爆轰加载下高纯铜界面Rayleigh-Taylor不稳定性实验研究

金属界面不稳定性是内爆物理压缩过程中关注的重要问题,与传统流体界面不稳定性具有显著区别.由于相关理论和实验诊断技术的限制,目前该问题的研究还明显不足.为加深对金属界面不稳定性扰动增长行为的认识,本文建立了爆轰加载下高纯铜界面Rayleigh-Taylor不稳定性研究的实验诊断技术和数据处理方法,得到了扰动发展早期不同时刻界面扰动增长的X光图像.实验结果分析表明:在爆轰产物的无冲击加载条件下扰动波长基本保持不变,而初始扰动幅值越大,界面扰动增长的趋势就越明显;同时随着样品前界面扰动的不断发展,在样品的后自由面也出现了与前界面初始相位相反的扰动特征,即样品前界面扰动为波谷的位置所对应的后界面先运动而逐渐演变为波峰,而前界面扰动为波峰的位置所对应的后界面则演变为波谷;在5.26μs时刻,界面扰动幅值增长为初始值的700%左右,应变率达到了约105/s.结合数值模拟研究表明:在此情况下常用的Steinberg-Cochran-Guinan模型在一定程度上低估了高纯铜材料强度的强化特性,无法准确地描述强度对界面扰动增长的制稳作用,从而导致数值模拟结果要大于实验测量结果.     

纳晶铜晶粒尺寸对热导率的影响

用热压烧结法制备得到纳晶铜块体. 用激光法测定了不同温度下制备得到的纳晶铜块体的热导率, 并建立卡皮查热阻模型对样品热导率进行模拟. 通过对比, 模拟结果与实验数据基本一致. 随着热压烧结温度的升高, 纳晶铜晶粒尺寸也随之增大. 在900和700 ℃其热导率分别达到了最大和最小值且所对应的热导率分别为200.63和233.37 W·m^-1·K^-1, 各占粗晶铜块体热导率的53.4%和60.6%. 验证了纳晶铜热导率在一定的晶粒尺寸范围内具有尺寸效应, 随着晶粒尺寸的减小, 热导率逐渐减小.     

Roles of grain boundary and dislocations at different deformation stages of nanocrystalline copper under tension

The plastic deformation of nanocrystalline copper subjected to tension has been studied using molecular dynamics simulation. The results show that, in the initial stage, the deformation is mainly boundary-mediated in small grains; while in the late stage, the deformation is accommodated by dislocations in large grains. It is also found that the stress-assisted grain growth occurs owing to atomic diffusion and grain boundary migration. These results are consistent with recent experimental observations.     

Effect of a fullerene C60 addition on the strength properties of nanocrystalline copper and aluminum under shock-wave loading

The Hugoniot elastic limit and the spall strength of aluminum and copper samples pressed from a mixture of a metallic powder and 2–5 wt % C₆₀ fullerene powder are measured under a shock loading pressure up to 6 GPa and a strain rate of 10⁵ s^?1 by recording and analyzing full wave profiles using a VISAR laser interferometer. It is shown that a 5% C₆₀ fullerene addition to an initial aluminum sample leads to an increase in its Hugoniot elastic limit by an order of magnitude. Mixture copper samples with 2% fullerene also exhibit a multiple increase in the elastic limit as compared to commercial-grade copper. The elastic limits calculated from the wave profiles are 0.82–1.56 GPa for aluminum samples and 1.35–3.46 GPa for copper samples depending on the sample porosity. The spall strength of both aluminum and copper samples with fullerene additions decreases approximately threefold because of the effect of high-hardness fullerene particles, which serve as tensile stress concentrators in a material under dynamic fracture.     

