High Mechanical Performance Research Articles

Bio-derived modified halloysite nanotubes as eco-friendly flame retardants to endow epoxy with high thermal stability, mechanical performance and flame retardancy

Bio-derived modified halloysite nanotubes as eco-friendly flame retardants to endow epoxy with high thermal stability, mechanical performance and flame retardancy

Transforming Element Sulfur to High Performance Closed‐Loop Recyclable Polymer via Proton Transfer Enabled Anionic Hybrid Copolymerization

AbstractThe utilization of sulfur has been a global issue. Copolymerization of element sulfur (S8) with other monomers is a promising route to convert it to useful materials but is limited by the comonomers. Here, we report anionic hybrid copolymerization of S8 with acrylate and epoxide at room temperature, where S8 does not copolymerize with epoxide in the absence of acrylate. Yet, the proton transfer from the methyne in acrylate to the oxygen anion enables the ring‐opening of the cyclic comonomer and hence the copolymerization. The cyclic comonomers can be expanded to lactone and cyclic carbonate. Specifically, the copolymer of S8 with bisphenl A diglycidyl ether and diacrylate displays mechanical properties comparable to those of most common plastics, namely, it has ultimate tensile strength as high as 60.8 MPa and Young's modulus up to 680 MPa. It also exhibits high UV resistance and good transparency. Particularly, it has excellent UV‐induced self‐healing, reprocessability and closed‐loop recyclability due to the abundant dynamic S−S bonds and ester groups. This study provides an efficient strategy to turn element sulfur into closed‐loop recyclable polymer with high mechanical and optical performances.

A Review on the Partitioning of Solutes Along Dislocations and Stacking Faults in Superalloys

AbstractChemical and microstructural alterations at near-atomic scale can influence the high temperature mechanical performance of superalloys. These alterations are strongly associated with solute segregation at crystal defects, such as dislocations and stacking faults. This review provides an overview of the phenomena that occurs during deformation at elevated temperatures due to the interactions of solutes with crystal defects. These interactions are discussed based on investigations conducted by exploiting the recent technological advancements of advanced characterization methods, such as transmission electron microscopy and atom probe tomography. Insights on local phase transformation mechanisms along stacking faults are discussed providing perspectives on new alloy design concepts. Besides, various microstructural alterations controlled by the interactions of solutes with dislocations are discussed. Bringing together observations at near-atomic scale that control superalloys in the macroscopic level, we aim to bridge an atomic scale microanalysis gap. Thus, providing insights that future alloy designers, modelers, and engineers can incorporate these effects into their analyses, alloy design models and life prediction calculations.

Self-Repairable Carbon Fiber-Reinforced Epoxy Vitrimer Actuator with Multistimulus Responses and Programmable Morphing.

Smart shape-changing structures in aerospace applications are vulnerable to damage in harsh environments. Balancing high mechanical performance with self-repair capabilities poses a challenge due to inherent trade-offs between strength and flexibility. To address this challenge, an asymmetric bilayer-structured actuator was fabricated using commercially available continuous carbon fiber tows (CFs) as the passive layer and a dynamic cross-linked epoxy vitrimer as the active layer. The construction of the vitrimer-CF actuator involves a simple and scalable hot-pressing process, resulting in a tensile strength of 234 MPa and an interfacial bonding strength of 405 N·m-1. This actuator exhibits remarkable deformation capability (210°/7 s) and an efficient self-repair ability under various stimuli, including thermal (60-160 °C), light (0.4-1.0 W·cm-2), electric (2-4 V), and solvent (acetone). By adjustment of the orientation angle of CFs, complex left-handed and right-handed curling structures can be achieved. Leveraging the insights from photothermal/electrothermal actuation mechanisms, a quadruped crawling robot is developed capable of crawling 4 cm with a single light illumination. The actuator can lift objects 45 times its weight when subjected to light stimuli. Additionally, a flap actuator is constructed to achieve an angle change of 63° within 10 s under an electric stimulus, enabling remote control over the aircraft flight angle. These results demonstrate the potential of the vitrimer-CF actuator for advanced applications in intelligent aerospace structures.

