Fracture of high carbon high strength anchor rods

During a heavy windstorm, there was failure of anchors supporting transmission towers. We were given the mandate to examine the reasons for the failure of the anchor rods and suggest measures to prevent such failures from occurring. The study involved the in-depth examination of the chemical composition, microstructures, mechanical properties and fracture morphologies of specimens from failed anchors. Results indicated that the chemical composition, yield and tensile strengths of the anchor rods are within the norm of ASTM standard A722. The chemical composition corresponds to that of AISI 1070 with slightly higher manganese and silicon levels. Microstructure is ferrite–pearlite with dominance of pearlite due to the relatively high carbon content. Fracture surfaces of failed anchor rods exhibited pronounced cleavage facets (cleavage steps and river pattern) indicating that failure mode is brittle and the mechanism of fracture is cleavage. There were no signs for the occurrence of fatigue – any beach mark or striations. Final area of fracture showed traces of ductility (small shallow dimples). To prevent brittle failure of anchor rods, their toughness has to be improved. To achieve this, the potentiality of applying HSLA steel technology of micro alloying and TMCP (thermo mechanical control process) has been suggested.     

Black silicon with high density and high aspect ratio nanowhiskers

The physical properties of black silicon (b-Si) formed on Si wafers by reactive ion etching in chlorine plasma are reported in an attempt to clarify the formation mechanism and the origin of the observed optical and electrical phenomena, which are promising for a variety of applications. The b-Si consisting of high density and high aspect ratio sub-micron length whiskers or pillars with tip diameters of well under 3 nm exhibits strong photoluminescence (PL) both in the visible and the infrared, which is interpreted in conjunction with defects, confinement effects and near band-edge emission. Structural analysis indicates that the whiskers are all crystalline and encapsulated by a thin Si oxide layer. The infrared vibrational spectrum of Si-O-Si bondings in terms of transverse-optic (TO) and longitudinal-optic (LO) phonons indicates that disorder induced LO-TO optical mode coupling can be an effective tool in assessing the structural quality of the b-Si. The same phonons are likely coupled to electrons in visible region PL transitions. Field emission properties of these nanoscopic features are demonstrated indicating the influence of the tip shape on the emission. Overall properties are discussed in terms of the surface morphology of the nanowhiskers.     

Nanostructured organic-inorganic photodiodes with high rectification ratio

High quality organic-inorganic heterojunction photodiodes based on nanostructured copper (II) phthalocyanine (CuPc) and intrinsic zinc oxide (i-ZnO) have been fabricated. The i-ZnO thin films/layers were grown by RF magnetron sputtering on clean indium tin oxide (ITO) coated glass substrates. These films have been characterized by optical absorption and field emission scanning electron microscopy (FESEM). CuPc thin films deposited at room temperature on i-ZnO have exhibited a change in their surface morphology with the post-deposition annealing temperature under normal atmosphere. The electrical dark conductivity and the photoconductivity of ITO/i-ZnO/CuPc/Au sandwich structures have been measured under various photoexcitation intensities using a xenon light source. The devices have shown excellent reproducibility of their electrical characteristics and high rectification ratios. The highest rectification ratio is nearly 831 calculated above the threshold voltage at room temperature for the sample annealed at 250?°C (i.e.?Pc 250). The effects of the annealing temperature of CuPc on the surface morphology, rectification ratio, and optical properties have been discussed.     

Penetration with instrumented rods

The response of long rods during penetration is being examined by strain measurements performed with foil resistance gages. Early experiments in this investigation employed the reverse ballistic approach in which stationary rods were impacted by armor targets launched from a light-gas gun. Although satisfactory results were obtained for both normal and oblique impacts, the reverse ballistic approach strictly limited the target diameter, and the target mass limited the impact velocity to values below the range of current ballistic interest. In order to overcome the major limitations imposed by reverse ballistics a technique for launcing instrumented rods has been developed. With this technique strain gages on the rod are connected to thin metal contacts located on the front surface of the plastic sabot. Prior to impact, the contacts are pierced by stationary probes and a low-resistance electrical path is provided during approximately 100 mm of travel by the sabot. A series of impact tests has been performed at normal incidence with steel rods impacting steel targets at a velocity of 1000 m/s. Strain-time signals from these tests were amenable to a simple wave analysis which provided relationships between stress and strain, and particle velocity and strain, to strain of 15%. Results of the analysis are discussed in the context of their relationship to the experimental technique. Details of the experimental technique and its refinement are presented and problem areas are considered.     