爆轰加载下金属样品的熔化破碎现象诊断

本文在传统Asay窗技术基础上设计发展了一种用于诊断熔化状态下 金属样品表面附近一定厚度区域内熔化破碎现象的Asay-F窗技术, 较准确给出了该区域熔化破碎物质的质量和密度分布信息, 并与表面微喷和固体层裂片的特征进行了比对分析, 为熔化破碎现象的形成机理认识和物理建模提供了重要实验数据. 而且研究表明Asay-F窗技术可在一定程度上弥补目前熔化破碎现象 主要依靠高成本质子照相技术诊断的不足. 关键词： 爆轰加载 熔化破碎 Asay-F窗     

Mechanical properties of nanocrystalline copper under thermal load

The material properties of nanocrystallines are known to generally have a strong dependence on their nanoscale morphology, such as the grain size. The Hall-Petch effect states that the mechanical strength of nanocrystalline materials can vary substantially for a wide range of grain sizes; this is attributed to the competition between intergranular and intragranular deformations. We employed classical molecular dynamics simulations to investigate the morphology-dependent mechanical properties of nanocrystalline copper. The degradation of material properties under thermal load was investigated during fast strain rate deformation, particularly for the grain size. Our simulation results showed that the thermal load on the nanocrystalline materials alters the grain-size behavior of the mechanical properties.     

Study of the effects of grain size on the mechanical properties of nanocrystalline copper using molecular dynamics simulation with initial realistic samples

Abstract

Molecular dynamics simulations have been performed to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 9.0 and 24 nm. A melting–cooling method has been used to generate the initial samples: this method produces realistic samples that contain defects inside the grains such as dislocations and vacancies. The results of uniaxial tensile tests applied to these samples reveal the presence of a critical mean grain size between 16 and 20 nm, for which there is an inversion of the conventional Hall–Petch relation. The principal mechanisms of deformation present in the samples correspond to a combination of dislocations and grain boundary sliding. In addition, this analysis shows the presence of sliding planes generated by the motion of perfect edge dislocations that are absorbed by grain boundaries. It is the initial defects present inside the grains that lead to this mechanism of deformation. An analysis of the atomic configurations further shows that nucleation and propagation of cracks are localised on the grain boundaries especially on the triple grains junctions.     

光斑尺寸对光学薄膜元件温升的影响

 实验测量了波长1 064 nm, 10 kHz高重复频率激光辐照下在白宝石、石英玻璃、K9基片上制备的Ta₂O₅/SiO₂高反膜的温度变化,有限元分析的结果与实验结果相一致。用ANSYS程序计算了不同光斑直径、相同功率激光和相同功率密度激光辐照下薄膜元件温升的变化。结果表明：相同功率激光辐照光学薄膜元件时,光斑大小只影响激光辐照点的温升,对基板温升没有影响。基板温升只与激光功率有关,激光功率越大,基板温升越大。相同功率密度激光辐照光学薄膜元件时,光斑越大,激光辐照点温度及基板温度均越高。从激光损伤的热效应考虑,小光斑激光辐照时,光学薄膜的激光损伤阈值较高。     

The effect of grain refining on the microsegregation of aluminium–magnesium alloy 5182

Aluminium alloy 5182 (AA5182) contains approximately 4.5% Mg as its principal alloying addition, and is most commonly used to make the lid of the aluminium can. With a view to the possible future development of a micro-macro model to describe the casting of this alloy, the effect of grain refinement on the microsegregation of magnesium in industrial rolling ingots of AA5182 has been investigated at three different depths beneath the edge of the ingot (and hence three different cooling rates)—60, 140 and 600 mm. The accuracy with which published microsegregation models are able to predict the solute distribution profile is assessed. It has been found that the magnesium segregation range (C_max–C_min) of the grain refined samples actually increases as cooling rate decreases. The range of the non grain refined samples is independent of cooling rate. The solute concentration profiles of the theoretical microsegregation models examined do not correlate well with the experimentally measured profiles. It is concluded that this poor correlation is due to either the effect of post solidification homogenisation or the influence of macroscopic variables during the cast. A more accurate model of post solidification homogenisation is required to assess the relative contribution of each of these factors to the poor correlation. In addition, it is concluded that the measurement of segregation is best done using a combination of EDX mapping and point analysis techniques to locate and quantify the areas of maximum and minimum solute concentration.     

