Search Results (381)

In the shale oil reservoirs, sandstone and shale often overlie each other. This significantly affects the vertical propagation of hydraulic fractures (HFs); however, the underlying mechanisms still remain unclear. This study employs Xsite software to investigate the influence of rock fracture toughness, tensile strength, elastic modulus, Poisson’s ratio, interlayer stress contrast, and the flow rate and viscosity of fracturing fluid on the propagation behaviour of HFs in sandstone–shale interbeds. As the type-I fracture toughness of the shale layer increases, the area of the vertical HF decreases and the average HF width becomes smaller. As the tensile strength of the sandstone layer increases, the distribution range of fluid pressure at the interface expands. The HF prefers to propagate in the softer rock rather than the harder one. A relatively narrower HF width is created in the layer with a higher elastic modulus resulting in a higher flow resistance to fracturing fluid. A shale layer with a high Poisson’s ratio is more likely to undergo a lateral expansion, causing stress at the fracture tip to be dispersed. When the effect of lithological interfaces is considered, an increasing interlayer stress contrast causes HFs to gradually transition from penetrating the interfaces to becoming confined between the two interfaces. When the influence of the lithological interface is not considered, an increasing interlayer stress contrast causes the HF to gradually transition from a penny-shaped fracture to a blade-shaped fracture. The HF penetrates the interfaces more easily at a higher injection rate and fluid viscosity, because most of the injected energy is used to create new fractures rather than leakoff into the interfaces. Understanding the influence of these factors on the HF propagation behaviour is of great significance for optimising hydraulic fracturing design. Full article

Waste cooking oil (WCO), a significant urban waste stream, presents untapped potential for synthesizing high-value materials. This study introduces an innovative “epoxidation-hydrolysis-blending” strategy to conveniently transform WCO into a highly flexible, photocurable elastomer suitable for 3D printing. Initially, WCO is converted into WCO-based hydroxy fatty acids (WHFA) via epoxidation and hydrolysis, yielding linear chains functionalized with multiple hydrogen-bonding sites. Subsequently, blending WHFA with hydroxyethyl acrylate (HEA) yields a novel photocurable WHFA/HEA elastomer. This elastomer exhibits excellent dimensional accuracy during vat photopolymerization 3D printing. Within the WHFA/HEA system, WHFA acts as a dual-functional modifier: its flexible alkyl chains enhance conformational freedom through plasticization while serving as dynamic hydrogen-bonding cross-linking sites that synergize with HEA chains to achieve unprecedented flexibility via reversible bond reconfiguration. Mechanical testing reveals that the optimized WHFA/HEA elastomer (mass ratio 1:3) exhibits ultra-high flexibility, with an elongation at break of 1184.66% (surpassing pure HEA by 360%). Furthermore, the elastomer demonstrates significant weldability (44.23% elongation retention after 12 h at 25 °C), physical reprocessability (7.60% elongation retention after two cycles), pressure-sensitive adhesion (glass interface adhesion toughness: 32.60 J/m²), and notable biodegradability (14.35% mass loss after 30-day soil burial). These properties indicate broad application potential in flexible electronics, biomedical scaffolds, and related fields. This research not only pioneers a low-cost route to multifunctional photocurable 3D printing materials but also provides a novel, sustainable solution for the high-value valorization of waste cooking oil. Full article

Gradient structure provides an effective approach to improve the combination of high strength and toughness compared to a uniform one. The gradient interfaces or boundaries in gradient-structured metallic glass composites play a crucial role in influencing mechanical properties. Our findings indicate the gradient microstructure significantly induces temporal and spatial stress localization, which can modulate the generation and propagation of shear bands. The synergistic gradient effects generated by heterogeneous grain sizes and interface characteristics can enhance both the strength (yield stress and peak stress) and the toughness of gradient network-structured metallic glass composites as the grain size gradient and the boundary width increase. Our work demonstrates the appropriate gradient of grain size, and the boundary structure should potentially lead to enhanced work hardening. Full article

