Gradient Structure Research Articles

Species-Specific Spillover Patterns Detected by Biomass Gradients in Mediterranean Marine Protected Areas

The aim of this paper is to provide evidence of the species-specific export of adult fishes for some species or group of species from six well-enforced Mediterranean marine protected areas (MPAs): Cerbère-Banyuls and Carry-le-Rouet in France and Medes, Cabrera, Tabarca, and Cabo de Palos in Spain. We estimated the distance at which spillover of those individual or groups of species occur by directly assessing the existence of gradients of biomass across the MPA boundaries by means of underwater visual census, asuming that such gradients will be specifics in terms of structure (sharpness, slope, and intercept) for every species and group of species. A significant “reserve effect” was observed for biomass of some of the individual and grouped species in all MPAs. Decreasing gradients of biomass differ among taxons and are not related with the insular nature of the location. Different gradients of biomass resulted from the interaction between species characteristics and some ecological and structural drivers, and we did not find regular patterns for each taxa among MPAs, even though the same species can exhibit different gradient structure and/or spillover distances in the same MPA depending on the orientation. Habitat patch distribution and continuity seems the most important environmental factor explaining the existence and pattern of gradients at species level, interacting with fish home range and fishing pressure close to the limits of the MPAs. Managers should take in account the surrounding distribution of habitats in terms of complexity and quality in order to optimize the spillover capacity of the MPAs.

Progress in the study of dry shrinkage deformation and drying stress of raw bamboo

Bamboo is a sustainable material that supports carbon sequestration and helps address the imbalance of timber supply vs. demand. Drying is a crucial step in bamboo processing, in the course of which shrinkage and stress accumulation can lead to defects such as cracking and deformation. Understanding stress and strain development during drying is critical for improving bamboo processing. This review paper explores bamboo’s gradient structure and moisture migration characteristics, focusing on the mechanisms behind shrinkage strain formation and the sources of stress. It reviews literature on bamboo drying and cellular structural changes, evaluating the evolution of stress and strain testing methods, from traditional sectioning techniques to advanced methods such as digital imaging and acoustic emission. The paper also summarizes progress in stress-strain research at both macroscopic and cellular scales. Current challenges include species-specific shrinkage variations, limitations in measurement techniques, and insufficient research on shrinkage above the fiber saturation point. To address these issues, the study recommends developing universal theoretical models, employing advanced detection technologies, comparing shrinkage patterns between bamboo culms and nodes, exploring drying stress composition, and adopting multi-scale research approaches. These strategies aim to enhance the quality of bamboo processing and promote higher-value applications within the industry.

Intelligent design of spacecraft functionally gradient structures for thermal-mechanical performance regulation

Intelligent design of spacecraft functionally gradient structures for thermal-mechanical performance regulation

Damage characterization of carbonated cement pastes with a gradient structure

Damage characterization of carbonated cement pastes with a gradient structure

Structural design and enhanced energy density of Ba0.6Sr0.4TiO3/PVDF nanocomposites with multilayer gradient structure

With the development of science and technology, the application of electronic products is extensive, and it is developing in the direction of miniaturization, integration, and high performance. However, the development of electronic products is limited due to capacitors low energy storage density. This study selects inorganic nanoparticles with high dielectric constant as fillers and polyvinylidene fluoride as the matrix of composite materials. It adopts a layer-by-layer casting method to prepare multilayer Ba0.6Sr0.4TiO3/PVDF composites. It is found that the dielectric and energy storage performances of the multilayer composites doped with Ba0.6Sr0.4TiO3 are improved compared with the pure PVDF polymer films after the electrical properties test. A multi-layer composite material with a gradient distribution of fillers was designed and prepared to improve the energy storage density. The energy storage density of multilayer composites with a favorable gradient structure can reach up to 9.3 J/cm3 at 300 kV/mm. By analyzing the improved storage density mechanism, the results show that the design of the multilayer gradient structure can significantly reduce the electric field's local concentration, inhibit the formation of conductive paths, and significantly improve the composites' energy storage density.

Improving the strength-ductility synergy in medium manganese steel via gradient structure fabricated by friction stir processing

Improving the strength-ductility synergy in medium manganese steel via gradient structure fabricated by friction stir processing

Enhanced wind energy harvesting through omnidirectional airflow metamaterial concentrators

Wind energy generation is constrained by low density and intermittency. To address these challenges, this study proposes an omnidirectional airflow metamaterial concentrator lens that utilizes a novel complex gradient structure inspired by metamaterial principles. The study's framework includes the design, simulation, and performance evaluation of the concentration lens under varying wind conditions. The lens amplifies the local flow energy density by up to 360% compared to the impinging influx. Numerical simulation analysis elucidates the underlying operational mechanism, demonstrating a significant reduction in the startup wind speed and increased energy capture efficiency. Results indicate that concentrator lens can enhance wind energy exploitation by improving the efficiency of energy capture and providing a viable solution to mitigate the limitations of current wind energy technologies.

