Study on the Collapse of Pin-Reinforced Foam Sandwich Panel Cores

New fabrication technologies now allow for hybrid sandwich structures, known as X-core, to be manufactured. The X-core panels consist of a pin reinforced polymer foam core with carbon fiber face sheets. Carbon fiber or metallic (Titanium/Steel) pins are inserted into the foam core in the out-of-plane direction and extend from face sheet to face sheet. The through thickness three-point simply supported bending behavior of these panels is used to evaluate the collapse characteristics of the panels. Explicit experimental observations are used to calibrate analytical energy balance models describing the panel collapse as a function of geometry and properties. The mechanical response of X-core sandwich panels is compared to current sandwich materials for material selection.     

Fly ash particles and precipitated silica as fillers in NR/CR vulcanizates under thermal and thermal‐oil ageing

The loading effect of precipitated silica (PSi) and fly ash‐based silica (FASi) on mechanical properties of natural rubber/chloroprene (NR/CR) under thermal and thermal‐oil ageing was investigated with variation in NR content in the NR/CR blends. The selected results were compared with vulcanized NR/nitrile rubber (NR/NBR) blends. The cure time of CR vulcanizate was found to decrease with increasing NR content, but increased with silica fillers. The Mooney viscosity for CR vulcanizates reduced with increasing NR content. The addition of NR had no effect on tensile modulus and tensile strength for the FASi filled NR/CR, but the opposite trend was observed for the PSi filled NR/CR. The post‐curing effect was more significant in PSi filled NR/CR than in FASi filled NR/CR. The tensile strength of the NR/CR vulcanizates was slightly reduced after thermal ageing especially at high NR content, more extreme reduction being found by thermal‐oil ageing. The elongation at break of NR/CR with both silica fillers ranged from 400 to 900%. The hardness results were similar to the tensile modulus. The addition of PSi in NR/CR considerably increased the tear strength, but less pronounced effect was found for FASi. The resilience properties of NR/CR tended to decrease with increasing silica content. The compression set became poorer when NR content was increased. The PSi showed higher improvement in compression set than the FASi. The effects of silica and ageing on the mechanical properties for NR/CR vulcanizates were similar to those for NR/NBR vulcanizates. Copyright © 2009 John Wiley & Sons, Ltd.     

电磁脉冲对数字信号处理器的干扰及其防护

为寻找有效的电磁脉冲防护加固措施,首先对电磁脉冲模拟器的干扰路径进行分析,包括数字信号处理器（DSP）与放电回路的共地耦合干扰及共网电耦合干扰,并将结构优化设计、硬件屏蔽加固措施与设置软件陷阱、开启看门狗等抗干扰措施相结合,对数字信号处理器（DSP）内核工作电压、输入/输出（I/O）端口以及显示屏等进行了干扰测试。实验结果表明,采用硬件与软件相结合的防护加固技术后,DSP主板的内核工作电压及I/O端口的干扰脉冲幅值减小,且干扰持续时间由2 s减少到400 ns,干扰脉冲获得了有效抑制。     

Space-Air-Ground Integrated Mobile Crowdsensing for Partially Observable Data Collection by Multi-Scale Convolutional Graph Reinforcement Learning

Mobile crowdsensing (MCS) is attracting considerable attention in the past few years as a new paradigm for large-scale information sensing. Unmanned aerial vehicles (UAVs) have played a significant role in MCS tasks and served as crucial nodes in the newly-proposed space-air-ground integrated network (SAGIN). In this paper, we incorporate SAGIN into MCS task and present a Space-Air-Ground integrated Mobile CrowdSensing (SAG-MCS) problem. Based on multi-source observations from embedded sensors and satellites, an aerial UAV swarm is required to carry out energy-efficient data collection and recharging tasks. Up to date, few studies have explored such multi-task MCS problem with the cooperation of UAV swarm and satellites. To address this multi-agent problem, we propose a novel deep reinforcement learning (DRL) based method called Multi-Scale Soft Deep Recurrent Graph Network (ms-SDRGN). Our ms-SDRGN approach incorporates a multi-scale convolutional encoder to process multi-source raw observations for better feature exploitation. We also use a graph attention mechanism to model inter-UAV communications and aggregate extra neighboring information, and utilize a gated recurrent unit for long-term performance. In addition, a stochastic policy can be learned through a maximum-entropy method with an adjustable temperature parameter. Specifically, we design a heuristic reward function to encourage the agents to achieve global cooperation under partial observability. We train the model to convergence and conduct a series of case studies. Evaluation results show statistical significance and that ms-SDRGN outperforms three state-of-the-art DRL baselines in SAG-MCS. Compared with the best-performing baseline, ms-SDRGN improves 29.0% reward and 3.8% CFE score. We also investigate the scalability and robustness of ms-SDRGN towards DRL environments with diverse observation scales or demanding communication conditions.     

