Simultaneous High Strength Research Articles

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.

Grain refinement and phase precipitation simultaneously improve the strength and ductility of ultra-high strength titanium alloy sheets

The simultaneous high strength and high plasticity of metastable-β titanium alloy sheets remains a difficult challenge. In this work, a 1.2 ​mm thick sheet of Ti–15Mo–3Al-2.7Nb-0.25Si titanium alloy was obtained after rolling and annealing, and then subjected to a duplex-ageing treatment. The pre-ageing temperatures fell in the range of 300–390 ​°C for 0.5–2h. The re-ageing temperatures were in the range of 500–600 ​°C. After characterization, it was found that the alloy precipitates ω-phases during the pre-ageing process, and the distribution of such ω-phases evolves unevenly and increases in number with the increase of the pre-ageing temperature. Therefore, the strengthening mechanism of the alloy sheet is mainly α-phase nucleation assisted by ω-phase. Moreover, grain refinement appears as a mechanism to ensure the plasticity of the alloy. Finally the ω-phase evolution law is discussed in detail and the strengthening mechanism of the alloy sheet is also analyzed. At this work, a metastable-β titanium alloy sheet with strength of 1445.75 ​MPa and elongation of 6.55 ​% was obtained. This study provides a new idea for the microstructure design and process improvement of the metastable-β titanium alloy sheet.

Fracture mechanics model of biological composites reinforced by helical fibers

Many biological materials such as tendons and muscles contain helical fibers. In this paper, the fracture behavior of such chiral composites is investigated through a combination of theoretical analysis and finite element simulations. A mesoscopic fracture mechanics model of helical fiber-reinforced biological composites is presented, with the effects of interfacial damage and fiber breakage. A cohesive law is adopted to characterize the interfacial damage induced by the relative slipping between the fibers and the matrix. The theoretical model agrees well with the numerical results. The optimized fiber radius that can maximize the fracture toughness of the composites is determined. The effects of interfacial (e.g., bonding strength and energy dissipation) and material properties (e.g., strength and elastic modulus) on the resistance to crack propagation are revealed. Our results show that the composites reinforced by helical fibers exhibit comprehensively excellent mechanical properties, e.g., simultaneous high strength, stiffness, and fracture toughness. This work not only helps understand the structure–property interrelations of biological chiral composites, but also provides inspirations for designing high-performance engineering materials.

Chromium gradient stainless steels with simultaneous high strength, ductility, and corrosion-resistant: In-depth study of continuous hardening mechanisms

Cr-rich stainless steel sheets exhibit superior corrosion resistance but low ductility, which presents a trade-off between fabrication complexity and performance of the materials in multiple industrial applications, such as marine equipment and microreactors. By transitioning the Cr-rich (30 wt.% Cr) stainless steel component to SS 316 L with a smooth composition gradient in the thickness direction, the intrinsic homogeneous elongation of the Cr-rich layer was increased by 260 % while maintaining the naturally high corrosion resistance (100 %) and retaining most of the strength (more than 80 %). By employing in-situ tensile testing and electron backscatter diffraction analysis, it was revealed that the Cr-rich layer in the gradient structure underwent a profound deformation mechanism, including significant heterogeneous deformation-induced hardening and grain reorientation induced by multiplication and accumulation of geometrically necessary dislocations, in such a way to enable a substantial plastic strain and thereby retarding the occurrence of fracture. The proportion of the Cr-rich layer makes a significant impact on the magnitude of the strain gradient in the gradient specimens, therefore affecting the increment of density of geometrically necessary dislocations. The critical proportion value of the Cr-rich layer is found to be around 22 %. Before and after the critical value the gradient specimens showed different sensitivities to the proportion. This discovery underlines the significance of intrinsic plasticity in low-ductility metals and the role of compositional gradient materials in enhancing strength and ductility.

