The effect of homogenization on the recrystallization of an Al-Mn-Mg alloy sheet

The present study examines the effect of homogenization of the roll-cast material on the microstructure and ductility of an Al-Mn-Mg alloy sheet. The phenomenon ofrecrystallization and the effect of precipitation and second phase particles have beeninvestigated in cold rolled sheets by means of differential scanning calorimetry (DSC),electrical conductivity measurement and image analysis. It appears that recrystallizationcharacteristics in different homogenization conditions are important parameters thatcontrol the grain sizes and consequently the ductility of the homogenized sheets. It isbelieved that homogenization promotes normal discontinuous recrystallization andsubsequent grain coarsening mainly due to the elimination of precipitation interaction andthe coarsening of the second phase particles.     

3D Bridged Carbon Nanoring/Graphene Hybrid Paper as a High‐Performance Lateral Heat Spreader

Graphene paper (GP) has attracted great attention as a heat dissipation material due to its unique thermal transfer property exceeding the limit of graphite. However, the relatively poor thermal transfer properties in the normal direction of GP restricts its wider applications in thermal management. In this work, a 3D bridged carbon nanoring (CNR)/graphene hybrid paper is constructed by the intercalation of polymer carbon source and metal catalyst particles, and the subsequent in situ growth of CNRs in the confined intergallery spaces between graphene sheets through thermal annealing. Further investigation demonstrates that the CNRs are covalently bonded to the graphene sheets and highly improve the thermal transport in the normal direction of the CNR/graphene hybrid paper. This full‐carbon architecture shows excellent heat dissipation ability and is much more efficient in removing hot spots than the reduced GP without CNR bridges. This highly thermally conductive CNR/graphene hybrid paper can be easily integrated into next generation commercial high‐power electronics and stretchable/foldable devices as high‐performance lateral heat spreader materials. This full‐carbon architecture also has a great potential in acting as electrodes in supercapacitors or hydrogen storage devices due to the high surface area.     

A comparative study of laser beam welding and laser-MIG hybrid welding of Ti-Al-Zr-Fe titanium alloy

Ti-Al-Zr-Fe titanium alloy sheets with thickness of 4 mm were welded using laser beam welding (LBW) and laser-MIG hybrid welding (LAMIG) methods. To investigate the influence of the methods difference on the joint properties, optical microscope observation, microhardness measurement and mechanical tests were conducted. Experimental results show that the sheets can be welded at a high speed of 1.8 m/min and power of 8 kW, with no defects such as, surface oxidation, porosity, cracks and lack of penetration in the welding seam. In addition, all tensile test specimens fractured at the parent metal. Compared with the LBW, the LAMIG welding method can produce joints with higher ductility, due to the improvement of seam formation and lower microhardness by employing a low strength TA-10 welding wire. It can be concluded that LAMIG is much more feasible for welding the Ti-Al-Zr-Fe titanium alloy sheets.     

Production of microfibrillated cellulose (MFC)-reinforced polylactic acid (PLA) nanocomposites from sheets obtained by a papermaking-like process

The fabrication of cellulose nanofiber-reinforced composites has been so far problematic due to difficulties in obtaining good dispersion of hydrophilic cellulose fibers in a hydrophobic polymer matrix. A new manufacturing process similar to papermaking, which enables the production of thin sheets made of uniformly dispersed microfibrillated cellulose (MFC) with polylactic acid (PLA) fibers was devised, and the composites were obtained by compression molding of the stacked sheets. The process is suitable for adoption at an industrial scale owing to the high yields and fast dewatering times. The measurement of tensile properties revealed that the modulus, strength, and strain at fracture increased linearly with the MFC content. The improvement in toughness was considered one of the key benefits brought by MFC reinforcement.     

Nanostructure and Properties of a Shinbone

Scanning electron microscope (SEM) observation shows that a shinbone is composed of large-volume-fraction hydroxyapatite and small-volume-fraction collagen protein materials. The hydroxyapatite is of laminated structure and consists of numberless hydroxyapatite sheets. The observation also shows that the hydroxyapatite sheets are parallel with each other and of nanometer scale. The high fracture toughness and fracture strength of the bone are investigated based on the calculation formula of the dissipation work and Griffith criterion. The investigated results reveal that the large-volume fraction and the nanometer scale of the hydroxyapatite sheets are the important factors to the high mechanical performance of the bone.     