Influence of expansion ratio and multilayered gradient structure on the electromagnetic interference shielding performance of lightweight poly (lactic acid)/carbon nanostructures composite foams

Influence of expansion ratio and multilayered gradient structure on the electromagnetic interference shielding performance of lightweight poly (lactic acid)/carbon nanostructures composite foams

Formation of a functionally gradient structure of the surface layer in medium-carbon steels by plasma hardening

Formation of a functionally gradient structure of the surface layer in medium-carbon steels by plasma hardening

Facile fabrication of curved furniture by bamboo restructuring plasticizing for green furniture manufacturing

Eco-friendly bamboo curved components (BCCs) hold significant potential for use in furniture. However, the indiscriminate use of functionally graded bamboo and the cumbersome molding process severely limited the efficient production of the BCCs. Here, multi-layer BCCs were facilely fabricated using graded bamboo strips through integrated bamboo restructuring plasticizing technology. The properties of bamboo strips, curved bamboo strips (CBSs), and BCCs were systematically investigated to establish relationships among raw material attributes, product unit characteristics, and final product performance. The bamboo strips with vascular bundle gradient structure exhibited asymmetric bending behaviors under applied forces. Applying bending force to the side of bamboo strips with a low fiber volume fraction could result in a higher bending pass rate and bending stability. The intrinsically high toughness of bamboo strips was the performance basis to enable CBSs and BCCs to acquire a high yield. The 4-mm-thick bamboo strips with a high proportion of parenchyma tissues exhibited higher ductility and stress relaxation rates, thereby improving their bending stability. Multi-layer gluing reconstruction enabled large-thickness BCCs to possess higher bending stability than CBSs, with a bending recovery rate of 6–9 % under less harsh molding conditions. The bending and bonding strengths of the 12-mm-thick BCCs, which were fabricated from 2-mm-thick bamboo strips, were 96.31 MPa and 3.77 MPa, respectively. These values were much higher than the standard requirements for general-use plywood. The results provide the scientific basis for manufacturing bamboo curved furniture and pushing for green manufacturing in the furniture field.

Solvent-assisted thermogalvanic cell for enhanced low-grade heat harvesting over an extended temperature range

In the pursuit of sustainable energy harvesting from low-grade heat, thermogalvanic cells (TGCs) have received considerable attention, but still confront profound challenges in efficiency and cost-effectiveness, limiting their real-world applications. To expedite the deployment of TGCs, this study delves into the mechanistic interplay of three crucial determinants: intrinsic temperature coefficient, concentration gradient, and activity coefficient of redox couples, elucidating their impact on TGCs' thermoelectric performance. We report a solvent-assisted liquid-state thermogalvanic cell (SA-LTC) by incorporating organic solvents into the sodium ferrocyanide-based TGCs system. With ethanol as a regulator to the concentration gradient and solvation structure, the temperature coefficient of [Fe(CN)6]3-/4- can be enhanced from − 1.39 to − 4.32 mV K−1, leading to a five-fold increase in thermoelectric power and efficiency. Meanwhile, ethanol imparts a lower freezing point and wider working temperature range to the system, showing its better environmental adaptability. In particular, SA-LTC performs better at lower temperatures, at which it achieved a record-high temperature coefficient of − 5.26 mV K−1 and a power density of 2.17 mW m−2 K−2 at 10–20 °C. This study not only provides useful guidance to the optimization of electrolyte design, but also highlights the potential of TGCs for sustainable energy conversion in varied thermal conditions for practical applications.

Rapid curing dynamics of PEG-thiol-ene resins allow facile 3D bioprinting and in-air cell-laden microgel fabrication

