平面冲击下铜的拉伸应变率相关特性研究

本文对冲击加载下高纯无氧铜的拉伸应变率相关特性进行了实验研究.实验中利用磁测速系统测试撞击前飞片速度,利用光纤位移仪——多普勒探针系统测试样品自由面粒子速度剖面.对自由面速度剖面的特征参量进行计算分析,结果表明:铜样品的层裂强度随着拉伸应变率的增加而增加,对比发现层裂强度不仅受加载条件的影响,同时受到材料本身微细观结构影响;同时随着拉伸应变率的增加,自由面速度的回跳斜率呈现出先缓慢增加后迅速增加的临界特性;最后,通过层裂样品中波系相互作用,给出了自由面速度回跳过程中的振荡特征随着拉伸应变率增加而逐渐消失的物理过程.     

散体介质SHPB被动围压试验体应力计算的理论修正方法

SHPB被动围压试验为探究散体介质在爆炸和冲击荷载作用下的力学行为提供了一个行之有效的方法。针对相关试验设计和计算中存在的弊端和不足,借助经典板壳理论将SHPB被动围压试验中用于约束散体介质的刚性套筒简化为受均匀带状内压作用的圆柱形壳体。理论计算了套筒径向位移、环向应变与均匀带状内压及套筒几何、力学参数的关系,得到了套筒径向位移、环向应变沿其轴向的分布规律;分析了套筒长度、厚度、内外径以及均匀带状内压宽度之间等无量纲几何参数对计算结果的影响;将理论计算结果与试验和数值模拟结果进行对比,验证了理论计算结果的正确性。本文中提出的理论修正方法可为指导散体介质SHPB被动围压试验提供参考。     

轴向增强战斗部端部惰性填充物对端部破片飞散特性的影响

在当前破片战斗部动态毁伤场设计中,中心盲区效应被视为影响战斗部毁伤效率提高的关键因素。轴向增强战斗部作为消除战斗部动态中心盲区的重要手段,越来越受到相关研究人员的重视。本文中基于光滑粒子流体力学计算方法,建立了一系列轴向增强战斗部（端部分别含有惰性聚氨酯填充物、尼龙填充物和爆炸填充物）在爆炸载荷作用下的破碎和碎片散布过程的数值模型,并用于研究战斗部前端填充物特性对壳体动态响应的影响。数值模拟结果表明,填充物对战斗部前部破片的速度影响显著,但对破片飞散角度影响较弱。通过比较特定碎片的速度历史曲线,分析了惰性填料对碎片速度的影响机理。研究结果表明,聚氨酯泡沫填充物可以显著延缓爆炸冲击波对前破片的加速过程,并在一定程度上降低爆炸载荷,尼龙填充物可以在一定程度上降低前向破片和侧向破片的加速度,从而表明爆炸载荷被引导均匀分布在末端位置周围。结合战斗部自身的牵连速度,使用低密度和低质量填料代替头部装药具有相同的动态毁伤效果,可以提高轴向增强战斗部的能量利用效率。     

Enantioselective synthesis of enol lactones from tandem Michael addition/lactonization catalyzed by a chiral squaramide catalyst

The enantioselective tandem Michael addition reaction of dimedone and related 1,3-dicarbonyl compounds with α,β-unsaturated N-acylated succinimides catalyzed by a chiral squaramide catalyst has been investigated. This reaction provides a new approach for the synthesis of chiral enol lactones in good yields with moderate to high enantioselectivities (up to 88% ee) through the enantioselective Michael addition followed by lactonization and removal of the succinimide auxiliary.     

A theoretical prediction of the molecular and electronic structures,thermodynamic properties,and stability of 1,3-diazido-2-methyl-2-nitropropane (DAMNP)

1,3-Diazido-2-methyl-2-nitropropane (DAMNP) is a newly synthesized azido compound and may be a potential candidate of the plasticizer of propellants. For better understanding its properties, the molecular conformations, electronic structure, IR spectrum, thermodynamic properties, pyrolysis mechanism, and specific impulse (I _S) were studied using the B3LYP/6-31++G** method of density functional theory (DFT). The electronic structure of DAMNP was analyzed by the natural atomic charges, bond orders, donor–acceptor interactions, and molecular electrostatic potential (MEP). Results show that the main contributions to the highest occupied molecular orbital and the lowest unoccupied molecular orbital are from –N₃ and –NO₂, respectively. The most negative area on the MEP locates at the O atoms of –NO₂, which agrees with the atomic charges distributions. The pyrolysis mechanism was investigated by considering three possible bond dissociations (C–N₃, C–NO₂, and N–N₂). Results show that the pyrolysis of DAMNP starts from the rupture of N–N₂ finished cooperatively via the H-transfer process to eliminate N₂. The lowest energy needed for pyrolysis is 165.13 kJ mol^?1. To verify the reliability of the method, the organic azido compound CH₃N₃ was also considered. DAMNP has a slightly higher thermal stability than CH₃N₃. However, using DAMNP to replace the plasticizer nitroglycerin of the nitramine modified double-base propellant leads to a decrease in I _S. Therefore, whether DAMNP can be really used as a plasticizer or not is worth further considerations.     