Multi-objective optimization of multi-principal element alloys via high-throughput simulation and active learning

It is a great challenge to optimize the composition and improve the multi-properties of multi-principal element alloys (MPEAs) by traditional trial-and-error method. Here, an active learning strategy is proposed to design the multi-objective properties of MPEAs based on molecular dynamics (MD) simulation, machine learning (ML) models and multi-objective optimization algorithms. A database is established via a tensile test of 120 FeCrNiCoMn single-crystal samples by MD simulation. Six ML models are employed to predict the yield strength and Young's modulus based on domain knowledge, among which the support vector machine (SVM) model shows the better predictive performance, with low mean absolute error of 0.12 and 0.61 for cross validation, respectively. Then, by combining the SVM model and three multi-objective optimization algorithms, optimal alloy compositions are rapidly searched in a virtual composition space containing 885681 alloys. After four optimization-testing iterations, Co35Cr30Ni35 is synthesized with simultaneous high yield strength and Young's modulus, which are 2.9 and 1.6 times as equiatomic FeCrNiCoMn alloy, respectively.

Induction of polymer-grafted cellulose nanocrystals in hydrogel nanocomposites to increase anti-swelling, mechanical properties and conductive self-recovery for underwater strain sensing

Anti-swelling conductive hydrogels with simultaneous high tensile strength (>1 MPa) and fast self-recovery are promising candidates for underwater strain sensing, but their preparation remains challenging. Herein, novel anti-swelling conductive nanocomposite hydrogels were fabricated based on poly(acrylamide-co-acrylic acid) (P(AM-co-AA)), polymer-grafted cellulose nanocrystals (CNCs) and Fe3+ ions through a strategy combining nano-reinforcing and multiple physical crosslinking. Due to the presence of interfacial H-bonds, polymer-grafted cellulose nanocrystals played important role in endowing hydrogels with anti-swelling capacity and enhanced mechanical performance. The obtained nanocomposite hydrogels exhibited relatively low swelling ratio (2.9–3.3 g/g), high tensile strength (>1.5 MPa), fast self-recovery (86 % recovery of hysteresis within 5 min) and conductivities of 0.0534–0.0593 S/m. The combination of excellent tensile properties and conductivity endowed the hydrogel-based strain sensors with good sensitivity (GF ≈ 0.8) and reliable cycling repeatability in 0–100 % strain range. Notably, the nanocomposite hydrogels can maintain their mechanical and sensing performance after soaking in water for 14 days, making them applicable for human motion detection both in air and underwater. Hence, this work provided a facile method to construct highly robust and anti-swelling CNC-reinforced conductive hydrogels, which have potential applications in underwater strain sensing and beyond.

Numerical and experimental evaluation of a variable-stiffness wedge anchorage for basalt-fiber-reinforced polymer tendons

The small-sized variable-stiffness wedge (VSW) anchorage, a second-generation solution, was numerically optimized to anchor basalt-fiber-reinforced polymer tendons, building upon the previous first-generation anchorage. The static, fatigue, and relaxation characteristics of the anchorage were experimentally evaluated. Results revealed that VSWs effectively mitigated radial stress concentration within the tendons compared to constant stiffness wedges. Bonding optimization techniques involving cross-splitting and sandblasting proved advantageous in accurately assessing the tensile properties of round tendons. The second-generation anchorage demonstrated an 87% anchoring efficiency, surpassing that of a longer commercial steel-wedge anchorage significantly. The tendon-anchorage assembly can sustain 2 million cyclic loadings under a maximum fatigue stress of 0.44 ffpk (standard value for tendon tensile strength) and a stress range of 0.04 ffpk; moreover, sliding between wedges and tendons resulted in negligible stress reduction across various stress ranges. A logarithmic function effectively modeled the relationship between relaxation time and load retention in tendons with R-squared values consistently above 0.94 throughout; furthermore, the million-hour relaxation rate closely aligned with observed tendon behavior. The application of an initial tensile stress of 0.5 ffpk to tendons allowed for simultaneous high strength and minimal prestress loss.

