Excellent Mechanical Properties Research Articles

Large-Scale additive fabrication of tough nanocellulose yarns

Nanocellulose is a promising candidate for fabricating high-performance cellulosic materials due to its extremely fine structure and excellent mechanical properties. However, converting the extraordinary properties of individual nanofibers to macroscopic fibers through large-scale preparation remains a challenge. Inspired by the staple spun yarns, herein, we demonstrate a facile and scalable strategy for continuously additive fabrication of nanocellulose yarns by twisting stacked short nanocellulose slivers. Benefiting from the wet-stretching and twisting process, the resultant yarns with tightly intertwined cellulose nanofibers (CNFs) exhibit outstanding toughness (42.9MJm-‍3) and fracture strain (20 %), respectively. Importantly, this approach can be extended to develop functional yarns such as fluorescent yarns, magnetic yarns, and conductive yarns. This work provides a new method for large-scale preparation of tough nanocellulose yarns for future functional materials, such as smart textiles and wearable electronics.

Addition of AlO(OH) nanoparticles to assist stabilizing emulsion for digital light processing lightweight but robust porous alumina ceramics

It is proposed here that introducing AlO(OH) nanoparticles to build a wide range of particle size distribution to assist stabilizing emulsion and regulate its properties is an important prerequisite for using Pickering emulsion as digital light processing (DLP) feedstock. Combined with DLP, porous alumina ceramics with hierarchical porosity composed of macro-pores from the designed model (based on body-centered cubic lattice) and micro-pores formed by emulsion droplet, can be prepared by adjusting the microstructure of framework via changing AlO(OH) content, oil-to-water ratio and dispersant content. The AlO(OH) addition facilitates the further filling of particles at the phase interface of emulsion, thus increasing the viscosity and reducing the pore size. Porous alumina ceramics exhibit an average pore size distribution of 4.71 μm to 6.06 μm, porosity of 71.92%-78.60%, and relatively high compressive strength ranging from 5.02 MPa to 10.36 MPa, demonstrating a combination of high porosity and excellent mechanical properties.

Optimizing Fatigue Performance in Gradient Structural Steels by Manipulating the Grain Size Gradient Rate.

As a new type of high-performance material, gradient structural steel is widely used in engineering fields due to its unique microstructure and excellent mechanical properties. For the prevalent fatigue failure problem, the rate of change in the local grain size gradients along the structure (referred to as the gradient rate) is a key parameter in the design of gradient structures, which significantly affects the fatigue performance of gradient structural steel. In this study, a new method of 'Voronoi primary + secondary modeling' is adopted to successfully establish three typical high-strength steel models corresponding to the convex-, linear-, and concave-type gradient rates for gradient structures, focusing on the stress-strain response and crack propagation in structural steel with different gradient rates under cyclic loading. It was found that the concave gradient rate structural model is dominated by finer grains with larger volume fraction, which is conducive to hindering fatigue crack propagation and has the longest fatigue life, which is 16.16% longer than that of the linear gradient rate structure and 23.66% longer than that of the convex gradient rate structure. The simulation results in this study are consistent with the relevant experimental phenomena. Therefore, when regulating the gradient rate, priority should be given to increasing the volume fraction of fine grains and designing a gradient rate structure dominated by fine grains to improve the fatigue life of the material. This study presents a new strategy for designing engineering materials with better service performance.

High wear resistance of metallocene polyethylene with long-chain branch for artificial joints

