A Direct Comparison of the Fragmentation Test and the Microbond Pull-out Test for Determining the Interfacial Shear Strength

Experiments were conducted to compare the fragmentation test with the microbond pull-out test for determining the interfacial shear strength between carbon AS4 fibers and a thermoset matrix consisting of a Di-Glycidyl Ether of Bisphenol A (DGEBA) resin cured with a diamine (meta-phenylenediamine, m-PDA) curing agent. The results indicate that, for the microbond test, diffusion of the rather volatile m-PDA curing agent at early stages of cure leads to low values of interfacial shear strengths when compared with results obtained for the same system with the fragmentation test.

With the microbond test, a distinct relationship between the glass transition temperature of the droplets and their size is noticed. Smaller (< 150 μm) droplets have very low Tg's and are incompletely cured. While changing to a modified curing cycle and/or using a m-PDA-rich curing environment alleviates the diffusion problem, the interfacial shear strength values are still not in good agreement with the fragmentation test results. Microbond data from another system consisting of DGEBA resin cured with a different, less volatile dimaine curing agent indicates that diffusion of the curing agent becomes less severe as the volatility of the curing agent decreases and the corresponding microbond interfacial shear strengths agree better with fragmentation test results.     

Emulsifier‐free reversible addition–fragmentation chain transfer emulsion polymerization of alkyl acrylates mediated by symmetrical trithiocarbonates based on poly(acrylic acid)

Emulsifier‐free batch emulsion polymerization of n‐butyl acrylate and its semi‐batch copolymerization with 2,2,3,3,4,4,5,5‐octafluoropentyl acrylate and 2,2,3,4,4,4‐hexafluorobutyl acrylate both mediated by poly(acrylic acid) containing the trithiocarbonate group in the chain was employed to produce amphiphilic triblock copolymers. The polymerization‐induced self‐assembly of these copolymers in aqueous media gave rise to spherical core–shell particles. Irrespective of the experimental conditions, the polymeric product was characterized by a bimodal molecular weight distribution. The apparent violation of the reversible addition–fragmentation chain transfer polymerization mechanism may be attributed to restricted accessibility of the trithiocarbonate group in the self‐assembled block copolymers for propagating radicals that enter into the particle. Mean‐field theoretical arguments were employed to explain the exclusively spherical morphology of the particles observed in the experiment. © 2019 Society of Chemical Industry     

双曲线型聚焦战斗部破片的设计方法

为解决预制破片聚焦战斗部加工中存在效率低的问题,基于正反圆柱螺旋线相交性原理,通过局部淬火预制工艺提出了一种新的高效率战斗部破片设计方法,并给出了一种聚焦式战斗部的加工实例。结果表明,局部淬火工艺对战斗部破片的控制效果良好,破片形状规则、质量分布均匀,有效破片质量分数达90%,符合毁伤要求,验证了其设计原理的正确性和可行性。     

Synthesis of Gemini‐Like Methyl Acrylate‐Acrylic Acid‐Methyl Acrylate Triblock Copolymers Surfactants by RAFT Polymerization in Solution and Investigation of their Behavior at the Air–Water Interface

A series of methyl acrylate‐acrylic acid amphiphilic triblock copolymers (PMA‐PAA‐PMA) were prepared by solution polymerization using S,S′‐bis (α,α‐dimethy1acetic acid) trithiocarbonate (BDAT) as a reversible addition fragmentation chain transfer (RAFT) agent and methyl acrylate (MA) as the first monomer. The triblock copolymers and their common MA homopolymer precursors were characterized in terms of their compositions, molecular weights and behavior at the air–water interface using ¹H‐NMR spectroscopy, thermogravimetric analysis, gel permeation chromatography, surface tension, transmission electron microscopy (TEM) and dynamic light scattering respectively. The results indicated that PMA‐PAA‐PMA was successfully synthesized through RAFT polymerization. The polydispersity index (PDI) decreased when the molar ratio [n(MA)/n(AA)] increased, the lowest PDI was obtained at 5.23 wt% RAFT and the molecular weights were consistent with the theoretical value as the RAFT agent percentage varied. The polymer neutralized by sodium hydroxide solution shows a low critical micelle concentration (CMC), which was <10^?2 mol L^?1 in water. The A_min values increased and showed a maximum with decreased AA chain length. TEM showed that the neutralized polymer formed a special vesicle structure with large pore structure which led to a low CMC and surface tension of water.     

