Dynamic and electrical responses of a curved sandwich beam with glass reinforced laminate layers and a pliable core in the presence of a piezoelectric layer under low-velocity impact

The dynamic responses and generated voltage in a curved sandwich beam with glass reinforced laminate(GRL)layers and a pliable core in the presence of a piezoelectric layer under low-velocity impact(LVI)are investigated.The current study aims to carry out a dynamic analysis on the sandwich beam when the impactor hits the top face sheet with an initial velocity.For the layer analysis,the high-order shear deformation theory(HSDT)and Frostig's second model for the displacement fields of the core layer are used.The classical non-adhesive elastic contact theory and Hunter's principle are used to calculate the dynamic responses in terms of time.In order to validate the analytical method,the outcomes of the current investigation are compared with those gained by the experimental tests carried out by other researchers for a rectangular composite plate subject to the LVI.Finite element(FE)simulations are conducted by means of the ABAQUS software.The effects of the parameters such as foam modulus,layer material,fiber angle,impactor mass,and its velocity on the generated voltage are reviewed.

Mechanical Properties of Layered Steel Fiber and Hybrid Fiber Reinforced Concrete

To explore a new structure form of fiber reinforced concrete, namely, the layered steel fiber and layered hybrid fiber reinforced concrete （LSFRC and LHFRC）, the mechanical properties of LSFRC and LHFRC, such as compressive strength, tensile strength, flexural strength, fatigue and durability were focused on. The experimental results show that LSFRC and LHFRC can improve the flexural strength of concrete by 20%-50%. In the aspect of improving the flexural strength of concrete, adulterant rate has more obvious effect than length/diameter ratio. Double logarithmic fatigue equation considered liveability was founded. The impermeability of LHFRC is superior to LSFRC and plain concrete （C）. However, the porosity of LHFRC is lower than LSFRC and C. The shrinkage of LHFRC at every age is obviously lower than C. The antifreeze durability of LHFRC is also better than C.

Mechanical Properties of Layered Hybrid Fiber Reinforced Concrete

To improve the mechanical properties of concrete,Layered Hybrid Fiber Reinforced Concrete (LHFRC) was developed in this paper.Through comparative tests,the effects of layered hybrid fibers on a series of mechanical properties of concrete were discussed.The mechanical properties include compressive strength,tensile strength,flexural strength,compressive stress-strain relationship,flexural toughness and cracking resistance of concrete.The testing results and analysis demonstrate that layered hybrid fibers can significantly improve the flexural strength,toughness and cracking resistance of concrete while the cost of concrete increases slightly.

Simulation of Corrosion-Induced Cracking of Reinforced Concrete Based on Fracture Phase Field Method

Accurate simulation of the cracking process caused by rust expansion of reinforced concrete(RC)structures plays an intuitive role in revealing the corrosion-induced failure mechanism.Considering the quasi-brittle fracture of concrete,the fracture phase field driven by the compressive-shear term is constructed and added to the traditional brittle fracture phase field model.The rationality of the proposed model is verified by a mixed fracture example under a shear displacement load.Then,the extended fracture phase model is applied to simulate the corrosion-induced cracking process of RC.The cracking patterns caused by non-uniform corrosion expansion are discussed for RC specimens with homogeneous macroscopically or heterogeneous with different polygonal aggregate distributions at the mesoscopic scale.Then,the effects of the protective layer on the crack propagation trajectory and cracking resistance are investigated,illustrating that the cracking angle and cracking resistance increase with the increase of the protective layer thickness,consistent with the experimental observation.Finally,the corrosion-induced cracking process of concrete specimens with large and small spacing rebars is simulated,and the interaction of multiple corrosion cracking is easily influenced by the reinforcement spacing,which increases with the decrease of the steel bar interval.These conclusions play an important role in the design of engineering anti-corrosion measures.The fracture phase field model can provide strong support for the life assessment of RC structures.