Ultra-low-wear polyethylene (ULWPE) is a promising material for artificial joint implants, owing to its good biocompatibility and wear resistance. However, its molecular weight is almost an order of magnitude lower than that of Ultrahigh molecular weight polyethylene (UHMWPE). The mechanism between wear resistance and the structure of ULWPE is still unknown. This study analyzed their attributes from microstructure to macroscopic performance and revealed the wear resistance mechanisms of ULWPE by conducting an in-depth investigation of four types of polyethylene, including ULWPE, UHMWPE, and high-density polyethylene. Impact tests showed that ULWPE, with a molecular weight of 282 kg/mol, exhibited an impact energy of 110 kJ/m2, surpassing the 97 kJ/m2 recorded for UHMWPE (molecular weight over 5000 kg/mol). Furthermore, tribology tests indicated that the wear rate of the most anti-wear ULWPE was 4.479±0.040 mm³/Mc, which was significantly lower than the 5.601±0.456 mm³/Mc for UHMWPE. The excellent mechanical properties and wear resistance of ULWPE were derived from its unique structure. Dynamic rheological assessments and thermal classification techniques confirmed that ULWPE had long-branched chains. The long-branched chains markedly increased the proportion of the high entanglement and the tie molecules in the amorphous regions, endowing it with superior toughness. At the same time, the high crystallinity of ULWPE gives it sufficient hardness and strength. The combination of high crystallinity and high entanglement endowed ULWPE with a good balance between strength and toughness, leading to its exceptional mechanical properties and wear resistance. This study provided robust data for ULWPE's clinical use and theoretical insights for designing durable, implantable polymers.

Strengthened solid solution and homogenized eutectic structure of Al-based multi-component alloy via electromagnetic stirring

Macro-segregation and coarse intermetallic compounds (IMCs) are common problems in lightweight multi-component alloys (MCAs), in this work, electromagnetic stirring treatment (EST) and mixed eutectic strategy were proposed to tune the solidified microstructure of Al-based MCA. For the studied MCA, the positive and negative segregation of solute elements (except for Si) were found both lower than 5% in the ingot, and the macro-segregation was reduced by approximately 50% after the EST utilized. Also, the dispersion of the fine eutectic β-Mg2Si phase was significantly promoted by applying EST, specifically, its size at the edge of the ingot was ranged in 2-4 μm. Consequently, the alloy prepared by EST present superior strength-plasticity synergy at room temperature (RT), with the ultimate compressive strength reaching 724MPa at the edge of the ingot and the strain reaching 15.1% at the center of the ingot. Moreover, EST was determined enhance the content of solid-solutioned Al atoms in the eutectic β-phase, thus varied its crystal structure and reduced its hardness and Young's modulus, and futher enhanced the deformation coordination between the IMCs and the matrix, thereby improving the mechanical properties of the alloy. This study elaborated the underlying mechanism of microstructural homogeneity regulation, the obtained results could offer guidance for fabricating large-sized Al-based MCAs with excellent mechanical properties.

Pulsed TIG wire arc additive manufactured 17-4PH stainless steel: Effect of Cu-rich precipitates and δ-ferrite on the mechanical properties

Thin-wall samples of 17-4PH stainless steel were prepared by pulsed TIG wire arc additive manufacturing technology (P-TIG WAAM), and the microstructure and mechanical properties of the samples in different regions (bottom, middle, top) were studied. The results show that the microstructure of the thin-wall samples are mainly consisted of martensite matrix embedded by worm-like (bottom) and strip-shaped (top) δ-ferrite, with a small amount of austenite. The δ-ferrite content gradually decreases along the building direction, resulting in a gradual increase in microhardness from the bottom to the top. Along the building direction, the precipitation density and size distribution of nano-scale CRPs (Cu-rich precipitates) in δ-ferrite and martensite, as well as at the δ-ferrite / martensite interface are significantly different: the CRPs in δ-ferrite is precipitated with lower density, larger size, and inhomogeneous distribution at the bottom region, while that in martensite is precipitated with higher density, smaller size, and homogeneous distribution. At the bottom region, a chain of large size fcc-CRPs (∼65 nm) is precipitated along the δ-ferrite / martensite interface to coordinate the strain between them and improve the strength and ductility simultaneously, thus excellent mechanical properties (tensile strength = 1356±24 MPa, elongation =15.16±2.6%) are obtained. The relationship between the evolution of CRPs and the intrinsic heat treatment (IHT) during P-TIG WAAM is also discussed.