Wet–dry cycles are a key factor aggravating the durability degradation of foam concrete. To address this issue, this study prepared bentonite slurry–steel slag foam concrete (with steel slag and cement as main raw materials, and bentonite slurry as admixture) using the physical foaming method. Based on 7-day unconfined compressive strength tests with different mix proportions, the optimal mix proportion was determined as follows: mass ratio of bentonite to water 1:15, steel slag content 10%, and mass fraction of bentonite slurry 5%. Based on this optimal mix proportion, dry–wet cycle tests were carried out in both water and salt solution environments to systematically analyze the improvement effect of steel slag and bentonite slurry on the durability of foam concrete. The results show the following: steel slag can act as fine aggregate to play a skeleton role; after fully mixing with cement paste, it wraps the outer wall of foam, which not only reduces foam breakage but also inhibits the formation of large pores inside the specimen; bentonite slurry can densify the interface transition zone, improve the toughness of foam concrete, and inhibit the initiation and propagation of matrix cracks during the dry–wet cycle process; the composite addition of the two can significantly enhance the water erosion resistance and salt solution erosion resistance of foam concrete. The dry–wet cycle in the salt solution environment causes more severe erosion damage to foam concrete. The main reason is that, after chloride ions invade the cement matrix, they erode hydration products and generate expansive substances, thereby aggravating the matrix damage. Scanning Electron Microscopy (SEM) analysis shows that, whether in water environment or salt solution environment, the fractal dimension of foam concrete decreased slightly with an increasing number of wet–dry cycle times. Based on fractal theory, this study established a compressive strength–porosity prediction model and a dense concrete compressive strength–dry–wet cycle times prediction model, and both models were validated against experimental data from other researchers. The research results can provide technical support for the development of durable foam concrete in harsh environments and the high-value utilization of steel slag solid waste, and are applicable to civil engineering lightweight porous material application scenarios requiring resistance to dry–wet cycle erosion, such as wall bodies and subgrade filling. Full article

The combined effects of accelerated carbonation and lime sludge incorporation on the mechanical and durability performance of fiber-cement composites were assessed in this study. Lime sludge was used to replace 0%, 10%, and 20% of the cement in the composites, which were then autoclave-cured and carbonated more quickly for two or eight hours. With LS20-C8 (20% lime sludge, 8 h carbonation) achieving the highest carbonation efficiency (74.0%), X-ray diffraction (XRD) verified the gradual conversion of portlandite into well-crystallized calcium carbonate (CaCO₃). In terms of mechanical performance, LS20-C8 outperformed the control by increasing toughness by 16.7%, flexural strength by 14.2%, compressive strength by 14.6%, and compressive modulus by 20.3%. The properties of LS20-C8 were better preserved after aging under wetting-drying cycles, as evidenced by lower losses of toughness (10.0%) and compressive strength (10.1%) compared to the control (14.6% and 18.3%, respectively). The mechanical improvements were explained by optical microscopy, which showed decreased porosity and an enhanced fiber–matrix interface. Overall, the findings show that adding lime sludge to accelerated carbonation improves durability, toughness, strength, and stiffness while decreasing porosity. This method helps to value industrial byproducts and is a sustainable and efficient way to create long-lasting fiber-cement composites. Full article

Ceramic matrix composites (CMCs) are promising candidates for high-temperature structural applications. However, their fracture toughness remains low due to strong chemical bonding between fibers and the matrix. To improve toughness, engineered interfaces such as pyrolytic carbon (PyC) and hexagonal boron nitride (h-BN) are commonly introduced. These interfaces promote crack deflection and fiber bridging, leading to improved damage tolerance and pseudo-ductile behavior. To investigate the influence of interface thickness on mechanical performance and to identify optimal thickness ranges, we propose a microscopic phase-field model that accurately resolves interface thickness and material contrast. This model overcomes the limitations of conventional smeared interface approaches, particularly in systems with variable interface thickness and closely packed fibers. We apply the model to simulate the fracture behavior of unidirectional SiC fiber reinforced SiC matrix (SiC_f/SiC_m) composites with PyC and h-BN interfaces of varying thickness. The numerical results show strong agreement with experimental findings from the literature and reveal optimal interface thicknesses that maximize toughening effects. These results demonstrate the model’s predictive capabilities and its potential as a tool for interface design in brittle composite systems. Full article

