A multi-photon(7×7)-focus 3D laser printer based on a 3D-printed diffractive optical element and a 3D-printed multi-lens array

One of the challenges in the field of multi-photon 3D laser printing lies in further increasing the print speed in terms of voxels/s.Here,we present a setup based on a 7×7 focus array(rather than 3×3 in our previous work)and using a focus velocity of about 1 m/s(rather than 0.5 m/s in our previous work)at the diffraction limit(40×/NA1.4 microscope objective lens).Combined,this advance leads to a ten times increased print speed of about 108 voxels/s.We demonstrate polymer printing of a chiral metamaterial containing more than 1.7×10^(12) voxels as well as millions of printed microparticles for potential pharmaceutical applications.The critical high-quality micro-optical components of the setup,namely a diffractive optical element generating the 7×7 beamlets and a 7×7 lens array,are manufactured by using a commercial two-photon grayscale 3D laser printer.

Lateral ring compression test applied to a small caliber steel jacket:Identification of a constitutive model

The evolution of threats and scenarios requires continuous performance improvements of ballistic protections for armed forces.From a modeling point of view,it is necessary to use sufficiently precise material behavior models to accurately describe the phenomena observed during the impact of a projectile on a protective equipment.In this context,the goal of this paper is to characterize the behavior of a small caliber steel jacket by combining experimental and numerical approaches.The experimental method is based on the lateral compression of ring specimens directly machined from the thin and small ammunition.Various speeds and temperatures are considered in a quasi-static regime in order to reveal the strain rate and temperature dependencies of the tested material.The Finite Element Updating Method(FEMU)is used.Experimental results are coupled with an inverse optimization method and a finite element numerical model in order to determine the parameters of a constitutive model representative of the jacket material.Predictions of the present model are verified against experimental results and a parametric study as well as a discussion on the identified material parameters are proposed.The results indicate that the strain hardening parameter can be neglected and the behavior of the thin steel jacket can be described by a modeling without strain hardening sensitivity.

LEM携高效HMS传感器参展 推出双量程电流传感器

2008年3月18日，全球一流的电量传感器制造商LEM的全资子公司北京莱姆电子有限公司（以下简称北京莱姆），参加了3月18日～20日在上海举办的第七届慕尼黑电子展，并在展会上发布了其高效、环保的新型表面贴装传感器HMS，进一步扩充了其由单一5V供电的电流传感器家族系列产品。LEM集团工业行业副总裁Hans Dieter Huber为此专程访华，体现了LEM对中国市场的重视。

LEM 将第一台小型直流“一级精度”DV电压传感器投放牵引市场

近日，LEM电子宣布，将推出用于测量1200～4200V绝缘电压的DV系列电压传感器。该产品使用LEM专利绝缘技术，体积比当今市场上的其他同类产品都小很多，外形尺寸仅为134×54．22×147．25mm。

Impact of W alloying on microstructure, mechanical property and corrosion resistance of face-centered cubic high entropy alloys: A review

Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μphase,σphase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO_(3) film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure,mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.

A Smart Home Energy Monitoring System Based on Internet of Things and Inter Planetary File System for Secure Data Sharing

Energy demand will continue to rise as a result of predicted population growth. In this work, a user-friendly home energy monitoring system based on IoT is described, which is capable of collecting, analyzing, and displaying data. Users register their sensors and devices on the monitoring platform. PostgreSQL and Elasticsearch databases are used to store the resulting measurements. In a smart home, the wireless sensor ACS712 was used to monitor the flow of electricity (current and voltage) for a household device. The user can share data about electricity consumption and costs with a third party via the private IPFS (InterPlanetary File System) network. A third party can download all the energy consumption data for a device or many devices from the platform for 1 day, 3 months, 6 months, and 1 year. The studies on the development of energy-efficient technology for home devices benefit greatly from the gathered data. For security in the system, it is preferred to run Keyrock Idm, Wilma Pep Proxy, and Orion Context Broker in HTTPS mode, and MQTTS is used to retrieve sensor data. The experimental results showed that the energy monitoring system accurately records voltage, current, active power, and the total amount of power used and offers low-cost solutions to the users using household devices in a day.

土石坝带裂缝黏土心墙破坏机理试验研究

针对土石坝黏土心墙破坏机理的实际特点和物理机制,根据实际工程中黏土心墙所处的应力状态和应力路径的变化,设计了带裂缝黏土心墙的破坏机理试验,探究了裂缝宽度、水压力及反滤层对黏土心墙水力劈裂破坏的影响。结果表明,宽度较小的裂缝在浸水后会闭合,而宽度较大的裂缝则有可能成为土样水力劈裂破坏的通道;一定大小的水压力和加载速率是水力劈裂发生的必要条件;反滤层对于预防水力劈裂破坏的发生具有积极的作用。试验结果对黏土心墙坝体设计有一定的参考价值。