Influence of shielding gas flow on the TIG welding process using stainless steel 304 material

A common issue encountered with main heat exchanger equipment is improper operation, which can lead to the development of cracks in the stainless-steel pipes. The welding process alters the metal microstructure in the heat-affected zone, thereby affecting the mechanical properties of the welded joint. To mitigate this issue, TIG welding with argon shielding gas is employed. This method helps prevent oxidation and ensures the formation of a stable welding arc in 304 stainless steel, which is renowned for its excellent mechanical properties and corrosion resistance. The objective of this study is to evaluate the impact of variations in shielding gas flow on the mechanical properties of 304 stainless steel plates during the TIG welding process. The aim is to determine the optimal settings for producing robust and long-lasting welded joints. To assess the hardness of the welded joints, we employed a Brinell-type Hardness Tester FB-3000LC machine. A Brinell steel ball indenter measuring 5 mm on the HBW scale and applying a load of 125 Kgf was utilized. At a protective gas flow rate of 8 L/min, the average tensile stress was 44.72 N/mm², strain was 0.177, modulus of elasticity was 2518 MPa, and hardness was 99.712 HBW. Increasing the gas flow rate to 13 L/min resulted in an average tensile stress of 47.50 N/mm², strain of 0.189, elastic modulus of 2525 MPa, and hardness of 105.522 HBW. Further increasing the gas flow rate to 18 L/min led to an average tensile stress of 49.69 N/mm², strain of 0.192, modulus of elasticity of 2597 MPa, and hardness of 106.704 HBW. Based on the research findings, it was observed that the weld area exhibited an increase in hardness values due to the heat generated during the welding process. The use of protective gas flow during welding is deemed effective in producing well-formed welded joints, as it prevents fractures from occurring within the weld area during the tensile test process. The choice of protective gas is determined by the dimensions of the material plate.

Preparation and application of waste cigarette butts-derived mulch film with excellent mechanical properties and optical transparency

Preparation and application of waste cigarette butts-derived mulch film with excellent mechanical properties and optical transparency

Waterborne bio-based UV-thermal dual-curable coatings with excellent mechanical properties and thermal resistance based on citric acid modified epoxidised soybean oil

Waterborne bio-based UV-curable coatings have attracted enormous attentions due to their environment friendliness and safety. However, residual neutralizing agents, long-chain aliphatic hydrocarbons derived from epoxidised soybean oil, and the oxygen inhibition inherent in the UV curing process often cause poor thermal resistance and mechanical properties of the epoxidised soybean oil-based waterborne bio-based UV-curable coatings. Herein, the epoxidised soybean oil was hydrophilized by citric acid and poly (ethylene glycol) diglycidyl ether without the use of neutralising agents. The hydrophilized epoxidised soybean oil was subsequently compounded with bisphenol A epoxy resin to prepare high-performance waterborne bio-based epoxy methacrylates. Finally, a high-performance waterborne bio-based UV-thermal dual-curable coating was obtained by blending waterborne bio-based epoxy methacrylates with waterborne isocyanate curing agent. The results demonstrated that waterborne bio-based epoxy methacrylates possess high bio-based content, low viscosity, and remarkable storage stability. Furthermore, waterborne bio-based UV-thermal dual-curable coatings with high cross-linking density exhibited outstanding mechanical properties and thermal resistance. For example, the waterborne bio-based UV-thermal dual-curable coatings P0805I4 exhibits a breaking elongation of 30.75%, maximum tensile strength of 16.68 MPa, T10% at 285.33°C, and adhesion class level of 0. Our research not only introduces high-performance waterborne bio-based UV-thermal dual-curable coatings, thereby extending the application domains of soybean oil-derived waterborne bio-based coatings, but also presents a valuable strategy for advancing high-performance, sustainable, waterborne, and environmentally friendly materials.

Oxhide gelatin-regulated aramid nanofiber/liquid metal films with sandwiched structure for electromagnetic interference shielding

Liquid metal (LM) based electromagnetic interference (EMI) shielding materials with high conductivity and continuous deformation capacity are important needs for meeting modern advanced electronic equipment. However, an independent free-standing film with LM is difficult to achieve due to its unique fluidity properties. Here, a simple alternating filtration film-forming method was utilized to orderly construct a sandwiched EMI shielding film with LM stabilized by bio-based oxhide gelatin (gel) as the intermediate conductive layer, and two films of aramid nanofibers/oxhide gel (ANF/gel) as the external insulating protective layers. This design not only prevents LM from being exposed to environmental conditions, but also reduces the risk of chemical corrosion in practical applications. Under optimal LM addition conditions, the sandwiched film (0.3-3 L) exhibited better EMI shielding performance of 50.4 dB in the X-band than the blended film (0.7 dB), as well as excellent mechanical properties (tensile strength of 65.8 MPa, strain 8.6 %). More importantly, the sandwiched film still maintained reliable EMI shielding performance after being experienced largely physical deformation. This study provides a new solution for preparing LM-based EMI shielding composites, and is expected to arouse pursuit of high EMI shielding effects of bio-based gel while also paying attention to their safety.

