Search Results (101)

The growing demand for lightweight and reliable structures across aerospace, automotive, marine, and civil engineering has driven significant advances in polymer adhesive technology. These materials serve dual roles, functioning as matrices in composites and as structural bonding agents, where they must balance strength, toughness, durability, and sometimes sustainability. Recent review efforts have greatly enriched understanding, yet most approach the topic from specialized angles—whether emphasizing nanoscale toughening, multifunctional formulations, sustainable alternatives, or microscopic failure processes in bonded joints. While such perspectives provide valuable insights, they often remain fragmented, leaving open questions about how nanoscale mechanisms translate into macroscopic reliability, how durability evolves under realistic service conditions, and how mechanical responses interact across different loading modes. To address this, the present review consolidates knowledge on the performance of polymer adhesives under tension, shear, fracture, fatigue, creep, and impact. By integrating experimental findings with computational modeling and emerging data-driven approaches, it situates localized mechanisms within a broader structure–performance framework. This unified perspective not only highlights persistent gaps—such as predictive modeling of complex failure, scalability of nanomodified systems, and long-term durability under coupled environments—but also outlines strategies for developing next-generation adhesives capable of delivering reliable, high-performance bonding solutions for demanding applications. Full article

Due to post-cementing hydraulic fracturing and other operational stresses, inadequate mechanical properties or suboptimal design of the cement sheath can lead to tensile failure and microcrack development, compromising both hydrocarbon recovery and well integrity. In this study, three field-deployed cement slurry systems were compared on the basis of their basic mechanical properties such as compressive and tensile strength. Laboratory-scale physical simulations of hydraulic fracturing during shale oil production were conducted, using dynamic permeability as a quantitative indicator of integrity loss. The experimental results show that evaluating only basic mechanical properties is insufficient for cement slurry system design. A more comprehensive mechanical assessment is re-quired. Incorporation of an expansive agent into the cement slurry system can alleviate the damage caused by the microannulus to the interfacial sealing performance of the cement sheath, while adding a toughening agent can alleviate the damage caused by tensile cracks to the sealing performance of the cement sheath matrix. Through this research, a microexpansive and toughened cement slurry system, modified with both expansive and toughening agents, was optimized. The expansive agent and toughening agent can significantly enhance the shear strength, the flexural strength, and the interfacial hydraulic isolation strength of cement stone. Moreover, the expansion agents mitigate the detrimental effects of microannulus generation on the interfacial sealing, while the toughening agents alleviate the damage caused by tensile cracking to the bulk sealing performance of the cement sheath matrix. This system has been successfully implemented in over 100 wells in the GL block of Daqing Oilfield. Field application results show that the proportion of high-quality well sections in the horizontal section reached 88.63%, indicating the system’s high performance in enhancing zonal isolation and cementing quality. Full article

The development of high-impact denture base formulations that are suitable for digital light processing (DLP) 3D printing is demanding. Indeed, a combination of high flexural strength/modulus and high fracture toughness is required. In this contribution, eight urethane macromonomers (UMs1-8) were synthesized in a one-pot, two-step procedure. Several rigid diols were first reacted with two equivalents of trimethylhexamethylene diisocyanate. The resulting diisocyanates were subsequently end-capped with a free-radically polymerizable monomer bearing a hydroxy group. UMs1-8 were combined with the monofunctional monomer (octahydro-4,7-methano-1H-indenyl)methyl acrylate and a poly(ε-caprolactone)-polydimethylsiloxane-poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymer (BCP1) as a toughening agent. The double-bond conversion, glass transition temperature (T_g), and mechanical properties (flexural strength/modulus, fracture toughness) of corresponding light-cured materials were measured (cured in a mold using a light-curing unit). The results showed that the incorporation of BCP1 was highly efficient at significantly increasing the fracture toughness, as long as the obtained networks exhibited a low crosslink density. The structure of the urethane macromonomer (nature of the rigid group in the spacer; nature and number of polymerizable groups) was demonstrated to be crucial to reach the desired properties (balance between flexural strength/modulus and fracture toughness). Amongst the evaluated macromonomers, UM1 and UM2 were particularly promising. By correctly adjusting the BCP1 content, light-cured formulations based on those two urethane dimethacrylates were able to fulfill ISO20795-1:2013 standard requirements regarding high-impact materials. These formulations are therefore suitable for the development of 3D printable high-impact denture bases. 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