Synthesis and performance studies of 1,5-diaminotetrazolium nitrate

1,5-Diaminotetrazolium nitrate (HDATN) was synthesized with 1,5-diaminotetrazole (DAT) as the raw material. The maximum yield of HDATN was 95.3 %. The structure was characterized by elemental analysis, infrared spectrum, nuclear magnetic resonance spectrum and mass spectrum, and the possible fragmentation mechanism was discussed. The morphology was analyzed by SEM. The thermal stability of HDATN was investigated by TG-DSC and DTA techniques. The kinetic parameters including activation energy and pro-exponential factor were calculated by Kissinger equation. The performance of combustion, combustion heat, and formation enthalpy of HDATN were measured. The detonation products of HDATN were most nitrogen, which were analyzed by gas chromatograph and smoke analyzer. The density, formation heat, detonation pressure, and detonation velocity of HDATN were calculated. It exhibited prospective application in environmentally friendly gas generant and explosion field.     

Mechanisms and kinetics for preparing carbohydrazide by reacting dimethyl carbonate with hydrazine: A theoretical study

The mechanism and kinetic modeling for preparing carbohydrazide from dimethyl carbonate and hydrazine has been declared. The geometries of all the stationary points (reactants, intermediates, transition states, and products) are optimized by using the B3LYP method with the cc‐pVDZ basis set, and the harmonic vibrational frequencies as well as infrared intensities are predicted with the same method. The minimum‐energy paths are obtained by using the intrinsic reaction coordinate (IRC) theory at the B3LYP/cc‐pVDZ level of theory with the step length 0.02 (amu)^1/2·bohr. The rate constants are evaluated by using the TST, TST/Eckart, and RRKM (T)/Eckart methods. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A Luminescent Metal-Organic Framework with Boosted Picric Acid Fluorescence Detection Performance via a Complementary Capture-Quench Mechanism

The strong explosiveness, toxicity and environmental pollution of picric acid make its sensitive detection important. Recently, LMOF materials are showing great potential toward efficient detection of PA. However, hindered by the weak connections between LMOFs and analytes, a feasible fluorescence selectivity and sensitivity to desired compounds by constructed LMOFs remain challenging. Herein, we propose a new strategy by using the innate adsorption ability of MOFs. We choose NDC−Zn, a highly stable LMOF with unique pore structures. The topology of ligands can capture PAs specifically inside the pores and the selectivities are further elevated. PET effects are boosted due to longer and closer contact between ligands and trapped PAs, thus higher sensitivity is also achieved. Besides, a fluorescence enhancement at a visible wavelength was found as the concentration of PA increased, suggesting a potential application of naked-eye recognition for PA. NDC−Zn exhibited an outstanding detection sensitivity for PA with a quenching constant of 49657 M⁻¹, as well as distinctive fluorescence quenching among 9 nitro explosives. From DFT calculations, the fluorescence quenching mechanisms such as PET and the complexation between H₂NDC and PA were supported.     

Synthesis, Crystal Structure and Thermal Analysis of (TAGH)2(TNR)

A new energetic compound (TAGH)₂(TNR) (TAG: triaminoguanidine, TNR: 2,4,6-trinitroresorcinol) was prepared by reacting triaminoguanidine with 2,4,6-trinitroresorcinol (styphnic acid) in aqueous solution under nitrogen atmosphere, and characterized by elemental analysis and Fourier transform infrared (FTIR) spectra. Its crystal structure was determined by single crystal X-ray diffraction analysis. The crystal belonged to a monoclinic, C 2/c space group. The unit cell parameters were as follows: a=2.2892(6) nm, b=1.2802(3) nm, c=1.3661(4) nm, β=111.174(5)°, V=3.7333(16) nm³, and Z=8. The compound consisted of two cations C(N₂H₃)₃⁺ and an anion (C₆HN₃O₈)²⁻. The C(N₂H₃)₃⁺ and (C₆HN₃O₈)²⁻ were bonded together by electrostatic attraction and hydrogen bonds, and this effect made the compound more stable. The thermal analysis of the compound was studied by using differential scanning calorimetry (DSC), thermogravimetry-derivative thermogravimetry (TG-DTG). Under nitrogen atmosphere with a heating rate of 10 K·min⁻¹, the thermal decomposition of the compound contained only one intense exothermic decomposition process in the range of 450.1-477.7 K in the DSC curve, and the decomposition products were nearly gaseous products.     

富氮配合物[Co(DAT)6](PA)2∙4H2O的制备、晶体结构和热分析

以1,5-二氨基四唑（DAT）为配体,苦味酸根（PA）为外阴离子制备得到了一种新的配合物[Co(DAT)6](PA)2∙4H2O,并通过X射线单晶衍射分析、元素分析和FT-IR分析技术对其进行了结构表征。中心钴（II）离子与六个DAT分子的六个N原子配位,形成一个六配位、略微畸变的八面体结构。配离子位于两个苯环互相平行的PA离子之间。在[Co(DAT)6](PA)2∙4H2O的分子单元中,配离子和PA离子通过静电引力连接;分子单元间通过分子间氢键连接形成配合物的晶体结构,DAT配体分子对于晶体结构的形成起到了重要作用。采用TG-DTG、DSC和FT-IR分析技术对目标化合物的热分解过程进行了研究,并采用Kissinger法和Ozawa-Doyle法对目标配合物第一放热分解过程的非等温反应动力学进行了计算。