A bioinspired switchable adhesive patch with adhesion and suction mechanisms for laparoscopic surgeries

Medical adhesives play an important role in clinical medicine because of their flexibility and convenient operation. However, they are still limited to laparoscopic surgeries, which have demonstrated urgent demand for liver retraction with minimal damage to the human body. Here, inspired by the suction cup structure of octopus, an adhesive patch with excellent mechanical properties, robust and switchable adhesiveness, and biocompatibility is proposed. The adhesive patch is combined by the attachment body mainly made of poly(acrylic acid) grafted with N-hydroxysuccinimide ester, crosslinked biodegradable gelatin methacrylate and biodegradable biopolymer gelatin to mimic the adhesive sucker rim, and the temperature-sensitive telescopic layer of microgel-crosslinked poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) to shrink and form internal cavity with reduced pressure. Through mechanical tests, adhesion evaluation, and biocompatibility analysis, the bioinspired adhesive patch has demonstrated its capacity not only in adhesion to tissues but also in potential treatment for medical applications, especially laparoscopic technology. The bioinspired adhesive patch can break through the limitations of traditional retraction methods, and become an ideal candidate for liver retraction in laparoscopic surgery and related clinical medicine.

Unraveling and in-situ observation on the interfacial mechanical behavior of the NEPE propellant reinforced by NPBA via molecular dynamics simulation

Excellent mechanical properties are the lifeline for the application of solid propellants. Understanding the strengthening mechanism of bonding agent is of great significance for design and application of high-performance bonding agents. In this study, the strengthening mechanism of neutral polymer bonding agent (NPBA) for the NEPE propellant and dynamic mechanical response were explored through MD simulation. Significant difference in bonding role for RDX and HMX surface is first revealed with a more effective improvement in HMX surface. NPBA requires higher peak pulling force to achieve conformational transformation compared with binder throughout the peeling process. The chain orientation and movement undergo significant changes in nitroglycerin environment and an interface peeling model is proposed to reveal the potential mechanism. Finally, the effect of NPBA insertion on interfacial micro-peeling process indicates that no significant detachment of NPBA until the binder was severely deformed, resulting in a higher pulling force required.

One-step additive manufacturing of melt-growth porous ceramics by laser directed energy deposition

Porous ceramics, as a new type of lightweight ceramic materials, have attracted much attention in recent decades due to their low thermal conductivity and high surface area, which are crucial for applications in aerospace and biomedicine. In this work, we report a novel approach for the one-step additive manufacturing of melt-growth Al2O3-ZrO2-SiCp porous ceramics using laser directed energy deposition (LDED). The fracture surfaces of as-fabricated specimens show obvious porous structures when SiCp content exceeds 50wt.%. The porosity and compressive strength of Al2O3-ZrO2-70 wt.% SiCp (AZS70) specimens can reach 48 ± 4% and 95 ± 5MPa, respectively. In addition, the compressive strength of AZS70 is found to increase by a factor of 2-3 compared to the case of oxide porous ceramics with similar porosity prepared by other additive manufacturing technologies. Our approach may provide a valid option for achieving porous ceramics with excellent mechanical properties.

Self-assembled Ti3C2Tx membrane driven by Marangoni effect for anti-corrosive and anti-wear applications

The recent rise of Ti3C2Tx has extended the applications in epoxy resin due to its large specific surface area and excellent mechanical properties. Whereas, the synergy between epoxy and Ti3C2Tx restricts properties enhancements when Ti3C2Tx is subjected to random orientation and discontinuous distribution. To optimize the barrier and lubrication characteristics of Ti3C2Tx, we have successfully prepared Ti3C2Tx membrane by using the Marangoni effect self-assembled method to move Ti3C2Tx nanosheets to the same latitude and deposit them on epoxy resin for the first time. Meanwhile, micro-arc oxidation technology was adopted to enhance the bonding strength of the substrate with epoxy. Due to the effective corrosion resistance offered by the Ti3C2Tx membrane, even after 28days of immersion, the pure epoxy coating had completely failed, while the |Z|0.01Hz value of the multilayer coating still increased by 36.5 % compared to MAO/EP/EP. Furthermore, the wear rate and the friction coefficient reduced by 58.2 % and 21.4 % in comparison to the pure epoxy coating. This exceptional lubrication property stems from the interlayer shear sliding of the expansive Ti3C2Tx nanosheets, effectively preventing direct contact between the friction ball and the epoxy.

