TATB基PBX结合能和力学性能的理论研究

以SCF-MO-AM1方法和MM-COMPASS力场, 对TATB (1,3,5-三氨基-2,4,6-三硝基苯)与系列高聚物组成的PBX(高聚物粘结炸药)尺寸匹配原子簇, 分别进行全优化几何构型计算, 发现两种方法求得的结合能存在良好的线性关系. 对TATB (3×3×4)超晶胞及其与系列氟聚物组成的双组分PBX, 实施COMPASS力场下的分子动力学(MD)周期性模拟计算, 首次求得其弹性系数、模量和泊松比, 发现添加少量高聚物即能有效改善炸药的力学性能.     

TATB/氟聚物PBX沿不同晶面力学性能的分子动力学模拟

用分子动力学(MD)方法, 模拟计算了著名钝感炸药TATB(1, 3, 5-三氨基-2, 4, 6-三硝基苯)与四种氟聚合物[聚偏二氟乙烯(PVDF)、聚三氟氯乙烯(PCTFE)、氟橡胶(F₂₃₁₁)、氟树脂(F₂₃₁₄)]构成的高聚物粘结炸药(PBX)的力学性能. 结果表明, 在TATB中添加少量氟聚物能有效改善其力学性能; 沿TATB不同晶面与氟聚物“粘结”, 构成PBX的力学性能有所不同, 改善力学性能的整体效应为(010)≈(100)>(001).     

HMX/TATB复合材料弹性性能的MD模拟

用分子动力学(MD)方法COMPASS力场, 分别在正则系综(NVT)和等温等压系综(NPT)下, 模拟计算了著名常用高能炸药HMX(环四甲撑四硝胺)与著名钝感炸药TATB (1,3,5-三氨基-2,4,6三硝基苯)所构成的混合体系在室温时的弹性性能和结合能. 结果表明, 在NVT和NPT两种系综下模拟所得结果呈平行一致的趋势; 与纯HMX相比, HMX/TATB复合材料的拉伸模量、体模量和剪切模量均有所下降; 在NVT系综下, 还完成了HMX/TATB混合体系的不同温度的MD模拟. 发现当温度在245～345 K范围时, 体系的刚性和弹性变化很小; 但当温度达到395 K时, 材料的刚性减弱, 柔性增强.     

VDF-CTFE共聚物在TATB表面吸附链构象的分子动力学模拟

采用COMPASS力场和NVT正则系综的动力学计算模拟了偏氟乙烯(PVDF)与三氟氯乙烯(PCTFE)及其共聚物在1,3,5-三氨基-2,4,6-三硝基苯(TATB)表面吸附能和吸附链的构象. 结果表明, 氟聚合物链与TATB表面距离小于0.8 nm时, 产生吸附放热效应. 在TATB表面, PVDF有强吸附作用, 而PCTFE的吸附能力差. 对VDF与CTFE单体摩尔比为1∶1, 1∶2, 1∶3和1∶4的共聚物吸附模拟结果表明, 共聚物的组成和链的序列结构对其在TATB表面的吸附行为和吸附链构象影响很大. 单体摩尔比为1∶2的交替共聚物链的吸附效果最佳. 随着共聚物链段中PCTFE链节的增加, 聚合物链的刚性增大, 在TATB表面吸附能力逐渐下降、吸附能亦降低, 尾型(tail)或环型(loop)构象数逐渐增多.     

PETN基PBX结合能和力学性能的理论研究

PETN(季戊四醇四硝酸酯)是著名的硝酸酯类猛炸药,用量子力学(QM)、分子力学(MM)和分子动力学(MD)方法,计算模拟其与高聚物组成的PBX(高聚物粘结炸药)的结合能和力学性能.以AM1-MO法和MM方法取PETN与系列高聚物的尺寸匹配原子簇模型,经几何全优化计算,发现两种方法求得的结合能彼此线性相关.对PETN超晶胞及其与系列氟聚物组成的双组分PBX,实施COMPASS力场下的分子动力学(MD)周期性模拟,求得其弹性系数、拉伸模量、体模量、剪切模量和泊松比,发现添加少量高聚物确能有效改善炸药的力学性能.     

