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.

High-sensitivity phase imaging eddy current magneto-optical system for carbon fiber reinforced polymers detection

This paper proposed a high-sensitivity phase imaging eddy current magneto-optical (PI-ECMO) system for carbon fiber reinforced polymer (CFRP) defect detection. In contrast to other eddy current-based detection systems, the proposed system employs a fixed position excitation coil while enabling the detection point to move within the detection region. This configuration effectively mitigates the interference caused by the lift-off effect, which is commonly observed in systems with moving excitation coils. Correspondingly, the relationship between the defect characteristics (orientation and position) and the surface vertical magnetic field distribution (amplitude and phase) is studied in detail by theoretical analysis and numerical simulations. Experiments conducted on woven CFRP plates demonstrate that the designed PI-ECMO system is capable of effectively detecting both surface and internal cracks, as well as impact defects. The excitation current is significantly reduced compared with traditional eddy current magneto-optical (ECMO) systems.

Discrete Phase Shifts Control and Beam Selection in RIS-Aided MISO System via Deep Reinforcement Learning

Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.

Microstructure and mechanical properties of a compound reinforced Mg95Y2.5Zn2.5 alloy with long period stacking ordered phase and W phase

The microstructure evolution of Mg100-2xYxZnx （x=2, 2.5, 3, 3.5） alloys was investigated. Results show that the Mg100-2xYxZnx alloys are composed of a-Mg, long period stacking ordered （LPSO） phase and eutectic structure phase （W phase）, and the Mg95Y2.5Zn2.5 alloy has the best comprehensive mechanical properties. Subsequently, the microstructure evolution of the optimized alloy Mg95Y2.5Zn2.5 during solidification and heat treatment processes was analyzed and discussed by means of OM, SEM, TEM, XRD and DTA. After heat treatment, the lamellar phase 14H-LPSO precipitated in a-Mg and W phase transforms into particle phase （MgyZn2）. Due to the compound reinforcement effect of the particle phase and LPSO phase （18R＋14H）, the mechanical properties of the alloy are enhanced. The tensile strength and elongation of the Mg95Y2.5Zn2.5 alloy is improved by 9.1% and 31.3% to 215 MPa and 10.5%, respectively, after solid-solution treatment.

Electron density measurement of laser-induced epoxy fiber reinforced polymer plasma

Interferograms of laser-induced epoxy fiber reinforced polymer plasmas are obtained through aMach-Zehnder interferometry system. An improved digital double-exposure Fourier method is applied to extractinitial wrapped phases from interferograms, and then an improved phase unwrapping algorithm based on a maskand a branch-cut method is proposed to solve the problem of phase unwrapping. After the inverse Abel transfor-mation of the unwrapped phase, spatial distributions of the electron density of laser-induced epoxy fiber rein-forced polymer plasma at various delays are acquired. Results show that the measured electron density of theplasma is mainly distributed on the order of 10^18 cm^3. The experiment also indicates that the total amount oflaser plasma electrons changes slightly within the recorded time and the change of the electron density is approx-imately inversely proportional to the change of the plasma volume.

CHARACTERIZATION OF THERMO-MECHANICAL FATIGUE PROPERTIES FOR PARTICULATE REINFORCED COMPOSITES

A Voronoi cell dement, formulated with creep, thermal and plastic strain was applied for investigation of thermo-mechanical fatigue behavior for particulate reinforced composites. Under the in-phase fatigue loading, the maximum of tensile deformation at the maximum given loading are larger than that at the same maximum under the out-phase fatigue. The stiffness decreases nonlinearly with the increasing of the phase angle, which results in increasing of the area of fatigue loop curve and the decrease in fatigue life. The spatially centralizing of inclusions results in decreasing of the plastic strain amplitude and the area of fatigue loop curve, which will also reduce the consumption of single-circle plastic strain energy and prolong the fatigue life.

