Bulk Structural Materials Research Articles

Multiscale Engineered Waste Wood Particles toward a Sustainable, Scalable, and High‐Performance Structural Material

AbstractDeveloping sustainable and lightweight structural materials is a promising strategy for reducing carbon emissions in transportation and buildings. However, producing high‐performance bulk structural materials from sustainable biomass materials while maintaining excellent mechanical strength remains a major challenge, especially for further scale‐up. Herein, a scalable and robust bottom‐up strategy is reported to fabricate bulk wooden plate (W‐plate) with a typical “brick‐and‐mortar” structure from engineered wood particles via moderate delignification and in situ LiCl/DMAc treatment followed by hot‐pressing. The W‐plate constructed by delignified wood particles and regenerated cellulose nanofibers can achieve a confluence of mechanical strengthening and toughening by the ordered lamination structure and multiscale cellulose micro/nanofiber crosslinking interactions, resulting in high flexural strength (225.17 ± 12.18 MPa) and high fracture toughness (4.01 ± 0.53 MPa m0.5) while maintaining a low density (1.34 g cm−3), superior to typical metals and ceramics. Moreover, the W‐plate exhibits advantageous thermal properties, including a low thermal expansion coefficient (<19 × 10−6 K−1) and a high storage modulus (>7.5 GPa) compared to those of petroleum‐based polymers. Coupled with abundant and renewable raw materials, all‐cellulose components, and scalable and recyclable fabrication, the W‐plate can potentially be used as a high‐performance, cost‐effective, and environmentally friendly alternative for engineering applications.

Tribological properties of 100% cellulose nanofiber (CNF) molding under dry- and boundary lubrication-conditions at CNF/steel contacts

Cellulose nanofibers (CNFs), which are plant-derived materials, have recently garnered considerable attention owing to their excellent mechanical properties, such as their low weight and high Young’s modulus. Novel methods for producing 100% CNF bulk structural materials have been developed. However, the tribological properties of CNFs have not been investigated thus far although their mechanical properties are known and are comparable to those of some conventional structural materials. In this study, the tribological properties of a novel biomass material, 100% CNF molding, were investigated based on CNF/steel contacts under dry and boundary lubrication conditions at various temperatures. The friction test results showed that the friction coefficient and wear volume of the CNF molding increased with the test temperature of the CNF/steel tribopair under dry-sliding conditions. Conversely, no significant temperature dependence of the friction and wear properties was observed upon lubrication with a pure polyalfaolefin. The surface analytical results revealed that the amorphization of the CNF molding progressed on the worn surface, especially under dry-sliding conditions at a high temperature. All the results suggested that the friction and wear performance of the 100% CNF moldings strongly depends on the sliding test conditions, and the amorphization process of the CNF molding can affect its friction and wear performance.

Nonthermal plasma synthesis of silicon carbonitride

AbstractThe use of a low‐temperature plasma for the synthesis of amorphous silicon carbonitride (SiCN) nanoparticles enables the realization of sintered bulk samples with high thermal stability. Amorphous SiCN nanoparticles are produced from a mixture of silane, methane, and ammonia utilizing a mid‐pressure, radio‐frequency, continuous flow reactor. Particle characterization shows that the nanoparticles are largely amorphous with some crystalline silicon and silicon carbide domains <10 nm in size. Compositional tuning, controlled by varying the precursor flow rates, coupled with the uniform mixing of elements at the nanoscale, results in samples that resist crystallization even when sintered at temperatures as high as 2000°C. This study suggests that the low‐temperature plasma synthesis of nanoparticles has great potential to produce bulk structural materials for application in harsh environments.

Constructing An All-Natural Bulk Structural Material from Surface-Charged Bamboo Cellulose Fibers with Enhanced Mechanical and Thermal Properties.

Bamboo is widely distributed, rapidly regenerable, and incorporates long cellulose fibers, which make it one of the most lightweight and strong natural materials. Processing bamboo into a high-performance structural material for plastic replacement is highly promising but challenging. In this study, an all-natural, high-performance structural material is derived from natural bamboo with superior mechanical and thermal properties that benefit from the introduction of surface charge and further layer-by-layer assembly of bamboo cellulose fibers. The obtained modified bamboo fiber plate (MBFP) transcends the constraints of the natural size and anisotropy of bamboo, showing high flexural strength (ca. 179 MPa) and flexural modulus (ca. 12 GPa). Moreover, the product has an extremely low coefficient of thermal expansion (ca. 11.3×10-6 K-1 ), high thermal stability, and superior fire resistance. The excellent mechanical and thermal properties combined with the efficient and rational manufacturing process make MBFP a powerful plastic alternative for furniture, construction, and automotive industries.