Synthesis of thermoresponsive block and graft copolymers via the combination of living cationic polymerization and RAFT polymerization using a vinyl ether-type RAFT agent

A novel vinyl ether-type RAFT agent, benzyl 2-(vinyloxy)ethyl carbonotrithioate (BVCT) was synthesized for various block copolymers via the combination of living cationic polymerization of vinyl ethers and reversible addition−fragmentation chain transfer (RAFT) polymerization. The novel BVCT–trifluoroacetic acid adduct play an important role to produce well-defined block copolymers, which is both as a cationogen under EtAlCl₂ initiation system in the presence of ethyl acetate for living cationic polymerization and a RAFT agent for blocks by RAFT polymerization. The resulting polymer, poly(vinyl ether)s, by living cationic polymerization had a high number average α-end functionality (≥0.9) as determined by both ¹H NMR and MALDI-TOF-MS spectrometry. In addition, this poly(vinyl ether)s worked well as a macromolecular chain transfer agent for RAFT polymerization. The RAFT polymerization of radically polymerizable monomers was conducted in toluene using 2,2′-azobis(isobutyronitrile) at 70 °C. For example, a double thermoresponsive block copolymer (MOVE₆₁-b-NIPAM₁₅₀) consisting of 2-methoxyethyl vinyl ether (MOVE) and N-isopropylacrylamide (NIPAM) was prepared via the combination of living cationic polymerization and RAFT polymerization. The block copolymer reversibly formed and deformed micellar assemblies above the phase separation temperature (T_ps) of poly(NIPAM) block in water. This BVCT is not only functioned as an initiator, but also acted as a monomer. When BVCT was copolymerized with MOVE by living cationic polymerization, followed by graft copolymerization with NIPAM via RAFT polymerization, well-defined graft copolymers (MOVE_n-co-BVCT_m)-g-NIPAM_x (n = 62–73, m = 1–9, x = 19–214) were successfully obtained. However, no micelle formed in water above T_ps of poly(NIPAM) graft chain unlike the case of block copolymers.     

Reversible addition fragmentation chain transfer copolymerization: influence of the RAFT process on the copolymer composition

Reversible addition fragmentation chain transfer (RAFT) mediated and conventional copolymerizations at low monomer conversions have been carried out for the systems methyl methacrylate (MMA)-styrene, methyl acrylate (MA)-styrene and methyl methacrylate-butyl acrylate (BA). The polymer samples have been analyzed via ¹H-NMR spectroscopy to obtain the copolymer composition and the terminal model reactivity ratios. In the RAFT mediated copolymerizations, the polymer mole fraction of the monomer with the larger reactivity ratio is increased compared to the conventional copolymerization. Simulations have been carried out using the program package PREDICI^® to examine possible explanations for the experimental findings. The simulations demonstrate that the RAFT process itself may alter the macroradical populations and the copolymer composition by offering additional reaction pathways. Further, the rate coefficients for the initiation reaction and the pre-equilibrium play an important role in determining the copolymer composition. The rate coefficients governing the main equilibrium of the RAFT process have only a minor impact on the copolymer composition.     

基于SIMBOX的导弹杀伤空中目标的视景仿真研究

研究了一种基于SIMBOX的导弹杀伤空中目标的视景仿真方法。介绍了空空导弹对目标的杀伤概率模型及其影响因素,文中分别给出了攻击区、制导误差规律、引信引爆点散布规律、引信引爆概率、目标坐标杀伤概率的计算模型,确定了杀伤概率模型。在SIMBOX平台上,以破片式战斗部为例进行了仿真计算,给出了直观的视景仿真三维动画过程。文中通过对仿真结果进行分析,指出了目标初始速度与瞄准线的夹角和目标及导弹速度会对杀伤概率产生影响,证明了所建的模型具有较高的可信性和可依赖性。     

轴线场分爆式防空舰炮榴弹威力分析

在初步确定某轴线场分爆式防空舰炮榴弹总体结构的基础上，结合此类型弹药的毁伤方式，对此榴弹威力进行分析，从而论证此榴弹毁伤目标的有效性．     

降低裂隙性矿体爆破大块率的探讨

通过采取微差挤压爆破技术,选取适合于裂隙性矿体的爆破参数,以及合适的起爆方法和微差间隔时间等控制爆破技术后,使大块率由过去的３０％降至目前的１０％．     

复合岩体的TBM破岩机理数值模拟

为了指导TBM刀盘刀具的研制和不同地质条件下刀盘刀具的选型,TBM破岩机理的研究成为核心。在TBM滚刀的作用下,岩体中裂纹的生成、扩展和连接规律是深刻理解TBM破岩机理的前提,因此,TBM滚刀破岩机理的研究具有重要的工程应用价值。目前,TBM滚刀破岩机理的研究主要集中在单一岩体中,但在TBM施工过程中会遇到各种复杂的地质条件。笔者采用离散元方法,研究了复合岩体的破岩机理,复合岩体中岩片的形成不同于单一岩体,其裂纹的最终连接是由起裂于复合岩体交界面上的微裂纹的扩展,将两滚刀之间的赫兹裂纹连接,最终形成岩片。因此,在一定情况下复合岩体更有利于TBM隧道施工。