Outstanding Mechanical Performance Research Articles

Tensile Properties of a Non-Equiatomic Ni–Co–V Medium Entropy Alloy at Cryogenic Temperature

The development of strong and ductile alloys for application in cryogenic temperatures has long been sought after. In this work, we have developed a face-centered cubic Ni10Co56.5V33.5 multi-principal element alloy (MPEA) that exhibits a balanced combination of high strength and good ductility at 77 K, based on the considerations of large local lattice distortion (LLD) and low stacking fault energy. The small-grained Ni10Co56.5V33.5 MPEA exhibits a yield strength of 1400 MPa and an ultimate tensile strength of 1890 MPa, while preserving a good ductility of 23%. Moreover, precession electron diffraction and transmission electron microscopy revealed multiple deformation mechanisms, including wavy dislocations, atypically severely twisted dislocation bands, hierarchical stacking faults, and deformation twins, which are implicated in the alloy’s outstanding mechanical performance. These insights offer a strategic guide for the design of strong and ductile alloys, particularly for utilization in extreme environments.

Laser Powder Bed Fusion Processing of Low Cost CoCrFeNiMoxNby High Entropy Alloys with Promising High-Temperature Properties via In Situ Alloying Commercial Powders

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications.

Efficient mechanical modeling of sandwich panels with functionally graded lattice cores under thermal environments

3D-printed sandwich panels with functionally graded (FG) lattice cores have garnered widespread attention owing to their outstanding mechanical performance. However, the straightforward interplay between the service environment, strut structure, and their mechanical behavior has not been systematically explored. In this study, an analytical two-step prediction modeling is developed to efficiently obtain the mechanical response of 3D printed sandwich panels with FG lattice cores. Initially, the effective elastic moduli of FG lattice cores are identified based on finite element (FE) analysis. The stress and deformation of the core-homogenized sandwiches in thermal environments are predicted using the higher-order shear deformation theory. Subsequently, the de-homogenization is employed to calculate strut stresses. The prediction shows excellent agreement with the FE results in the literature. Furthermore, parametric analysis is performed to uncover the impact of crucial variables on the strut stresses within the FG lattice cores. The results show that the strut stress decreases with the increased transverse layer number and power index, while increasing with the higher ambient temperature, length-to-thickness ratio, and thermal expansion of the sandwich panels. The proposed model can serve as an efficient tool for the design and printing of high-performance lattice-core sandwich panels.

Self-standing and compressible SiCnw/SiCnf composite aerogel via free carbon in-situ transformation mechanism: Towards thermal and electromagnetic wave protection

SiC nanofiber-based composite aerogel represents a promising lightweight, high-temperature-resistant, and broadband-absorbing material. However, the residual carbon phase during the pyrolysis process would threaten the high-temperature oxidation tolerance. Herein, a free carbon in-situ transformation (FCIT) strategy was proposed to convert the amorphous free carbon on the surface of SiC nanofibers into SiC nanowires, constructing a multi-scale SiC nanowire/SiC nanofiber (SiCnw/SiCnf) composite aerogel. The SiCnw great broaden the inner fibrous framework, and the hierarchical network offers great enhancement for EM attenuation, compression resistance and thermal insulation. The self-standing composite aerogel possesses excellent flexibility (1500 cycles in 180°-bending test) and compression resistance (100 cycles at 40 % strain). With only 10 wt% filler content, the SiCnw/SiCnf sample displays an effective absorption bandwidth (EAB) of 8.81 GHz (9.19–18.00 GHz) at a thickness of 2.94 mm. Even after enduring oxidation at 800 °C, the EAB still remains substantial at 6.92 GHz (11.08–18.00 GHz). Moreover, the outstanding mechanical performance were also retained under high temperature and oxidation environment due the reduced density and thermal conductivity. Therefore, the multifunctional SiCnw/SiCnf composite aerogel prepared by FCIT strategy could be served as efficient thermal and EMW protection candidate.