Surface modification of self-adhesive straw-based fiberboard via alkali treatment combined with DES

Self adhesion is a simple and effective bonding technique that can be used to produce environmentally friendly and green straw-based fiberboard (CLS) through deep eutectic-like solvent (DES) treatment. This article mainly introduces the use of DES composed of choline chloride and oxalic acid. DES is diluted with deionized water and straw is immersed in it, and finally dried into pretreated fiber raw materials. Fiber boards are prepared by adjusting the hot pressing parameters and the preset moisture content of straw itself for hot pressing solidification. The aim of this study was to investigate the effects of different processing parameters (hot pressing temperature and straw moisture content) on the microstructure, physical properties, and mechanical properties of CLS. Straw-based fiberboard heated at 180 ° C exhibited the best mechanical and water resistance performance. The fiberboard reached its highest mechanical performance at a moisture content of 50%. The bending performance of fiberboard produced at 180 °C reached 13.5 MPa, and compared with the board manufactured at 120 °C, the bending strength, tensile strength, and internal bonding strength increased by 320%, 224%, and 280%, respectively.

Laser-Induced Self-Limiting Welding of Ag Nanowires with High Mechanical and Electrical Performance.

The high-efficiency and high-precision welding technology of Ag nanowires is of great engineering significance for the integration of new-generation micro- and nanodevices, and the mechanical behavior of its interconnect joints is also essential for their reliable application, especially for some flexible device. In this paper, based on the nano-focusing and localized plasma enhancement properties of Ag nanowires under laser irradiation, Ag nanowire self-limiting joints with mechanical and electrical properties comparable to those of the base material are obtained. At the same time, the local plasma enhancement characteristics of Ag nanowire joints are scanned and analyzed with nanoscale resolution by using cathodoluminescence technology, and the local multi-physical field coupling regulation mechanism of Ag nanowire joints induced by different laser parameters is systematically investigated by combining theoretical simulations. Meanwhile, based on the in situ laser welding and nanomechanical tensile experiments, the mechanical properties of single Ag nanowires and their welded joints are systematically analyzed, and the characteristics of the interfacial atomic behaviors and the evolution process during the welding and tensile processes are investigated.

Thermomechanical properties and microstructure of concrete made with recycled concrete aggregates after exposure to high temperatures

AbstractUsing recycled concrete aggregates (RCA) in concrete has emerged as a promising solution to produce concrete with reduced environmental impact and adequate performance. However, a deeper understanding of the thermal and mechanical behavior of concrete made with RCA is still needed for further application in real structures. The present paper addresses one of the crucial issues for structural concrete: its behavior after exposure to high temperature. Four concrete mixes are studied: a reference concrete made with natural aggregates (NA), two concretes including 40% and 100% of coarse RCA as a direct replacement (DR) for coarse NA, and a concrete made with 100% of coarse RCA relying on a strength‐based replacement (SBR). The SBR concrete mix was designed to achieve the same performance (28 days compressive strength and slump) as the reference concrete. All specimens were exposed to temperatures of 200, 400, and 600°C. After cooling, samples were evaluated for residual mass loss, thermal, and mechanical properties. Microstructural quantitative analyses were conducted over several square millimeters to show that interfaces between the old and new cement pastes, peculiar to concrete made with RCA, do not further promote fracture development. The results show that after exposure to high temperatures, the thermal and mechanical performances of concrete made with RCA are reduced in the same manner and extent as in concrete made with NA. When the RCA‐based concrete is designed to achieve similar performance as concrete with NA at room temperature (SBR), the residual thermomechanical behavior is similar between both concretes.

High Mechanical Performance of Lattice Structures Fabricated by Additive Manufacturing

Lattice structures show advantages in mechanical properties and energy absorption efficiency owing to their lightweight, high strength and adjustable geometry. This article reviews lattice structure classification, design and applications, especially those based on additive manufacturing (AM) technology. This article first introduces the basic concepts and classification of lattice structures, including the classification based on topological shapes, such as strut, surface, shell, hollow-strut, and so on, and the classification based on the deformation mechanism. Then, the design methods of lattice structure are analyzed in detail, including the design based on basic unit, mathematical algorithm and gradient structure. Next, the effects of different lattice elements, relative density, material system, load direction and fabrication methods on the mechanical performance of AM-produced lattice structures are discussed. Finally, the advantages of lattice structures in energy absorption performance are summarized, aiming at providing theoretical guidance for further optimizing and expanding the engineering application potential of lattices.

