Study of the anti-penetration performance of concrete with different coarse aggregate content

Abstract Deep penetration experiments were performed on five types of concrete with different coarse aggregate content. The projectile diameter was 29.9 mm, the initial velocity was 647 m/s, and the volume fraction of the coarse aggregate was between 0% and 59.0%. The damage laws and damage mechanism of the target were analyzed. The pure mortar target had the smallest radial crack origin diameter and crater depth. Too high of the coarse aggregate content led to the formation of many voids, which led to the disappearance of radial cracks, crater surface bypassing the coarse aggregate and a large reduction of crater diameter. The influence laws and mechanism of the coarse aggregate on the penetration depth were also analyzed. The increase of volume fraction of coarse aggregate was beneficial to reducing penetration depth and the increase of voids volume fraction was opposite. The penetration depth was the lowest when the volume fraction of the coarse aggregate reached the maximum and no voids formed. By modifying the static resistance stress in the Forrestal penetration formula, a penetration depth model considering the volume fractions of the coarse aggregate and voids was established. The predicted results were in good agreement with the experimental results.</div

Study of cracks in concrete target under deep penetration by a projectile

Abstract A large number of cracks occur in concrete structure after projectile penetration. The study of crack distribution and propagation process is the basis of damage assessment, structural repair and high dynamic fracture mechanism. In this paper, wire saw cutting, X-ray computed tomography (X-CT) and mechanical property testing of damaged concrete were carried out on deep penetration targets. According to X-CT images of radial core samples in target and the mechanical properties of damaged concrete, the crack distribution in the target was divided into a plastic damage zone and a brittle damage zone, and the microcracks only existed in the plastic damage zone. The initial growth process of three-dimensional cracks was obtained by X-CT images of axial core samples in target, that is, the cracks in the pure mortar target gradually developed from the radial direction to the tangential direction, and the target containing coarse aggregate directly formed tangential cracks. The propagation progress of cracks was obtained through the target section, that is, the tangential cracks bent in the pure mortar target, and were relatively straight in the target containing coarse aggregate. A crack propagation model was established, and the tangential crack formula and the crack propagation velocity were obtained.</div

Uncovering the Structure of Lignin from Moso Bamboo with Different Tissues and Growing Ages for Efficient Ambient-Pressure Lignin Depolymerization

Lignin is a complex and heterogeneous biomacromolecule, exhibiting significant variations in its structure based on plant species, growth stages, and tissue types. Uncovering the structure of lignin is crucial for guiding the chemical processing of bamboo and developing an efficient production of monophenols. Herein, the double enzymatic lignin (DEL) was isolated from bamboo with different tissues (parenchyma cells and fiber) and growing ages (1, 5, and 8 years), and the structural heterogeneity of this DEL was characterized. A hydrogen-free green ambient-pressure reductive catalytic depolymerization (ARCD) reaction of DEL aids in understanding the relationships between the molecular composition and the depolymerization performance of the lignin. The results revealed that the predominant interunit linkage of lignin in bamboo is β–O–4 linkages, particularly in parenchyma, with distinct distributions of typical lignin units such as tricin, ferulate (FA), and p-coumarate (pCA) between parenchyma and fibers. The macromolecular structure of lignin had a significant influence on the yield and selectivity for the production of monophenols, with higher yields observed for parenchyma cells. These findings highlight the potential of lignin depolymerization in 5-year-old moso bamboo parenchymal cells, rich in β–O–4 linkages, as a promising feedstock in lignin-first biorefineries. This work provides a valuable example of the selection of high-aryl-ether lignin feedstock for efficient lignin depolymerization and mass production of phenolic compounds

Mechanical and Viscoelastic Properties of Polymer-Grafted Nanorod Composites from Molecular Dynamics Simulation