Polymerizable alkyl 2-(tosylmethyl)acrylates: Highly efficient addition-fragmentation chain transfer agents for the development of low shrinkage dental composites

One of the major drawbacks for restorative dentistry is the polymerization shrinkage and the consequential shrinkage stress in methacrylate-based dental composites. An efficient way to reduce shrinkage stress is the incorporation of addition fragmentation chain transfer agents (AFCT agents). In this contribution, five novel polymerizable allyl sulfones were synthesized in four to five steps. A photo-DSC study was carried out in order to evaluate the influence of the addition of each AFCT agent on the polymerization rate of a dimethacrylate-based monomer mixture. The glass transition temperature (Tg) of the resulting networks was measured using DMTA. Dental composites based on these new chain transfer agents (CTAs) were prepared. A combination of camphorquinone, ethyl 4-(dimethylamino)benzoate and bis-(4-t-butylphenyl)-iodonium hexafluorophosphate was selected as photoinitiator system. Low shrinkage force values, suitable ambient light working time and excellent mechanical properties were obtained for all CTA based materials. Composites based on three of the synthesized CTAs even exhibited higher flexural modulus than the corresponding CTA-free material. Furthermore, a significant reduction of unreacted CTA leaching was found if a polymerizable moiety was introduced in the CTA structure. Hence, the incorporation of polymerizable allyl sulfones in dental composites is a promising strategy to obtain low shrinkage materials exhibiting improved biocompatibility.

Cellulose nanofiber-induced metal–organic framework “armor” for the fabrication of carbon fibre composites with enhanced mechanical properties and electrical conductivity

Metal-organic frameworks (MOFs) possess significant potential in enhancing the interfacial performance of composites owing to their exceptional skeletal structures and substantial specific surface area. Herein, we prepared typical conductive MOFs (Ni-HHTP, HHTP = 2, 3, 6, 7, 10, 11-hexahydroxybenzene) at the interface by in situ synthesis using cellulose nanofibers (CNFs) assembled on the surface of carbon fibres (CFs) as precursors. CNFs can not only act as a smart cushion to promote stress release but also provide abundant oxygen-containing functional groups, such as hydroxyl and carboxyl groups, which can facilitate the growth of MOF on the surface of CFs. Furthermore, MOFs with porous structure and large specific surface area increase the interphase region for interfacial load transmission. The CF composites prepared using this strategy exhibited improvements in interlaminar shear strength (ILSS), interfacial shear strength (IFSS), flexural strength and flexural modulus by 57.9 %, 54.9 %, 35.1 % and 46.7 %, respectively. Additionally, the electrical conductivities of the composites in both thickness and in-plane directions were 1.04 × 10−4 S/cm and 7.3770 S/cm, respectively, which was attributed to the MOFs on the surface of the fibres facilitating the formation of good conductive channels between the fibres and resin. This study proposes an advanced interfacial modification approach to prepare CF composites with excellent mechanical and electrical conductivity properties.

Investigation on tribological behaviors of a novel generation polymer-coated ceramsite particle for fracturing

During fracturing, proppant particles can create favorable pathways for shale gas production. To solve the problem of low production efficiency of shale gas, a new polymer coated particle was prepared by experiment. And its mechanical properties were tested and tribological properties were studied under different speeds, loads and medium states. The results show that the new polymer coated particles have excellent tribological and mechanical properties. The friction coefficient between proppant particles and fracture surface decreases with increasing velocity. In addition, the new proppant particles have excellent hydrophobicity under lubricating conditions, indicating that the proppant has excellent migration efficiency. When proppants just pumped into the fracture, it can reach the fracture depth quickly. In addition, the friction coefficient between proppant particles and fracture surface gradually increases with the increase of load. It is further proved that when the proppant particles enter the fracture, the friction coefficient increases due to the extrusion of the fracture, and the reverse displacement can be effectively reduced.This research has important theoretical and practical engineering application value for improving the efficiency of shale gas stimulation.