Simulated defect growth avalanches during deformation of nanocrystalline copper

In this work we introduce a method to capture the proliferation of material defects that carry inelastic deformation, in microstructures simulated through isobaric–isothermal molecular dynamics. Based on the premise that inelastic dissipation is accompanied by a local temperature rise, our method involves analyzing the response of a chain of Nosé–Hoover thermostats that are coupled to the atomic velocities, while the microstructure deforms under the influence of a ramped external stress. We report results obtained from the uniaxial deformation of two nanocrystalline copper microstructures and show that our analysis allows the dissipative signal of a variety of inelastic events to be effectively unified via an ‘avalanche’ of dissipation. Based on this avalanche, we quantitatively compare dissipation for inelastic deformation under tension vs. compression, observing a significant tension–compression asymmetry in this regard. It is concluded that the present method is useful for discerning critical points that correspond to collective yield and inelastic flow.     

单级电磁感应线圈发射器温升研究

同步感应式线圈型电磁发射器主要采用脉冲电流对线圈直接供电,其实际工作过程中电枢和线圈会产生温升,这是当前制约线圈发射器向小型化、高速发展的一个主要因素。本文通过建立电磁线圈的温升模型,对于单次触发的情况,分别利用Comsol和自编程序Coilgun进行计算,并搭建相应的试验平台进行验证。采用直接耦合方式的Comsol计算结果最为准确,也能考虑材料参数随温度的变化。仿真得到电枢的温升大约为4.2 ℃,线圈最大温升为7.7 ℃。由于热电偶温度传感器的测量延迟性与采样频率的限制,电枢温度试验曲线未能测量到仿真曲线中出现的温度最大值点,可记录到整个试验过程中温度变化曲线,其变化形势以及最终稳定的温度与仿真的基本一致,误差最大为6.1%,说明了仿真的准确性。为后续进行多级线圈连续发射奠定基础。     

Study of temperature rise during focused Ga ion beam irradiation using nanothermo-probe

Estimation of temperature rise during focused ion beam irradiation is of immense importance, since it affects various processes related to micro-machining and deposition. When ion beam impinges on a surface, it transfers its kinetic energy by way of electronic excitations and collisions, which eventually gets converted in the form of heat leading to rise in local temperature. This temperature rise affects and governs the properties of the machined region. The temperature rise can be calculated on the basis of energy deposition and heat transfer. However, there are very few reports on the measurement of such local temperature rise which lasts for very short time. We have designed and fabricated nanothermocouples of Pt-W to monitor local temperature rise (i) near a microheater and (ii) in the close proximity of an intense focused ion beam spot on a substrate. The junctions having size of 100 nm × 100 nm have been fabricated using focused ion beam chemical vapor deposition (FIB-CVD). The nanothermocouples have shown a fast response to the changes in temperature. These nanothermocouples can find useful applications in thermal characterization of nanomaterials and for understanding of temperature mediated phenomena in the samples treated under directed energy deposition processes, e.g. ion, laser and electron beam treatment.     

Size effect on the magnetism of nanocrystalline Ni films at ambient temperature

Size effect on the magnetization and the coercivity of nanocrystalline Ni films has been examined at room temperature. Agreement between modeling predictions and measurements reveals that the size-suppressed magnetization results from the drop of spin-spin exchange energy due to the coordination number (CN) imperfection of atoms near the surface edges, and that the size-enhanced coercivity arises from intergrain interaction that is proportional to the inverse of particle size. Findings herewith and reported previously on the size-induced lattice contraction and Curie temperature suppression evidence the significance of atomic CN imperfection on the unusual behavior of a ferromagnetic nanosolid.     