楔块耦合的碳纤维增强复合材料褶皱缺陷全聚焦成像

褶皱是碳纤维增强复合材料中最主要的缺陷类型之一,当使用超声相控阵对复合材料薄板进行检测时,由于采集系统非线性效应和电子串扰等干扰会引发盲区现象,掩盖了薄板内的褶皱信息。为削弱盲区影响,考虑在相控阵与复合材料薄板(小于10 mm)之间增加楔块,提出楔块耦合的最短路径射线追踪全聚焦方法。基于费马原理与斯涅耳定律,建立楔块耦合的多层介质超声波传播模型;制备含褶皱缺陷的碳纤维增强复合材料试样,搭建超声相控阵数据采集系统,采集全矩阵数据;将楔块耦合的最短路径射线追踪全聚焦方法和传统全聚焦方法的成像效果进行对比。结果表明,基于楔块耦合的最短路径射线追踪全聚焦方法能减小试样表面盲区深度,修正声时偏差,削弱盲区影响,恢复出试样内的褶皱缺陷。相比传统全聚焦方法,纤维褶皱长度、褶皱顶部高度、褶皱角度这3个参数表征的精准程度分别提高了5.9%、4.1%、4.2%。该文为碳纤维增强复合材料薄板褶皱缺陷的检测提供了新思路。

剧场式演播厅调音系统和扬声器系统设计与实施

本文通过对扬声器系统的选型和扩声系统设计,使具有4000座位、台口达27米的超大型演播剧场满足大型综艺节目、演唱会、音乐剧等节目制作,并获得了均匀的声能覆盖、合适的直达声能和混响声能比值,以及较高的应用性价比。

秸秆纤维增强相变石膏板的制备与性能研究

以石蜡微胶囊为相变储热材料,秸秆纤维为增强材料,采用共混法制备了秸秆纤维增强相变石膏板,并采用SEM、DSC和FTIR对相变石膏板的微观结构、储放热性能及冷热循环耐久性进行了研究。结果表明,石蜡微胶囊掺量为25%时,秸秆纤维增强相变石膏板具有很好的储热性能、力学性能和经济性。此时,相变石膏板的熔融相变温度为26.88℃,结晶相变温度为20.02℃,符合人体最舒适的温度范围;其熔融相变焓为19.03 J/g,结晶相变焓为20.54 J/g,导热系数为0.2978 W/(m·K),比热容为0.5597 J/(kg·K),具有良好的相变储热性能。相变石膏板冷热循环200次后的质量损失率仅为0.84%,储热性能基本保持不变,耐热性良好。

高性能金属基复合材料研究进展

金属材料因其具备优良的可加工性、导电性、导热性、耐磨耐腐蚀性能,被广泛地应用于医疗、航空、军事等领域,所以研究高性能的金属基复合材料成为复合材料学科的一大热点。目前高性能金属基复合材料的理论制备方法较多,但可用于工业化生产技术方案却相对较少;对单一增强相的研究颇多,多相强化基体的研究较少,这两类矛盾问题突出。文章通过综述金属基复合材料的常用制备方法及其常用增强相的种类与效果,以及对多相强化、稀土调控展开分析,以期为实验探索提供理论依据。

考虑附加强化效应的金属材料多轴低周疲劳寿命预测模型

针对等效应变模型在多轴非比例加载时不能考虑到材料的附加强化作用,而造成疲劳寿命预测误差较大的缺陷,基于临界面理论,将最大剪切应变幅作为主要的疲劳损伤参量。同时,将相位差、最大法向应力和剪切应力组成一个附加损伤系数作为次要损伤参量,来反映金属材料在多轴非比例加载下产生的附加强化效应;损伤系数中最大剪切面上的剪切应力对最大法向应力进行归一化处理来反映两个应力相互作用对疲劳寿命的影响。提出的模型在不引入额外的经验拟合常数的情形下,不仅保留了等效应变模型参数的所有优点,还有助于发现裂纹产生的机制和反映裂纹延伸方向。采用6种均为薄壁圆管的金属材料数据对提出的模型和3种经典模型进行数据验证,对比分析后的结果显示,提出的模型相对另外3种模型,得到的预测结果精确度更高且数据分布更稳定。

Precipitating thermally reinforcement phase in aluminum alloys for enhanced strength at 400℃