A Hierarchical Energy Dissipated Structure Enabled Strong, Ultra‐Tough, and Sustainable Adhesives

AbstractSustainable adhesives with simultaneous high strength and excellent ductility are important but still challenging. Here, an epoxy adhesive with simultaneously strong, tough, and sustainable features by designing a new hierarchical energy‐dissipated cross‐linking structure is reported: an annular structure containing quadruple internal B─N coordination boronic esters (AQBN). Under small strain, the AQBN structure is rigid to enhance the tensile strength of the adhesive. With medium strain applied, its non‐coplanar ring and internal quadruple B─N coordination can orderly open, providing mechanical energy dissipation and excellent ductility. Therefore, this multilevel structure can endow epoxy adhesives with both high strength and toughness. Besides, the rapid dynamic exchange and internal B─N coordination in boronic esters enable the adhesives to have good sustainability and environmental tolerance, respectively. As a result, the epoxy adhesives exhibit simultaneous high adhesive strength (18.5 MPa), outstanding toughness (work of debonding of 29692 N m−1), good chemical/physical recyclability, and excellent environmental reliability (humidity, water, high/ultralow temperature, and organic solvents). This work provides a new strategy for balancing the strength, toughness, and sustainability of adhesives.

Microstructure and mechanical properties of multi-principal component CoCrNiMo medium entropy alloys

In traditional high entropy alloy (HEA) systems, achieving a synergistic enhancement of alloy strength and ductility remains a challenge. However, dual-phase high entropy alloys, with their simultaneous high strength and high ductility, have shown potential for industrial applications. In this study, three multi-principal element CoCrNiMo alloys were synthesized by adding varying amounts of Mo to the base medium entropy Co45Cr27Ni28 alloy, which possesses a single face-centered cubic (FCC) phase. The impact of variations in Mo content on the alloy's microstructure and mechanical properties was investigated. Experimental data revealed that all three alloys formed dual-phase (FCC + μ) precipitation-strengthened medium entropy alloys (MEAs), where the μ phase is enriched with Mo, and its quantity increases with the increase in Mo content. With the rise in Mo content, the alloy's hardness increased from 240 ± 20 HV to 668 ± 35 HV, and tensile strength also increased, albeit at the cost of reduced plasticity. The single-phase medium entropy Co45Cr27Ni28 alloy exhibited a tensile strength and elongation rate of 591 ± 15 MPa and 44 ± 3%, respectively. The tensile strength of the dual-phase CoCrNiMo HEAs could be elevated to 857 ± 16 MPa and 1045 ± 25 MPa, while maintaining considerable elongation rates of 16 ± 2% and 5 ± 1%, respectively. This work provides a pathway for strengthening CoCrNi alloys and contributes positively to the development of high-performance HEAs.

A biomimetic flexible sensor inspired by Albuca namaquensis for simultaneous high stretchability and strength

In the realm of intelligent human-machine interaction, the expansive potential of robust flexible wearable electronic devices emerges prominently. However, the practicality of such flexible electronic devices is often constrained within scenarios involving substantial mechanical strains, such as high-intensity (>100 MPa) and high tensile (>1000%) deformation, particularly in articulation-rich joint regions. Specifically, the substrates of flexible sensors confront challenges in reconciling elongation rates and tensile strengths, for which a cogent strategy is currently lacking to address the aforementioned mechanical parameter requisites. To address this quandary, the present study employs a paradigm of microscale materials that synergistically integrate rigid-flexible coupling enhancements, coupled with a biomimetic progressively asymptotic stretch optimization approach at the macroscale structural level. Through an inside-out methodology, we have ingeniously devised a biomimetic flexible sensory electronic device that seamlessly integrates sensing media and load-bearing capabilities, uniquely poised for simultaneous deployment within high-intensity and high-stretchability scenarios. By employing a judicious combination of rigidly supporting styrene monomers and the polymerized three-dimensional scaffold, formed through the coupling of elastomeric sustaining ethylene-butadiene monomers, with the high-strength, highly conductive discrete medium of graphene, we have achieved the successful synthesis of a substrate boasting a mechanical strength of 121.4 MPa alongside an impressive 1109% elongation capacity. This substrate exhibits a remarkable electrical conductivity up to 106 S*m−1. Furthermore, drawing inspiration from the serpentine architecture of the Albuca namaquensis, a two-tiered gradient stretching approach has been harnessed, resulting in an approximate 2.8-fold enhancement in stretchability. Leveraging the ingeniously designed GSBS sensor, an online testing platform for human-machine interaction capable of accommodating substantial deformations at joint interfaces is established. Through this innovation, we have effectively orchestrated the synchronization and emulation of extensive tensile movements between mechanical prosthetics and human articulations.