Numerical investigation of the effects of soil-structure and granular material-structure interaction on the seismic response of a flat-bottom reinforced concrete silo

In this work,a numerical study of the effects of soil-structure interaction(SSI)and granular material-structure interaction(GSI)on the nonlinear response and seismic capacity of flat-bottomed storage silos is conducted.A series of incremental dynamic analyses(IDA)are performed on a case of large reinforced concrete silo using 10 seismic recordings.The IDA results are given by two average IDA capacity curves,which are represented,as well as the seismic capacity of the studied structure,with and without a consideration of the SSI while accounting for the effect of GSI.These curves are used to quantify and evaluate the damage of the studied silo by utilizing two damage indices,one based on dissipated energy and the other on displacement and dissipated energy.The cumulative energy dissipation curves obtained by the average IDA capacity curves with and without SSI are presented as a function of the base shear,and these curves allow one to obtain the two critical points and the different limit states of the structure.It is observed that the SSI and GSI significantly influence the seismic response and capacity of the studied structure,particularly at higher levels of PGA.Moreover,the effect of the SSI reduces the damage index of the studied structure by 4%.

Flexural Fatigue Behavior of Layered Hybrid Fiber Reinforced Concrete

In order to obtain the fatigue life of layered hybrid fiber reinforced concrete （LHFRC） at different stress levels, flexural fatigue tests were carried out on specimens. The relation between fatigue lives and stress levels was simulated using the two-parameter Weibull distribution. Furthermore, both single- logarithmic and double-logarithmic regressive equations of various reliabilities were derived. It is evident that LHFRC gets the advantage of longer fatigue life over common concrete.

Surface effects on a mode-III reinforced nano-elliptical hole embedded in one-dimensional hexagonal piezoelectric quasicrystals

To effectively reduce the field concentration around a hole or crack,an anti-plane shear problem of a nano-elliptical hole or a nano-crack pasting a reinforcement layer in a one-dimensional(1D)hexagonal piezoelectric quasicrystal(PQC)is investigated subject to remotely mechanical and electrical loadings.The surface effect and dielectric characteristics inside the hole are considered for actuality.By utilizing the technique of conformal mapping and the complex variable method,the phonon stresses,phason stresses,and electric displacements in the matrix and reinforcement layer are exactly derived under both electrically permeable and impermeable boundary conditions.Three size-dependent field intensity factors near the nano-crack tip are further obtained when the nano-elliptical hole is reduced to the nano-crack.Numerical examples are illustrated to show the effects of material properties of the surface layer and reinforced layer,the aspect ratio of the hole,and the thickness of the reinforcing layer on the field concentration of the nano-elliptical hole and the field intensity factors near the nano-crack tip.The results indicate that the properties of the surface layer and reinforcement layer and the electrical boundary conditions have great effects on the field concentration of the nano-hole and nano-crack,which are useful for optimizing and designing the microdevices by PQC nanocomposites in engineering practice.

Analytic model of non-uniform corrosion induced cracking of reinforced concrete structure

In order to perfectly reflect the dynamic corrosion of reinforced concrete (RC) cover in practical engineering,an analytic model of non-uniform corrosion induced cracking was presented based on the elastic-plastic fracture mechanics theory.Comparisons with the published experimental data show that the predictions given by the present model are in good agreement with the results both for natural exposed experiments and short-time indoor tests (the best difference is about 2.7%).Also it obviously provides much better precision than those models under the assumption of uniform corrosion (the maximal improved precision is about 48%).Therefore,it is pointed out that the so-called uniform corrosion models to describe the cover cracking of RC should be adopted cautiously.Finally,the influences of thickness of local rusty layer around the reinforcing steel bar on the critical corrosion-induced crack indexes were investigated.It is found that the thickness of local rusty layer has great effect on the critical mass loss of reinforcing steel,threshold expansion pressure,and time to cover cracking.For local rusty layer thickness with a size of a=0.5 mm,the time to cover cracking will increase by about one times when a/b (a,semi-minor axis;b,semi-major axis) changes from 0.1 to 1 mm.