Heat-resistant aluminum alloys are widely used in aerospace and automotive fields for manufacturing hot components due to their advantages in lightweight design and energy conservation.However,the high-temperature strength of existing cast aluminum alloys is always limited to about 100 MPa at 350℃due to coarsening and transformation of strengthening phases.Here,we reveal that the yield strength and ultimate tensile strength of the T6 state Al-8.4Cu-2.3Ce-1.0Mn-0.5Ni-0.2Zr alloy at 400◦C increase by 34%and 44%after re-aging at 300℃for 100 h,and its thermal strength exhibits distinguished ad-vantage over traditional heat-resistant aluminum alloys.The enhanced elevated-temperature strength is attributed to the reprecipitation of the Ni-bearing T-Al_(20)Cu_(2)Mn_(3)phase,whose number density increases over one time.The significant segregation of Ni,Ce,and Zr elements at the interfaces helps improve the thermal stability of the T phase.The thermostable T phase effectively strengthens the matrix by in-hibiting dislocation motion.Meanwhile,a highly interconnected 3D intermetallic network along the grain boundaries can still remain after long-term re-aging at 300℃,which is conducive to imposing a drag on the grain boundaries at high temperatures.This finding offers a viable route for enhancing the elevated-temperature strength of heat-resistant aluminum alloys,which could provide expanded opportunities for higher-temperature applications.

Self organizing optimization and phase transition in reinforcement learning minority game system

Whether the complex game system composed of a large number of artificial intelligence(AI)agents empowered with reinforcement learning can produce extremely favorable collective behaviors just through the way of agent self-exploration is a matter of practical importance.In this paper,we address this question by combining the typical theoretical model of resource allocation system,the minority game model,with reinforcement learning.Each individual participating in the game is set to have a certain degree of intelligence based on reinforcement learning algorithm.In particular,we demonstrate that as AI agents gradually becomes familiar with the unknown environment and tries to provide optimal actions to maximize payoff,the whole system continues to approach the optimal state under certain parameter combinations,herding is effectively suppressed by an oscillating collective behavior which is a self-organizing pattern without any external interference.An interesting phenomenon is that a first-order phase transition is revealed based on some numerical results in our multi-agents system with reinforcement learning.In order to further understand the dynamic behavior of agent learning,we define and analyze the conversion path of belief mode,and find that the self-organizing condensation of belief modes appeared for the given trial and error rates in the AI system.Finally,we provide a detection method for period-two oscillation collective pattern emergence based on the Kullback–Leibler divergence and give the parameter position where the period-two appears.

多维度强化结合阶段性康复训练对骨折患者康复及静脉血栓栓塞症发生的影响

目的:探究多维度强化结合阶段性康复训练对骨折患者康复及静脉血栓栓塞症发生的影响。方法:选取景德镇市第三人民医院于2020年1月—2023年3月收治的下肢骨折患者88例,根据单双数标记法,将单数归为对照组,双数归为观察组,各44例。对照组采用常规护理干预,观察组采用多维度强化结合阶段性康复训练,干预周期为6个月。比较两组患者干预疗效(住院时间、下床活动时间、骨折愈合时间)、疼痛程度[视觉模拟评分法(visual analog scale,VAS)评分]、自护能力[自我护理能力量表(exercise of self-care ability,ESCA)]、下肢运动功能恢复情况[简式下肢Fugl-Meyer运动评估表(Fugl-Meyer assessment scale,FMA)和Berg平衡量表(Berg balance scale,BBS)]及静脉血栓栓塞症(VTE)发生率。结果:干预后,两组患者VAS评分均低于干预前,ESCA各维度评分、FMA评分及BBS评分均高于干预前,差异均有统计学意义(P<0.05);观察组住院时间、骨折愈合时间均短于对照组,下床活动时间早于对照组,VAS评分低于对照组,ESCA各维度评分、FMA评分、BBS评分均高于对照组,差异均有统计学意义(P<0.05)。干预6个月,观察组VTE发生率低于对照组(P<0.05)。结论:多维度强化结合阶段性康复训练能显著缩短下肢骨折患者的住院和恢复时间,降低疼痛程度,提高下肢运动功能和自护能力,并有效减少VTE的发生。

丝粉协同电弧增材制造机械刀具耐磨层组织及性能

机械刀具在农用机械、轨道交通等领域中应用广泛。基于热源和耐磨层增强相体积分数要求,建立了丝粉协同电弧增材制造系统,制备了不同送粉气体流量下的碳化钨增强铁基耐磨层,采用金相显微镜、X射线衍射仪、扫描电镜和能谱仪分析耐磨层组织及成分。结果表明:送粉气体流量为8L/min时,增强相体积分数为60%,耐磨层由α-Fe基体、WC和W_(2)C颗粒以及Fe_(3)W_(3)C析出相组成,耐磨层基体显微硬度≥1000HV,增强相最高显微硬度为2385HV,具有优良的耐磨性。