TATB基PBX结合能的分子动力学模拟

用分子动力学（MD）方法, 模拟计算了四种氟聚合物(聚偏二氟乙烯（PVDF）、聚三氟氯乙烯（PCTFE）、氟橡胶（F₂₃₁₁)、氟树脂(F₂₃₁₄))与TATB(1,3,5- 三氨基- 2,4,6- 三硝基苯)晶体的相互作用. 结果发现, 四种氟聚物与TATB的结合能大小排序为PVDF>F₂₃₁₁>F₂₃₁₄>PCTFE, 各氟聚物在TATB不同晶面上的结合能大小排序为(001)>(010)>(100), 结合能主要由分子间氢键决定.     

ε-CL-20基PBX结构和性能的分子动力学模拟——HEDM理论配方设计初探

以高能量密度化合物ε-CL-20(六硝基六氮杂异伍兹烷)为主体,分别添加5种高聚物黏结剂(Estane5703、GAP、HTPB、PEG和F2314)构成高聚物黏结炸药(PBXs).用分子动力学(MD)方法模拟研究各PBX的结合能、相容性、安全性、力学性能和能量性质,通过比较和分析,为优选黏结剂、指导HEDMs配方设计提供信息和规律.由结合能预测各PBX的相容性和稳定性排序为:ε-CL-20/PEG>ε-CL-20/Estane5703≈ε-CL-20/GAP>ε-CL-20/HTPB>ε-CL-20/F2314.以对相关函数g(r)描述了组分之间相互作用的方式.5种黏结剂的少量加入均能显著改善ε-CL-20的弹性力学性能,增强各向同性.各黏结剂并非通过改变ε-CL-20的分子结构影响PBX的感度.它们主要通过自身的热容(C°p)和密度(ρ)影响PBX的安全性和能量性质.     

HMX/F2311 NPT高聚物粘合炸药力学性能的NPT系综分子动力学模拟研究

本文用分子动力学模拟方法研究了以β型奥克托金(β-HMX)含能材料为基,以氟聚物F2311为粘合剂的高聚物粘合炸药(PBX)的力学性能。β-HMX晶体和以其为基的高聚物粘合炸药的弹性常数均由静态弹性常数分析法计算求得，而工程模量和泊松比则由Reuss平均法导出。根据柯西压和本体模量与剪切模量的比值，发现通过加入少量该种聚合物可有效地提高HMX晶体的延展性。     

HMX和HMX/HTPB PBX的晶体缺陷理论研究

建立空位和掺杂点缺陷模型, 用分子动力学(MD)方法, 研究晶体缺陷对β-环四亚甲基硝胺(HMX)和β-HMX/HTPB(端羟基聚丁二烯)高聚物粘结炸药(PBX)的力学性能和爆炸性能的影响. 结果表明, 相对于HMX“完美”晶体(1)考察缺陷晶体(2和3), 以及相对于HMX完美晶体基PBX(1)考察缺陷PBX 2和PBX 3, 均发现弹性系数和(拉伸、体积、剪切)模量下降, 导致体系刚性减弱, 延展性和韧性增强. 这与在基炸药HMX晶体(1, 2和3)中分别加入HTPB高聚物粘结剂形成PBX 1, PBX 2和PBX 3呈现类似的相应的变化趋势和效果. 此外, 研究表明, 爆炸性质也依赖于体系的组成和结构. 因加入的是低能高聚物, 故PBX(1), PBX(2)和PBX(3)的爆热、爆速和爆压均比相应的基炸药(1, 2和3)低, 即晶体(1)＞PBX(1), 晶体(2)＞PBX(2), 晶体(3)＞PBX(3). PBX(1), PBX(2), PBX(3)与对应基炸药(1, 2, 3)的爆速和爆压取相同变化次序, 亦即PBX(1)＞PBX(2)＞PBX(3)对应于晶体(1)＞晶体(2)＞晶体(3). 这些计算结果和规律对PBX配方设计显然具有指导作用.     

