Fracture toughness of open-cell Kelvin foam

Brittle fracture behavior of a perfect open-cell Kelvin foam is considered. The foam is modeled as a spatial lattice consisting of brittle elastic struts rigidly connected to each other at the nodal points. The fracture toughness is determined from the analysis of a quasi-plane problem for a slice of the foam with an embedded finite length crack generated by broken struts. The crack plane is chosen on the basis of a previous study of crack nucleation phenomenon, and the crack length, which assures the self-similar K-field in the tip vicinity, is established by numerical experiments. For the considered densities range the crack includes several hundreds of broken struts and, consequently, the portion of the foam to be considered in the analysis has a very large number of nodal degrees of freedom. The computational cost is reduced significantly by using for the analysis the representative cell method based on the discrete Fourier transform. As a result, the initial problem for the foam slice is reduced to the problem for the repetitive cell which includes 12 struts.     

A Novel Strategy for Achieving High Melt Strength Polypropylene and an Investigation of Its Foamability

A novel and feasible strategy for preparing high melt strength polypropylene (HMSPP) was developed by a melt grafting reaction in the presence of macro-monomer vinyl polydimethylsiloxane (VS), co-monomer styrene (St), and initiator benzoyl peroxide through a one-step reactive extrusion. The rheological behaviors, melt strength, and foaming ability of HMSPP were studied. The results showed that VS and St were successfully grafted onto polypropylene (PP), and the weight average molecular weight, molecular weight distribution, and melt strength of HMSPP were dramatically increased compared with those of the virgin isotactic polypropylene (iPP). Especially, the melt strength of HMSPP increased from 0.022 N for the virgin iPP to 0.29 N, which made the foamability of HMSPP significantly improved when supercritical carbon dioxide was used as the blowing agent. The foaming condition was optimized to 160°C and 14 MPa, for which HMSPP foams with a high expansion ratio of 66 times and a high cell density of about 5.8×10⁷ cell/cm³ were obtained, while the virgin iPP did not yield foams with good cell structure. Moreover, the resultant HMSPP could be foamed in a remarkably wide temperature range from 145°C to 165°C, which would be of great significance for industrial application.     

PMP/Cu泡沫材料中Cu颗粒的三维分布

为观测和分析铜掺杂聚-4-甲基-1-戊烯(PMP/Cu)低密度泡沫材料中铜颗粒的三维空间分布,采用高分辨X射线断层扫描技术,扫描PMP/Cu泡沫材料样品,对铜颗粒在聚合物泡沫中的分布进行了成像分析。经过图像处理和三维重构,获得铜颗粒在PMP聚合物泡沫中的三维立体分布图。结果分析显示:铜纳米粒子在PMP泡沫中存在团聚现象;不同尺寸的团聚物形态呈现出明显的多样化特征,小颗粒团聚物趋于球形,大颗粒团聚物趋于不规则的短木棒状,与在电子显微镜下直接观测到的结果一致。研究表明,该技术可以在不破坏样品的前提下,实现对有机聚合物泡沫材料中掺杂金属颗粒空间分布情况的直接观测。     

无人机自组网中改进型反应-贪婪-反应路由协议

无人机自组网具有网络拓扑变化剧烈,链路断开频繁等特点.反应-贪婪-反应(reactive-greedy-reac-tive,RGR)路由协议是针对无人机自组网而提出的改进型协议,在高动态环境下具有较好的网络性能.针对RGR协议具有网络开销大、易出现网络拥塞等问题,提出了一种基于负载均衡和高贪婪地理转发成功概率的改进RGR路由协议.该协议在RGR协议的基础上,提出基于节点负载状态和地理位置信息辅助的受限洪泛机制、GGF模式下高分组成功传输概率的路径选择策略和基于节点负载预测和运动特征的分组转发策略3项关键改进措施.仿真结果表明,相较于AODV和RGR及其改进型协议,该协议提高了分组投递率,降低了网络的控制开销和平均端到端时延,提升了网络应对拓扑高度动态变化的能力,有效改善了网络性能.     