Functionally graded tungsten/EUROFER coating for DEMO first wall: From laboratory to industrial production

The First Wall is a crucial component for the realisation of DEMO. It has to protect the tritium breeding blanket from erosion by high-energy particles while letting neutrons pass to enable breeding of tritium fuel. Furthermore, the First Wall needs to pass incoming heat in the MW/m² range to a cooling system for conversion to electric power. These requirements sum up to one of the harshest environments imaginable for a man-made material. Structural steel components alone cannot withstand these conditions. Tungsten is a viable armour material for the First Wall because of its low sputtering yield, high melting point, low activation and good thermal conductivity. It is not suitable though as bulk structural material because of its brittleness. Instead, the DEMO design foresees a First Wall of reduced-activation EUROFER steel, covered with a protective layer of tungsten. Direct tungsten-steel joints suffer from failure during processing or operation because of the thermal expansion mismatch between the two materials. This is solved by application of a functionally graded material as intermediate layer between steel and tungsten. Such coatings made of both tungsten and EUROFER, with a compositional gradient, have been produced with vacuum plasma spray technology. This technology enables manufacturing of the required millimetre-thick coatings and is suitable for upscaling. The development was supported by thermo-mechanical finite element simulations of load scenarios during processing and in-vessel service. Driven by promising results of high heat flux tests on larger, coated mock-ups the technology was transferred to industry for upscaling. Plates with a record size of 500 × 250 mm² and cooling channels were successfully coated. This contribution presents an overview of the development process, covers the latest results of ongoing research on the coating of curved First Wall structures and addresses future requirements.

Matrix-Directed Mineralization for Bulk Structural Materials.

Mineral-based bulk structural materials (MBSMs) are known for their long history and extensive range of usage. The inherent brittleness of minerals poses a major problem to the performance of MBSMs. To overcome this problem, design principles have been extracted from natural biominerals, in which the extraordinary mechanical performance is achieved via the hierarchical organization of minerals and organics. Nevertheless, precise and efficient fabrication of MBSMs with bioinspired hierarchical structures under mild conditions has long been a big challenge. This Perspective provides a panoramic view of an emerging fabrication strategy, matrix-directed mineralization, which imitates the in vivo growth of some biominerals. The advantages of the strategy are revealed by comparatively analyzing the conventional fabrication techniques of artificial hierarchically structured MBSMs and the biomineral growth processes. By introducing recent advances, we demonstrate that this strategy can be used to fabricate artificial MBSMs with hierarchical structures. Particular attention is paid to the mass transport and the precursors that are involved in the mineralization process. We hope this Perspective can provide some inspiring viewpoints on the importance of biomimetic mineralization in material fabrication and thereby spur the biomimetic fabrication of high-performance MBSMs.

Scalable Production of Sustainable Bulk Structural Materials from Surface-Charged Bamboo Fibers with Enhanced Mechanical and Thermal Properties

Scalable Production of Sustainable Bulk Structural Materials from Surface-Charged Bamboo Fibers with Enhanced Mechanical and Thermal Properties

Chemically Activated SS Metathesis for Adhesive‐Free Bonding of Polysulfide Surfaces

AbstractA polysulfide terpolymer made from canola oil, dicyclopentadiene, and elemental sulfur is synthesized and evaluated as bulk structural material. The unique polysulfide structure in this material allows the two polymer blocks to be bonded together through amine‐catalyzed SS metathesis. No exogenous adhesive is required: the polysulfide is both the bulk material and the mortar. The strength of the joined polymers is evaluated by a series of shear tests and compared to the bond strength obtained with commercially available superglue. The adhesion obtained via the SS metathesis is stronger in all tests. To improve the mechanical properties of the terpolymer, carbon nanorods and carbon fibers are embedded in the polymer, with the latter leading to nearly a 16‐fold increase in flexural strength. Prospects in sustainable construction are discussed.

Ultra-Strong, Ultra-Tough, Transparent, and Sustainable Nanocomposite Films for Plastic Substitute

Summary Plastics play a critical role in daily life but possess a considerably increasing negative impact on the environment and human health. Fabrication of biodegradable and eco-friendly alternatives with competitive properties for plastic substitute is urgently needed. Here, inspired by the hierarchical structure of nacre, we firstly developed a high-performance nacre-inspired composite with high transmittance (83.4% at 550 nm) and high haze (88.8% at 550 nm) via an aerosol-assisted biosynthesis process combined with the hot-press technique. The nacre-inspired composite film combines higher strength (482 MPa) and toughness (17.71 MJ m−3) than most other nacre-inspired films, and can be folded into various shapes without visible failure after unfolding. Moreover, compared with most commercial plastic films, it exhibits a lower thermal expansion coefficient (∼3 ppm K−1) and higher maximum service temperature besides better mechanical properties, which makes it a promising alternative to plastics in many technical fields.

Sustainable Bulk Structural Material Engineered from Cellulose Nanofibers

Materials define ages, and ages are named after the dominant material, say stone-age or bronze-age. Are we entering a cellulose-age soon?