Fabrication of a multiple-self-healing and self-cleaning polymer coating for mechanical-damaged optical glass surface

Mobile screens and optical glass devices encounter formidable engineering and technological bottlenecks in achieving irreversible restoration from surface mechanical scratches. Conventional methodologies involving glass surface micromachining and coatings technology have proven inadequate in effectively addressing the multiple recovery of optical transparency. Here, the synergistic integration principle of inorganic rigid cage-like structures and organic flexible chain segments is employed. A bionic “octopus” textured surface pattern, featuring ordered arrays of nano nodes acting as “post stations” and micro-nano wrinkles serving as “channels”, is one-step fabricated by a dipping-curing coating process. The polymer coating exhibits smooth, transparent, and multiple-self-healing function with patterned antifouling. Introducing and matching the coating onto mobile screens, transparency of wiped/scratched glass is significantly restored by the synergistic use of protonic/non-protonic solvent systems in a dipping-assisted healing process. Intriguingly, the coating achieves surface/internal pattern reconstruction along with excellent transparency, antifouling, and interfacial adhesion mechanical properties, characterized by surface micro-nano textures and internal micro-nano spheres organization, after undergoing multiple treatments with the biocompatible disinfectant and cleaning agent ethanol. In the future, it is expected to develop highly versatile engineering materials for mobile screens, optical lenses and automotive glass, enabling multiple self-healing, self-cleaning, and antifouling properties with broad industrial applications.

Soil improved with a hybrid alkali-activated cement from waste stone wool and OPC

The use of OPC as a construction material is currently being reconsidered owing to the generation of greenhouse gases during production. Geopolymers or alkali-activated cement (AAC) have been proposed as partial replacements because of their excellent chemical and mechanical properties, which are equal to or superior to those of OPC. The use of these alkaline types of cement in soil stabilization has also gained significant interest in the academic community because of the possibility of it being derived from industrial waste. In this study, clay soil stabilized with AAC using waste stone wool fiber (SW) as a precursor and stabilized with hybrid alkali-activated cement (HAAC) using SW and OPC was prepared and subsequently evaluated mechanically and chemically after 28 days of curing. The results showed a significant increase in soil strength with both stabilization processes. The maximum achieved unconfined compressive strength (UCS) in the soil stabilized with AAC was 0.9MPa (15% SW), while the strength achieved with HAAC was 1.7MPa (10.5% SW - 4.5% OPC). The California Bearing Ratio (CBR) of the latter combination was also determined, finding a value of 133%, well above that of the soil without treatment (3.32%). Through XRD, the A-type zeolite was identified as a product of the alkaline reaction, whereas the formation of N-A-S-H and C-A-S-H gels was observed via SEM. EDS mapping showed an increase in the atomic percentages of Si and Al in the soil specimens with HAAC, indicating the formation of Si-O-Si and Si-O-Al bonds. In addition to the potential application of this material in civil infrastructure related to soils (e.g., embankments and wall fillings), a sustainable construction material using industrial waste SW with a lower percentage of OPC is proposed.

Influence of the high temperature impact resistance of cutting tool coatings on their cutting performance

Metal cutting is a highly dynamic process, where the loading condition of tool coating is very complex. Excellent static mechanical properties of tool coatings are not enough to meet the dynamic cutting environment, including impact load, cyclic load and so on. The high-frequency and high-temperature cycle impact test device based on ultrasonic vibration was developed in this study. The device performed the high-frequency impact on coating samples through high-frequency reciprocating motion of ultrasonic horn, whose impact frequency could reach 20 kHz. In addition, a high-temperature module was added to perform high-frequency fatigue test at high temperature. Cutting experiments of titanium alloy and impact tests with different temperatures and loads were carried out for the bilayer TiSiN/TiAlN coating. The results of cutting experiments and impact tests were compared and analyzed. The relationship between impact test and cutting experiment was proposed to characterize and evaluate the cutting performance of coated cutting tool by using the high-temperature impact tests.