Digital measurement station for power quality analysis in distributed environments

Today there is a wide application of different electronic apparatus that both produce electromagnetic disturbances on the supply power system and are sensitive to them. Power disturbances present on typical electric utility distribution systems degrade product quality, increase process downtime, and dissatisfy commercial customers. For these reasons, the monitoring of the quality of the supply networks has become an issue of international interest. To monitor power quality, in this paper, we propose a digital measurement station. Its main features are remote data transmission capability and reduced cost. It is a PC-based virtual instrument that offers the flexibility due to the high-level programming language, the familiar working environment of Windows, and the low cost of a widely used computer. The local area network or a modem card allows the measurement system to be controlled via a transmission control protocol/Internet protocol network, implementing in this way a distributed power quality evaluation system.     

Current distribution in a parallel set of conducting strips

The current distribution in a parallel set of thin conducting sheets due to an external applied source is investigated. All sheets are placed in one plane. The source, and all excited fields, are time-harmonic. The frequency is low enough to allow for an electro quasi-static approximation (neglecting the displacement current). The conducting sheets are infinitely long and the current is uniform in the longitudinal direction of the sheets. The sheets have a thin rectangular cross-section, so thin that the current can be assumed uniform in the thickness-direction. Hence, the current distribution only depends on the transverse coordinate. Due to the mutual induction between the sheets, the current distribution over the width of the cross-section becomes non-uniform: it accumulates at the edges of the sheets. It is especially this so-called edge-effect, and its dependence on the applied frequency and the distances between the sheets, that is the aim of this investigation. From the Maxwell equations, a set of integral equations for the current distribution in the sheets is derived. These integral equations are solved, as far as possible by analytical means, by writing the current distribution in each sheet as a series of Legendre polynomials. The general method is worked out for N (N 1) sheets, but explicit results are presented for N=1 and 3. It turns out that the edge-effect becomes stronger for increasing frequencies. For this solution, only a very restricted number of Legendre polynomials are needed.     

Measurement of Moisture Content in Cardboard Bales by Microwave

In this work, a system for measuring moisture content in bundles of recycled cardboard sheets using microwaves is proposed and evaluated. For the development of this system, a microwave generator and an antenna tuned in the X-band were used. The detector system used was formed by a diode array point of contact. Calibration curves of moisture content in bales versus voltage in the array were obtained for two orientations or positions of the cardboard sheets in the sample bales. The results showed that the higher the moisture content, the lower the voltage is induced in the diodes. It was also observed that the attenuation of the microwave signal depends on the position of the cardboard sheets and that the measurement can be made in samples of bales with a maximum of 35% humidity, because on this percentage, the variation of voltage in the diode array is almost zero.     

组合FRP技术加固混凝土矩形柱的抗震性能试验研究

研究了一种利用植筋及纤维增强复合材料(FRP)布横向包裹钢筋混凝土柱来改善其抗震性能的新型加固技术.通过5个钢筋混凝土方柱的模型试验,分别研究了植玻璃纤维(GFRP)筋、横向包裹碳纤维(CFRP)布及两者组合的加固技术对提高混凝土柱抗震性能的作用,分析讨论了不同加固方法对混凝土柱位移延性系数的提高、刚度退化及能量耗散能力的影响.试验结果表明,采用植GFRP筋和包裹CFRP布的组合加固技术较前两种加固方法能更加有效地改善钢筋混凝土柱的抗震性能.     

