Search Results (56)

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

4,4’-Methylenebis(N,N-diglycidylaniline) (AG80), as a high-performance thermosetting material, holds significant application value due to the enhancement of its strength, toughness, and thermal stability. However, conventional toughening methods often lead to a decrease in material strength, limiting their application. Modification of AG80 epoxy resin was performed using hydroxy-terminated polyphenylpropylsiloxane (Z-6018) and a self-synthesized epoxy compatibilizer (P/E30) to regulate the phase structure of the modified resin, achieving a synergistic enhancement in both strength and toughness. The modified resin was characterized by Fourier transform infrared analysis (FTIR), proton nuclear magnetic resonance (¹H NMR) spectroscopy, silicon-29 nuclear magnetic resonance (²⁹Si NMR) spectroscopy, and epoxy value titration. It was found that the phase structure of the modified resin significantly affects mechanical properties. Thus, P/E30 was introduced to regulate the phase structure, achieving enhanced toughness and strength. At 20 wt.% P/E30 addition, the tensile strength, impact strength, and fracture toughness increased by 50.89%, 454.79%, and 152.43%, respectively, compared to AG80. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses indicate that P/E30 regulates the silicon-rich spherical phase and interfacial compatibility, establishing a bicontinuous structure within the spherical phase, which is crucial for excellent mechanical properties. Additionally, the introduction of Z-6018 enhances the thermal stability of the resin. Full article

ZrO₂ and multi-walled carbon nanotubes (MWCNTs) were selected as single-phase and composite toughening agents to investigate the influence on the mechanical properties of CaZr₄(PO₄)₆ (CZP) ceramics. The results revealed that the addition of single-phase or composite toughening agents had minimal impact on the phase composition and crystallinity of CZP ceramics. When the content of the single-phase ZrO₂ toughening agent reached 10 wt.%, the flexural strength of CZP ceramics increased to 71.60 MPa due to the particle toughening mechanism of ZrO₂. With the addition of 1.0 wt.% ZrO₂ and 0.3 wt.% MWCNTs, the CZP ceramics demonstrated enhanced densification and improved sintering activity. The small-sized ZrO₂ particles were evenly dispersed within the ceramic matrix, accompanied by a phase transformation during sintering. Together with MWCNTs, this combination resulted in a significant increase in flexural strength, reaching 138.43 MPa. An in-depth analysis of the toughening mechanisms indicated that the CZP ceramic matrix primarily featured ZrO₂ phase transformation toughening and the pull-out and bridging toughening provided by MWCNTs. The synergistic interaction of these multiple toughening mechanisms significantly enhanced the mechanical properties of CZP ceramics, providing valuable theoretical insights for optimizing the performance of phosphate ceramics in practical applications. Full article

Multifunctional self-healing supramolecular structural toughened resins, formulated to counteract the insulating properties of epoxy polymers and integrating auto-repair mechanisms, are morphologically and spectroscopically characterized using Tunneling Atomic Force Microscopy (TUNA) and Fourier transform infrared spectroscopy (FT-IR), respectively. Specifically, the multifunctional resin comprises self-healing molecular fillers and electrically conductive carbon nanotubes (CNTs) embedded in the matrix. The selected self-healing molecules can form non-covalent bonds with the hydroxyl (OH) and carbonyl (C=O) groups of the toughened epoxy matrix through their H-bonding donor and acceptor sites. An FT-IR analysis has been conducted to evaluate the interactions that the barbiturate acid derivatives, serving as self-healing fillers, can form with the constituent parts of the toughened epoxy blend. Tunneling Atomic Force Microscopy (TUNA) highlights the morphological characteristics of CNTs, their dispersion within the polymeric matrix, and their affinity for the globular rubber domains. The TUNA technique maps the samples’ electrical conductivity at micro- and nanoscale spatial domains. Detecting electrical currents reveals supramolecular networks, determined by hydrogen bonds, within the samples, showcasing the morphological features of the sample containing an embedded conductive nanofiller in the hosting matrix. Full article