Lightweight, tough, and sustainable cellulose nanofiber-derived bulk structural materials with low thermal expansion coefficient.

Sustainable structural materials with light weight, great thermal dimensional stability, and superb mechanical properties are vitally important for engineering application, but the intrinsic conflict among some material properties (e.g., strength and toughness) makes it challenging to realize these performance indexes at the same time under wide service conditions. Here, we report a robust and feasible strategy to process cellulose nanofiber (CNF) into a high-performance sustainable bulk structural material with low density, excellent strength and toughness, and great thermal dimensional stability. The obtained cellulose nanofiber plate (CNFP) has high specific strength [~198 MPa/(Mg m-3)], high specific impact toughness [~67 kJ m-2/(Mg m-3)], and low thermal expansion coefficient (<5 × 10-6 K-1), which shows distinct and superior properties to typical polymers, metals, and ceramics, making it a low-cost, high-performance, and environmental-friendly alternative for engineering requirement, especially for aerospace applications.

A Strong, Tough, and Scalable Structural Material from Fast-Growing Bamboo.

Lightweight structural materials with high strength are desirable for advanced applications in transportation, construction, automotive, and aerospace. Bamboo is one of the fastest growing plants with a peak growth rate up to 100 cm per day. Here, a simple and effective top-down approach is designed for processing natural bamboo into a lightweight yet strong bulk structural material with a record high tensile strength of ≈1 GPa and toughness of 9.74 MJ m-3 . More specifically, bamboo is densified by the partial removal of its lignin and hemicellulose, followed by hot-pressing. Long, aligned cellulose nanofibrils with dramatically increased hydrogen bonds and largely reduced structural defects in the densified bamboo structure contribute to its high mechanical tensile strength, flexural strength, and toughness. The low density of lignocellulose in the densified bamboo leads to a specific strength of 777 MPa cm3 g-1 , which is significantly greater than other reported bamboo materials and most structural materials (e.g., natural polymers, plastics, steels, and alloys). This work demonstrates a potential large-scale production of lightweight, strong bulk structural materials from abundant, fast-growing, and sustainable bamboo.

Superior Biomimetic Nacreous Bulk Nanocomposites by a Multiscale Soft-Rigid Dual-Network Interfacial Design Strategy

Summary Biomimetic bulk structural materials have been paid increasing attention for their huge application prospects. Integrating close-to-ideal, ultrathin, and flexible nanostructured units into high-performance nacreous bulk nanocomposites is worth considering yet remains challenging due to the elusive micro- and nano-interface connections. Here, by introducing a multiscale soft-rigid polymer dual-network interfacial design strategy that enables us to appropriately reinforce the nanoscale building blocks or their bridging, we can construct a type of nacreous bulk nanocomposites with tunable mechanical properties in the mild, eco-friendly, and highly efficient bottom-up assembly process. The resultant nanocomposites can achieve continuously reinforced mechanical transformation without experiencing environmentally threatening interfacial manipulation processes. This interfacial design strategy, supported by sufficient experiments and simulations, endows the assembled nacreous nanocomposite with superior mechanical enhancement and improved stability under high humidity and temperature conditions. Combined with the scalable assembly technique, it will pave the way for the design of high-performance biomimetic bulk nanocomposites for structural applications.

Air Trapping Mechanism in Artificial Salvinia-Like Micro-Hairs Fabricated via Direct Laser Lithography.

Salvinia leaves represent an extraordinary example of how nature found a strategy for the long term retainment of air, and thus oxygen, on a surface, the so-called ‘Salvinia effect’, thanks to the peculiar three-dimensional and hierarchical shape of the hairs covering the leaves. Here, starting from the natural model, we have microfabricated hairs inspired by those present on the Salvinia molesta leaves, by means of direct laser lithography. Artificial hairs, like their natural counterpart, are composed of a stalk and a crown-like head, and have been reproduced in the microscale since this ensures, if using a proper design, an air-retaining behavior even if the bulk structural material is hydrophilic. We have investigated the capability of air retainment inside the heads of the hairs that can last up to 100 h, demonstrating the stability of the phenomenon. For a given dimension of the head, the greater the number of filaments, the greater the amount of air that can be trapped inside the heads since the increase in the number of solid–air interfaces able to pin the liquid phase. For this reason, such type of pattern could be used for the fabrication of surfaces for controlled gas retainment and gas release in liquid phases. The range of applications would be quite large, including industrial, medical, and biological fields.