一种非饱和土相对渗透系数的试验数值联合估计法

由于非饱和土相对渗透系数对饱和度的变化十分敏感,因此通过试验测定非饱和土相对渗透系数并不容易。以广义达西定律和van Genuchten模型为理论依据,可通过简单的蒸发试验和数值分析,获得非饱和状态下土壤的相对渗透系数。模拟结果和试验数据的对比分析表明,该方法得到的非饱和土相对渗透系数具有一定的可靠性,在有限元反分析模型参数方面具有一定的创新性,但其实际精度还有待通过试验对比来进一步验证。

挤压AZ31B镁合金的低周疲劳性能(英文)

通过外加总应变幅控制的拉-压对称疲劳试验,研究常温下挤压AZ31B镁合金在不同应变幅下的疲劳性能。结果表明,除了在低应变幅0.5%外,样品均呈现循环应变硬化;应变幅为0.5%时,样品在初始阶段呈现循环硬化,随后保持应力恒定;在压缩过程中孪晶的产生以及随后的卸载和反向拉伸过程中的去孪晶行为导致了高应变幅下的滞回环形状拉-压不对称现象,而低应变幅0.5%下的滞回环形状基本对称,说明低应变幅下孪生-去孪生现象不明显。在整个疲劳过程中,高应变和低应变下的应力—应变曲线呈现2种不同的滞回环形状,这是由不同疲劳阶段孪生和位错滑移2种不同的变形机制所导致。

盐渍土与混凝土衬砌冻结强度直剪试验研究

盐渍土、冻土作为特殊土一直是岩土工程领域研究的热点,但盐渍化冻土与结构之间的相互作用却鲜有报道。为研究山东季冻区、盐碱地渠系工程破坏问题,开展了氯盐、硫酸盐渍土在不同含盐量、不同法向应力条件下与混凝土衬砌冻结接触面的直剪试验研究。结果表明:冻结接触面剪切破坏的性状与含盐类型和含盐量均有关,随氯化钠含量的增加,破坏性状由脆性破坏转为塑性破坏,且氯化钠含量约为2%时是破坏性状的转折点,硫酸钠含量的增加,不会改变接触面的脆性破坏性状;初始冻结强度来源于接触面上冰晶的胶结作用,随含盐量的增大,冻结强度降低,且含盐类型对冻结强度影响不同,氯化钠比硫酸钠对初始冻结强度降低作用更显著,当氯化钠含量接近2%、硫酸钠含量超过4%时,接触面完全丧失初始冻结强度;随着含盐量的增大,内摩擦角由不变到开始减小,黏聚力由开始降低到趋于稳定。

重塑黏土恒压湿化变形试验研究

针对某重塑黏土,通过常规固结仪,研究了恒压下初始孔隙比、应力及初始饱和度对湿化变形的影响。试验结果显示,应力和初始孔隙比e对湿化变形影响明显,低应力下,变形随e的提高逐渐由膨胀变为压缩;高应力下,试样均发生压缩,压缩量随e的增大而增大;定量分析了湿化变形与应力和e之间的关系。试样湿化稳定时间t0受应力和初始孔隙比e影响明显,t0随应力的增加而增大;低应力下,t0随e的增加而增大,高应力下,t0随e的增加先增大后减小。初始饱和度Sr对湿化变形也有较大影响,低压应力下,试样膨胀量随着Sr的增加先减小后增大,可能存在"最优初始饱和度",使得变形量最小;高压应力下,试样压缩量随Sr的增加而减小,二者可近似用直线拟合。

屈服点的不稳定性对超高周疲劳的影响研究

核电站的蒸汽发生器管道采用碳锰钢制成,设计寿命40年,长期受循环温度载荷和高频振动载荷作用后,在管道连接处出现裂纹。实际工作中,循环温度载荷作用后的材料产生循环塑性变形,屈服点这一重要力学性能发生变化。材料在单向拉伸载荷作用下超过Lüders带后,出现硬化效应,屈服强度提高。研究屈服应力点的变化对材料的超高周疲劳性能的影响。试验采用压电陶瓷超声疲劳试验机,考察并比较单向拉伸、低周疲劳载荷作用后,材料超高周疲劳性能的变化。实验结果表明:单向拉伸(5%)提高了材料的屈服点,同时也提高了超高周疲劳强度;而低周疲劳载荷作用后,随着屈服应力点的降低,超高周疲劳性能下降。

渠道下卧土-混凝土衬砌冻结接触面直剪试验研究

为研究渠道下卧土-混凝土衬砌冻结接触面抗剪强度及其随主要影响因素的变化规律,采用直剪仪开展了不同含水率、冻结温度、法向应力及冻结时间条件下渠道下卧土-混凝土衬砌冻结接触面直剪试验研究。结果表明:剪切的初始阶段,接触面存在局部剪应力释放现象,释放量大小受土体含水率、法向应力、冻结时间因素影响,但不受冻结温度的影响;在本试验参数范围内,接触面峰值抗剪强度随着土体含水率、法向应力、冻结时间的增加而增大,随冻结温度的降低而增大;接触面的抗剪强度实质上是冻土中的冰晶与混凝土衬砌接触面之间的胶结力,以及土体与混凝土衬砌接触面之间的黏聚力与摩擦力;峰值抗剪强度大小主要受胶结力影响;黏聚力和摩擦力主要受法向应力、冻结时间的影响。