CL-20/HMX共晶及其为基PBX界面作用和力学性能的MD模拟研究

为提高共晶炸药的实际使用价值, 改善其安全性和力学性能, 以CL-20/HMX共晶炸药为基, 分别添加2种高聚物粘结剂Estane 5703(聚氨基甲酸乙酯)和HTPB(端羟基聚丁二烯), 共构建两种共晶基高聚物粘结炸药(PBX)模型, 进行细致的295 K NPT分子动力学(MD)模拟研究. 通过两种PBX模型及其与该共晶炸药的MD模拟结果比较表明, 与基炸药之间的结合能Estane 5703大于HTPB, 预示含少量Estane 5703的PBX稳定性和相容性更佳; 对相关函数g(r)揭示粘结剂与基炸药界面相互作用的方式, 以基炸药中H分别与Estane 5703中羰基O和HTPB中端羟基O之间的氢键较强. 与CL-20/HMX共晶炸药相比, 少量粘结剂Estane 5703或HTPB的加入, 使弹性系数C_ij下降, 拉伸模量(E)、体积模量(K)和剪切模量(G)均显著减小, 而泊松比(ν), 柯西压(C₁₂－C₄₄)和K/G值明显增大, 表明PBXs体系刚性减小, 延展性增强, 力学性能大为改善. 少量粘结剂包覆使PBXs致钝, 主要归因于其隔热、吸热并使体系变“软”的缓冲作用, 而界面作用造成的分子结构引发键键长变化变为次要因素.     

TATB/聚三氟氯乙烯复合材料力学性能的MD模拟

Molecular dynamics（MD）was performed to simulate and calculate the combination energy and static mechanical properties（i. e. elastic coefficient,modulus and poisson's ratio）of composite material,1,3,5-triamino-2,4,6-trinitrobenzene coated with polychlorotrifluoethylene（TATB / PCTFE）. It is found that the intermolecular interaction especially H-bond is quite strong. The results show that the elastic properties of Fluorine-Polymer Bonded Explosive（PBX）have changed much compared to those of pure TATB. Its tensile modulus,bulk modulus and shear modulus are reduced evidently. The rigidity of PBX is lowered while the elasticity is increased,which manifests the mechanical property of PBX is improved greatly.     

Temperature dependence of the dynamic mechanical properties of filled polymers

A theory has been developed to explain the jump in the relative modulus of filled polymers near the glass transition temperature T_g and the subsequent decrease in relative modulus at temperatures above the glass transition temperature. The theory is based upon the concept that there are some particle–particle contacts in doublets and in agglomerates containing a larger number of particles. Below T_g motion of particles at the contact points is possible because of the high modulus of the polymer. At T_g particle–particle motion mostly ceases because of the low modulus of the polymer. At higher temperatures, the mismatch in the coefficients of expansion allows some motion to occur at points of contact and slippage may occur at the polymer–particle interfaces, so the modulus decreases. It is shown theoretically and experimentally that both the elastic modulus and the mechanical damping depend upon the nature of the surface of the particles.     

Structural,mechanical, electronic,and thermodynamic properties of pure tungsten metal under different pressures: A first-principles study

The structural, mechanical, electronic, and thermodynamic properties of pure W metal under different pressures have been investigated using the first-principles method. Our calculated structural parameters are in good agreement with experimental and previous theoretical results. The obtained elastic constants show that pure W metal is mechanically stable. Elastic properties such as the bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (ν), Cauchy pressure (C′), and anisotropy coefficients (A) are calculated by the Voigt-Reuss-Hill method. The results show that the pressure can improve the strength of pure tungsten and has little effect on the ductility. In addition, the total density of states as a function of pressure is analyzed. Thermodynamic properties such as the Debye temperature, phonon dispersion spectrum, free energy, entropy, enthalpy, and heat capacity are also discussed.     

TATB/氟聚物PBX力学性能、结合能和爆炸性能的模拟计算

Molecular dynamics （MD） method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene （TATB） coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It was found that when the number of chain monomers of fluorine containing polymers was the same, the elasticity of TATB/F2314 was increased more greatly than others and the binding energy of TATB/F2311 was the largest among four PBXs. Detonation heat and velocity of such four PBXs were calculated according to theoretical and empirical formulas. The results show that the order of detonation heat is TATB〉TATB/PVDF〉TATB/F2311〉TATB/ F2314 〉 TATB/PCTFE while the order of detonation velocity is TATB/PVDF 〈 TATB/F2311 〈 TATB/F2314 〈 TATB/PCTFE 〈TATB.     