Manipulating Cis-Trans Copolymer Chain Conformation to Simultaneously Improve Permittivity and DC Breakdown Strength in Polythiourea.

Polythioureas (PTUs) show great potentials for applications in the new generation of film capacitors due to their excellent dielectric properties. Herein, the cis-trans copolymer chain of PTU is successfully tailored by employing cis and trans cyclohexyl spacers. The relationship between the copolymer chain conformation, microstructure, and dielectric properties is carefully explored by a series of analysis. Compared with cis conformation, the trans with less steric hindrance can promote the formation of H-bonds. The enhanced H-bonding interactions not only reduce the molecular inter-chain spacing, but also drive the self-assembly of molecular chains to form cylindrical and droplet nano-morphologies. The phase separation between cis and trans PTUs is confirmed by combining the experimental results of TEM and DSC, and the CT64-PTU with the most two-phase interface thus obtains the highest permittivity of 5.5 (@10Hz). The reduced molecular inter-chain spacing is accompanied by a decreased hopping distance of charges, which improves breakdown strength by 17% from 498 MV/m to 580 MV/m. Therefore, the cis-trans copolymer chain conformation in PTU provides a simultaneous high permittivity and breakdown strength. This research offers a strategy to further design high-performance dielectrics via regulation of copolymer chain conformation.

Achieving remarkable enhancement of yield strength and high ductility in a fine-grained Mg-6Zn-0.2Ca alloy via rotated hard-plate rolling

Developing Mg alloys with high strength-ductility synergy presents a major challenge. In this work, a novel Mg-6Zn-0.2Ca alloy prepared via rotated hard-plate rolling (RHPR) exhibits a simultaneous high yield strength (YS) of ∼268 MPa and ductility of ∼22%. The RHPRed alloy features a fine-grained structure containing high-density low angle boundaries (LAGBs) and densely distributed nano-coherent precipitates, contributing to a remarkable improvement of YS (∼82 MPa) in comparison to the conventional rolling counterpart, while homogenizing tensile deformation. In the RHPRed alloy, the presence of ellipse-shape texture and grain-boundary disclinations adjacent to LAGBs promotes the activity of pyramidal <a> and <c + a> slip that governs the high ductility. The current work demonstrates the essential role played by high-density LAGBs and nano-coherent precipitates to the high strength-ductility synergy, which may provide insights into microstructural control strategy towards superior performance of Mg-Zn-Ca alloys.

Fabrication of Al2O3 ceramic cores with high porosity and high strength by vat photopolymerization 3D printing and sacrificial templating

When preparing ceramic materials, high porosity and high strength are often played against each other. How to balance porosity and strength has become a core issue in the 3D printing of ceramic cores. In this work, alumina ceramic cores with a high porosity (36.93%) and a high flexural strength (75.4 MPa) were prepared by combining the vat photopolymerization 3D printing with sacrificial templating. The porosity of alumina ceramic cores was improved by the sacrificial templating method, and the flexural strength was enhanced with alumina particle grading. The effects of pore former (PMMA) content and particle size on the shrinkage, porosity, microstructure, and comprehensive performance of alumina ceramic cores were investigated to reveal the mechanism of simultaneous high porosity and high strength.