基于压汞法的改良土渗透特性研究

为探讨改良剂(水泥、固化剂)对土壤渗透性及微观孔隙分布的影响机理,以平原水库粉质黏土为研究对象,采用渗透试验和压汞试验,对改良土的渗透系数及微观孔隙进行研究。结果表明:固化剂使孔隙体积变小,降低改良土的渗透系数,但并非呈线性减小关系;当掺量为2%时,水泥和固化剂之间产生较大的抑制作用。固化剂速凝,可明显缩短施工周期,为工程抢修提供新的发展方向。水泥对改良土渗透性影响最大,随着水泥掺量增加,土体内部由大孔隙向小孔隙过渡。当龄期超过7d,土体渗透性降幅较大,大孔、中孔含量减少,微孔、极微孔逐渐增多;该研究建立了渗透系数与大孔、中大孔孔隙率的函数关系,为改良土作为防渗材料的稳定性分析提供理论依据。

土石坝心墙裂缝发展的扩展有限元模拟

由于土石坝水力劈裂过程复杂,关于其发展机理目前仍有争议。无论是总应力法还是有效应力法都不能计算裂缝的扩展过程。为了进一步研究土石坝水力劈裂的发展机理,参照混凝土材料损伤模型的建模思路,根据土石坝水力劈裂中裂缝的形成过程,并结合非饱和土的力学特点,提出了压实黏土的孔隙扩展模型和裂缝张开模型,用来描述土样裂缝产生前后的状态。借助扩展有限元方法,对裂缝的扩展过程进行了数值模拟。最后通过一个简单的算例,验证了该方法的可行性。该方法对于水力劈裂的数值研究有一定的参考价值。

保护电路的最佳部件—电流传感器

一、概述随着电力电子的更新和发展,大功率晶体管(GTR)、门极可关断晶闸管(GTO)、功率MOS场效应管、绝缘栅极晶闸管等等,被不断地大量采用,但随之而来的是过流保护问题。

Forming condition of transient saturated zone and its distribution in residual slope under rainfall conditions

Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.

Formation mechanisms of water inrush and mud burst in a migmatite tunnel：a case study in China

This paper presents a case study of water inrush and mud burst occurring in a migmatite tunnel to study its formation mechanisms. The geological investigation and mineralogical analysis showed that water inrush and mud burst in the migmatite was closely related to the component of the host rock. High content of soluble minerals,e.g.,calcite and dolomite,would make the migmatite rock prone to be fragmentized,isintegrated and eventually form different sorts of connected or semi-connected veins. The field exploration revealed most cavities in the magmatite tunnel were eroded by groundwater and formed large interconnected networks. The two faults and the dike in the magmatite tunnel became the preferred paths and provided great convenience for plenty of precipitation and mud slurry. Due to high water pressure and blast disturbance,the cavities can soon connect each other as well as all sorts of veins,forming a complex ground channel for water inrush and mud burst. To estimate the potential occurrenceof water inrush and mud burst,the water bursting coefficient was employed. The results showed the water bursting coefficient of the magmatite tunnel was much bigger than the threshold values and it can be used to explain the accident of water inrush and mud burst occurring in the magmatite tunnel.

Elaboration of AlSi10Mg casting alloys using directional solidification processing

The effects of pulling velocity on the solidification behavior and microstructural parameters of A1Sil0Mg alloys prepared in a Bridgman-type directional solidification furnace were investigated. The microstructure, particularly the secondary dendritic arm spacing （SDAS）, and the Brinell hardness （BH） of the solidified A1Sil0Mg alloys were characterized for samples with cylindrical shapes and differ- ent conicities （θ = 0°, 5°, and 10°）. Microstructural studies revealed an increased density of ct-A1 phase dendrites and a decreased interden- dritic distance with increasing pulling velocity. The dendrites were found to be preferentially oriented along the pulling direction for low pulling velocities. For larger pulling velocities, the dendrites grew first in the cooling direction but then broke as others nucleated and coars- ened. The HB values of the solidified samples increased as the pulling velocity increased. In regard to sample conicity, smaller dendrites were observed for an apex angle of θ = 5°, resulting in the largest HB value. This result was interpreted in terms of the favorable orientation of the dendrite along the pulling direction.

Degradation and Mechanism of the Mechanics and Durability of Reinforced Concrete Slab in A Marine Environment

An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete（RC） slab at different ages in a marine environment.Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab.In the first stage,cracks appear.In the second stage,cracks develop from the edges to the middle of the slab.In the third stage,longitudinal and transverse corrosion-induced cracks coexist.The corrosion ratio of reinforcements nonlinearly increases with the age,and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established.The flexural capacity of the corroded RC slab nonlinearly decreases with the age,and the model for the bearing capacity factor of the corroded RC slab is established.The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio.Finally,the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.