Polylactic acid (PLA) exhibits remarkable biocompatibility and biodegradability, rendering it a highly promising material for applications in packaging and disposable products. However, its inherent brittleness, low melt strength, and slow crystallization rate significantly restrict its practical uses. Our previous studies have shown that incorporating the ADR chain extender can yield chitosan–polylactic acid–ADR (CS/PLA-ADR) composites with outstanding antibacterial properties, enhanced biodegradability, and the capability to effectively block water vapor and oxygen. However, the low elongation at break (less than 10%) limits its application in scenarios that require high ductility. To enhance the toughness of the CS/PLA-ADR composites, the flexible biodegradable polybutylene succinate (PBS) is innovatively introduced. The mechanical properties of PBS can be compared with polyethylene and polypropylene, providing high strength and toughness. The mechanism of introducing PBS is to construct a good, toughened structure through the flexible structure of PBS in collaboration with ADR toughening agent, achieving a balance between strength and toughness in CS/PLA-ADR-PBS composites. The incorporation of PBS is anticipated to improve the ductility of CS/PLA-ADR composites. This study systematically investigates the effects of varying PBS content (0–30%) on the properties of CS/PLA-ADR-PBS composites, aiming to determine the optimal PBS content and elucidate the mechanism by which PBS enhances the overall performance of the composites. The results indicate that when the PBS content is 20%, the composites exhibit optimal overall properties. This research provides a theoretical foundation and technical support for the development of environmentally friendly and sustainable packaging materials, offering significant research value and broad application prospects. Full article

This work provides a comprehensive review of the recent advancements in the toughening modification methods for epoxy resins. The study explores a variety of approaches, including the incorporation of liquid rubbers, core–shell rubber particles, thermoplastic resins, hyperbranched polymers, and the nanoparticle toughening method, each of which contributes to improving the mechanical properties and fracture toughness of epoxy resins. Special attention is given to the mechanisms underlying these toughening methods, such as reaction-induced phase separation, crack pinning, and energy dissipation through particle deformation. The paper also examines the synergistic effects achieved by combining different toughening agents, such as phenoxy thermoplastic rubber and core–shell rubber particles, which significantly enhance the critical fracture energy and impact strength of epoxy composites. Additionally, the challenges associated with each method, such as the potential reduction in mechanical properties and the influence of phase separation on material performance, are discussed. Through a detailed analysis of experimental studies, this paper highlights the effectiveness of various toughening strategies and suggests future research directions aimed at further optimizing epoxy resin toughening techniques for diverse industrial applications. Emerging computational modeling and machine learning applications in epoxy resin development are also systematically reviewed to highlight their potential in advancing predictive design frameworks. Full article

A recent composite technique, namely Resin Pre-Coating (RPC), has demonstrated remarkably high effectiveness in the repair of Carbon Fiber-Reinforced Polymer (CFRP) composites. Compared to widely used scarf repair and injection repair, this non-destructive method offers advantages in addressing subsurface damages from the millimeter to micron scale, such as edge delaminations that frequently occur due to machining or low-energy impacts. The acetone-rich RPC solution can spontaneously transport sticky resin and other toughening agents into defects through capillary action. In this study, we further improved the solution by adopting a self-curing resin (i.e., SC-RPC), reducing the repair duration from the initial 2–3 months to merely a few hours. Using this modified solution, the CFRP specimens prepared containing delamination cracks were largely restored, reaching up to 94.9% of the original compressive strength. With the additional incorporation of carbon nanotubes (CNTs), full restoration was achieved, as is evidenced by load-bearing capacities and overload failure modes comparable to those of pristine specimens. The findings of this study may help alleviate concerns regarding substandard post-repair performance and prolonged repair durations, which are frequently criticized in real-world CFRP maintenance projects. The preparation of two new formulations, SC-RPC and SC-RPC+CNT, along with the optimization of key parameters, was carefully detailed in the manuscript to ensure experimental reproducibility. Full article