Thermal conductivity of epoxy composites containing 3D honeycomb boron nitride filler

Polymer matrix composites with excellent thermal management performance have emerged as remarkable materials in the realms of microelectronic devices and wireless communication technologies. However, achieving high thermal conductivity in most composites often requires a high filling load, which will compromise other desirable properties. Herein, utilizing physical foaming and vacuum infiltration methods, we introduce a 3D honeycomb composite consisting of surface-hydroxylated hexagonal boron nitride (OH-BN) and epoxy. The 3D OH-BN honeycomb foam in the composite features a lightweight design (0.33 g/cm3), high strength (7178 times its own weight) and prominent heat transfer performance. Significantly, these composites achieve notable thermal properties, including high through-plane thermal conductivity (2.073 W m−1 K−1) and relatively low thermal resistance (0.995 °C/W) at a reduced filling load (17.2 vol%). In comparison with pure epoxy, the through-plane thermal conductivity is enhanced by an impressive 894 %, while the thermal resistance is reduced to 1/9.4 of that observed in pure epoxy. Besides, the 3D honeycomb composites combine outstanding mechanical performance, low dielectric properties and excellent insulation, underscoring their potential in the field of thermal management applications in microelectronic devices, wireless communication systems and integrated circuits.

Atomic contributions to ZnO mechanical properties at negative and positive pressures

The energy-volume curve of a crystalline solid is critically examined in terms of the mechanical contributions of its constituent atoms. In addition to the usual analysis in the positive compression regime, our computational approach covers the tensile behavior in the negative pressure region up to the spinodal stability limit. Using the rich polymorphism of ZnO as a test-bed example, we propose two atomic decomposition schemes that are able to recover the bulk moduli and the critical strengths of four ZnO phases providing an intriguing interpretation of the chemical bonding network as a parallel circuit of mechanical resistors. Our scheme also allows the identification of the role played by the cation and anion in the densification of the high-pressure polymorphs and up to the material rupture points. This approach may help in the quest for tailored materials with outstanding mechanical performance.

Enhanced high-temperature ductility without strength drop in a lean Co Ni-based superalloy

The conventional Ni-based IN738LC superalloy series are typically hardened by a fine distribution of closely spaced fine and coarse Ni3(Al, Ti)-type L12 ordered γ' precipitates, which is formed by solid-state nucleation and growth in the disordered γ matrix. However, outstanding high-temperature mechanical performance requires a high amount (∼9 wt%) of Co, which is the alloy's most expensive adding element. Here, we report a compositionally modified IN738LC alloy with a 50% reduction in Co content and a 20% increase in comparatively cheaper Mo content. This compositional modification caused more γ' precipitates with uniform distribution than those in the conventional counterpart subjected to the same heat treatments. The modified superalloy showed a twofold increase in high-temperature (750 °C) tensile elongation while maintaining the conventional one's strength (∼1.1 GPa) at the temperature. This remarkable ductility gain, while no loss in strength, was predominantly attributed to a transition in the high-temperature deformation mechanism, i.e., from multiple intersecting slip bands-indued stress localization for the conventional IN738LC alloy to unidirectional microtwins for the modified IN738LC material. More Mo and less Co contents could drive more coherent γ' precipitates in the annealed state and the high density of microtwins in the deformed state, resulting in stress delocalization and enhanced ductility at comparable strength. The findings of this study have significant implications for the development of cost-effective, strong, and ductile superalloys for high-temperature applications.