Complete conversion of eucalyptus wood to dynamic covalent networks: An in-situ plasticising strategy

Ongoing innovation in bio-based plastics aims to meet more economical and diverse societal needs. However, the dependence on a single biomass source and the generally inadequate wet stability and moisture mechanical properties of traditional bio-based plastics severely limit their competitiveness. We have developed a high mechanical performance, fully bio-based, thermoset in-suit plastic from an almost worthless agricultural and forestry waste (eucalyptus) through a simple and environmentally friendly deconstruction-reconstruction strategy. In this process, the hydrogen and covalent bonds in the lignin and cellulose of eucalyptus are broken and then reorganised through dynamic covalent bonds. The resulting eucalyptus-based plastic exhibits high mechanical strength, excellent water resistance, UV ageing resistance, photothermal performance and light/heat controllable shape memory properties. By preserving the original structure of the lignin and cellulose, its natural degradability is ensured. This strategy for developing full-component plastics from solid agricultural and forestry waste offers a new approach to producing more competitive fully bio-based plastics.

The impact of heat treatment process on the drilling characteristics of Al–5Si–1Cu–Mg alloy produced by sand casting

Aluminum–Silicon (Al–Si) based materials are commonly preferred in engineering studies requiring high mechanical performance as an alternative to steel materials. These alloys are especially preferred in the automotive industry, aerospace components and heavy machinery parts. In post-casting processes, machining operations are of great importance for high geometric precision, surface quality and longer fatigue life in mechanical environments. In this research, the microstructural, mechanical and machining characteristics of the Al–5Si–1Cu–Mg material produced by sand casting method in both as-cast (AC) and heat-treated (HTed) (Solid solution, quenching and aging-SQA) states were experimentally investigated. Microstructural examinations were carried out with optical microscope and SEM images. Mechanical properties were determined by tensile and hardness tests. Then, drilling experiments were performed in the CNC vertical machining center with 8 mm diameter uncoated HSS (High Speed Steel) cutting tools at constant cutting conditions (i.e., cutting speed-V: 125 m/min, feed rate-f: 0.05 mm/rev and depth of cut-DoC: 15 mm). In microstructural investigations, it was determined that the microstructure of the Al–5Si–1Cu–Mg material in AC state consists of α-Al, eutectic Si, β-Fe (β-Al5FeSi) and π-Fe (π-Al8Mg3FeSi6) intermetallics. After the SQA, the existing phases generally exhibited a spherical structure, and it was seen that the β phase in the microstructure transformed into the Ɵ (Al7FeCu2) phase. SQA improved the hardness, yield and tensile durability of the material, whereas decreasing the elongation to fracture. SQA process improved the machining characteristics of the material by decreasing thrust force, moment, surface roughness and built-up edge (BUE) formation. The machined subsurface structure of HTed alloy under constant cutting conditions was determined to be more stable and smooth and the machined surface microhardness of HTed alloy was higher compared to as-cast alloy due to the effect of solid precipitation hardening. In addition, shorter and more broken chips occurred in the machining of HTed alloys due to the effect of low elongation to fracture.

Highly Conductive Supramolecular Salt Gel Electrolyte for Flexible Supercapacitors.