An understanding of the structure–property relationship in polymer/nanorod (NR) nanocomposites is of fundamental importance in designing and fabricating polymer nanocomposites (PNCs) with desired properties. Here, we study the structural, mechanical, and viscoelastic properties of polymer-grafted NR filled PNCs, using coarse-grained molecular dynamics simulation. The mechanical reinforcement efficiency is found to be determined by the NR/polymer interfacial properties, which are in turn modulated by the grafting density, the grafted chain length, and the graft–matrix interaction strength. By systematically analyzing the evolution of the polymer-grafted NRs during mechanical deformation, we find that the NRs aligning side by side with each other do not contribute much to the mechanical reinforcement. Simulation results also indicate that the strain-dependent viscoelastic behavior (the Payne effect) originates from the failure of the local filler network and, especially, NR clusters constructed via site-to-site contacts. PNCs with low grafting density and short grafted chains are found to form NR aggregates, mostly through the site-to-site contact state, which leads to a more pronounced Payne effect as reflected in the slope of the storage modulus versus shear amplitude. Furthermore, for stronger graft–matrix interactions, the NRs dispersed in the polymer matrix act as the temporary cross-linking points for a polymer shell layer-bridged NR network, accounting for the significant improvement in the mechanical property and the large increase in the Payne effect at high graft–matrix interaction strengths. In general, higher grafting density, longer grafted chains, and moderate graft–matrix interactions can effectively minimize the nonlinear viscoelastic behavior of PNCs

Biomass-Derived Fe₂N@NCNTs from Bioaccumulation as an Efficient Electrocatalyst for Oxygen Reduction and Zn–Air Battery

Metal compounds encapsulated in carbon materials exhibit promising properties as potential oxygen electrocatalysts. Herein, we first report Fe2N@C derived from the biomass bioaccumulation doping method, which offers a new perspective for exploring oxygen reduction reaction (ORR) electrocatalysts with low cost and high performance. The Fe2N@NCNTs prepared with our biodoping method display excellent ORR activity with a low half-wave potential (E1/2) and long-term stability in a broad pH range. More importantly, a zinc–air battery (ZAB) constructed with Fe2N@NCNTs’ catalysts exhibits a high open-circuit voltage (1.53 V), high peak power density (135 mW cm–2), and excellent stability (over 200 h). The significantly improved ORR performance can be attributed to the high N-doping level and its hierarchically porous structure. This work offers a path for the development of ORR catalysts for environmental governance and efficient energy conversion

Engineered and Durable Antimicrobial Polymer via Controllable Immobilization of Ionic Liquids onto the Poly(lactic acid) Chains

Nowadays, the development of effective modification methods for PLA has gained significant interest because of the wide application of antimicrobial PLA materials in the medical progress. Herein, the ionic liquid (IL) 1-vinyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide, has been grafted onto the PLA chains successfully in the PLA/IL blending films via electron beam (EB) radiation for the miscibility between PLA and IL. It was found that the existence of IL in the PLA matrix can significantly improve the chemical stability under EB radiation. The Mn of PLA-g-IL copolymer did not change obviously but was just decreased from 6.80 × 104 g/mol to 5.20 × 104 g/mol after radiation with 10 kGy. The obtained PLA-g-IL copolymers showed excellent filament forming property during electrospinning process. The spindle structure on the nanofibers can be completely eliminated after feeding only 0.5 wt % ILs for the improvement of ionic conductivity. Specially, the prepared PLA-g-IL nonwovens exhibited outstanding and durable antimicrobial activity for the enrichment of immobilized ILs on the nanofiber surface. This work provides a feasible strategy to realize the modification of functional ILs onto PLA chains with low EB radiation doses, which may have huge potential application in the medical and packaging industry

Monolayer NbSe₂ Favors Ultralow Friction and Super Wear Resistance

The urgent demand for atomically thin, superlubricating, and super wear-resistant materials in micro/nanoelectromechanical systems has stimulated the research of friction-reducing and antiwear materials. However, the fabrication of subnanometer-thick films with superlubricating and super wear-resistant properties under ambient conditions remains a huge challenge. Herein, high-quality monolayer (ML) NbSe2 (∼0.8 nm) with ultralow friction and super wear resistance in an atmospheric environment was successfully grown by chemical vapor deposition (CVD) for the first time. Moreover, compared with few-layered (FL) NbSe2, ML NbSe2 has a lower friction coefficient and better wear resistance. On the basis of density function theory (DFT) calculations, the adhesion and the degree of charge transfer between ML NbSe2 and the substrate is larger than that of the topmost layer to the underlying layers of NbSe2 with two or more layers, which can be used to explain that the ML NbSe2 favors ultralow friction and super wear resistance