Glass science behind lithium silicate glass-ceramics

ObjectivesLithium silicate-based glass ceramics have evolved as a paramount restorative material in restorative and prosthetic dentistry, exhibiting outstanding esthetic and mechanical performance. Along with subtractive machining techniques, this material class has conquered the market and satisfied the patients’ needs for a long-lasting, excellent, and metal-free alternative for single tooth replacements and even smaller bridgework. Despite the popularity, not much is known about the material chemistry, microstructure and terminal behaviour. MethodsThis article combines a set of own experimental data with extensive review of data from literature and other resources. Starting at manufacturer claims on unique selling propositions, properties, and microstructural features, the aim is to validate those claims, based on glass science. Deep knowledge is mandatory for understanding the microstructure evolution during the glass ceramic process. ResultsFundamental glass characteristics have been addressed, leading to formation of time-temperature-transformation (TTT) diagrams, which are the basis for kinetic description of the glass ceramic process. Nucleation and crystallization kinetics are outlined in this contribution as well as analytical methods to describe the crystalline fraction and composition qualitatively and quantitatively. In relation to microstructure, the mechanical performance of lithium silicate-based glass ceramics has been investigated with focus on fracture strength versus fracture toughness as relevant clinical predictors. ConclusionFracture toughness has been found to be a stronger link to initially outlined manufacturer claims, and to more precisely match ISO recommendations for clinical indications.

Robust, self-healing AIE fluorescent supramolecular elastomers for smart anti-counterfeiting

Providing aggregation-induced emission (AIE) polyurethane with self-healing capability can increase the lifetime of the material and adapt it to multiple application scenarios, which is a huge challenge in the development of luminescent smart materials. Herein, a range of transparent fluorescence polyurethanes (FPUs) with prominent strength were designed and synthesized. The optimization of robust FPUs exhibits outstanding mechanical performance (33.5 MPa tensile strength, 120.2 MJ m−3 toughness) and self-healing ability (88.9 %, at 80 °C for 2 h). Furthermore, the aggregation of tetraphenylethylene structure in the hard segment causes the system to emit bright blue fluoresence. We successfully screen-printed designable patterns on the self-healing polyurethane substrates. The concealed patterns self-repair after damage, and can be clearly and robustly displayed under 365 nm light irradiation. The as-prepared multifunctional self-healing material, exhibiting stable AIE fluorescence, is anticipated to possess significant value in the domains of smart anti-counterfeiting materials, flexible display screens and intelligent optoelectronics.

Microstructual evolution in Ti-185 alloy prepared using electrostatic levitation and conventional casting techniques

Ti and its alloys have been widely applied in various fields of national economy due to their excellent combinations of specific mechanical properties and outstanding corrosion behavior. Among Ti alloys, Ti–1Al–8V–5Fe (Ti-185) alloy is a metastable and low-cost β-Ti alloy, and owns extremely outstanding mechanical performance. In the paper, to overcome the issue of β flecks associated with Fe segregation in conventional ingot metallurgy process, Ti-185 alloy was prepared by electrostatic levitation (ESL) technique at various supercoolings, and its solidification behavior and dendrite growth were systematically analyzed. Moreover, the thermophysical parameters of liquid Ti-185 alloy were tested, and the microstructure, hardness and compressive property were compared to that of cast ingot. Results shown that the maximum supercooling of 311 K in the liquid Ti-185 alloy can be achieved, and a noticeable recalescence phenomenon appears during ESL process. The density and the ratio of specific heat to emissivity of liquid Ti-185 alloy increases linearly with temperature decreasing. Once the crystal nucleus is formed, the nonfacted interface will advance promptly. Moreover, the dendritic growth velocity (v) exhibits an exponential relationship with the supercooling (ΔT), and can be depicted as the equation of v = 1.59·ΔT1.65 mm s−1. Additionally, at a supercooling of 229 K or above, single crystal can be formed using ESL technique. Furthermore, the microhardness, elastic modulus and compressive strength of as-levitated Ti-185 alloy are hardly affected by the supercooling, but the plasticity of as-levitated sample is obviously higher than that of as-cast one.