Thiol-norbornene photoclick hydrogels are highly efficient in tissue engineering applications due to their fast gelation, cytocompatibility, and tunability. In this work, we utilized the advantageous features of polyethylene glycol (PEG)-thiol-ene resins to enable fabrication of complex and heterogeneous tissue scaffolds using 3D bioprinting and in-air drop encapsulation techniques. We demonstrated that photoclickable PEG-thiol-ene resins could be tuned by varying the ratio of PEG-dithiol to PEG norbornene to generate a wide range of mechanical stiffness (0.5-12 kPa) and swelling ratios. Importantly, all formulations maintained a constant, rapid gelation time (<0.5 s). We used this resin in biological projection microstereolithography (BioPµSL) to print complex structures with geometric fidelity and demonstrated biocompatibility by printing cell-laden microgrids. Moreover, the rapid gelling kinetics of this resin permitted high-throughput fabrication of tunable, cell-laden microgels in air using a biological in-air drop encapsulation apparatus (BioIDEA). We demonstrated that these microgels could support cell viability and be assembled into a gradient structure. This PEG-thiol-ene resin, along with BioPµSL and BioIDEA technology, will allow rapid fabrication of complex and heterogeneous tissues that mimic native tissues with cellular and mechanical gradients. The engineered tissue scaffolds with a controlled microscale porosity could be utilized in applications including gradient tissue engineering, biosensing, andin vitrotissue models.

Gradient 2D re-entrant cores for sandwich structures under low-velocity impact

Auxetic metamaterials, known for their unusual properties, are being explored as cores for sandwich structures to improve impact resistance. This study investigated the low-velocity impact response of sandwich panels with various core designs using finite element method (FEM) and experiments on 3D-printed specimens. These cores include pure honeycomb, pure auxetic, and gradient variations with controlled gradients of Poisson’s ratio, transitioning from negative to positive (NTP), positive to negative (PTN), negative-to-positive-to-negative (NTPTN), and positive-to-negative-to-positive (PTNTP). These gradients were achieved by adjusting the unit cell angle within the core. Under quasi-static indentation, the gradient PTN design improved energy absorption by 26% compared to the honeycomb structure, while the gradient NTP structure showed a 9% improvement over the auxetic core. As for the impact tests, the gradient NTP and PTN structures significantly enhanced the indentation resistance of auxetic and honeycomb structures by 21.3% and 6.5%, respectively. Interestingly, while the optimal core for peak energy absorption varied with impact velocity, gradient structures generally provided superior energy absorption, particularly at lower velocities. FEM results at initial impact velocities of 10, 15, 20 m/s confirmed that structures having negative Poisson’s ratio at their top layer exhibited the lowest penetration depth. Additionally, gradient structures, particularly NTP and NTPTN, demonstrated superior energy absorption capability compared to purely auxetic or honeycomb structures, especially at lower velocities. The study highlights the benefits of utilizing gradient auxetic metamaterial cores in high-performance sandwich structures for impact resistance applications. These structures showed minimal localized damage, reduced densification risk due to uniform crushing, and lower penetration depth.

Unveiling Unidirectional Transport within Janus Membranes

Janus membranes with unidirectional transport capacity have shown broad potential across various fields of mass–energy transmission and conversion. However, the underlying mechanisms driving this transport remain unclear. In this study, a three‐stage model—encompassing liquid intrusion, capillary wetting, and liquid transport—is proposed to elucidate the unidirectional liquid transport within Janus membranes. Finite element analysis reveals two key mechanisms: direct contact‐driven liquid intrusion in bilayer structures and surface‐energy‐driven intrusion in gradient structures. It is also demonstrated that capillary forces within the hydrophilic pores predominantly control the second stage, while droplet Laplace pressure dictates continuous liquid transport at the last stage. Furthermore, critical structural parameters that influence the transport process are identified, aligning with experimental observations. These findings lay a theoretical foundation for optimizing the Janus membrane structures and expanding their applications.

Analyzing heat transfer performance of ARCH lattice microchannel heat exchanger fabricated using selective laser melting