Niobium–graphene oxide–zirconia-toughened alumina (ZTA) composites were produced by wet mixing and spark plasma sintering. The microstructure and mechanical properties of this novel composite have been studied. The results show that niobium particles are homogeneously dispersed in the ZTA matrix. Raman spectroscopy confirmed the thermal reduction in graphene oxide during sintering. The presence of ductile metal and graphene flakes leads to an increase in the crack resistance value of the ZTA matrix. The developed composites demonstrate a fracture toughness of 16 MPa∙m^1/2, which is three times higher than ZTA ceramic composites. The high toughness values found in this new composite are a consequence of the strong interaction between the simultaneous action of several toughening mechanisms, specifically involving crack trapping, crack blunting, crack renucleation, and the bridging mechanisms of the metallic and graphene particles. Moreover, this increase has also occurred due to the enhancement of the transformability of zirconia in ceramic–metal composites. Full article

The interfacial properties of blends play a crucial role in determining the mechanical characteristics of polyamide alloys. This study focused on the preparation of PA6/PBS alloys via a melt blending method, utilizing 3-aminopropyltriethoxysilane (KH550) as the compatibilizer to examine the impact of KH550 on the interfacial and mechanical properties of these binary blends. The results demonstrated that the amino groups in KH550 reacted with the terminal carboxyl groups in polyamide 6 (PA6) and the B-OH in polyborosiloxane (PBS), which significantly enhanced interfacial adhesion between the two phases. A reduction in the particle size and interparticle distance of PBS particles was related to increased interfacial adhesion within the blends. The superior dispersion and robust interfacial adhesion caused a notable improvement in the notched Izod impact strength, rising from 7.9 kJ/m² to 29.7 kJ/m² at 25 °C and from 6.3 kJ/m² to 16.6 kJ/m² at −50 °C. Consequently, KH550 proved to be an effective toughening agent for the PA6/PBS system. Furthermore, the PA6/PBS blends containing a high content of KH550 induced a morphological transformation from a “sea-island” structure to a partially interpenetrating polymer network, leading to the absence of a double-yield phenomenon in the tensile curve. Full article

High-entropy alloys, since their development, have demonstrated great potential for applications in extreme temperatures. This article reviews recent progress in their mechanical performance, microstructural evolution, and deformation mechanisms at low and high temperatures. Under low-temperature conditions, the focus is on alloys with face-centered cubic, body-centered cubic, and multi-phase structures. Special attention is given to their strength, toughness, strain-hardening capacity, and plastic-toughening mechanisms in cold environments. The key roles of lattice distortion, nanoscale twin formation, and deformation-induced martensitic transformation in enhancing low-temperature performance are highlighted. Dynamic mechanical behavior, microstructural evolution, and deformation characteristics at various strain rates under cold conditions are also summarized. Research progress on transition metal-based and refractory high-entropy alloys is reviewed for high-temperature environments, emphasizing their thermal stability, oxidation resistance, and frictional properties. The discussion reveals the importance of precipitation strengthening and multi-phase microstructure design in improving high-temperature strength and elasticity. Advanced fabrication methods, including additive manufacturing and high-pressure torsion, are examined to optimize microstructures and improve service performance. Finally, this review suggests that future research should focus on understanding low-temperature toughening mechanisms and enhancing high-temperature creep resistance. Further work on cost-effective alloy design, dynamic mechanical behavior exploration, and innovative fabrication methods will be essential. These efforts will help meet engineering demands in extreme environments. Full article

In this study, a new environmentally friendly and efficient method for recycling and reusing waste polyurethane sheets is proposed. SiO₂ aerogel was prepared using the sol–gel method, and mullite whiskers were introduced to enhance its toughness. The whisker-toughened aerogel was used in the degradation of waste polyurethane to produce modified recycled polyol, which was subsequently used to prepare recycled polyurethane foam insulation material. Following a series of tests, including Fourier-transform infrared spectroscopy, apparent density, viscosity, heat loss, and thermal conductivity, the results showed that when the aerogel with wt% = 0.9% mullite whiskers and 0.06 g of whisker-toughened aerogel were added, the viscosity was close to that of polyether polyol 4110. The optimal compressive strength of the resulting composite blister structure reached 817.93 MPa, with a thermal conductivity of 0.0228 W·(m·K)⁻¹, demonstrating good thermal stability. These results indicate that the whisker-toughened aerogel effectively reduces the viscosity of the degraded materials and significantly improves the mechanical properties and thermal stability of the regenerated polyurethane thermal insulation materials. This research provides new ideas and new methods for waste polyurethane recycling and offers a new perspective for the research and development of thermal insulation materials. Full article