Combining Carbon Nanoparticle Coatings and Laser Surface Texturing for Enhanced Lubricity Under High Loads

Developing new lubrication concepts greatly contributes to improving the energy efficiency of mechanical systems. Nanoparticles such as those based on carbon allotropes or 2D materials have received widespread attention due to their outstanding mechanical and tribological performance. However, these systems are limited by a short wear life. Combining nanoparticle coatings with laser surface texturing has been demonstrated to substantially improve their durability due to the reservoir effect which prevents immediate particle removal from the contact. In this study, we investigate the high-load (20 N) tribological performance of AISI 304 austenitic stainless-steel substrates, which are line-patterned by laser interference patterning and subsequently coated with different carbon nanoparticle coatings (carbon nanotubes, carbon onions, carbon nanohorns) against alumina and 100Cr6 counter bodies. In addition to that, benchmark testing is performed with conventional solid lubricant coatings (graphite, MoS2, WS2). Electrophoretic deposition is used as the main coating technique along with air spraying (for WS2). All coatings substantially improve friction compared to the purely laser-patterned reference. Among all coating materials, carbon nanotubes demonstrate superior lubricity and the longest wear life against 100Cr6 and alumina counter bodies. Detailed characterization of the resulting wear tracks by energy-dispersive X-ray spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy provides insights into the friction mechanisms of the various solid lubricant particles. Further, material transfer is identified as an important aspect for effective and long-lasting lubrication.

Assessing the stress-transfer capability of mineral impregnated PBO yarns in a limestone calcined clay cement-based (LC3) matrix

Technical textiles made of poly(p-phenylene-2,6-benzobisoxazole) (PBO) represent attractive candidates for strengthening and repairing damaged concrete and masonry structures, due to the outstanding durability and mechanical performance of PBO fibres. Similarly to their aramid counterparts, PBO fibres have proved very effective against dynamic and impact loading. In this contribution, the pull-out behaviour of PBO multifilament yarns embedded into a blended cement-based matrix is investigated, with particular reference to its stress-transfer capacity. In addition to the as-received PBO yarns, impregnation with a cement-based suspension, which can fully preserve the inorganic nature of the composite system, is also evaluated. Experimental results are presented and interpreted using a one-dimensional mechanical model. The findings indicate that mineral impregnation of the yarns provides a 40% increase in the stress-transfer capacity with the matrix, corresponding to a halving of the anchoring length. These performance gains are also supported by a transition in the failure mechanism which shifts from friction-based pull-out to fibre rupture.

A strength optimization approach for manufacturable 3D printed variable stiffness laminates with a strain-based approximation

The 3D printed continuous carbon fiber reinforced polymers (CFRP) are promising lightweight structures with outstanding mechanical performance. In this work, we propose a structure-manufacture integrated optimization approach for strength maximization of variable stiffness 3D printed CFRP composites by tailoring the steered printing paths. The rule of mixture is modified to evaluate material properties and strength of the printed laminates considering the effect of fiber volume fraction. To make this approach applicable to CFRP with asymmetric layups, a strain-based two-level convex approximation for the failure index based on the Tsai–Wu failure criterion is proposed, which can take the tension-bending coupling effect into consideration. The local failure indices are aggregated using the p-norm formula to reduce the size of the strength optimization model. In order to guarantee the manufacturability of the optimal design, the curvature of the steered printing fiber paths is constrained using a hybrid control method within the approach. The numerical cases show that the strength enhancement of the 3D printed variable stiffness laminates depends on the load, where an improvement between 35% and 46% can be achieved under the tension. Moreover, the proposed method can not only converge stably, but also be capable of optimizing structures with complex geometry.