Conductive gels have greatly facilitated the development of flexible energy storage devices, including supercapacitors, batteries, and triboelectric nanogenerators. However, it is challenging for gel electrolytes to tackle the trade-off issues between mechanical properties and conductivity. Herein, a strategy of all inorganic salt-driven supramolecular networks is presented to construct gel electrolytes with high conductivity and reliable mechanical performance for flexible supercapacitors. The salt gel is successfully fabricated by combining a salt supramolecular network constructed by NH4Mo7O24·4H2O and FeCl3·6H2O and a polymer network of poly(vinyl alcohol). The inorganic salt supramolecular network serves as a rigid self-supporting framework in the hydrogel system for improving the mechanical properties and providing abundant active sites for accelerating ion transport. Furthermore, the salt gel-enabled supercapacitors are equipped and exhibit a high specific capacitance (199.4 mF cm-2) and excellent energy density (27.69 μWh cm-2). Moreover, the flexible supercapacitors not only present remarkable cyclic stability after 3000 charging/discharging cycles but also exhibit good electrochemical stability even under severe deformation conditions. The strategy of salt-gel-driven flexible supercapacitors would provide fresh thinking for the development of advanced flexible energy storage fields.

Bioinspired 4D Printed Tubular/Helicoidal Shape Changing Metacomposites for Programmable Structural Morphing

AbstractBiological structures combine passive shape‐changing with force generation through intricate composite architectures. Natural fibers, with their tubular‐like structures and responsive components, have inspired the design of pneumatic tubular soft composite actuators. However, no development of passive structural actuation is available despite the recent rise of 4D printing. In this study, a biomimicry approach is proposed with inspiration from natural fiber architecture to create a novel concept of thermally active 4D printed tubular metacomposites. These metacomposites exhibit high mechanical performance and 3D‐to‐3D shape‐changing ability triggered by changes in temperature. A rotative printer is proposed for winding a continuous carbon fibers reinforced PolyAmide 6.I composite on a PolyAmide 6.6 polymer mandrel in a similar manner to the structure of cellulose microfibrils within the polysaccharide matrix of natural fiber cell‐walls. The resulting 4D printed tubular metacomposites exhibit programmable rotation and torque in response to thermal variations thanks to the control of their mesostructure and the overall geometry. Energy density values representing a trade‐off between the rotation and the torque are comparable to shape memory alloys when normalized by stiffness. Finally, a proof of concept for an autonomous solar tracker is presented, showcasing its potential for designing autonomous assemblies for structure morphing.

Low-carbon high-strength engineered geopolymer composites (HS-EGC) with full-volume fly ash precursor: Role of silica modulus

In this study, the influence of the silica modulus of alkaline activators on the overall performances of pure fly ash (FA)-based High-Strength Engineered/Strain-Hardening Geopolymer Composites (HS-EGC/SHGC) was comprehensively studied. The developed HS-EGC successfully presented simultaneous high compressive strength (over 90 MPa) and high tensile ductility (over 6.0 %) for the first time. Tensile strain-hardening and over-saturated cracking phenomena were observed for all the HS-EGC mixes. It was found that the increase of the silica modulus from 1.0 to 2.0 reduced the tensile strength and strain energy density of HS-EGC, but the most distinguished overall mechanical index was achieved in the mix with the silica modulus of 1.5. Additionally, the underlying mechanism behind the mechanical performances was explored by Back Scattering Electron and Energy Dispersive Spectroscopy (BSE-EDS) tests. According to the data comparison from literature review, the good sustainability and market potential of the developed material were successfully demonstrated, and the developed HS-EGC pushed the performance envelope of pure FA-based EGC materials. The findings could help promote the future development and practical applications of this strain-hardening geopolymer material with both good sustainability and high mechanical performances.

Vat photopolymerization of complex-shaped silicon nitride ceramics with high mechanical and thermal performance by optimization sintering aids and kinetics

In this study, the impact of sintering aid content and sintering time on the density, phase composition, microstructure, thermal conductivity, and mechanical properties of silicon nitride (Si3N4) ceramics through vat photopolymerization (VPP) was systematically investigated. The results revealed that an increase in sintering aid amount promoted the network distribution of the grain boundary phase along with densification, grain coarsening and microstructure uniformity. The extension of sintering time improved density, thermal conductivity, and mechanical properties of the material. Superior performance with density of 99.4%, thermal conductivity of 64.4W·m-1·K-1, flexural strength of 879 ± 37MPa, and hardness of 15.0 ± 0.4GPa was achieved in sample containing 8wt.% MgO/Y2O3 sintered for 12h. Finally, high-precision Si3N4 ceramic heat sink elements were successfully fabricated via VPP, opening up new prospects in thermal management applications associated with electronics and automotive industries.