Analytical solution for a strained reinforcement layer bonded to lip-shaped crack under remote modeⅢuniform load and concentrated load

In this paper, the analytical solution of stress field for a strained reinforcement layer bonded to a lip-shaped crack under a remote mode III uniform load and a concentrated load is obtained explicitly in the series form by using the technical of conformal mapping and the method of analytic continuation. The effects of material combinations, bond of interface and geometric configurations on interfaciai stresses generated by eigenstrain, remote load and concentrated load are studied. The results show that the stress concentration and interfaciai stresses can be reduced by rational material combinations and geometric configurations designs for different load forms.

Preparation of 6066/SiC-p composites by multilayer spray deposition

SiC particulate reinforced 6066 aluminium alloy metal matrix composites (MMCs) were prepared by multi layer spray forming. The preparation technology and process parameters were discussed. It is shown that SiC particulate can be continuously and evenly fed and co deposited in the spray forming process. The reciprocally scanning movement of spraying system can make the SiC particulates distribute homogeneously in the composite. The ratio of SiC particulates captured by the metal matrix is influenced by process parameters, especially the metal flow rate. 6066/SiC p composite preforms of d 300 mm×540 mm and tubes with a size of up to d 650/ d 300 mm×1 000 mm were made by the same process. After extrusion and T6 heat treatment, the multi layer spray deposited 6066/SiC p composites can achieve improved properties. [

Microstructure and mechanical properties of Fe/NbC composite layer prepared by in-situ reaction

NbC ceramic surface-reinforced steel matrix composites were prepared by an in-situ reaction method at different temperatures(1,050℃,1,100℃and 1,150℃)for different times(1 h,2 h and 3 h).The phase constitution,microstructure and fracture morphology of NbC ceramic surface-reinforced steel matrix composites were analyzed by XRD,SEM and EDS,and the effects of the in-situ reaction temperature and time on the mechanical properties were systematically studied.The results indicate that the NbC reinforcement layer is formed through the reaction between Nb atoms and carbon atoms diffused from the steel matrix to the Nb plate.The thickness of this reinforcement layer increases as the reaction time prolongs.Additionally,an increase in reaction temperature results in a thicker reinforcement layer,although the rate of increase gradually decreases.The relationship among the thickness of the Nb C reinforcement layer,the reaction time and temperature was established by data fitting.The optimal tensile performance is achieved at 1,100℃for 1 h,with a tensile strength of 228 MPa.It is also found that the defects between the reinforcement layer and the steel matrix are related to reaction temperature.At 1,100℃,these defects are minimal.Fracture mostly occurs in the NbC reinforced layer of the composites,and the fracture mode is characterized by typical intergranular brittle fracture.

Trajectory Design for UAV-Enabled Maritime Secure Communications:A Reinforcement Learning Approach

This paper investigates an unmanned aerial vehicle(UAV)-enabled maritime secure communication network,where the UAV aims to provide the communication service to a legitimate mobile vessel in the presence of multiple eavesdroppers.In this maritime communication networks(MCNs),it is challenging for the UAV to determine its trajectory on the ocean,since it cannot land or replenish energy on the sea surface,the trajectory should be pre-designed before the UAV takes off.Furthermore,the take-off location of the UAV and the sea lane of the vessel may be random,which leads to a highly dynamic environment.To address these issues,we propose two reinforcement learning schemes,Q-learning and deep deterministic policy gradient(DDPG)algorithms,to solve the discrete and continuous UAV trajectory design problem,respectively.Simulation results are provided to validate the effectiveness and superior performance of the proposed reinforcement learning schemes versus the existing schemes in the literature.Additionally,the proposed DDPG algorithm converges faster and achieves higher utilities for the UAV,compared to the Q-learning algorithm.