A new wear-resistant component system of copper-based composite materials: Modified sepiolite-complex ceramic powder

To balance mechanical strength, friction stability, and low wear, a novel wear-resistant component system: modified sepiolite-complex ceramic powder, was employed in copper-based composite materials, leading to the successful preparation of samples with outstanding mechanical and frictional performance. The material exhibits high friction stability, low wear, and the simultaneous occurrence of a high friction coefficient, which may be caused by uniquely composed dual friction film. The external layer of the friction film consists of Cu2O, Fe2O3, and CaO metal-films, while the internal layer consists of B2O3 film, graphite, and sepiolite. Additionally, modified sepiolite (composed of sepiolite, CaCO3 and enstatite) plays a dual role in wear resistance and high-temperature lubrication. Furthermore, the Gradient Boosting Decision Tree (Gbdt) model was found to provide more meaningful guidance for predicting friction coefficients.

Analysis and Suggestions for the Self-blast Problem of Glass Insulators on Transmission Lines

By virtue of many advantages such as good self-cleaning ability, outstanding mechanical performance, and excellent anti-vibration-fatigue ability, the glass insulators have been widely used in various alternating-current and direct-current transmission lines. However, the self-blast incidents of glass insulators have frequently occurred in transmission lines with various voltage levels, seriously affecting the safe operation of transmission lines. Herein, the main causes of self-blast problem of glass insulators are summarized and analysed from different perspectives, and some corresponding suggestions have been proposed to reduce the self-blast of glass insulators. In addition, the relevant prospects are provided for the future research work about the glass insulators. The viewpoints in this article have important theoretical and practical significance for improving the safety and reliability of transmission lines and ensuring the stable operation of electrical power systems.

Robust anti-impact, energy absorption and thermal properties of polyurethane nanocomposites modified by phenol-amine chemistry

It is still a considerable challenge for polyurethane elastomers (PUE) to possess outstanding mechanical and thermal performance simultaneously against harsh dynamic impact environment due to their heat accumulation, thermal stress softening and mechanical failure. Thus, this article innovatively prepared binary nanofibers composed of carbon nanofiber (CNFs) and aramid nanofibers (ANFs) to reinforce PUE, where catechol (CC) and polyethyleneimine (PEI) were served as interfacial modifier between nanofibers and polymer matrix. PUE with 1.5 wt% binary nanofibers achieve 31.62 % increase in crosslinking density, 146.8 °C improvement in thermal decomposition temperature compared to Neat PUE. Besides, the absorption energy and dynamic compression strength of composites were increased by 40.36 % and 38.26 %, respectively. Because reinforced nanofibers with crosslinking network structures improve the interface interaction between fillers and matrix, facilitate stress transfer and increase the energy threshold of thermal decomposition. The paper supplements the impact resistance analysis of PUE-based protective materials under impact loads, providing a systematic and scientific reference for the design and manufacture of impact resistant materials.

Functionalized liquid polyisoprene as a promising toughening agent for poly(lactic acid): Combining stiffness and toughness

AbstractLiquid polyisoprene rubbers (LIR) containing anhydride and carboxylic groups along their chains were successfully employed as toughening agent for poly(lactic acid) (PLA) without great influence on the stiffness of the matrix. In fact, the addition of 5% of these functionalized LIR resulted in an improvement of toughness and impact resistance of more than 2000%, whereas the reduction of the yield stress stayed in the range of 12%. No significant variation of the Young modulus was observed for the modified PLA samples. The effect of the LIR on the rheological and thermal properties of PLA was also investigated. The glass transition temperature obtained from dynamic‐mechanical analysis of the PLA matrix was not affected by the addition of 10% of the liquid rubber. The scanning electron microscopy analysis revealed a significant decrease in the rubber domains for the blends containing LIR functionalized with anhydride groups. Finally, the modified PLA with anhydride‐functionalized LIR was able to produce transparent film with outstanding mechanical performance than neat PLA, making this material a good option for food packaging.