Epoxy resin-based polymer-wall stabilized liquid crystal films with low driving voltages and improved mechanical performance for smart window applications

Polymer stabilized liquid crystals (PSLCs) have wide applications in smart windows and light shutters. However, for most applications, it requires low driving voltages and high mechanical performance, which is arduous to achieve both. Herein, a novel epoxy resin-based PSLC device is prepared showing improved electro-optical and mechanical properties simultaneously. This is benefited from the construction of a period polymer wall structure in liquid crystal matrix through cationic polymerization of epoxy monomers and preparation of multi-functional surfaces through self-assembly of silane mixtures. The multi-functional surfaces could ensure homeotropic alignment of liquid crystals and photo-polymerize with the polymer networks. As a result, the polymer-wall stabilized liqduid crystal (PWSLC) film with multi-functional surfaces shows lower (24%) saturation voltage, higher (20%) contrast ratio and improved (2.4 times) peel strength than the PSLC film with only vertical alignment surfaces. This research provides important reference to experiment and manufacture of reverse-mode dimming films for smart windows applications.

High mechanical performance and multifunctional degraded fucoidan-derived bioink for 3D bioprinting

While 3D bioprinting serves as a powerful tool in the field of tissue engineering, there is still a lack of natural biomaterial inks that simultaneously combine high mechanical performance with multiple biofunctionalities. Here, a single-component natural bioink with high strength and multi-biofunctionality was developed through the simple degradation and methacrylation of natural fucoidan. Hydrothermal degradation significantly decreased the natural fucoidan solution's viscosity by 99.9 %, meeting the necessary viscosity for Digital Light Processing (DLP) 3D printing. Meanwhile, various biofunctionalities of low molecular weight fucoidan obtained through degradation, such as antimicrobial and antioxidant properties, were developed. The resulting bioink exhibited good mechanical performance (compression modulus of 311 kPa), antimicrobial properties (antibacterial rates of 95.5 % and 97.9 % against E. coli and S. aureus, respectively), and antioxidant properties (intracellular ROS inhibition rates of 94.7 %). Using DLP 3D bioprinting, all printed products showed high shape fidelity with exceptional viability and activity of the encapsulated cells. Due to the unique sulfate structure resembling the natural components of chondroitin sulfate, the in vivo tests revealed its efficacy in promoting cartilage defect repair. In conclusion, the novel bioink blending high mechanical performance with multiple biofunctionalities, shows great potential in the 3D printing of tissue and organ regeneration.

Automated design of architectured polymer-concrete composites with high specific flexural strength and toughness using sequential learning

Architectured polymer-concrete composite (APCC) is a promising structural material with high mechanical performance while optimizing the design of APCC for a high flexural strength, high toughness, and light weight remains a challenge. This paper presents a machine learning-based approach to design APCC with high specific flexural strength and toughness. The proposed approach integrates sequential surrogate modelling, Latin hypercube sampling, and Lion Pride Optimization to predict and optimize the flexural properties of APCC. The proposed approach was implemented into designing APCC beams, which were fabricated via 3D printing and tested under flexural loads. Results show that the APCC beams achieved high flexural strength, high toughness, and light weight, simultaneously. The devised architecture of APCC arrested crack propagation and promoted energy dissipation. Parametric studies were performed to evaluate the effect of key design variables of APCC on flexural properties. This research advances the basic knowledge and capabilities of AI-assisted design of APCC.

Transforming Element Sulfur to High Performance Closed-Loop Recyclable Polymer via Proton Transfer Enabled Anionic Hybrid Copolymerization.