新型分阶段屈服型软钢阻尼器的试验研究及数值模拟

为弥补现有软钢阻尼器存在的不足,本文在耗能钢片的形状及组合规律方面加以改进,研发了一种剪切弯曲组合型分阶段屈服软钢阻尼器。采用试验和有限元模拟相结合的研究方法,探讨其基本性能和抗疲劳性能。试验结果显示这种阻尼器具有稳定的滞回性能和抗疲劳性能,表明了这种分阶段屈服型软钢阻尼器耗能效果明显,实现了两阶段屈服耗能机制,具有较好的减震效果,数值模拟结果与试验结果吻合良好。该型阻尼器构造简单,制作方便,可采用模块化组装设计方法,有广阔的工程应用前景。     

Paper multilayer with a fracture toughness of steel

We demonstrate in this paper that commercially available printing paper can reach very high fracture toughness, comparable to that of steel, simply due to a special arrangement of the paper sheets with respect to the crack. Fracture mechanics experiments are conducted on single sheets of paper as well as on multilayer specimens in crack divider and crack arrester configuration. It is demonstrated that an arrangement in crack arrester configuration leads to an increase of the fracture toughness by a factor ten. An explanation of the effect is given and the transferability to other materials is discussed.     

不可分离结构的损耗因子测量研究

提出对不可分离结构内损耗因子和耦合损耗因子的测量方法。对于内损耗因子测量，针对实际工程中子结构不可分离的问题，提出了用总损耗因子代替内损耗因子的方法。对于耦合损耗因子测量，利用已测得的内损耗因子结合稳态振动实验测得的能量可计算出结构间耦合损耗因子。同时分析了耦合损耗因子大小对总损耗因子代替内损耗因子差值的影响。仿真结果表明，当耦合损耗因子远小于内损耗因子时，内损耗因子和总损耗因子近似相等。对双圆柱壳耦合结构进行了实验验证，实验结果证明了该方法的正确性。     

An electrochemical route to graphene oxide

Large-scale graphene oxide (GO) with adjustable resistivity was synthesized from graphite via an electrochemical method using KCl solution as an effective electrolyte. During the exfoliation process, electrostatic force intercalates chloride ions between the expanded graphite layers on the anode. These chloride ions form small gas bubbles between the graphite layers in the electrochemical reaction. It is believed that the gas bubbles expand the gap between graphite sheets and produce a separating force between adjacent graphene layers. This separating force overcomes the Van der Waals force between adjacent sheets and exfoliates graphene layers from the starting graphite. Because the graphene is electrochemically oxidized by chorine during the exfoliation, the exfoliated GO sheets are hydrophilic and easily dispersed in the electrolyte solution. The GO solution prepared by the electrochemical exfoliation can be simply sprayed or spin-coated onto any substrate for device applications. The measured average thicknesses of a monolayer, bilayer, and trilayer exfoliated GO on SiO2 substrate were 1.9, 2.8, and 3.9 nm, respectively. It was observed that the measured resistance of the exfoliated GO sheets increases due to electrochemical oxidation in the solution. This electrochemical approach offers a low-cost and efficient route to the fabrication of graphene based devices.     

Vibrating superconductors

This review is concerned with effects in the energy dissipation and elastic modulus of superconductors vibrating in a magnetic field. The physics of superconducting vibrating reeds and reeds made of superconducting suspensions is thoroughly described as well as the main features observed in other oscillators applied to flux pinning studies. It is argued that among the diversity of methods to study superconducting and pinning properties as a function of magnetic field and temperature, the vibrating reed technique is one of the most sensitive due to the accurate measurement of frequency and dissipation with feasible magnetometry applications. Results of the elastic coupling between the flux line lattice and the atomic lattice in high- and low-T _c superconductors obtained with the vibrating reed are summarized as well as the behavior of vibrating type II superconductors near their lower critical field. Results from mechanical measurements in high-temperature superconductors are reviewed, which support the model of thermally activated depinning and vortex diffusion.     

Determination of scanning efficiencies in experiments using nuclear emulsion sheets

During their exposure, nuclear emulsion sheets detect both tracks from experiment-related particles, as well as a considerable amount of background tracks, mainly due to cosmic rays. Unless the exposure has been fairly short, it is therefore fairly likely that a fraction of the tracks that have been identified as belonging to the particles the experiment is interested in, are really due to background. A method, which allows measurement of this fraction reliably directly from the data, is described.     