Development of non-flammable high strength extruded Mg-Al-Ca-Mn alloys with high Ca/Al ratio

A series of non-flammable high strength Mg-Al-Ca-Mn alloys with high Ca/Al ratio were fabricated by water-cooled casting and hot extrusion. Microstructure and mechanical properties were investigated to study the effect of hot extrusion. The experimental results showed that hot extrusion significantly improved the mechanical properties by grain refinement and precipitates. Ignition temperature was measured by furnace test, and the highest temperature is up to approximately 1040?°C due to the composite oxide layer consisting of CaO and MgO. In addition, a laboratory-scale flame test was conducted to evaluate the flammability of smaller specimens. These alloys exhibited marvelous flame resistance attributed to the protective effect of dense and stable oxide film.     

Numerical analysis and modeling of jacketed rod penetration

A computational study to assess terminal ballistic performance issues of adding a steel sheath, or jacket, to a depleted uranium (DU) penetrator has been performed. The CTH hydrocode was used to model DU penetrators with steel sheaths of various thicknesses against semi-infinite rolled homogeneous armor (RHA), finite RHA, and oblique plate targets. Guided by the initial results, additional semi-infinite RHA simulations were performed to support the development of a generalized penetration model for jacketed rods. The model computes RHA penetration as a function of impact velocity and normalized jacket thickness (thickness over diameter) and compares very favorably with experimental DU and steel data. The model indicates that “bulk” density (areal density) can considerably underestimate jacketed rod penetration. In addition, some insight into the penetrator and target flow shape factors (k_p and k_t) is obtained.     

Formation of high aspect ratio GaAs nanostructures with metal-assisted chemical etching

Periodic high aspect ratio GaAs nanopillars with widths in the range of 500-1000 nm are produced by metal-assisted chemical etching (MacEtch) using n-type (100) GaAs substrates and Au catalyst films patterned with soft lithography. Depending on the etchant concentration and etching temperature, GaAs nanowires with either vertical or undulating sidewalls are formed with an etch rate of 1-2 μm/min. The realization of high aspect ratio III-V nanostructure arrays by wet etching can potentially transform the fabrication of a variety of optoelectronic device structures including distributed Bragg reflector (DBR) and distributed feedback (DFB) semiconductor lasers, where the surface grating is currently fabricated by dry etching.     

Experiments of high energy gain laser wakefield acceleration

The wakefield acceleration of electrons has a great potential for the future accelerator because of its high accelerating field gradient. We have obtained over 100 MeV acceleration gain by the wakefield generated by a 2 TW Ti: sapphire laser system. In the acceleration experiment, the 17 MeV electrons from a linac were used for the injection beam. The synchronization between the RF signal and the laser pulse was achieved within the time jitter of 3.7 ps. Due to the self-focusing and ionization, a long propagation length and high field gradient were realized. The self-focusing effect of the laser was confirmed by the laser spotsize measurement along the beam axis. The plasma density oscillation was measured by using the frequency domain interferometry. The acceleration gain expected from the plasma density measurement was consistent with the result of the acceleration experiments.     

Nanocomposites with increased energy density through high aspect ratio PZT nanowires

High energy storage plays an important role in the modern electric industry. Herein, we investigated the role of filler aspect ratio in nanocomposites for energy storage. Nanocomposites were synthesized using lead zirconate titanate (PZT) with two different aspect ratio (nanowires, nanorods) fillers at various volume fractions dispersed in a polyvinylidene fluoride (PVDF) matrix. The permittivity constants of composites containing nanowires (NWs) were higher than those with nanorods (NRs) at the same inclusion volume fraction. It was also indicated that the high frequency loss tangent of samples with PZT nanowires was smaller than for those with nanorods, demonstrating the high electrical energy storage efficiency of the PZT NW nanocomposite. The high aspect ratio PZT NWs showed a 77.8% increase in energy density over the lower aspect ratio PZT NRs, under an electric field of 15 kV mm(-1) and 50% volume fraction. The breakdown strength was found to decrease with the increasing volume fraction of PZT NWs, but to only change slightly from a volume fraction of around 20%-50%. The maximum calculated energy density of nanocomposites is as high as 1.158 J cm(-3) at 50% PZT NWs in PVDF. Since the breakdown strength is lower compared to a PVDF copolymer such as poly(vinylidene fluoride-tertrifluoroethylene-terchlorotrifluoroethylene) P(VDF-TreEE-CTFE) and poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP), the energy density of the nanocomposite could be significantly increased through the use of PZT NWs and a polymer with greater breakdown strength. These results indicate that higher aspect ratio fillers show promising potential to improve the energy density of nanocomposites, leading to the development of advanced capacitors with high energy density.     

