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This authoritative, widely cited book has been used all over the world. The Fourth Edition incorporates the latest developments in the field while maintaining the core objectives of previous editions: To correlate properties with chemical structure and to describe methods that permit the estimation and prediction of numerical properties from chemical structure, i.e. nearly all properties of the solid, liquid, and dissolved states of polymers.

Freestanding nanowires have ultrahigh elastic strain limits (4 to 7%) and yield strengths, but exploiting their intrinsic mechanical properties in bulk composites has proven to be difficult. We exploited the intrinsic mechanical properties of nanowires in a phase-transforming matrix based on the concept of elastic and transformation strain matching. By engineering the microstructure and residual stress to couple the true elasticity of Nb nanowires with the pseudoelasticity of a NiTi shape-memory alloy, we developed an in situ composite that possesses a large quasi-linear elastic strain of over 6%, a low Young's modulus of ∼28 gigapascals, and a high yield strength of ∼1.65 gigapascals. Our elastic strain-matching approach allows the exceptional mechanical properties of nanowires to be exploited in bulk materials.

During the additive manufacturing (AM) process, energy is transferred from the energy beam to the processed material. The high-energy input and uneven temperature distribution result in the high-temperature gradient, large thermal stress, and warping deformation. The scanning strategy, one of the representative AM processing parameters, plays an important role in the microstructures, mechanical properties, and residual stresses of 3D printed parts. It is necessary to review the current state of research about scanning strategy in additive manufacturing, and this paper seeks to address this need. This review mainly focuses on the scanning strategies in selective laser melting process. Various scanning strategies and their effects on mechanical properties, microstructures, and residual stresses of selective laser melted parts are summarized. Finally, some suggestions on the optimization of scanning strategy for better performance are provided based on the above analysis.

Graphene in its pristine form is one of the strongest materials tested, but defects influence its strength. Using atomistic calculations, we find that, counter to standard reasoning, graphene sheets with large-angle tilt boundaries that have a high density of defects are as strong as the pristine material and, unexpectedly, are much stronger than those with low-angle boundaries having fewer defects. We show that this trend is not explained by continuum fracture models but can be understood by considering the critical bonds in the strained seven-membered carbon rings that lead to failure; the large-angle boundaries are stronger because they are able to better accommodate these strained rings. Our results provide guidelines for designing growth methods to obtain sheets with strengths close to that of pristine graphene.

Crystal deformation to scale There are two main mechanisms at play when a crystal undergoes deformation: ordinary dislocation plasticity and deformation twinning. While the former is known to be dependent on the size of the crystal, hence influencing sample strength at the nanoscale, the latter's size dependence has not been explored to date. Ju Li and colleagues show, using microcompression and nanoindentation experiments, that deformation twinning is completely suppressed in crystals smaller than a micrometre in size, giving way to ordinary dislocation plasticity as the only deformation mode. This may be because deformation twinning is a collective phenomenon that cannot operate for small crystal sizes. The discovery paves the way for new approaches to manipulating the mechanical properties of materials at the microscale. Although deformation twinning in crystals controls the mechanical behaviour of many materials, its size-dependence has not been explored. Using micro-compression and in situ nano-compression experiments, the stress required for deformation twinning is now found to increase drastically with decreasing sample size of a titanium alloy single crystal, until the sample size is reduced to one micrometre; below this point, deformation twinning is replaced by dislocation plasticity. Deformation twinning 1 , 2 , 3 , 4 , 5 , 6 in crystals is a highly coherent inelastic shearing process that controls the mechanical behaviour of many materials, but its origin and spatio-temporal features are shrouded in mystery. Using micro-compression and in situ nano-compression experiments, here we find that the stress required for deformation twinning increases drastically with decreasing sample size of a titanium alloy single crystal 7 , 8 , until the sample size is reduced to one micrometre, below which the deformation twinning is entirely replaced by less correlated, ordinary dislocation plasticity. Accompanying the transition in deformation mechanism, the maximum flow stress of the submicrometre-sized pillars was observed to saturate at a value close to titanium’s ideal strength 9 , 10 . We develop a ‘stimulated slip’ model to explain the strong size dependence of deformation twinning. The sample size in transition is relatively large and easily accessible in experiments, making our understanding of size dependence 11 , 12 , 13 , 14 , 15 , 16 , 17 relevant for applications.

The hardness, toughness and chemical stability of the well-known superhard material cubic boron nitride have been improved by using a synthesis technique based on specially prepared ‘onion-like’ precursor materials. How to make superhard materials ultrahard Superhard polycrystalline cubic boron nitride, second only to diamond in hardness, is superior to diamond in terms of thermal and chemical stability and is used widely as an abrasive. The hardness of many materials can be improved by decreasing the grain size, and here Yongjun Tian and colleagues use this principle in a new synthesis technique — based on specially prepared 'onion-like' precursor materials — capable of increasing the hardness of cubic boron nitride. The structure of the resulting polycrystalline material is dominated by nanometre-scale twin domains, yielding a solid combining ultrahigh hardness (exceeding that of a synthetic diamond single crystal) with a high oxidization temperature and extreme fracture toughness. If nanotwins at similar scales can be reproduced in polycrystalline diamond, it may be possible to raise diamond itself to new levels of hardness and stability. Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall–Petch effect—the tendency for hardness to increase with decreasing grain size 1 , 2 . Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers 3 . Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1 , 2 , 4 , 5 ). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m 1/2 , well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m 1/2 ). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall–Petch effect below a critical grain size or the twin thickness of ∼10–15 nm found in metals and alloys.