Focusing on the practical application requirements of adhesive-bonded structures in aerospace engineering, this study aims to investigate the mechanical performance and failure mechanisms of adhesive interfaces. Adhesive bonding, valued for its uniform load distribution, low stress concentration, superior sealing, and lightweight properties, serves as a critical joining technology in aerospace engineering. However, its reliable application is constrained by complex multimode failure issues, such as cohesive failure, interfacial debonding, and matrix damage. To address these challenges, a comprehensive evaluation of the novel high-strength epoxy adhesive Dq622JD-136 (Adhesive III) was conducted through systematic tests, including bulk tension, butt joint tension, single lap shear, compressive shear, and fracture toughness (TDCB/ENF) tests. These tests characterized its mechanical properties and fracture behavior under mode-I and mode-II loading, with comparative analyses against conventional adhesives HYJ-16 (Adhesive I) and HYJ-29 (Adhesive II). Key findings reveal that Adhesive III exhibits outstanding elastic modulus, significantly outperforming the comparative adhesives. While its normal and shear strengths are slightly lower than Adhesive I, they surpass Adhesive II. A common characteristic across all adhesives is that normal strength exceeds shear strength. In terms of fracture toughness, Adhesive III demonstrates superior mode-II toughness but relatively lower mode-I toughness. These results elucidate the brittle characteristics of such adhesives, mixed failure modes under normal loading, and cohesive failure behavior under shear loading. The innovation of this work lies in systematically correlating the macroscopic performance of adhesives with failure mechanisms through multi-dimensional testing. Its findings provide critical technical support for multiscale performance evaluation and adhesive selection in aerospace joints subjected to extreme thermomechanical loads. Full article

A large number of wind turbine blades will be retired in the near future. Glass fiber-reinforced composites from retired blades, due to their extraordinary strength, toughness, and durability, are promising aggregate candidates in asphalt mixtures. This work studied the interfacial behavior between asphalt and glass fiber-reinforced composites through combined molecular modeling and experimental approaches. Predictions from molecular modeling were first verified through experimental findings using particle probe scanning force microscopy. Then, molecular simulations were conducted to examine the chemical adhesion between binders and aggregates made from minerals and wind turbine blades. The results showed that epoxy–binder adhesion was higher than calcite–binder and silica–binder adhesion but lower than alumina–binder adhesion, denoting that the glass fiber composite aggregates were comparable in chemical adhesion to mineral aggregates. The adhesion was primarily due to van der Waals forces (>80%). Furthermore, the dependence of epoxy–asphalt adhesion on loading rates was examined, during which the high-speed, transitions, and low-speed regions were identified. The impact of water on interfacial behavior was illustrated by examining how water molecules infiltrated interfaces between aggregates and binders at different speeds. The results showed that interfacial adhesion in a hydrated state at low speeds was 20–40% lower than that in a dry state, whereas at high speeds, interfacial adhesion in a hydrated state was 5–15% higher than that in dry conditions. These results could provide essential guidance for the application of retired wind turbine blades as asphalt aggregates. Full article

Polylactic acid (PLA) materials face inherent limitations in many applications due to their low toughness. To address this challenge, this study employed a reactive melt-grafting method to prepare maleic anhydride (MA)-grafted poly(butylene adipate-co-terephthalate) (PBAT–MA), providing an effective approach to improve the interfacial compatibility between PLA and PBAT, thereby significantly enhancing the toughness and impact resistance of PLA and expanding its application scope. The grafting reaction process of PBAT–MA was investigated, as well as its toughening mechanism and effect on PLA. The results showed that at a maleic anhydride concentration of 2 wt%, the obtained PLA–PBAT–MA composite material exhibited the best performance, with a fracture elongation of 358.1%, 450.4% higher than that of the unmodified composite material. The impact strength was 333.9 kJ/m², 917.3% higher than that of the unmodified composite material. This enhanced effect is attributed to the optimal MA concentration preserving the tough structure of PBAT while effectively bridging the interface between PLA and PBAT, promoting efficient stress transfer between the two phases, and ultimately achieving exceptional toughness. Full article