Thermoresponsive actuation enabled by permittivity switching in an electrostatically anisotropic hydrogel

Electrostatic repulsion, long used for attenuating surface friction, is not typically employed for the design of bulk structural materials. We recently developed a hydrogel with a layered structure consisting of cofacially oriented electrolyte nanosheets. Because this unusual geometry imparts a large anisotropic electrostatic repulsion to the hydrogel interior, the hydrogel resisted compression orthogonal to the sheets but readily deformed along parallel shear. Building on this concept, here we show a hydrogel actuator that operates by modulating its anisotropic electrostatics in response to changes of electrostatic permittivity associated with a lower critical solution temperature transition. In the absence of substantial water uptake and release, the distance between the nanosheets rapidly expands and contracts on heating and cooling, respectively, so that the hydrogel lengthens and shortens significantly, even in air. An L-shaped hydrogel with an oblique nanosheet configuration can thus act as a unidirectionally proceeding actuator that operates without the need for external physical biases.

New observations of a nanoscaled pseudomorphic bcc Co phase in bulk Co–Al–(W,Ta) superalloys

The influence of composition on microstructural phase stability has been assessed for an emerging class of Co-based superalloys. This has been achieved using a combinatorial approach that incorporates both material synthesis and state-of-the-art characterization techniques. A compositionally graded Co–11Al–xW–yTa alloy (x⩽10, y=10−x, all in wt.%) was produced using Laser Engineered Net Shaping (LENS™) and subsequently solutionized and water quenched. At selected locations along the gradient, the microstructures present were characterized in detail, and phase identification was conducted on site-specific thin specimens using transmission electron microscopy (TEM), providing details regarding the earliest stages of microstructural evolution in these alloys. The partitioning behavior of the alloying elements W, Ta and Al was characterized using a 3-D local electrode atom probe, revealing the existence of Co-rich clusters. In addition, high-resolution TEM and precession electron diffraction have revealed and confirmed that these clusters are a pseudomorphic body-centered cubic (bcc) structure that has resulted from the decomposition of a B2 ordered region. Although bcc Co has previously been reported in some thin-film multilayers, owing to the relative stabilities of the bcc phase and the face-centered cubic (fcc) phase, this observation has not been previously reported in bulk structural materials. It is argued that this nanoscaled pseudomorphic bcc Co phase may be a precursor to the fcc phase.

OS1715 表面活性化現象を利用したバルク構造材用常温接合技術の検討

OS1715 表面活性化現象を利用したバルク構造材用常温接合技術の検討

Rapid alloy prototyping: Compositional and thermo-mechanical high throughput bulk combinatorial design of structural materials based on the example of 30Mn–1.2C–xAl triplex steels

We introduce a new experimental approach to the compositional and thermo-mechanical design and rapid maturation of bulk structural materials. This method, termed rapid alloy prototyping (RAP), is based on semi-continuous high throughput bulk casting, rolling, heat treatment and sample preparation techniques. 45 Material conditions, i.e. 5 alloys with systematically varied compositions, each modified by 9 different ageing treatments, were produced and investigated within 35h. This accelerated screening of the tensile, hardness and microstructural properties as a function of chemical and thermo-mechanical parameters allows the highly efficient and knowledge-based design of bulk structural alloys. The efficiency of the approach was demonstrated on a group of Fe–30Mn–1.2C–xAl steels which exhibit a wide spectrum of structural and mechanical characteristics, depending on the respective Al concentration. High amounts of Al addition (>8wt.%) resulted in pronounced strengthening, while low concentrations (<2wt.%) led to embrittlement of the material during ageing.

The conflicts between strength and toughness

The attainment of both strength and toughness is a vital requirement for most structural materials; unfortunately these properties are generally mutually exclusive. Although the quest continues for stronger and harder materials, these have little to no use as bulk structural materials without appropriate fracture resistance. It is the lower-strength, and hence higher-toughness, materials that find use for most safety-critical applications where premature or, worse still, catastrophic fracture is unacceptable. For these reasons, the development of strong and tough (damage-tolerant) materials has traditionally been an exercise in compromise between hardness versus ductility. Drawing examples from metallic glasses, natural and biological materials, and structural and biomimetic ceramics, we examine some of the newer strategies in dealing with this conflict. Specifically, we focus on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture. We show how these new and natural materials can defeat the conflict of strength versus toughness and achieve unprecedented levels of damage tolerance within their respective material classes.

Production of Open Cell Aluminium Metal Foam with Lost Foam Technique

AbstractMetallic foams represent materials with low densities as well as good physical, mechanical, thermal, and electrical properties. Since they have pores, metal foams have a set of unusual properties compared with bulk structural materials, i. e. the can offer a unique combination of several properties that can not be obtained in one conventional material at the same time. Metal foams can be produced by different processing technologies and many of them are still under development. The lost foam technique is an alternative foundry process as compared to other conventional techniques. This paper reports about a new approach for the production of open-cell aluminium foam metal by such casting procedure. During the process, an expanded polystyrene cell has been used for pattern making and all critical steps for manufacturing open-cell metal foam by the new technique are described in detail.