爆轰加载下弹塑性固体Richtmyer-Meshkov流动的扰动增长规律

研究了冲击波加载弹塑性材料扰动自由面的动力学演化过程,分析了高能炸药爆轰驱动时初始扰动与材料性质对扰动增长的影响.研究结果表明:初始扰动的振幅与波长之比越高,扰动越易增长,强度越高的材料扰动增长幅度越小;扰动增长被抑制时,尖钉的最大振幅与增长速度无量纲数之间存在线性近似关系,进一步理论分析表明尖钉的振幅增长因子与加载压力、初始扰动形态和材料强度有关,该理论关系作为扰动增长规律的线性近似在一定范围内适用于多种金属材料.     

空腔铜靶的化学镀制研究

介绍了在预处理芯轴(聚甲基丙烯酸甲酯)表面采用化学镀的方法制备铜空腔的技术,研究了镀液中硫酸铜含量、甲醛含量,镀液pH值、温度等对化学镀铜沉积速率和溶液稳定性的影响。根据实验确定了适宜的化学镀铜工艺规范：硫酸铜质量浓度10~20 g/L,TART·K·Na质量浓度10~30 g/L,EDTA·2Na质量浓度10~28 g/L,甲醛体积浓度10~25 mL/L,添加剂质量浓度10 mg/L,pH值12~13,温度35~65 ℃。通过该工艺制备出的镀层厚度达到10～25 μm,均匀性达到95%,表面无砂眼、裂纹等缺陷,刻蚀芯轴后空腔能自持。该方法为ICF研究制备金属或合金材料靶提供了新的途径。     

空腔铜靶的化学镀制研究

 介绍了在预处理芯轴(聚甲基丙烯酸甲酯)表面采用化学镀的方法制备铜空腔的技术,研究了镀液中硫酸铜含量、甲醛含量,镀液pH值、温度等对化学镀铜沉积速率和溶液稳定性的影响。根据实验确定了适宜的化学镀铜工艺规范：硫酸铜质量浓度10~20 g/L,TART·K·Na质量浓度10~30 g/L,EDTA·2Na质量浓度10~28 g/L,甲醛体积浓度10~25 mL/L,添加剂质量浓度10 mg/L,pH值12~13,温度35~65 ℃。通过该工艺制备出的镀层厚度达到10～25 μm,均匀性达到95%,表面无砂眼、裂纹等缺陷,刻蚀芯轴后空腔能自持。该方法为ICF研究制备金属或合金材料靶提供了新的途径。     

Study on the negative bias temperature instability effect under dynamic stress

This paper studies negative bias temperature instability (NBTI) under alternant and alternating current (AC) stress.Under alternant stress,the degradation smaller than that of single negative stress is obtained.The smaller degradation is resulted from the recovery of positive stress.There are two reasons for the recovery.One is the passivation of H dangling bonds,and another is the detrapping of charges trapped in the oxide.Under different frequencies of AC stress,the parameters all show regular degradation,and also smaller than that of the direct current stress.The higher the frequency is,the smaller the degradation becomes.As the negative stress time is too small under higher frequency,the deeper defects are hard to be filled in.Therefore,the detrapping of oxide charges is easy to occur under positive bias and the degradation is smaller with higher frequency.     

二氧化硅气凝胶的防爆震性能及机理研究

利用聚偏二氟乙烯压电传感器研究了爆炸加载下冲击波在二氧化硅气凝胶中的传播特性,并对冲击波在二氧化硅气凝胶和泡沫铝中的传播特性进行了比较.结果表明:在二氧化硅气凝胶中冲击波的强度随传播距离的增加呈现指数衰减的趋势.冲击波在二氧化硅气凝胶中衰减比在泡沫铝中衰减明显.由于二氧化硅气凝胶内部特殊的纳米多孔网状结构,导致冲击波在二氧化硅气凝胶中的衰减效果较好.冲击波在二氧化硅气凝胶中的传播速度极低,因此冲击波在二氧化硅气凝胶中传播时卸载波的追赶卸载效应非常明显,这又进一步促进了冲击波的衰减.