As a building material, recycled concrete (RC) has significant advantages in environmental protection and sustainable development. In the cold conditions of northwest China, in order to maintain the toughness and durability of buildings during service, polyacrylonitrile fiber (PANF) is often used as a toughening agent with RC. In this study, mechanical tests and frost durability tests were conducted on polyacrylonitrile fiber-reinforced recycled concrete (PAN-RC). The mixing contents of PANF were 0.7 kg/m³, 0.8 kg/m³, and 0.9 kg/m³, while the substitution rates of recycled coarse aggregate (RCA) were 30%, 40%, and 50%. The experimental results indicate that the incorporation of PANF into recycled concrete significantly improves the mechanical properties and frost resistance durability of the material. From the test results, the freezing resistance of concrete is the best when the replacement amount of RCA is 40% and the amount of PANF is 0.8 kg/m³. Meanwhile, a freeze–thaw damage model for PAN-RC was developed based on experimental research. This model is feasible to predict the freeze–thaw damage degree of fiber-reinforced recycled concrete under various replacement rates of RCA and different dosages of PANF. It is considerable significant for both theoretical understanding and practical engineering applications of RC. Full article

Fracture toughness is a key property of epoxy resins with a high glass transition temperature (T_g), used in carbon fiber/epoxy composites for aerospace applications. Conventional toughening methods rely on adding toughening agents, often compromising the processibility and thermal stability. This study introduces a simple self-toughening approach that enhances the fracture toughness without sacrificing other properties by controlling the cured epoxy network structure. Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) epoxy resin was cured using mixtures of structural isomeric curing agents, 3,3′- and 4,4′-diaminodiphenyl sulfone (3,3′- and 4,4′-DDS), at ratios of 7:3, 5:5, and 3:7. The optimal 7:3 ratio produced a resin with 30% higher fracture toughness compared to TGDDM/3,3′-DDS and 100% higher than the TGDDM/4,4′-DDS system. The T_g of the self-toughened resin ranged from 241 to 266 °C, which was intermediate between the T_g values of the TGDDM/3,3′-DDS and TGDDM/4,4′-DDS systems. This improvement is attributed to the higher crosslink density and reduced free volume of the epoxy network. These findings demonstrate that simply mixing isomeric curing agents enables self-toughening, providing a practical and efficient strategy to enhance the performance of high-T_g epoxy resins in advanced composite applications. Full article

This study investigates the effect of incorporating modified calcium carbonate whiskers, treated with tetraethyl orthosilicate (TEOS), to enhance the mechanical properties and sealing integrity of oil well cement under high-temperature and high-pressure (HTHP) conditions. Traditional cement systems are prone to brittleness and cracking under dynamic loads, leading to compromised wellbore sealing performance. Our findings demonstrate that fiber-toughened cement slurry improves the toughness and sealing performance of the cement annulus, maintaining gas tightness and mechanical integrity under cyclic alternating pressures at 150 °C. Specifically, the inclusion of 5% modified whisker fibers improves compressive strength by 24.5% and flexural strength by 43.3% while maintaining stable rheological and thickening properties. These results support the hypothesis that modified whisker fibers enhance the durability and sealing integrity of cement wellbores under extreme conditions, providing a practical solution for challenging cementing applications. 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