Comparison Research of Bed Joints Construction and Bed Joints Reinforcement on Shear Parameters of AAC Masonry Walls

The work presents the results of tests on the shear parameters of walls made of AAC （autoclaved aerated concrete, fb = 4.0 N/mm2） on the system mortar for thin M5 and M10 joints （fm = 6.1 N/mm2 and fro = 11.9 N/mm2） and on polyurethane glue and also walls without mortar （dry masonry）. The wall compression strength （on mortar M5 class） （per EN 1052-1：2000） amounted tofc,mv= 2.97 N/mm2 （fk = 2.48 N/mm2）, elastic modulus was Ecru = 2,040 N/mm2. Various structure of bed joints and head joints were applied and the following were used as reinforcement： steel trusses of EFZ 140/Z 140 type （Z1 type） and meshes made of plastics （Z2 type）. Based on the tests carried out with regard to unreinforced elements, it was shown that the filling in of head joints with mortar had an advantageous effect on the values of cracking and destruction stresses. While, with the use of reinforcement, advantageous increase of stress was obtained only when the mortar was laid twice on both bed surfaces of masonry units. The application of reinforcement in the bed joints when the mortar was laid only on one bed joints surface of the masonry units reduced the values of cracking and destruction stresses in relation to the values obtained in the unreinforced walls.

玄武岩筋混凝土桥面铺装试验研究

目的研究玄武岩筋替换桥面铺装层中传统钢筋的抗弯性能,为该类加铺玄武岩筋混凝土铺装层提供参考。方法笔者制作了7根玄武岩筋混凝土桥面铺装试验梁和3根普通钢筋混凝土梁对其进行四点加载试验,研究钢筋直径、数量以及铺装层厚度等对试验梁抗弯性能的影响。结果只改变铺装层纵筋类型,铺装层纵筋为玄武岩筋的矩形梁屈服荷载提高了1.23%~8.96%,抗弯承载力提高了0.6%~2.65%;相同筋材类型,随着钢筋直径增大到10 mm,普通钢筋混凝土梁的抗弯承载力提高了13.86%,玄武岩筋混凝土梁的抗弯承载力提高了16.17%;铺装层纵筋数量的改变,对梁的开裂荷载、抗弯承载力的作用较小;只增加铺装层厚度,玄武岩筋混凝土桥面铺装试验梁开裂荷载最大提高了50%,屈服荷载最大提高了14.47%,极限荷载最大提高了11.43%。结论在一定的铺装层厚度和纵筋根数条件下,将铺装层中玄武岩筋代替普通钢筋,不仅可以发挥玄武岩筋抗腐蚀的特点,还能提高抗弯承载力。

外露型聚氨酯防水涂料在混凝土屋面防水维修中的应用

GES-W308外露型水性聚氨酯防水涂料是以脂肪族水性聚氨酯分散体为主要成膜物质,配以助剂、颜填料,采用先进自动化设备制备而成,兼具水性防水涂料的环保性能和油性聚氨酯防水涂料的力学性能,同时具有优良的耐候性、耐脏污性以及施工性能。以北京国贸区域嘉里中心项目为例,介绍了该防水涂料在复杂混凝土屋面防水维修工程中的应用,包括基层处理、加强层施工、细部节点处理、胎体增强材料选用、防水涂料涂刷等。

面向能源感知的虚拟机深度强化学习调度算法研究

随着计算机技术的快速发展,云计算技术成为了解决用户存储、算力需求的最佳方法之一。其中,基于NUMA架构的动态虚拟机调度成为了学术界和工业界关注的热点方向。但是,目前的研究中,基于启发式的算法难以对虚拟机进行实时调度,并且大多数文献没有考虑NUMA架构下虚拟机调度产生的能耗等问题。对此,提出了一种基于深度强化学习的大型移动云中心虚拟机服务迁移框架,构建了NUMA架构下的能耗模型;提出了自适应奖励的分层自适应柔性演员评论家算法(Hie-rarchical Adaptive Sampling Soft Actor Critic,HASAC);在云计算场景下,将所提算法与3种经典的深度强化学习方法进行实验对比。实验结果表明,所提改进算法在不同场景下可以处理更多的用户请求,且消耗的能源较少。此外,对算法中各种策略进行消融实验,证明了所提策略的有效性。

