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The replacement of historical load-bearing wooden elements made from not commonly used species such as Populus tremula L. presents significant challenges. As these species are seldomly used in modern construction, a knowledge gap exists regarding their implementation in accordance with current building codes. This study investigates the mechanical properties of European aspen (Populus tremula L.) from central Slovakia as a potential replacement for historical structures. Notably, poplar species, including European aspen, have historically been utilized for construction across various landscapes in Europe. We conducted experimental testing on visually graded aspen timber to determine the dynamic modulus of elasticity (MOEdyn,ultr), modulus of elasticity (MOE), modulus of rupture (MOR), and density. The results were analyzed and compared to established standards for structural timber. Notably, the 5th percentileof the strength distribution (f0.05) was determined to be 28.78 MPa, while the characteristic strength (fk) was 26.23 MPa, and the modulus of elasticity (Eg12) was 13.60 MPa. The correlation between MOR and dynamic MOE facilitated the determination of MOR by non-destructive testing (NDT) using the Sylvatest Duo®. This simple linear model could grade 49% of boards into the higher strength class C30. The additional parameters and their interactions in multiregresssion models improved the predictability of the bending strength of aspen. The advanced model graded 68% of boards into C30. These characteristics, along with aspen’s growth potential, make it a promising candidate for replacing damaged structural elements in historical constructions. Our findings contribute to the understanding of the potential of European aspen as a structural timber, highlighting its viability as a fast-growing hardwood species.

This literature review examined the functionality of the connection or connections and disassembly as a general strategy. The prerequisites that arose for disassembly were, among other things, damage tolerance, reduction of emissions compared to raw materials, costs, and guaranteeing safety. The set of criteria for disassembly was defined from the structural engineers’ perspective through the literature review. The criteria focus on joints, which are key to the success of disassembly. Five different criteria were used to evaluate joints in this study. The criteria were ease of access to components, ease of disassembly, independence, simplicity, and standardization. The evaluation was executed for different widely used connections in timber constructions. The criteria were evaluated subjectively from one to four. As a conclusion, the load-bearing timber elements have a promising future in design for disassembly. Design for disassembly aims to promote reuse and other features to increase the life cycle of structural elements. It has the potential to reduce the usage of raw materials and significantly decrease the emissions of construction.

Metallic materials have enabled technological progress over thousands of years. The accelerated demand for structural (that is, load-bearing) alloys in key sectors such as energy, construction, safety and transportation is resulting in predicted production growth rates of up to 200 per cent until 2050. Yet most of these materials require a lot of energy when extracted and manufactured and these processes emit large amounts of greenhouse gases and pollution. Here we review methods of improving the direct sustainability of structural metals, in areas including reduced-carbon-dioxide primary production, recycling, scrap-compatible alloy design, contaminant tolerance of alloys and improved alloy longevity. We discuss the effectiveness and technological readiness of individual measures and also show how novel structural materials enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties than currently available alloys. Structural metals enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties; here, methods of improving the sustainability of structural metals, from recycling to contaminant tolerance, are described.

Robust damage-tolerant hydrogel fibers with high strength, crack resistance, and self-healing properties are indispensable for their long-term uses in soft machines and robots as load-bearing and actuating elements. However, current hydrogel fibers with inherent homogeneous structure are generally vulnerable to defects and cracks and thus local mechanical failure readily occurs across fiber normal. Here, inspired by spider spinning, we introduce a facile, energy-efficient aqueous pultrusion spinning process to continuously produce stiff yet extensible hydrogel microfibers at ambient conditions. The resulting microfibers are not only crack-insensitive but also rapidly heal the cracks in 30 s by moisture, owing to their structural nanoconfinement with hydrogen bond clusters embedded in an ionically complexed hygroscopic matrix. Moreover, the nanoconfined structure is highly energy-dissipating, moisture-sensitive but stable in water, leading to excellent damping and supercontraction properties. This work creates opportunities for the sustainable spinning of robust hydrogel-based fibrous materials towards diverse intelligent applications. Hydrogels with homogenous structure are vulnerable to defects and cracks, and local mechanical failure occurs consequently. Here, the authors develop a spinning process to produce robust hydrogel microfibers with both crack insensitivity and self-healability.

Fabrics are ubiquitous materials that have conventionally been passive assemblies of interlacing, inactive fibers. However, the recent emergence of active fibers with actuation, sensing, and structural capabilities provides the opportunity to impart robotic function into fabric substrates. Here we present an implementation of robotic fabrics by integrating functional fibers into conventional fabrics using typical textile manufacturing techniques. We introduce a set of actuating and variable-stiffness fibers, as well as printable in-fabric sensors, which allows for robotic closed-loop control of everyday fabrics while remaining lightweight and maintaining breathability. Finally, we demonstrate the utility of robotic fabrics through their application to an active wearable tourniquet, a transforming and load-bearing deployable structure, and an untethered, self-stowing airfoil.

Gram-negative bacteria possess a complex cell envelope that consists of a plasma membrane, a peptidoglycan cell wall and an outer membrane. The envelope is a selective chemical barrier 1 that defines cell shape 2 and allows the cell to sustain large mechanical loads such as turgor pressure 3 . It is widely believed that the covalently cross-linked cell wall underpins the mechanical properties of the envelope 4 , 5 . Here we show that the stiffness and strength of Escherichia coli cells are largely due to the outer membrane. Compromising the outer membrane, either chemically or genetically, greatly increased deformation of the cell envelope in response to stretching, bending and indentation forces, and induced increased levels of cell lysis upon mechanical perturbation and during L-form proliferation. Both lipopolysaccharides and proteins contributed to the stiffness of the outer membrane. These findings overturn the prevailing dogma that the cell wall is the dominant mechanical element within Gram-negative bacteria, instead demonstrating that the outer membrane can be stiffer than the cell wall, and that mechanical loads are often balanced between these structures. The outer membrane of Gram-negative bacteria is shown to be at least as stiff as the cell wall, and this property enables it to protect cells from mechanical pertubations.