Conductive and self-healing hydrogels are among the emerging materials that mimic the human skin and are important due to their probable prospects in soft robots and wearable electronics. However, the mechanical properties of the hydrogel matrix limit their applications. In this study, we developed a physicochemically dual cross-linked chemically modified-cellulose nanofibers-carbon nanotubes/polyacrylic acid (TOCNF-CNTs/PAA) hydrogel. The TOCNFs acted both as a nanofiller and dispersant to increase the mechanical strength of the PAA matrix and break the agglomerates of the CNTs. The final self-healing and conductive TOCNF-CNTs/PAA-0.7 (mass ratio of CNTs to AA) hydrogel with a uniform texture exhibited highly intrinsic stretchability (breaking elongation to ca. 850%), enhanced tensile properties (ca. 59 kPa), ideal conductivity (ca. 2.88 S m− 1) and pressure sensitivity. Besides, the composite hydrogels achieved up to approximately 98.36% and 99.99% self-healing efficiency for mechanical and electrical properties, respectively, without any external stimuli. Therefore, the as-designed multi-functional self-healing hydrogels, combined with stretching, sensitivity, and repeatability, possess the ability to monitor human activity and develop multifunctional, advanced, and commercial products such as wearable strain sensors, health monitors, and smart robots.Graphic abstract

SignificanceArtificial synthesis of spider silk has been actively pursued. However, until now, the natural mechanical properties of spider silk have been largely unreproducible. We thoroughly investigated the genomes and transcripts of four related species of orb-weaver spiders as well as the proteins in their silk threads. Then, in addition to spidroin, we found several low-molecular-weight proteins in common. Interestingly, the low-molecular-weight protein component of spider dragline silk doubled the tensile strength of artificial silk–based material. This discovery will greatly advance the industry and research on the use of protein-based materials. Dragline silk of golden orb-weaver spiders (Nephilinae) is noted for its unsurpassed toughness, combining extraordinary extensibility and tensile strength, suggesting industrial application as a sustainable biopolymer material. To pinpoint the molecular composition of dragline silk and the roles of its constituents in achieving its mechanical properties, we report a multiomics approach, combining high-quality genome sequencing and assembly, silk gland transcriptomics, and dragline silk proteomics of four Nephilinae spiders. We observed the consistent presence of the MaSp3B spidroin unique to this subfamily as well as several nonspidroin SpiCE proteins. Artificial synthesis and the combination of these components in vitro showed that the multicomponent nature of dragline silk, including MaSp3B and SpiCE, along with MaSp1 and MaSp2, is essential to realize the mechanical properties of spider dragline silk.

This review article summarizes the last few decades of research on nickel hydroxide, an important material in physics and chemistry, that has many applications in engineering including, significantly, batteries. First, the structures of the two known polymorphs, denoted as α-Ni(OH)2 and β-Ni(OH)2, are described. The various types of disorder,which are frequently present in nickel hydroxide materials, are discussed including hydration, stacking fault disorder, mechanical stresses and the incorporation of ionic impurities. Several related materials are discussed, including intercalated α-derivatives and basic nickel salts. Next, a number of methods to prepare, or synthesize, nickel hydroxides are summarized, including chemical precipitation, electrochemical precipitation, sol - gel synthesis, chemical ageing, hydrothermal and solvothermal synthesis, electrochemical oxidation, microwaveassisted synthesis, and sonochemical methods. Finally, the known physical properties of the nickel hydroxides are reviewed, including their magnetic, vibrational, optical, electrical and mechanical properties. The last section in this paper is intended to serve as a summary of both the potentially useful properties of these materials and the methods for the identification and characterization of 'unknown' nickel hydroxide-based samples.

Highlights An ultrathin and flexible carbon nanotubes/MXene/cellulose nanofibrils composite paper with gradient and sandwich structure was successfully fabricated via a facile alternating vacuum-assisted filtration process. The composite paper exhibits excellent mechanical property and electromagnetic interference shielding performance. As the rapid development of portable and wearable devices, different electromagnetic interference (EMI) shielding materials with high efficiency have been desired to eliminate the resulting radiation pollution. However, limited EMI shielding materials are successfully used in practical applications, due to the heavy thickness and absence of sufficient strength or flexibility. Herein, an ultrathin and flexible carbon nanotubes/MXene/cellulose nanofibrils composite paper with gradient and sandwich structure is constructed for EMI shielding application via a facile alternating vacuum-assisted filtration process. The composite paper exhibits outstanding mechanical properties with a tensile strength of 97.9 ± 5.0 MPa and a fracture strain of 4.6 ± 0.2%. Particularly, the paper shows a high electrical conductivity of 2506.6 S m −1 and EMI shielding effectiveness (EMI SE) of 38.4 dB due to the sandwich structure in improving EMI SE, and the gradient structure on regulating the contributions from reflection and absorption. This strategy is of great significance in fabricating ultrathin and flexible composite paper for highly efficient EMI shielding performance and in broadening the practical applications of MXene-based composite materials.