Aluminum matrix composites provide an ideal solution for lightweight brake disks, but conventional casting processes are prone to crack initiation due to inhomogeneous reinforcement dispersion, gas porosity, and inadequate toughness. To break the conventional trade-off between high wear resistance and low toughness of brake disks, this study fabricated a bimetallic structure of SiC_p/Al–Fe–V–Si aluminum matrix composite and cast ZL101 alloy using friction stir lap welding (FSLW). Then, the microstructural evolution, mechanical properties, and tribological behavior of the FSLW joints were studied by XRD, SEM, TEM, tensile testing, and tribological tests. The results showed that the FSLW process homogenized the distribution of SiC particle reinforcements in the SiC_p/Al–Fe–V–Si composites. The Al₁₂(Fe,V)₃Si heat-resistant phase was not decomposed or coarsened, and the mechanical properties were maintained. The FSLW process refined the grains of the ZL101 aluminum alloy through recrystallization and fragmented eutectic silicon, improving elongation to 22%. A metallurgical bond formed at the joint interface. Tensile fracture occurred within the ZL101 matrix, demonstrating that the interfacial bond strength exceeded the alloy’s load-bearing capacity. In addition, the composites exhibited significantly enhanced wear resistance after FSLW, with their wear rate reduced by approximately 40% compared to the as-received materials, which was attributed to the homogenized SiC particle distribution and the activation of an oxidative wear mechanism. Full article

To investigate the crack extension mechanism in CFRP-reinforced concrete, this paper derives analytical expressions for the external load and crack opening displacement in the fracture process of CFRP concrete beams based on the crack emergence toughness criterion and the Paris displacement formula as the theoretical basis. A numerical iterative method was used to computationally simulate the fracture process of CFRP-reinforced concrete beams and to analyze the effect of different initial crack lengths on the fracture process. The research results indicate that the numerical simulation results of the crack initiation load are in good agreement with the test results, and the crack propagation curves and the test results are basically consistent before the CFRP-concrete interface peels off. The numerical results of ultimate load are lower than the test results, but it is safe for fracture prediction in actual engineering. With the increase in the initial crack length, the effect of the initial crack length on the critical effective crack propagation length is more obvious. Full article

Organic polymer introduction effectively enhances the toughness, bond strength, and durability of ordinary cement-based materials, and is often used for concrete repair and reinforcement. However, the entrained air effect simultaneously induced by polymer and the inhibitory action on cement hydration kinetics often lead to degradation in mechanical performances of polymer-modified cement-based composite (PMC). Nanomaterials provide unique advantages in enhancing the properties of PMC due to their characteristic ultrahigh specific surface area, quantum effects, and interface modulation capabilities. This review systematically examines recent advances in nano-reinforced PMC (NPMC), elucidating their synergistic optimization mechanisms. The synergistic effects of nanomaterials—nano-nucleation, pore-filling, and templating mechanisms—refine the microstructure, significantly enhancing the mechanical strength, impermeability, and erosion resistance of NPMC. Furthermore, nanomaterials establish interpenetrating network structures (A composite structure composed of polymer networks and other materials interwoven with each other) with polymer cured film (The film formed after the polymer loses water), enhancing load-transfer efficiency through physical and chemical action while optimizing dispersion and compatibility of nanomaterials and polymers. By systematically analyzing the synergy among nanomaterials, polymer, and cement matrix, this work provides valuable insights for advancing high-performance repair materials. Full article

