The Laser Selective Sintering Controlled Forming of Flexible TPMS Structures.

Sports equipment crafted from flexible mechanical metamaterials offers advantages due to its lightweight, comfort, and energy absorption, enhancing athletes' well-being and optimizing their competitive performance. The utilization of metamaterials in sports gear like insoles, protective equipment, and helmets has garnered increasing attention. In comparison to traditional truss and honeycomb metamaterials, the triply periodic minimal surface lattice structure stands out due to its parametric design capabilities, enabling controllable performance. Furthermore, the use of flexible materials empowers this structure to endure significant deformation while boasting a higher energy absorption capacity. Consequently, this study first introduces a parametric method based on the modeling equation of the triply periodic minimal surface structure and homogenization theory simulation. Experimental results demonstrate the efficacy of this method in designing triply periodic minimal surface lattice structures with a controllable and adjustable elastic modulus. Subsequently, the uniform flexible triply periodic minimal surface lattice structure is fabricated using laser selective sintering thermoplastic polyurethane technology. Compression tests and finite element simulations analyze the hyperelastic response characteristics, including the element type, deformation behavior, elastic modulus, and energy absorption performance, elucidating the stress-strain curve of the flexible lattice structure. Upon analyzing the compressive mechanical properties of the uniform flexible triply periodic minimal surface structure, it is evident that the structure's geometric shape and volume fraction predominantly influence its mechanical properties. Consequently, we delve into the advantages of gradient and hybrid lattice structure designs concerning their elasticity, energy absorption, and shock absorption.

3D Printing of Flexible Mechanical Metamaterials: Synergistic Design of Process and Geometric Parameters.

Mechanical metamaterials with ultralight and ultrastrong mechanical properties are extensively employed in various industrial sectors, with three-periodic minimal surface (TPMS) structures gaining significant research attention due to their symmetry, equation-driven characteristics, and exceptional mechanical properties. Compared to traditional lattice structures, TPMS structures exhibit superior mechanical performance. The mechanical properties of TPMS structures depend on the base material, structural porosity (volume fraction), and wall thickness. Hard rigid lattice structures such as Gyroid, diamond, and primitive exhibit outstanding performance in terms of elastic modulus, energy absorption, heat dissipation, and heat transfer. Flexible TPMS lattice structures, on the other hand, offer higher elasticity and recoverable large deformations, drawing attention for use in applications such as seat cushions and helmet impact-absorbing layers. Conventional fabrication methods often fail to guarantee the quality of TPMS structure samples, and additive manufacturing technology provides a new avenue. Selective laser sintering (SLS) has successfully been used to process various materials. However, due to the layer-by-layer manufacturing process, it cannot eliminate the anisotropy caused by interlayer bonding, which impacts the mechanical properties of 3D-printed parts. This paper introduces a process data-driven optimization design approach for TPMS structure geometry by adjusting volume fraction gradients to overcome the elastic anisotropy of 3D-printed isotropic lattice structures. Experimental validation and analysis are conducted using TPMS structures fabricated using TPU material via SLS. Furthermore, the advantages of volume fraction gradient-designed TPMS structures in functions such as energy absorption and heat dissipation are explored.

[Regionalization and Analysis of PM2.5 and O3 Synergetic Prevention and Control Areas Based on Remote Sensing Data].

Site-based air pollution monitoring data cannot support the regionalization of air pollution prevention and control areas. Faced with this problem, this study proposed a method of regionalizing synergetic prevention and control areas based on multi-source remote sensing data and GIS spatial statistical analysis methods and carried out quantitative analyses of PM2.5 and O3 air pollution in China from 2015 to 2020. The results showed that there was an obvious decrease in PM2.5 concentrations, and O3concentrations remained stable; PM2.5 pollution mostly occurred in autumn and winter, and O3 pollution occurred in spring and summer. A significant spatial inconsistency was shown between the change rate of PM2.5 and O3 concentrations, in which the proportions of PM2.5 decreasing and O3 increasing, PM2.5 and O3 both decreasing, PM2.5 and O3 both increasing, and PM2.5 increasing and O3 decreasing accounted for 38.34%, 35.12%, 15.24%, and 10.89%, respectively. The results also showed that the boundary of PM2.5 and O3 synergetic prevention and control areas was dynamic during 2015 and 2020, showing a trend of expanding from 2015 to 2018 and then becoming smaller after 2019. Generally, the scope of PM2.5 and O3 synergetic prevention and control areas was concentrated in "2+26" cities, Fenwei plain, north of the Yangtze River Delta, and Shandong. In contrast, the regional scopes of "PM2.5 first" and "O3 first" were relatively stable. Areas of "PM2.5 first" were mainly carried out in Liaoning-Jilin, Hubei-Hunan-Jiangxi, Chengdu-Chongqing, and Taklimakan-Hexi Corridor, whereas "O3 first" areas were mainly in specific regions of the Pearl River Delta, Yangtze River Delta, and surrounding areas of Bohai Bay. Remote sensing-based PM2.5 and O3 mapping has the advantages of full-coverage and fine spatial simulation, which can support the regionalization of synergetic prevention and control areas and implementation of policies.