A parametric study on synthesis of Ag nanowires with high aspect ratio

In this study, the effect of the experimental parameters of the polyol process on the aspect ratio of silver nanowires (AgNWs) was investigated. The one-factor-at-a-time method was adopted to analyze the effect of various parameters, such as the amount of reducing agent, seeds and the ratio of PVP/Ag, on the growth of AgNWs. The optimal parameters were determined to obtain a high aspect ratio of AgNWs. Synthesized AgNWs were analyzed by SEM, TEM, and XRD, and the four-point probe method was applied to measure the average aspect ratio, morphology, crystal direction, crystalline structure, and the electrically property of its sheet resistance. From the result of the morphology measurement, a high aspect ratio of 74.85 can be fabricated, where the average diameter and length were about ~55 and 4117 nm, respectively. Regarding electrical property, the sheet resistance of AgNWs with a high aspect ratio is about ~16.34 kΩ/sq with the film thickness of 142.1 nm. However, when the film thickness was increased to 1.123 µm, the resistance decreased to 3.012 Ω/sq.     

Experiments on expanded liquid metals at high temperatures

The electrical resistivity of liquid tungsten was measured using electric pulse heating of the wires inside capillary tubes. Under fast heating (10 µs) or slow heating (50 µs), the wire expands and fills the inner cavity of the capillary. On the oscillogram traces of the voltage drop across the wire, one can see the phases solid, liquid, fast expansion, and then the moment when the cavity is filled with the metal. Using the voltage drop, current, and volume of the capillary cavity, one can calculate the electrical resistivity,, of the expanded metal. Tungsten densities from 7.5 to 1 g · cm^–3(3 x 10²² to 0.5 x 10²² atoms · cm^–3) were investigated at temperatures from 10 x 10³ to 14 x 10³ K. For these densities, the electrical resistivity increased from 0.5 to 5m·cm.     

逐层剥离法测量高碳钢盘条残余应力

基于ASTXSTRESS3000型应力仪,结合化学腐蚀逐层剥离技术的基础上,研究了热轧高碳钢盘条及其拉拔钢丝的表面轴向应力,并测量了盘条内部铁素体的轴向应力分布.研究表明盘条及钢丝的表面状态对残余应力的测量值有重要的影响,盘条轴向应力沿横截面直径方向的分布比较均匀,接近于零应力的水平.经过应变量为1.8的连续拉拔形变后,钢丝外表面的轴向应力值明显提高,由原始盘条表面的6.4MPa,增加到500MPa左右.     

深高宽比微结构的干法刻蚀

介绍了深高宽比微结构在干法刻蚀过程中遇到的刻蚀滞后、刻蚀中止、侧壁弯曲和开槽效应等与传统器件刻蚀不同的现象,讨论了制作高深宽比结构所需的关键技术和检测手段.     

Profile simulation of high aspect ratio contact etch

A semi-empirical profile simulator was employed to better understand fundamental mechanisms of feature evolution in a high aspect ratio contact plasma etch process. Simulation results showed that the net deposition rate of polymer on sidewall defined the necking and surface scattering of ions from the secondary facet caused the formation of bowing. As neutral depositor flux was increased, the resulting profile showed a monotonic increase in necking. In contrast, the extent of bowing showed a maximum, such that minimal bowing was obtained at low and at high depositor fluxes. Primary faceting of photo resist showed only a small influence on the SiO₂ etch profile.     

大展弦比机翼随动加载方法与装置研究

大展弦比机翼载荷标定实验中,随着载荷的增加,机翼会发生弯曲变形,导致加载点的法向载荷方向发生变化,对载荷标定实验的准确性产生影响。为解决此问题,设计了一套大展弦比随动加载装置,该装置通过电缸控制加载点竖直方向的位移,通过位移台控制电缸水平方向的位移,利用联动控制系统使载荷标定实验中施加在机翼翼面的作用力与翼面始终保持垂直,保证机翼所受载荷始终沿法向。开展随动加载与砝码垂向加载对比实验,结果表明：随动加载获得的数据相关系数达到0.999,相较砝码垂向加载获得的数据相关系数0.976更优,验证了随动加载装置的有效性。该装置不仅具有体积较小、操作简便的优点,还为推动大展弦比机翼性能研究提供了有力支撑。