To address the poor thermal shock resistance and high brittleness of traditional ceramic tools, a novel Si₃N₄/Sc₂W₃O₁₂ (SNS) composite ceramic material was developed via in situ synthesis using WO₃ and Sc₂O₃ as precursors and consolidated by spark plasma sintering. Sc₂W₃O₁₂ with negative thermal expansion was introduced to compensate for matrix shrinkage and modulate interfacial stress. The effects of varying Sc₂W₃O₁₂ content on thermal expansion, residual stress, microstructure, and mechanical properties were systematically investigated. Among the compositions, SNS3 (12 wt.% Sc₂W₃O₁₂) exhibited the best overall performance: relative density of 98.8 ± 0.2%, flexural strength of 712.4 ± 30 MPa, fracture toughness of 7.5 ± 0.3 MPa·m^1/2, Vickers hardness of 16.3 ± 0.3 GPa, and an average thermal expansion coefficient of 2.81 × 10⁻⁶·K⁻¹. The formation of a spherical chain-like Sc-W-O phase at the grain boundaries created a “hard core–soft shell” interface that enhanced crack resistance and stress buffering. Cutting tests showed that the SNS3 tool reduced workpiece surface roughness by 32.91% and achieved a cutting distance of 9500 m. These results validate the potential of this novel multiphase ceramic system as a promising candidate for high-performance and thermally stable ceramic cutting tools. Full article

This paper reviews the applications and performance advantages of ultra-high-performance concrete (UHPC), engineered cementitious composite (ECC), and recycled aggregate concrete (RAC) in composite flexural members. UHPC is characterized by its ultra-high strength, high toughness, excellent durability, and microcrack self-healing capability, albeit with high costs and complex production processes. ECC demonstrates superior tensile, flexural, and compressive strength and durability, yet it exhibits a lower elastic modulus and greater drying shrinkage strain. RAC, as an eco-friendly concrete, offers cost-effectiveness and environmental benefits, although it poses certain performance challenges. The focus of this review is on how to enhance the load-bearing capacity of composite beams or slabs by modifying the interface roughness, adjusting the thickness of the ECC or UHPC layer, and altering the cross-sectional form. The integration of diverse concrete materials improves the performance of beam and slab elements while managing costs. For instance, increasing the thickness of the UHPC or ECC layer typically enhances the load-bearing capacity of composite beams or plates by approximately 10% to 40%. Increasing the roughness of the interface can significantly improve the interfacial bond strength and further augment the ultimate load-bearing capacity of composite components. Moreover, the optimized design of material mix proportions and cross-sectional shapes can also contribute to enhancing the load-bearing capacity, crack resistance, and ductility of composite components. Nevertheless, challenges persist in engineering applications, such as the scarcity of long-term monitoring data on durability, fatigue performance, and creep effects. Additionally, existing design codes inadequately address the nonlinear behavior of multi-material composite structures, necessitating further refinement of design theories. Full article

In this study, we investigated the electrochemical corrosion behavior and mechanisms of FeCrNi/WC alloys with varying contents of CTC-S (spherical WC) and CTC-A (angular WC) in a 3.5 wt.% NaCl solution, addressing the corrosion resistance requirements for stainless steel composites in marine environments. The electrochemical test results demonstrate that the corrosion resistance of the alloy initially increases with the CTC-A content, followed by a decrease, which is associated with the formation, stability, and rupture of the passivated film. Nyquist and Bode diagrams for electrochemical impedance spectroscopy confirm that the charge transfer resistance of the passivated film is the primary determinant of the composite’s corrosion performance. A modest increase in CTC-A contributes to the formation of a more heterogeneous second phase, providing a physical barrier and enhancing solid solution strengthening, and thus delaying the cracking and corrosion processes of the passivation film. However, excessive CTC-A content leads to significant dissolution of the alloy’s reinforcement phase and promotes decarburization, resulting in the formation of corrosion pits, craters, and cracks that compromise the passivation film and expose fresh alloy surfaces to further corrosion. When the CTC-A content is 10% and the CTC-S content is 30%, this combination results in minimal degradation in the corrosion performance (0.213 μA·cm²) while balancing the hardness and toughness of the alloy. Additionally, electrochemical evaluations reveal that incorporating angular CTC-A particles at 10 vol% effectively delays the breakdown of the passivation film by mitigating the interfacial galvanic coupling through enhancing the mechanical interlocking at the WC/FeCrNi interface. The CTC-A/CTC-S hybrid system exhibits a remarkable 62% reduction in the pitting propagation rate compared to composites reinforced solely with spherical WC, which is attributed to the preferential dissolution of angular WC protrusions that sacrificially suppress crack initiation at the phase boundaries. Full article