Strong and Tough Biofibers Designed by Dual Crosslinking for Sutures

AbstractHigh‐performance bio‐based fibers have unique advantages in biocompatibility for biomedical applications, such as sutures, hernia patches, and blood vessels. Herein, strong and tough biofibers based on regenerated silk fibroins (RSFs) are designed by a dual‐crosslinking strategy and prepared continuously in situ via a single‐channel microfluidic device. During the wet spinning process, covalent bonds between tyrosines are introduced by photo crosslinking and coordination interactions of Zn2+ ions with serines are built between RSFs, forming a dual‐crosslinked, and inter‐connected network and effectively improving the mechanical performances of RSF fibers. By optimizing the wet spinning parameters and applying an optimal post‐stretching treatment, dual‐crosslinked RSF fibers exhibit an excellent tensile strength of 891 MPa, a remarkable Young's modulus of 15.0 GPa, a large tensile strain of 20.1%, and an outstanding toughness of 114 MJ m−3, which are superior to other regenerated biofibers. In addition to the outstanding mechanical performances, dual‐crosslinked RSF fibers also possess excellent temperature adaptability, fatigue resistance, biocompatibility, and biodegradability, making them ideal candidates for biomedical applications. In vivo tests of dual‐crosslinked RSF fibers as sutures demonstrate a good wound healing performance with smaller scar and lower inflammation.

A pseudo-Double-Network Hydrogel Built upon Layered Double Hydroxides with Self-Strengthening Properties.

While great achievements have been made in the development of mechanically robust nanocomposite hydrogels, incorporating multiple interactions on the bases of two demensional inorganic cross-linkers to construct self-strengthening hydrogels has rarely been investigated. To this end, we propose here a new method for the coupling the dynamic covalent bonds and non-covalent interactions within a pseudo double-network system. The pseudo first network, formed through the Schiff Base reation between Tris-modified layered double hydroxides (Tris-LDHs) and oxidized dextran (ODex), is linked to the second network built upon non-covalent interactions between Tris-LDHs and poly(acrylamide-co-2-acrylamido-2-methyl-propanesulfonate) (p-(AM-co-AMPS). The swelling and mechanical properties of the resulting hydrogels have been investigated as a function of the ODex and AMPS contents. The as-prepared hydrogel can swell to 420 times of its original size and retain more than 99.9 wt.% of water. Mechanical tests show that the hydrogel can bear 90 % of compression and is able to be stretched to near 30 times of its original length. Cyclic tensile tests reveal that the hydrogels are capable of self-strengthening after mechanical training. The unique energy dissipation mechanism based on the dynamic covalent and non-covalent interactions is considered to be responsible for the outstanding swelling and mechanical performances.

Synthesis internal-plasticized PVC copolymer resin from industrial application view: Copolymerization of vinyl chloride with poly(ethylene glycol) monomethyl ether methacrylate via suspension polymerization

Developing internal-plasticized poly(vinyl chloride) (PVC) resin has been recognized as an effective way to deal with the issues of conventional PVC products such as toxicity and deterioration in properties caused by the migration of plasticizer. Herein, the copolymerization of vinyl chloride with commercial available poly(ethylene glycol) monomethyl ether methacrylate (PEGMA) is firstly conducted via suspension polymerization and internally plasticized random copolymers (PVEGA) are synthesized successfully. These PVEGA copolymers were intensively characterized by FTIR, 1H NMR, GPC, DSC, DMTA, and SEM to determine the composition, number-average molecular weight (Mn), dispersity, glass transition temperature (Tg), and the micromorphology. As a result, the high transparency and the fracture images demonstrated the good compatability between PVC chains with long-chain polyether. The Tg of PVEGA decreased gradually from 80 to 0 °C with the fraction of PEGMA in the copolymer increased from 7 to 37 %. Furthermore, the PVEGA copolymer exhibits outstanding processibility and mechanical performance. Under optimal composition, the tensile strength and the elongation at break can reach to 8 MPa and 525 %, respectively. Meanwhile, the PVEGA copolymers exhibit much lower migration either in water or in orgnic solvent and excellent performance in hemolysis and cytotoxicity, showing great application potential in medical devices.