深海浊积砂岩油田高效注水策略及实践

以尼日尔三角洲盆地典型的深海浊积砂岩油田AKPO为研究目标,剖析了浊积水道和朵叶的储层特征,以注采井组间砂体连通方式为基础,结合生产动态特征评价了注采井组间的连通性,确定油田在无水采油期的注水策略。基于时移地震揭示了不同储层类型的水驱波及特征,形成了油田注水突破后的注水以及控堵水策略,建立了适宜油田不同开发阶段的高效注水策略。在无水采油期阶段,基于注采井组间砂体的连通方式应用以“控制压力”为重点的注水强度优化策略,实现不同井组的分级配产配注;在中低含水阶段,基于储层沉积类型应用以“提高波及”为重点的注水强度优化方法,即依靠水动力学方法来改善水驱波及系数,水道储层注采井组采用周期注水提高“纵向”波及系数;朵叶储层注采井组采用改变液流方向提高“平面”波及系数;在高含水阶段,应用适宜深海油田的“低成本”分段控堵水方法,实现深海油田经济有效的控堵水。上述深海浊积砂岩油田高效注水策略经AKPO油田实践,实现AKPO油田高峰采油速度达到5.5%,连续7 a实现稳产,预测油田采收率达到53%。系统形成深海浊积砂岩油田在不同开发阶段的高效注水策略,该策略简单易行、经济有效,可以指导同类深海油田的注水优化。     

Study of the effect of chemical composition on the surface wettability of three-dimensional graphene foams

The chemical composition obviously affects the surface wettability of a three-dimensional (3D) graphene material apart from its surface energy and microstructure. In the hydrothermal preparation, the heteroatom doping changes the chemical composition and wettability of the 3D graphene material. To realize the controllable surface wettability of graphene materials, aminobenzene sulfonic acid (ABSA) was selected as a typical doping agent for the preparation of nitrogen and sulfur co-doped 3D graphene foam (SNGF) using a hydrothermal method. Different from using o-ABSA or p-ABSA as the dopant, SNGF with tunable surface wettability is obtained only when m-ABSA is used. This result indicates that the substituent position of -SO₃H group in the benzene ring of ABSA is rather important for the tunable wettability. This work provides some theoretical foundations for dopant selection and some new insights in manipulating the properties of 3D graphene foams by adjusting the configuration of dopants.     

Enhancement of PUR/PIR foam thermal stability after addition of Zostera marina biomass component investigated via thermal analysis and isoconversional kinetics

In the present work, a thorough thermogravimetric (TG) analysis of bio-based polyurethane–polyisocyanurate (PUR–PIR) foams in both nitrogen and oxygen atmosphere is performed. A sustainable element of the foam is a biopolyol obtained via acid-catalyzed liquefaction of Zostera marina and Enteromorpha Algae biomass. Based on isoconversional analysis and apparent activation energies, several conclusions are obtained. In contradiction to the common understanding, biopolyol based foams exhibit enhanced stability in both oxidative atmosphere and in nitrogen compared to purely petrochemical foams. Relationships between thermal stability and structure of the foams are established. Enhanced stability of bio-based foams in oxygen is attributed to two factors. First is an increased cross-linking density due to higher hydroxyl number of biopolyol compared to petrochemical one. Possibly the presence of more amount of aromatic compounds in the structure of polyols that come from lignin or aromatic ketones contribute to further enhancement of thermal stability. Those results suggest that the studied biobased foams are prospective alternatives to standard petrochemical PUR foams.     

Study of anodizing process on aluminium foam to improve the corrosion behavior

Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm² for 60 seconds and 0.01 A/cm² for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H₂SO₄ at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy.     

泡沫铝吸声系数的量纲分析

量纲分析是定性与半定量分析物理问题的重要方法之一，通过对影响泡沫铝吸声性能的结构参数的分析，利用瑞利分析法对泡沫金属的吸音性能进行了研究，尝试提供一种测量和计算相结合的新方法来预测泡沫金属的吸声性能．     

浅谈低倍数泡沫灭火系统设计、施工、验收应注意的几个问题

本文针对低倍数泡沫灭火系统在建筑工程项目设计、施工、验收中容易疏忽的问题,浅谈了自己的见解。