Multi-stage tandem thrust bearings have small radial dimensions and high axial load-bearing capacity, which are widely used in shafting structures with large axial load-bearing capacity requirements, such as screw extruders, and their load-bearing characteristics are directly related to the stability and service life of the equipment. In this paper, a mechanical model of multi-stage tandem thrust bearings is established based on the finite element method and verified by combining stiffness and ring strain tests. The load distribution characteristics of each level of thrust bearings and the outer spacer rings are analyzed. The results demonstrate that the mechanical model of multi-stage tandem thrust bearings has high accuracy compared with the experiment and displays superior load-sharing characteristics. The design stiffness deviation of the outer spacer ring thickness can also lead to a certain deviation. Hence, the design of the spacer ring holds a crucial role in the load-sharing characteristics of the multi-stage tandem thrust bearings.

Transition-metal coordination complexes are emerging as a broad class of supramolecular crosslinks that can be used to engineer the mechanical properties of advanced structural materials. Unlike conventional covalent bonds, metal-coordination bonds have the capacity to reform after rupture, thereby enabling dynamic, tunable and reversible (self-healing) mechanical properties. Several biological organisms, such as marine mussels, have been found to take advantage of these unique properties of metal-coordinate complexes in the assembly of load-bearing materials for complex extraorganismal functions. Accordingly, efforts to integrate metal-coordinate crosslinking in bioinspired synthetic protein and polymer hydrogels are an increasingly active area of research. However, a deeper understanding of how metal-coordination bonds affect bulk mechanical properties is still missing, rendering predicting the mechanical properties of metal-coordinated materials challenging. In this Review, we survey recent advances and open questions in our understanding of how chemical properties of metal-coordinate complexes influence multiscale mechanical behaviour, with the aim of presenting metal-coordination bonding as a rich, inorganic crosslinking chemistry tool. We also review applications of metal-coordinate crosslinking in the design of novel materials with tunable mechanical properties, ranging from tough gels to soft robots. These applications highlight the opportunities arising from the integration of this class of load-bearing crosslinks in structural materials design. The reversibility of transition-metal coordination bonds affords broad control over the structural dynamics of materials. This Review surveys the design principles underlying the utilization of this dynamic crosslink chemistry to engineer tunable mechanical properties in biological materials and protein and polymer hydrogels.

Biological tissues, such as cartilage, tendon, ligament, skin, and plant cell wall, simultaneously achieve high water content and high load-bearing capacity. The high water content enables the transport of nutrients and wastes, and the high load-bearing capacity provides structural support for the organisms. These functions are achieved through nanostructures. This biological fact has inspired synthetic mimics, but simultaneously achieving both functions has been challenging. The main difficulty is to construct nanostructures of high load-bearing capacity, characterized by multiple properties, including elastic modulus, strength, toughness, and fatigue threshold. Here we develop a process that self-assembles a nanocomposite using a hydrogel-forming polymer and a glassforming polymer. The process separates the polymers into a hydrogel phase and a glass phase. The two phases arrest at the nanoscale and are bicontinuous. Submerged in water, the nanocomposite maintains the structure and resists further swelling. We demonstrate the process using commercial polymers, achieving high water content, as well as loadbearing capacity comparable to that of polyethylene. During the process, a rubbery stage exists, enabling us to fabricate objects of complex shapes and fine features. We conduct further experiments to discuss likely molecular origins of arrested phase separation, swell resistance, and ductility. Potential applications of the nanocomposites include artificial tissues, high-pressure filters, low-friction coatings, and solid electrolytes.

Foamed concrete (FC) is a high-quality building material with densities from 300 to 1850 kg/m3, which can have potential use in civil engineering, both as insulation from heat and sound, and for load-bearing structures. However, due to the nature of the cement material and its high porosity, FC is very weak in withstanding tensile loads; therefore, it often cracks in a plastic state, during shrinkage while drying, and also in a solid state. This paper is the first comprehensive review of the use of man-made and natural fibres to produce fibre-reinforced foamed concrete (FRFC). For this purpose, various foaming agents, fibres and other components that can serve as a basis for FRFC are reviewed and discussed in detail. Several factors have been found to affect the mechanical properties of FRFC, namely: fresh and hardened densities, particle size distribution, percentage of pozzolanic material used and volume of chemical foam agent. It was found that the rheological properties of the FRFC mix are influenced by the properties of both fibres and foam; therefore, it is necessary to apply an additional dosage of a foam agent to enhance the adhesion and cohesion between the foam agent and the cementitious filler in comparison with materials without fibres. Various types of fibres allow the reduction of by autogenous shrinkage a factor of 1.2–1.8 and drying shrinkage by a factor of 1.3–1.8. Incorporation of fibres leads to only a slight increase in the compressive strength of foamed concrete; however, it can significantly improve the flexural strength (up to 4 times), tensile strength (up to 3 times) and impact strength (up to 6 times). At the same time, the addition of fibres leads to practically no change in the heat and sound insulation characteristics of foamed concrete and this is basically depended on the type of fibres used such as Nylon and aramid fibres. Thus, FRFC having the presented set of properties has applications in various areas of construction, both in the construction of load-bearing and enclosing structures.