Lattice structures are emerging as highly effective heat exchange mediums in exchangers and radiators due to their low weight, high specific stiffness and strength, and extensive surface area. These attributes render them particularly suitable for enhancing heat transfer efficiency while maintaining a lightweight and structurally sound design. Certain applications, such as hot stamping, demand both high heat transfer performance and significant load-bearing capacity. Arch micro-strut (ARCH) lattice is a kind of high load-bearing lattice. Currently, there is a gap in the research on its heat transfer performance. This study provides a comprehensive analysis of the heat transfer and mechanical performance of additively manufactured ARCH lattice structures. Deionized water (DI water) was selected as the working fluid in this study. The analysis spans various relative densities, inlet velocities, array orientations, and gradient configurations, employing both experimental and simulation approaches. The results of this study reveal that as relative density increases, the pressure drop gradually rises, while the convective heat transfer coefficient increases before stabilizing. The pressure drop reaches a maximum of 348 kPa at 4 m/s, 40 % relative density, and the convective heat transfer coefficient reaches a maximum of 13,805 W/m2·k at 4 m/s, 20 % relative density. At a relative density of 20 %, the convective heat transfer coefficient reaches its maximum at the same inlet velocity. Specifically, at an inlet velocity of 4 m/s, the convective heat transfer coefficient for a 20 % relative density is 115 % higher than that at 0 %. The maximum Von Mises stress and deformation decrease progressively as relative density increases, from 980.72 MPa to 236.05 MPa, suggesting a substantial enhancement in the compressive properties of the structure. Additionally, a higher inlet velocity results in an enhanced convective heat transfer coefficient. The convective heat transfer coefficient increased by an average of 2300 W/m2·k when the flow rate increased from 1 m/s to 4 m/s. The anisotropic nature of ARCH lattice structure significantly affects mechanical properties and heat transfer efficiency, with the heat transfer coefficient being higher at the inlet along X-direction compared to Z-direction, and a lower pressure drop in X-direction. The gradient structure is shown to effectively address the non-uniform heat dissipation requirements of various components. Specifically, decreasing gradient (DG) configuration offers superior heat transfer performance under similar pressure drop conditions, while increasing gradient (IG) configuration provides better temperature uniformity. Overall, ARCH lattice structure demonstrates superior performance compared to face-centered cubic with vertical strut (FCCZ) structure, with an efficiency index approximately 200 % higher than that of FCCZ structure.

Simultaneously achieving strength-ductility in additive-manufactured Ti6Al4V alloy via ultrasonic surface rolling process

Additively manufactured alloys have a great potential in engineering field, but there still have many issues to be addressed, i.e., the reliability, strength-ductility trade-off of manufactured parts. In this study, a treatment called ultrasonic surface rolling process (USRP) was utilized to achieve superior strength and ductility in the Ti6Al4V alloy prepared via electron beam melting (EBM). The treated additive-manufactured alloy obtained various gradient microstructures and excellent surface quality, as well as its mechanical properties were significantly improved. Especially, the USRP-3 specimen exhibited a high elongation of 17.1 ± 0.9 % and a good ultimate tensile strength of 1043 ± 5.0 MPa, which were both higher than those of untreated specimen; the fine laminated structure with a preferred orientation of (101‾0) direction and gradient structure promoted the hardening capacity and provided the rich dislocations sources, taking a better strength-ductility combination. In addition, the surface microhardness of the multi-pass processed specimen was markedly enhanced. However, excessive USRP treatment would induce micro-cracks in the nano-composite layer, resulting in a significant reduction in ductility. Therefore, appropriate USRP treatment is expected to expand the application range of additive-manufactured metallic materials.

Study on the mechanical properties of layered gradient structure PBT-based flame retardant composite materials

Abstract To enhance the flame retardancy of Polybutylene Terephthalate (PBT) based composite materials and overcome the decrease in mechanical properties due to the high content of nano-antimony trioxide (nano-Sb2O3), this study initially applies a composite modification method to treat the surface of nano-Sb2O3. Subsequently, composite materials with a gradient distribution of nano-Sb2O3 are prepared through lamination hot-pressing technology, and their mechanical and flame retardant properties are investigated. The results show that the modifiers CTAB and KH560 are successfully grafted onto the surface of nano-Sb2O3, altering its surface properties. Through lamination hot-pressing technology, a gradient distribution from the surface to the core is achieved. Compared to the homogeneous distribution P666, G828 exhibits a 6% increase in Limiting Oxygen Index (LOI), improving the flame retardancy of the composite material. As nano-Sb2O3 enriches on the composite material's surface, the amount of char residue increases. The tensile strength, bending strength, and impact strength of G828 composite material increase by 19.7%, 37.1%, and 103%, respectively, compared to the homogeneous composite material P666, proving the significant effect of G828's gradient distribution in enhancing the mechanical properties of the composite material.&amp;#xD;

Gradient Titanium Alloy with Bioactive Hydroxyapatite Porous Structures for Potential Biomedical Applications.