毫米波车联网多基站多用户下的安全传输方案

针对移动场景下毫米波安全波束形成的时效性和毫米波动态窃听场景下安全连接的鲁棒性等问题,提出了一种基于决斗双重深度Q网络(D3QN)-深度确定性策略梯度(DDPG)算法的多智能体安全协作通信方案。该方案利用路侧单元(RSU)辅助的协作干扰技术降低窃听者对合法信号的接收质量,并通过联合优化车辆用户(VU)的基站与波束连接控制、阻塞RSU的选择,以及RSU的协作干扰方向和发射功率控制,使得所有合法车辆的总保密传输速率最大化。在此基础上,针对车联网的高动态性,通过构建基于D3QN的VU智能体和基于D3QN-DDPG的RSU智能体,实现了实时的离散-连续混合决策。最后,通过多维度的性能分析和方案对比实验,验证了所提方案的有效性。

无人机辅助的双层深度强化学习任务卸载算法

为了解决无人机轨迹优化、用户功率分配和任务卸载策略问题,提出了一种双层深度强化学习任务卸载算法。上层采用多智能体深度强化学习来优化无人机的轨迹,并动态分配用户的传输功率以提高网络传输速率;下层采用多个并行的深度神经网络来求解最优卸载决策以最小化网络的时延和能耗。仿真结果表明,该算法使得无人机能够跟踪用户的移动,显著降低系统的时延和能耗,能够给用户提供更优质的任务卸载服务。

基于强化学习的无人机智能组网技术及应用综述

针对无人机在民用和军事等领域中的研究热度及应用需求日益增长,传统Mode1-Based的网络部署、设计、操作方法无法应对动态变化的无人机场景的问题,本文综述了灵活性高、适应性强的AI-Based的智能组网技术,并引入强化学习这一人工智能领域的重要分支。对现有利用强化学习技术解决无人机组网难题的研究进行了概述,结合无人机组网的特性梳理了此领域应用强化学习技术的主要思路。从几个应用场景,以及组网关键技术的角度进行了归纳,给出了基于强化学习的无人机智能组网技术所面临的机遇与挑战,并进行了总结。探究了无人机通信的感知能力与决策能力,适应了其动态变化且需要高度自治的环境需求。为未来无人机智能组网技术的发展提供了有价值的理论基础和实践指导。

循环荷载作用下土工格栅加筋黄土动力特性研究

【目的】由于黄土所具有的结构疏松、抗剪性低,以及对水、力及震动都十分敏感等工程特性,故探究采用双向土工格栅对西宁地区黄土加筋前后土体动力性能的改善效果。【方法】采用GDS双向动三轴测试系统开展不同加筋层间距、不同围压、不同动应力幅值工况条件下加筋黄土的动三轴试验,分析循环荷载作用下加筋层间距对黄土动强度、动剪切模量、阻尼比等动力响应特性的影响,探讨分析加筋黄土动力响应特性的演化规律。【结果】结果显示:黄土动应变随着动应力的增大而增大,骨干曲线呈现应变强化型,并且骨干曲线随加筋层间距的减小逐渐由曲线型过渡为直线型;随着加筋层间距的减小,黄土强度随之增大,随着围压和加筋层间距的增加,黄土幅值剪应力明显增大,动剪应变减小,阻尼比明显减小。【结论】结果表明:围压和加筋层间距对加筋黄土的动力特性具有显著的增强作用,且存在一个最优加筋层间距。研究成果可为西宁地区加筋黄土道路设计提供参考依据。