Fabrication of solid-phase-sintered Si C-based composites with short carbon fibers

Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

激光熔覆TC4/Inconel 625/316L不锈钢梯度材料组织与性能

为了提高不锈钢工件的综合性能,采用激光熔覆工艺在不锈钢上制备TC4熔覆层、Inconel 625熔覆层作为过渡层,通过光学显微镜、扫描电子显微镜、X射线衍射仪、能谱仪、硬度计、摩擦磨损和电化学测试等研究了TC4熔覆层微观组织、显微硬度、电化学性能和摩擦磨损性能.结果表明,熔覆层成形质量良好且具有均匀致密的微观组织.熔覆过程中,由于元素扩散与高温作用发生的共晶反应,熔覆层中生成CrNi_(2)和Ti_(2)Ni增强相,大大提升了熔覆层的硬度与耐磨性;TC4熔覆层磨损机制主要为磨粒磨损与氧化磨损,耐磨性优于基体;TC4熔覆层的腐蚀电流密度小于基体,耐蚀性显著高于基体.创新点:(1)通过激光熔覆实现了TC4/Inconel 625/316L不锈钢梯度材料的制备.(2)通过共晶反应生成Ti_(2)Ni,CrNi_(2)增强相,并研究其对熔覆层和基体的磨损机制与腐蚀机制的影响.

含夹杂缺陷碳纤维复合材料层压板的无损检测与评估研究

针对复合材料无损检测与评估问题,本文采用超声相控阵探伤仪对预埋夹杂缺陷的碳纤维复合材料层压板试样进行定量定位检测,并利用小波包分析和神经网络对缺陷进行定性识别。首先,在层压板中埋入聚四氟乙烯薄膜、CFRP片和塑料纸制备夹杂缺陷试样;然后,对试样进行超声相控阵检测,对得到的B、C扫图像进行缺陷定量定位评估,对得到的A扫信号进行缺陷定性评估。结果表明:通过对B、C扫图像进行分析,能准确分辨出缺陷所在的位置、尺寸及形状。利用小波包分析和BP神经网络对聚四氟乙烯薄膜、CFRP片和塑料纸三种夹杂缺陷进行识别,正确率为90.9%,对CFRP片和塑料纸两种缺陷进行识别,正确率达到100%,为以后能快速、准确地识别更多种类的缺陷奠定了良好的基础。

Ni-GNSs增强Sn2.5Ag0.7Cu0.1RE/Cu钎焊接头电迁移特性研究

针对微焊点服役下的电迁移可靠性检测,设计制造了满足焊点在理想电迁移环境下的试验装置。结果表明:通过热分解法制备Ni-GNSs增强相,得到的Ni-GNSs增强Sn2.5Ag0.7Cu0.1RE/Cu钎焊接头能有效抑制电迁移现象的发生。在电加载条件下,随电流密度升高,Ni-GNSs增强Sn2.5Ag0.7Cu0.1RE/Cu接头阳极区界面金属间化合物(IMC)由起伏扇贝状转变为平坦厚大的板状,并出现了明显Cu 3Sn;阴极区界面IMC由锯齿状转变为薄条状,且有明显空洞裂纹。钎焊接头断裂位置从阴极界面IMC/钎缝的过渡区向阴极界面IMC迁移,断裂方式由韧性断裂向脆性断裂转变,剪切强度明显下降。

高熵合金基复合材料的研究进展

高熵合金自2004年被提出以来,由于其表现出比传统合金更为优异的综合性能,在航空航天、石油化工等领域具有潜在的应用前景,逐渐成为金属材料领域的研究热点。在高熵合金基体中引入合适的增强相形成高熵合金基复合材料(HEAMCs),已成为改善高熵合金综合性能的方法之一。本文综述了近年来国内外关于高熵合金基复合材料的研究现状,就其增强相选择、制备工艺、相结构和组织进行系统的介绍,并归纳了包括强塑性、硬度以及耐磨耐蚀性等高熵合金基复合材料性能的演变规律以及强化机制,最后指出了当前高熵合金基复合材料面临的挑战并展望了未来的研究方向:增强相和基体之间的润湿性严重影响大尺寸复合材料的制备及性能,寻找一种高效简易的方法制备大尺寸复合材料是目前高熵合金基复合材料需要解决的一个问题;增强相颗粒会导致塑性下降,金属基复合材料强度与塑性之间的平衡也有待研究。