The utilization of sulfur has been a global issue. Copolymerization of element sulfur (S8) with other monomers is a promising route to convert it to useful materials but is limited by the comonomers. Here, we report anionic hybrid copolymerization of S8 with acrylate and epoxide at room temperature, where S8 does not copolymerize with epoxide in the absence of acrylate. Yet, the proton transfer from the methyne in acrylate to the oxygen anion enables the ring-opening of the cyclic comonomer and hence the copolymerization. The cyclic comonomers can be expanded to lactone and cyclic carbonate. Specifically, the copolymer of S8 with bisphenl A diglycidyl ether and diacrylate displays mechanical properties comparable to those of most common plastics, namely, it has ultimate tensile strength as high as 60.8 MPa and Young's modulus up to 680 MPa. It also exhibits high UV resistance and good transparency. Particularly, it has excellent UV-induced self-healing, reprocessability and closed-loop recyclability due to the abundant dynamic S-S bonds and ester groups. This study provides an efficient strategy to turn element sulfur into closed-loop recyclable polymer with high mechanical and optical performances.

Enhancing the performance of hydrogel strain/pressure sensors via gradient-entanglement-induced surface wrinkling patterns

Due to the advantages of high mechanical compliance and good biocompatibility, conductive hydrogels exhibit great application potential in flexible electronics. As the requirements in high sensitivity and high mechanical performance are increasing, the construction of patterned surfaces has been proven an effective approach, yet most of the common methods are complex and high-cost. Herein, we proposed a facile strategy to construct gradient entanglement dual network (GEDN) hydrogel with spontaneously patterned surface and consequent high surface area, which greatly enhances the sensitivity of hydrogel sensors. The strategy of high entanglement as well as the dual network in hydrogel achieved greatly improved mechanical performance. The prepared polyvinyl alcohol (PVA)/gradient entangled polyacrylamide (PAAm) DN and surface-patterned hydrogel possesses the advantages of excellent stretchability (681 %), high tensile strength (1.01 MPa), toughness (4.23 MJ/m3), and relatively low mechanical hysteresis. Meanwhile, it showed high sensitivity, wide detection range, and rapid response both as strain sensor (GFmax = 10.96, detection range = 681 %, an average response time of 170 ms) and pressure sensor (Smax = 0.17 kPa−1, detection range = 225 kPa, an average response time of 230 ms). In summary, it provides a new strategy for design of the multifunctional high-performance flexible devices, exhibiting great application prospects.

Investigation of the effect of Tideglusib on the hydroxyapatite formation, crystallinity and elasticity of conditioned resin-dentin interfaces

To investigate the effect of dentin infiltration with polymeric nanoparticles (NPs) doped with tideglusib (TDg) (TDg-NPs) on hydroxyapatite formation, crystallinity and elasticity of conditioned resin-dentin interfaces. Dentin conditioned surfaces were infiltrated with NPs or TDg-NPs. Bonded interfaces were created, stored for 24 h and submitted to mechanical and thermal challenging. Resin-dentin interfaces were evaluated through nanoindentation to determine the modulus of elasticity, X-ray diffraction and transmission electron microscopy through selected area diffraction and bright-filed imaging. TDg-NPs provoked peaks narrowing after the diffraction-intensity analysis that corresponded with high crystallinity, with an increased modulus of Young after load cycling in comparison with the samples treated with undoped NPs. New minerals, in the group of TDg-NPs, showed the greatest both deviation of line profile from perfect crystal diffraction and dimension of the lattice strain, i.e., crystallite, grain size and microstrain and 002 plane-texture. The new minerals generated after TDg-NPs application and mechanical loading followed a well defined lineation. Undoped NPs mostly produced small hydroxyapatite crystallites, non crystalline or amorphous in nature with poor maturity. Tideglusib promoted the precipitation of hydroxyapatite, as a major crystalline phase, at the intrafibrillar compartment of the collagen fibrils, enabling functional mineralization. TDg-NPs facilitated nucleation of crystals randomly oriented, showing less structural variation in angles and distances that improved crystallographic relative order of atoms and maturity. Nanocrystals inducted by TDg-NPs were hexagonal prisms of submicron size. Thermal challenging of dentin treated with TDg-NPs have provoked a decrease of functional mineralization and crystallinity, associated to immature hydroxyapatite. New polycrystalline lattice formation generated after TDg-NPs infiltration may become correlated with high mechanical performance. This association can be inferred from the superior crystallinity that was obtained in presence of tideglusib. Immature crystallites formed in dentin treated with undoped NPs will account for a high remineralizing activity.