Molecular dynamics simulations for pure epsilon-CL-20 and epsilon-CL-20-based PBXs

Molecular dynamics has been employed to simulate the well-known high energy density compound epsilon-CL-20 (hexanitrohexaazaisowurtzitane) crystal and 12 epsilon-CL-20-based PBXs (polymer bonded explosives) with four kinds of typical fluorine polymers, i.e., polyvinylidenedifluoride, polychlorotrifluoroethylene, fluorine rubber (F(2311)), and fluorine resin (F(2314)) individually. The elastic coefficients, isotropic mechanical properties (tensile moduli, bulk moduli, shear moduli, and poission's ratios), and bonding energy are first reported for epsilon-CL-20 crystal and epsilon-CL-20-based polymer bonded explosives (PBXs). The mechanical properties of epsilon-CL-20 can be effectively improved by blending with a small amount of fluorine polymers, and the whole effect of the adding fluorine polymers to improve mechanical properties of PBXs along the three crystalline surfaces of epsilon-CL-20 is found to be (100) approximately (001) > (010). The interaction between each of the crystalline surfaces and each of the fluorine polymers is different, and the ordering of binding energy for the three surfaces is (001) > (100) > (010); F(2314) always has the strongest binding ability with the three different surfaces. F(2314) can best improve the ductibility and tenacity of PBX when it is positioned on epsilon-CL-20 (001) crystal surface. The calculations on detonation performances for pure epsilon-CL-20 crystal and the four epsilon-CL-20-based PBXs show that adding a small amount of fluorine polymer into pure epsilon-CL-20 will lower detonation performance, but each detonation parameter of the obtained PBXs is still excellent.     

Mechanical and viscoelastic properties of confined amorphous polymers

Confinement of polymers to nanoscale dimensions can dramatically impact their physical properties. Substantial efforts have focused on the glass transition temperature (T_g) of polymers confined to thin films, but their mechanical properties are less studied despite their technological importance. In this review, challenges with mechanical measurements of polymer thin films are discussed along with novel metrologies that provide insight into their mechanical properties. A comparison of experimental measurements, simulations and theory provide several general conclusions about the mechanical properties under confinement. Confinement impacts the elastic modulus, rubbery compliance and viscosity of polystyrene, the archetypal polymer for confinement, but the confinement effect appears to depend on the measurement technique. This effect may be due to the details of averaging of gradients in properties that are dependent on the measurement details. Routes to minimize confinement effects are addressed. Despite progress in the measurements of mechanical properties of polymer thin films, there remain unresolved questions about the impact of confinement, which we highlight at the end of this review. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 9–30     

HTPB/增塑剂玻璃化转变温度及力学性能的分子动力学模拟

为了预测高分子粘结剂端羟基聚丁二烯(HTPB)与增塑剂癸二酸二辛酯(DOS)、硝化甘油(NG)的相容性及HTPB/增塑剂共混物的玻璃化转变温度(Tg)和力学性能,在COMPASS力场条件下采用分子动力学(MD)模拟方法对相容体系(HTPB-DOS)和不相容体系(HTPB-NG)进行了研究.结果表明,通过比较溶度参数差值(Δδ)的大小可以预测HTPB与增塑剂的相容性,即HTPB与DOS属于相容体系,而HTPB与NG不相容.通过温度-比容曲线可以得到HTPB、HTPB/DOS与HTPB/NG的Tg分别为197.54,176.30和200.03K.力学性能分析结果表明,添加DOS增塑剂后使HTPB的弹性模量(E),体积模量(K)和剪切模量(G)下降,材料刚性减弱,柔性增强,力学性能得到改善.本模拟方法可以作为预测聚合物/增塑剂共混物性能的有利工具,也可以为固体推进剂和高聚物粘结炸药的配方设计提供理论指导.