Formability of continuous cast 5052 alloy thin sheets

The formability of continuous cast 5052 alloy thin sheets from two different process schedules was examined. One was prepared in the laboratory by cold-rolling from a continuous cast thick plate followed by annealing (lab-processed sheet), and the other was produced by a new process involving hot-rolling followed immediately by in-line annealing (in-line annealed sheet). Tensile test results indicate that all the lab-processed sheets exhibit evident yield behavior. Increasing rolling reduction results in an increase of strength and a decrease of ductility in the lab-processed sheets due to increasing contribution of centerline segregation of second-phase particles. Both the lab-processed sheets annealed at 400 °C for 90 min and the in-line annealed sheets exhibit tensile elongation of more than 20% and two-stage strain hardening behavior. Compared with the lab-processed sheets, the in-line annealed sheet annealed at 454 °C has higher values of UTS and elongation. Furthermore, forming limit curves were determined. It is found that the level of the forming limit curve of the lab-processed thin sheet is lower than that of conventionally produced 5052-O Al, but close to that of 6111-T4 Al sheet. Moreover, the in-line annealed sheets have higher limit strains than the lab-processed sheets. These results demonstrate that the in-line annealing process results in the production of continuous cast alloy sheet with improved formability.     

Industrialization of Powder Compact Toaming Process

The potential for applying metal foams in lightweight construction is mainly based on the increased stiffness of two flat or curved sheets that are separated by a foam layer as compared to a single sheet of the same weight. By using sandwiches with an aluminum‐foam core, it is possible to obtain a higher stiffness and rigidity, maintaining stability against buckling and additionally making use of the high energy dissipation capability of the foams. A recent highlight in lightweight construction is the use of aluminum‐foam sandwiches (AFSs) in space‐frame constructions.     

基于ISO 13660的数字印刷线条质量分析与评价

根据ISO 13660标准建议的测量方法,使用基于扫描仪的数字印刷质量检测系统进行了线条印刷质量评价和分析。采用液体墨粉和固体墨粉的静电照相数字印刷机,分别在2种不同类型纸张上输出了数字印刷品作为测试样张。根据检测系统测得的数据,分别从线宽、粗糙度和模糊度等ISO 13660定义的线条和字符质量属性,分析和评估了2款数字印刷机输出的印刷品的线条质量。测量分析发现,由于2款数字印刷机在成像系统、结构设计和墨粉上的差异,使其线条质量上也存在差异。     

Measurement of cascade showers in lead with thermoluminescent sheets

A new type of detector, thermoluminescent (TL) sheets (BaSO₄:Eu), and a readout system for the TL sheets have been developed to study electromagnetic cascade showers in ultrahigh energy interactions. To perform a measurement of showers recorded in TL sheets, the longitudinal and radial development of an electromagnetic cascade shower in lead produced by accelerator electrons has been studied for comparison. Simulations of the longitudinal and radial development of cascade showers were also performed using the EGS code system.

This study is useful for the design of a thermoluminescent calorimeter (TLC) for the measurement of electromagnetic cascade showers originating from ultrahigh energy (above 10¹⁵ eV) interactions.     

Galvanomagnetic properties of AsF5-intercalated graphite

The galvanomagnetic properties of AsF₅-intercalated, highly-oriented, pyrolytic graphite (HOPG) were determined for stages 1 to 4 in the temperature range from 4.2 to 300 K using contactless eddy current methods forthe measurement of electrical conductivity and magneto-resistance and a new inductive technique forthe Hall effect. From the results p-type conduction, mean carrier mobility, total carrier concentration and charge transfer are deduced. The mobility is diminished upon intercalation due to an effective mass increase when the Fermi level is shifted by charge transferfrom AsF₅ to graphite layers. Charge transfer reaches a maximum of 1/3 for stage-2 compounds. The temperature dependence of galvanomagnetic effects yields carrier scattering at crystallite boundaries for low temperatures and scattering at phonons of both intercalated layers and graphite sheets for higher temperatures. Magnetoresistance of low-sage compounds exhibits anomalies at low temperatures resulting in an overestimation of mobility and saturation at magnetic Wd strengths where the low field approximation still should be vali? For magnetic fields of several kiloGGuss a reduction of the magnetoresistance was observed. It is suggested that these effects are due to trigonal warping of the graphite energy bands and to diffuse scattering at crystallite boundaries.