Comparison of Different Aerogel Granules for Use as Aggregate in Concrete

In previous work of this group, a structural lightweight concrete was developed by embedding silica aerogel granules in a high-strength cement matrix. This concrete, called high-performance aerogel concrete (HPAC), is a lightweight building material characterized by its simultaneous high compressive strength and very low thermal conductivity. Besides these features, high sound absorption, diffusion permeability, water repellence and fire resistance qualify HPAC as an interesting material for the construction of single-leaf exterior walls without any further insulation. During the development of HPAC, the type of silica aerogel was found to majorly influence both fresh and hardened concrete properties. To clarify these effects, a systematic comparison of SiO2 aerogel granules with different levels of hydrophobicity as well as different synthesis methods was conducted in the present study. The granules were analyzed for their chemical and physical properties as well as their compatibility in HPAC mixtures. These experiments included determinations of pore size distribution, thermal stability, porosity, specific surface and hydrophobicity, as well as fresh/hardened concrete experiments such as measurements of compressive strength, flexural bending strength, thermal conductivity and shrinking behavior. It was found that the type of aerogel has a major influence on the fresh and hardened concrete properties of HPAC, particularly compressive strength and shrinkage behavior, whereas the effect on thermal conductivity is not very pronounced.

Interpenetrating a Hollow Microlattice Metamaterial Enables Efficient Sound-Absorptive and Deformation-Recoverable Capabilities.

Owing to the pervasive noise and crash hazards, tough microlattices with sound absorption capabilities are sought-after. However, typical truss microlattices are unable to fulfill this requirement. To overcome this, herein, we report a new design strategy for truss microlattices via introducing the concept of interpenetrating hollow struts, which thereby constitutes a novel interpenetrating hollow microlattice metamaterial (IHMM). The design is based on interweaved unit cells of a hollow octet-truss (HOT) and a hollow rhombic dodecahedron-like (HRDL) truss. Experimentally demonstrated, the IHMM displays a synergistic gain in both sound absorption and mechanical properties that substantially surpass that of its constituent lattices. High sound absorption coefficients (α > 0.99) and broad half-absorption (3.2 kHz) are observed, with the average α being 110.6 and 85.3% higher than those of the HOT and HRDL, respectively. The sound absorption mechanism is attributed to the presence of cascaded Helmholtz resonance, which is then fully elucidated by impedance and damping analyses. The IHMM also outperforms its constituents in specific strength. A simultaneous high strength (4 MPa) and recoverability (80% strain) and pseudo-reusability are also observed. The mechanisms behind the mechanical reinforcement and exceptional robustness are thoroughly revealed. Overall, this work offers insights into developing multifunctional engineering materials.

Dithioester-terminated copolymers with simultaneous high dielectric constant and breakdown strength for energy storage

High-energy storable polymer dielectrics are highly desirable and applicable for compact and efficient power electronic devices. However, existing polymer dielectrics suffer from either a low dielectric constant or a low breakdown strength and exhibit an extremely low energy density. Here, the reversible addition−fragmentation chain transfer polymerization and polyaddition polymerization techniques are combined to create a dithioester-terminated polythiourea (PTU)-based copolymer dielectric with an extraordinarily high energy density of 10.7 J/cm3. The end-group functionalized copolymer significantly increases the dielectric constant from 6.0 to 7.6, which enhances the breakdown strength from 264 to 563 MV/m. The theoretical analysis from the proton nuclear magnetic resonance, atomic force microscope (AFM), and the dynamics of the polarization behaviors demonstrates conformational transitions between the two distinct trans/trans and cis/trans thioureas, along with the formation of polar PTU nanoregions. These result in a flexible polarization reorientation process and increased dielectric constant. Meanwhile, the density functional theory calculations for the electronic structures of the block copolymers indicate that the excellent breakdown strength of the end-group functionalized copolymer is attributed to strong charge trapping from the unique dithioesters. This work proposes a strategy to achieve a simultaneous high dielectric constant and breakdown strength toward excellent energy storage performances by end-group functionalization and composition modifications.

3D printing of architectured epoxy-based composite lattices with exceptional strength and toughness

Due to the exceptional mechanical properties, epoxy-based composites have been widely applied as critical aerospace components, semiconductor packaging materials, and multifunctional coatings and adhesives. However, the brittle nature of epoxy resin leads to poor resistance to crack initiation and propagation, significantly hindering their applications as high-performance composites. Herein, we develop an architectured composite lattice with simultaneous high toughness and strength through a 3D printing technique. Strengthening and toughening zones possessing solid and highly ordered lattice structures, respectively, are rationally assembled into a layered structure. The resultant composite lattices deliver significantly improved flexural properties and crack resistance properties, exhibiting 400%, 83% and 36% higher toughness, specific strength, and fracture toughness than their solid counterpart, respectively. The exceptional strength and toughness of the composite lattices come from the synergetic effect of the strengthening and toughening zones, as confirmed by both experimental and theoretical analysis. The current findings provide an effective strategy for the fabrication epoxy-based composites with precisely controlled structures and mechanical performances.