Hard bone disease is a clinical problem affecting more than 20 million people annually worldwide, with significant health, social, and economic consequences. For successful integration of any implant, the key aspects are bone regeneration, osseointegration at the bone-implant interface, and the mitigation of inflammation. The purpose of this research work is to demonstrate an innovative material system and method of biomaterial preparation for regenerative medicine. A number of studies were carried out for both hydroxyapatite powder and composites. Wet-precipitated synthesized hydroxyapatite was compared to commercial products through accurate physicochemical studies that confirmed the high purity of the obtained calcium phosphate without any impurities. Ti/HAp composites before and after sintering were compared by XRF, XRD, SEM, EDS, PSA, and roughness measurements, and the Vickers microhardness was analyzed. The fabrication of the biomaterial was based on a bottom-up approach, which involved fabricating HAp particles with specific morphologies using powder metallurgy (PM) to sinter Ti composites. The resulting gradient structures consisting of two compositions (5%HAp%5CMC and 10%HAp10%CMC) mimic the structure of bone tissue. The created pores of 10-100 µm in size will allow bone cells to penetrate the implant and regenerate bone. In turn, the introduction of hydroxyapatite into the material reduces the microhardness of the composite and introduces properties such as bioactivity. The developed composite material contains a combination of Ti alloy and hydroxyapatite (HAp), creating an excellent biomaterial that promotes bone growth and eliminates the problem of implant loosening by integrating it into the bone. This material requires further research, especially biological research. However, it shows promising potential for further experiments.

Obtaining Symmetrical Gradient Structure in Copper Wire by Combined Processing

Traditionally, structural wire is characterized by a homogeneous microstructure, where the average grain size in different parts of the wire is uniform. According to the classical Hall–Petch relationship, a homogeneous polycrystalline metal can be strengthened by decreasing the average grain size since an increase in the volume fraction of grain boundaries will further impede the motion of dislocations. However, a decrease in the grain size inevitably leads to a decrease in the ductility and deformability of the material due to limited dislocation mobility. Putting a gradient microstructure into the wire has promising potential for overcoming the compromise between strength and ductility. This is proposed a new combined technology in this paper in order to obtain a gradient microstructure. This technology consists of deforming the wire in a rotating equal-channel step die and subsequent traditional drawing. Deformation of copper wire with a diameter of 6.5 mm to a diameter of 5.0 mm was carried out in three passes at room temperature. As a result of such processing, a gradient microstructure with a surface nanostructured layer (grain size ~400 nm) with a gradual increase in grain size towards the center of the wire was obtained. As a result, the microhardness in the surface zone was 1150 MPa, 770 Mpa in the neutral zone, and 685 MPa in the central zone of the wire. Such a symmetrical spread of microhardness, observed over the entire cross-section of the rod, is a direct confirmation of the presence of a gradient microstructure in deformed materials. The strength characteristics of the wire were doubled: the tensile strength increased from 335 MPa to 675 MPa, and the yield strength from 230 MPa to 445 MPa. At the same time, the relative elongation decreased from 20% to 16%, and the relative contraction from 28% to 23%. Despite the fact that the ductility of copper is decreased after cyclic deformation, its values remain at a fairly high level. The validity of all results is confirmed by numerous experiments using a complex of traditional and modern research methods, which include optical, scanning, and transmission microscopy; determination of mechanical properties under tension; and measurement of hardness and electrical resistance. These methods allow reliable interpretation of the fine microstructure of the wire and provide information on its strength, plastic, and electrical properties.

Achieving stable lithium metal anode via constructing lithiophilicity gradient and regulating Li3N-rich SEI

Three-dimensional (3D) current collectors are studied for the application of Li metal anodes in high-energy battery systems. However, they still suffer from the preferential accumulation of Li on the outermost surface, resulting from an inadequate regulation of the Li+ transport. Herein, we propose a deposition regulation strategy involving the creation of a 3D lithiophilicity gradient structure of MoN on Cu3N nanowire-grown Cu foam (MCNCF) to induce a “bottom-up” Li deposition. During the initial Li deposition, the reaction between Li and Cu3N leads to the formation of Li3N while the lithiophilic MoN located at the bottom promotes the downward Li+ migration, resulting in the generation of a Li3N gradient. Such a “bottom-up” Li3N distribution results in the formation of a stable and Li3N-rich solid electrolyte interphase layer, facilitating the Li⁺ transport and promoting a uniform Li nucleation. Computational simulations and experimental results corroborate the preferential deposition of Li on the bottom of the substrate, leading to a uniform Li nucleation and growth throughout the electrode. The MCNCF electrode offers a significantly improved reversibility of the Li deposition, achieving a lifespan of more than 1200 h at a current density of 1 mA cm−2 in symmetric Li||Li cells. Furthermore, full-cells incorporating MCNCF@Li as the negative electrode and LiFePO4 cathodes exhibit outstanding electrochemical performance with a capacity retention of over 99.5 % after 250 cycles at 1 C, which significantly surpasses the performance achieved with CF@Li or CCF@Li electrodes. This innovative design strategy for 3D metallic current collectors, featuring a lithiophilicity gradient, provides new perspectives for the development of stable Li metal anodes and, as a result, for the advancement of Li-metal batteries.