钢筋混凝土旧工业厂房结构加固方案优选

当前人们选择旧工业厂房结构加固方案效率低下,且所考虑的因素较为片面,为了全面、高效地解决这一问题,通过综合考虑安全性、经济性、时间性、可行性和适用性等因素,以加固效果显著的工程案例为标准,以全面的18个参数为评价指标,构建了一种基于蛛网面积相似和形状相似的结构加固方案优选模型。该模型中首先运用熵权法确定18个指标权重,并将参数值归一化处理,随后运用Python计算蛛网结构相似度,检索出与目标范例最为相似的源范例。最后以结构加固效果显著的工程为例,验证了该模型能有效减少主观误差,具有较强的实用性,并以此模型优选出了某轧钢厂房结构加固方案。     

Scalable and Transferable Reinforcement Learning for Multi-Agent Mixed Cooperative–Competitive Environments Based on Hierarchical Graph Attention

Most previous studies on multi-agent systems aim to coordinate agents to achieve a common goal, but the lack of scalability and transferability prevents them from being applied to large-scale multi-agent tasks. To deal with these limitations, we propose a deep reinforcement learning (DRL) based multi-agent coordination control method for mixed cooperative–competitive environments. To improve scalability and transferability when applying in large-scale multi-agent systems, we construct inter-agent communication and use hierarchical graph attention networks (HGAT) to process the local observations of agents and received messages from neighbors. We also adopt the gated recurrent units (GRU) to address the partial observability issue by recording historical information. The simulation results based on a cooperative task and a competitive task not only show the superiority of our method, but also indicate the scalability and transferability of our method in various scale tasks.     

Torsional Swelling of a Hyperelastic Tube with Helically Wound Reinforcement

This paper examines the combination of radial deformation with torsion for a circular cylindrical tube composed of a transversely isotropic hyperelastic material subject to finite deformation swelling. The stored energy function involves separate matrix and fiber contributions such that the fiber contribution is minimized when the fiber direction is at a natural length. This natural length is not affected by the swelling. Hence swelling preferentially expands directions that are orthogonal to the fiber. The swelling itself is described via a swelling field that prescribes the local free volume at each location in the body. Such a treatment is a relatively simple generalization of the conventional incompressible theory. The direction of transverse isotropy associated with the fiber reinforcement is described by a helical winding about the tube axis. The swelling induced preferential expansion orthogonal to this direction induces the torsional aspect of the deformation. For a specific class of strain energy functions we find that the twist increases with swelling and approaches a limiting asymptotic value as the swelling becomes large. The fibers reorient such that fibers at the inner portion of the tube assume a more circumferential orientation whereas, at least for small and moderate swelling, the fibers in the outer portion of the tube assume a more axial orientation. For large swelling the fibers in the outer portion of the tube reorient beyond the axial orientation, and so are described by helices with orientation in the opposite sense to that in the reference configuration.      

利用时变全通滤波器减小扩声系统中的梳状滤波失真

根据人耳对声音信号相位不敏感的原理，采用时变全通滤波器，随机化每个声源输入信号的相位，从而减小声源输出信号之间的相关性，进而减小由于相关产生干涉而带来的梳状滤波失真。数值计算和实验结果均表明用时变全通滤波器随机化声源输入信号的相位能够有效地减小扩声系统中的梳状滤波失真。     

Study of ionizing radiation on the properties of polyamide 6 with fiberglass reinforcement

The use of polymers reinforced with fiberglass is becoming more and more common in the switches for household industries. These compounds perform a good tension resistance to the impact and the humidity absorption being used at the present time and also are in the automobile industry in parts underneath the hood, especially in the radiator frames. The aim of this work is to study the effect of ionizing radiation on the properties of polyamide 6 with fiberglass reinforcement and undergone to different irradiation doses. Samples were prepared and irradiated on JOB 188 accelerator with an electron beam energy of 1.5 MeV in air with different doses and a dose rate of 27.99 kGy/h. Afterward, the properties of the non-irradiated and irradiated polyamide 6 with fiberglass reinforcement were evaluated.     

Tensile Characterization of FRP Rods for Reinforced Concrete Structures

The application of FRP rods as an internal or external reinforcement in new or damaged concrete structures is based on the development of design equations that take into account the mechanical properties of FRP material systems.The measurement of mechanical characteristics of FRP requires a special anchoring and protocol, since it is well known that these characteristics depend on the direction and content of fibers. In this study, an effective tensile test method is described for the mechanical characterization of FRP rods. Twelve types of glass and carbon FRP specimens with different sizes and surface characteristics were tested to validate the procedure proposed. In all, 79 tensile tests were performed, and the results obtained are discussed in this paper. Recommendations are given for specimen preparation and test setup in order to facilitate the further investigation and standardization of the FRP rods used in civil engineering.