Quantitative investigation of strain partitioning and failure mechanism in ultrafine grained medium Mn steel through high resolution digital image correlation

Ultrafine grained medium Mn steel exhibits simultaneous high strength and ductility, however, often showing Lüders deformation and discontinuous yielding phenomena. The connections between martensite transformation and Lüders deformation as well as the localized failure behavior are quantitatively investigated through high resolution digital image correlation, enabled by nanoscale strain distribution and microstructural alignment. At a low global tensile strain level, strain localization happens in austenite domain resulted from a sequential slip deformation and martensite transformation, which then triggers the yielding of ferrite by generating thin strain channels to connect adjacent hotspots. This microscopic deformation mode promotes the formation of macroscopic deformation bands, resulting in Lüders band initiation and propagation. When increasing the applied load, the externally imposed strain is accommodated by ferrite instead, resulting in pronounced strain partitioning. The triple grains boundary having no further strain hardening capacity is favorable for void initiation and propagation.

Bulk-like ductility of cold spray additively manufactured copper in the as-sprayed state

• As-sprayed CSAM Cu can exhibit a simultaneous high ductility and strength. • This is triggered by a specific topology of bimodal grain size. • The deposits have a high thermal conductivity comparable to bulk. • They are perfectly gas-tight with He leakage rate of less than 1 × 10 −7 mbar•l/s. • All these were achieved with 99% efficiency using inexpensive nitrogen. In recent years, cold spray process is increasingly used for additive manufacturing of metallic components, referred to as cold spray additive manufacturing (CSAM). Unlike the fusion-based AM processes, CSAM is achieved in a solid-state, bringing several advantages such as the absence of severe oxidation or phase composition changes. At the moment, the main limitation of CSAM is the generally low ductility of the as-sprayed deposits. In this paper, using Cu as a model material, we demonstrate a way to overcome this limitation. Importantly, a high ductility of the deposits in their as-sprayed state is achieved without a trade-off in mechanical strength. Furthermore, we show that without any post-heat treatment, the properties of CSAM Cu are comparable to bulk, non-AM Cu.

Simultaneous high strength and mechanical stability of bcc Nb/Mg nanolaminates

While bimetallic nanocomposites have demonstrated extraordinary – three to even ten-fold – gains in strength with decreasing layer thickness, their strengths tend to plateau beyond a critical layer thickness. More disappointingly, such increases in strength are almost always accompanied by a decrease in their strains to failure (ductility). In this work we report simultaneous improvements in both strength and mechanical stability of Nb/Mg nanolaminates with decreasing layer thicknesses, a trend seldom reported in nanolaminates consisting of pure metals. Using micro-pillar compression and nanoindentation experiments we show that physical vapor deposited (PVD) Nb/Mg nanolaminates that contain a body center cubic (bcc) Mg pseudomorphic phase demonstrate a >60% increase in strength and a >80% increase in strain to failure over those containing the hexagonal close packed (hcp) Mg phase. Instead of a strength plateau, the hcp-to-bcc phase transition in Mg results in a renewed strengthening regime in the nanolaminate caused by the change to a coherent interface from an incoherent one, along with a concurrent increase in strain-to-failure due to the introduction of a more plastically isotropic bcc material from an anisotropic hcp structure. Using high resolution transmission electron microscopy (HR-TEM) we also demonstrate the presence of a thin layer of bcc Mg at the Nb/Mg interface at larger layer thicknesses when Mg is predominantly hcp. Our results suggest that the increases in strain to failure in the Nb/Mg nanolaminates with decreasing layer thicknesses can be corelated to the approximate volume fraction of the pseudomorphic bcc Mg present in the layers.