Carbon fibre-reinforced polymers (CFRPs) are a lightweight alternative solution for various applications due to their mechanical and structural properties. However, debonding at the fibre–matrix interface is an important failure mechanism in composite materials. Proposed solutions include using nano-scale reinforcements to strengthen and toughen structural composites. This study covers a comprehensive approach for evaluating occupational hazards during the sizing of 6k carbon fibres using multi-walled functionalized carbon nanotubes (MWCNTs) and few-layer graphene (FLG) at a pilot scale. Material hazard and exposure banding showed elevated risks of exposure to nanomaterials during the sizing process, while a ‘what-if’ process hazard analysis allowed for the evaluation of hazard control options against the hypothetical process failure scenarios of human error and utilities malfunctioning. On-site measurements of airborne particles highlighted that using MWCNTs or FLG as a sizing agent had negligible effects on the overall exposure potential, and higher micro-size particle concentrations were observed at the beginning of the process, while particle size distribution showcased high concentrations of particles below 50 nm. This analysis provides a thorough investigation of the risks and potential exposure to airborne hazardous substances during CF sizing while providing insights for the effective implementation of a safe-by-design strategy for designing targeted hazard control systems. Full article

The study investigated the effects of a toughening agent and micron-sized toughening particles (TP) on the resin and carbon fiber-reinforced polymer (CFRP) composites, with a particular focus on compressive strength. The results showed that the addition of the toughening agent improved the overall mechanical properties of both the resin and CFRP but had a minor effect on the residual compressive strength (CAI) of CFRP after impact. Compared to the pure toughening agent, the addition of TP increased the CAI, GIC, and GIIC of CFRP by 74%, 35%, and 68%, respectively. The SEM, ultrasonic C-scan, and metallographic microscopy were used to analyze the failure morphology and TP distribution. Compared to pure toughening agent modification, the introduction of TP led to the formation of continuous toughening particle layers, which reduced the compression damage area by 61%, significantly balancing and absorbing the load. This modification also resulted in typical kink band damage. This study found that resin toughening significantly improved the compressive strength of CFRP, while micron-sized toughening particles, in the form of toughening layers, notably improved the CAI. These findings provide valuable insights for enhancing the compression and impact resistance of CFRP. Full article

CaCO₃ whiskers, as a micron-level inorganic fiber material, can enhance and toughen composite materials. In order to study the technical feasibility of CaCO₃ whisker-modified asphalt, two types of silane coupling agent (SCA), KH-550 and KH-570, were applied to treat the surface of CaCO₃ whiskers, and the treatment effects of the original and treated whiskers were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and contact angle test. Meanwhile, models of CaCO₃ whiskers, SCA, and asphalt molecules were established by Material Studio (MS, 2020 version) software, and the adhesion mechanism between the CaCO₃ whiskers-and-asphalt interface was predicted. The results of microscopic characterization experiments indicate that the surface of the whiskers treated with SCA became rougher. Compared with the original whiskers, the contact angle between the treated whisker surface and water increased from 50° to 92.2° and 103.4°, and the surface of whiskers changed from hydrophilic to hydrophobic. The results of molecular dynamics simulation analysis show that the adhesion performance between the CaCO₃ whisker surface and asphalt increased from 100.1 mJ/m² to 112.5 mJ/m² and 126.6 mJ/m² after modification with SCA, and the increase in adhesion energy of KH550 is greater than that of KH570. The above research results indicate that the micro-characterization results were consistent with the molecular dynamics simulation results; that is, after treatment with SCA, the adhesion energy between the whiskers and asphalt was increased to varying degrees. The research method in this article combines micro-characterization with molecular dynamics simulation, which has a certain degree of innovation. Full article

This study aims to investigate the effects of three toughening agents—core–shell rubber particles (CSR), nano-silica particles (NSPs), and epoxidized polybutadiene (EPB)—on the performance of UV-LED-cured epoxy electronic encapsulants. By systematically comparing the curing behavior, thermomechanical properties, and impact resistance of different toughening agents in alicyclic epoxy resins, their potential applications in more environmentally friendly UV-cured electronic encapsulation are evaluated. The results show that NSP and CSR toughened samples have fast cured speed under 365 nm UV-LED light, but it affects the depth of curing under low energy conditions. They maintain high Tg, high modulus, and low thermal expansion coefficient (CTE), especially in the NSP-toughened sample. The EPB-toughened sample has good transparency for LED, but it has negative effects on Tg and CTE. This research provides essential theoretical and experimental data to support the development of high-performance UV-LED-cured epoxy encapsulation materials. Full article