Conventional polypropylene fibers, characterized by their smooth surfaces, exhibit relatively weak bonding with cement-based materials, limiting their effectiveness in enhancing these materials’ mechanical properties. This study investigates a graft-modified approach to activating polypropylene fibers, introducing amide groups onto their surfaces to improve fiber–matrix interaction. The active polypropylene fibers were produced using an ultraviolet (UV) grafting technique, where maleic anhydride was first used to graft carboxyl groups onto the fiber surfaces, followed by acylation with diethylenetriamine to introduce amide bonds. The optimal experimental conditions were identified by using the degree of amidation as the response metric. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed successful amination and surface activation, with a marked increase in specific surface area. The water contact angle of the active polypropylene fibers decreased significantly from 106.3° to 39.9°, indicating greatly improved wettability by the cement slurry and enhanced bonding strength between the fibers and the cement matrix. To evaluate the effects of the modified fibers, cement-stabilized macadam specimens incorporating various fiber contents were prepared and tested to determine their mechanical properties and shrinkage performance. The results indicated that, compared to conventional polypropylene fibers, the activated polypropylene fibers increased the 28-day compressive strength of CSM by 6.56%, enhanced tensile strength by 4.94%, reduced the rebound modulus by 7.42%, decreased the drying shrinkage coefficient by 25.55%, and lowered the thermal shrinkage coefficient by 13.16%. These findings demonstrate that the chemical bonding between the active polypropylene fibers and the cement matrix is significantly enhanced, leading to improved overall performance in crack resistance, material toughening, and shrinkage mitigation. Full article

Yttria-stabilized zirconia (Y-TZP) ceramics with a drastically reduced yttria content have been introduced by different manufacturers, aiming at improving the damage tolerance of ceramic components. In this study, an alumina-doped 1.5Y-TZP was axially pressed, pressureless sintered in air at 1250–1400 °C for 2 h and characterized with respect to mechanical properties, microstructure, and phase composition. The material exhibits a combination of a high strength of 1000 MPa and a high toughness of 8.5–10 MPa√m. The measured fracture toughness is, however, extremely dependent on the measurement protocol. Direct crack length measurements overestimate toughness due to trapping effects. The initially purely tetragonal material has a high transformability of >80%, the transformation behavior is predominantly dilational, and the measured R-curve-related toughness increments are in good agreement with the transformation toughness increments derived from XRD data. Full article

Defects such as interconnected pores and cracks can improve the abradability of ceramic-based abradable sealing coatings (ASCs) but may reduce the lifetime. Self-healing can potentially close cracks and transform interconnected pores into isolated ones through filling and sintering effects. Ti₃AlC₂ (TAC) was incorporated into LaMgAl₁₁O₁₉ (LMA) as both the self-healing agent and sintering aid, and plasma-sprayed LMA-based composite coatings were annealed at 1200 °C to assess their self-healing capabilities and then subjected to oxidation in air and corrosion in steam at 1300 °C to study their long-term stability. Results indicated that increasing TAC content significantly enhances self-healing effectiveness, evidenced by the closure of cracks and the isolation of pores. Oxidation and corrosion at 1300 °C led to significant grain growth and the formation of equiaxed grains with an aspect ratio of approximately 3, which may impair the toughening mechanism. Meanwhile, due to the preferential volatilization of Al in a steam environment, LTA decomposed into α-La_2/3TiO₃ and La₄Ti₃O₁₂ phases, and the accelerated mass transfer also resulted in grain coarsening. Interestingly, the L20T composite coating with a porosity of 32.17 ± 0.94% and a hardness of 74.88 ± 1.55 HR15Y showed great potential for abradable applications due to its stable phase composition and uniform pore distribution. Full article

