys through cold rolling and the addition of the Nd element, particularly in terms of microstructural control and crack passivation, offering theoretical guidance for the design of biodegradable zinc alloy materials. Full article

Mg-Sc body-centered cubic (BCC) phase-structured alloys not only exhibit superior room-temperature ductility and quasi-isotropic deformation behaviors compared to conventional hexagonal close-packed (HCP) Mg alloys in mechanical applications, but they also demonstrate a shape-memory effect that is applicable to intelligent devices. Due to the introduction of a dual-phase microstructure feature, the unveiled strengthening/toughening mechanism, and the potential benefit of Sc alloying in BCC creep deformation, it is necessary to investigate the composition and time-dependent creep behaviors of BCC Mg-Sc alloys, such as creep resistance and strain rate sensitivity at room temperature, through nano-indentation on the Mg-Sc diffusion couple. A critical finding is that as the Sc content increases from 23.01 at.% to 33.56 at.%, the BCC Mg-Sc alloy exhibits a progressive enhancement in creep resistance at room temperature, evidenced by the creep stress exponent (n) rising from 49.02 to 66.22. Furthermore, the strain rate sensitivity (m) increases from 0.02 at 26.94 at.% Sc to 0.11 at 32.63 at.% Sc, along with the Sc composition gradient. These phenomena can be attributed to the formation of ordered structures with the increasing Sc concentration, which introduce short-range local barriers to dislocation motion, as confirmed through atomic-scale microstructural analysis. Full article

A Mg-Gd-Y alloy prepared by surface mechanical attrition treatment (SMAT) was annealed at 450 °C combined with peak aging. The deformation and fracture mechanisms were investigated using in situ tensile tests. Through quantitative calculations of the geometrically necessary dislocation (GND) densities, it was found that the fine-grained (FG) layer in the gradient structure carried greater plastic strain than the coarse-grained (CG) layer during tension. The calculation results of the geometric compatibility parameter (m’) and microstructure characterization during in situ tests showed that crack initiation and propagation were prone to occur between adjacent coarse grains. However, the hetero-deformation-induced (HDI) strengthening and strain hardening induced by the strain gradient between the FG and CG layers effectively improved the strength–ductility synergy of the gradient-structured (GS) alloy. In addition, the synergistic effect of intrinsic and extrinsic toughening mechanisms in the GS alloy played a significant role in delaying premature failure. Full article

Functionally graded materials (FGMs) are fabricated on Ti-6Al-4V alloy surfaces to improve insufficient surface hardness and wear resistance. Microstructure and mechanical properties and strengthening–toughening mechanisms of FGMs were investigated. The FGM cladding layer exhibits distinct gradient differentiation, demonstrating gradient variations in the nanoindentation hardness, wear resistance, and Al/V elemental composition. Molten pool dynamics analysis reveals that Marangoni convection drives Al/V elements toward the molten pool surface, forming compositional gradients. TiN-AlN eutectic structures generated on the FGM surface enhance wear resistance. Rapid solidification enables heterogeneous nucleation for grain refinement. The irregular wavy interface morphology strengthens interfacial bonding through mechanical interlocking, dispersing impact loads and suppressing crack propagation. FGMs exhibit excellent wear resistance and impact toughness compared with Ti-6Al-4V titanium alloy. The specific wear rate is 1.17 × 10⁻² mm³/(N·m), dynamic compressive strength reaches 1701.6 MPa, and impact absorption energy achieves 189.6 MJ/m³. This work provides theoretical guidance for the design of FGM strengthening of Ti-6Al-4V surfaces. Full article

To solve the problem of inadequate plasticity of traditional processing routes in improving the plasticity of novel Co-saving 18Ni (300) maraging steel, a cold deformation-cycle solution treatment process was developed. Through systematic characterization and tensile property testing, the study focuses on elucidating the impact of the number of solution treatments on the microstructure and mechanical behavior. The results showed that with a 30% cold deformation, three times of solution treatment at 860 °C for 10 min refined the original austenite grains (equivalent circle radius: 3.3 μm) and martensite structure (length and width: 7 μm and 1.3 μm, respectively) to the utmost extent. The grains became uniformly equiaxed, and the texture was eliminated, and a moderate content (4.5%) of retained austenite was formed. At this time, the material achieves the best match between strength (tensile strength of 1240 MPa) and plasticity (elongation of 9.93%), which are increased by 15.3% and 94.3%, respectively, compared with the traditional process. Mechanistic analysis revealed that grain refinement and uniform equiaxialization were the primary drivers for enhancing strength and plasticity. This study has demonstrated that the cold deformation-cyclic solution treatment process is an effective methodology for tailoring the microstructure and mechanical properties of maraging steel. Full article

The increasing incidence of urban fires poses significant threats to structural integrity, underscoring the urgent need for concrete materials with enhanced mechanical properties post-fire. Incorporating recycled waste steel fibers (WSF) from industrial byproducts into concrete not only bolsters its crack resistance but also advances circular economy principles by transforming industrial waste into valuable resources. Although a large amount of research has focused on native steel fiber-reinforced concrete, there is still a lack of systematic exploration on the optimal dosage and effectiveness of waste steel fibers in slowing down the strength degradation of concrete after high-temperature action. In this study, two grades of concrete (C40 and C60) containing 0%, 1%, and 2% WSF by volume were subjected to heating cycles ranging from 200 °C to 800 °C. Post-cooling evaluations encompassed mass loss quantification, cube compressive strength testing (using 100 mm³ specimens), and splitting tensile tests conducted at a loading rate of 0.1 MPa/s. Results indicated that mass loss escalated to 11% at 800 °C, with C60 experiencing a 12% higher loss compared to C40. Compressive strength decreased by 15% for every 200 °C increment; however, the inclusion of 1% WSF significantly minimized this degradation, preserving 44.5% (for C40) and 37.8% (for C60) of the original strength at 800 °C. Notably, the splitting tensile strength of 1% WSF-reinforced C60 concrete exceeded that of plain concrete by 39.4% after exposure to 800 °C, demonstrating its superior crack-bridging capabilities. Full article