The utilization of polyamide 10,12 (PA10,12) composites in various industries has been limited constrained by their inherent low toughness, making it a challenge to achieve a balance between toughness and structural integrity through conventional elastomer addition strategies. Herein, we introduce a straightforward method for the concurrent toughening and reinforcement of PA10,12 composites. This is accomplished by blending polyolefin elastomer (POE) and 3-pentadecylphenol (PDP) with the PA10,12 matrix. The incorporation of 5 wt% PDP effectively blurred the PA10,12/POE interface due to PDP’s role as a compatibilizer. This phenomenon is attributed to the formation of intermolecular hydrogen bonds, as evidenced by Fourier Transform Infrared Spectroscopy (FTIR) analysis. Further investigation, using differential scanning calorimetry (DSC), elucidated the crystallization thermodynamics and kinetics of the resulting binary PA10,12/POE and ternary PA10,12/POE/PDP composites. Notably, the crystallization temperature (T_c) was observed to decrease from 163.1 °C in the binary composite to 161.5 °C upon the addition of PDP. Increasing the PDP content to 10% led to a further reduction in T_c to 159.5 °C due to PDP’s capacity to slow down crystallization. Consequently, the ternary composite of PA10,12/POE/PDP (92/3/5 wt%) demonstrated a synergistic improvement in mechanical properties, with an elongation at break of 579% and a notch impact strength of 61.54 kJ/m². This represents an approximately eightfold increase over the impact strength of unmodified PA10,12. Therefore, our work provides the potential of PDP as a compatibilizer to develop nylon composites with enhanced stiffness and toughness. Full article

The brittle behavior of poly(lactic acid) (PLA) and PLA composites with inorganic filler limits their applications; the addition of a toughening agent, such as a rubbery phase, was selected to transform the brittle to ductile behavior for versatility in various applications. This work aims to study the properties of PLA and PLA composite with filled nanosized hydroxyapatite (nHA) after adding modified natural rubber (MoNR), which acts as a toughening agent. MoNR refers to poly(acrylic acid-co-acrylamide)-grafted deproteinized natural rubber. nHA was prepared from fish scales. Its characteristics were investigated and was confirmed to be comparable to those of commercial grade. PLA-MoNR at various MoNR contents and PLA/nHA composites with/without MoNR were prepared by melt mixing. Their morphology, mechanical, and thermal properties were observed and investigated. Samples with MoNR added showed the dispersion of spherical particles, indicating incompatibility. However, the mechanical properties of PLA-MoNR, which had MoNR added at 10 phr, showed toughening behavior (increased impact strength by more than two times compared to that of neat PLA). The PLA/nHA composite with MoNR showed the same result. The addition of MoNR in the composite increased its impact strength by 1.27 times compared to the composite without MoNR. MoNR can be a stress concentrator, resulting in toughened PLA and PLA/nHA composite. Full article

It has been observed in recent years that zirconia (Zr) is being increasingly used for a wide range of clinical applications. There are several reasons for this, but the most significant one is its excellent mechanical properties, specifically its transformation toughening properties compared to other dental ceramics and its improved natural appearance when compared to ceramometal restorations. As a result of the advancement of chairside milling and developments in rapid-sintering technology, the fabrication of dental restorations has become more computerized, time-saving, and accurate over the past few decades. However, a main disadvantage of conventional Zr restorations is that they lack the translucency of glass–ceramics, although they are extremely strong. Recently, by increasing the yttrium %, changing the grain size, and reducing the impurities, the ultra-translucent monolithic zirconia “5-mol%-yttria-stabilized tetragonal zirconia polycrystals” has been introduced, with successful attempts to make translucent Zr an aesthetically attractive option for minimally invasive veneer restorations. It is important to note that veneer restorations do not possess the mechanical retentive features of the tooth preparations and rely primarily on bonding to resin cement. This presents a great challenge for the inert Zr since it does not bond chemically with resin cement, unlike glass–ceramic materials that establish chemical adhesion with resin cement, favoring their use for indirect veneer restorations. Taking this into account, this article aims to review the progressive development of ultra-translucent monolithic Zr materials as they are available today and, in the future, represents a concerted drive toward maximum translucency and strength, which renders them a viable treatment option for esthetic veneer restorations. Full article