水下爆炸冲击波在含吸收层结构中的传播规律的数值模拟

 利用ANSYS/LS-DYNA软件,对水下爆炸冲击波在含有吸收层的多层结构中的传播规律进行了数值模拟。结果表明：冲击波在吸收层中的衰减是由泡沫材料自身的本构引起的;在含泡沫材料吸收层的结构中峰值压力仅为不含吸收层的14%,冲击波传播波形发生改变;在含有泡沫混凝土的多层结构中应力波峰值的下降幅度比含泡沫铝的大,但冲击波传播波形的变化不是很明显;泡沫混凝土中的总能量大于泡沫铝中的总能量,因此泡沫混凝土作为防护吸收层要优于泡沫铝。     

三甲基硅烷化改性二氧化硅气凝胶

 采用六甲基二硅氮烷对二氧化硅凝胶进行疏水处理,得到了疏水性的二氧化硅气凝胶。用红外光谱和热分析表征处理前后二氧化硅气凝胶的性质,用测量显微镜跟踪处理前后气凝胶柱在空气中直径变化。结果表明,处理后气凝胶的表面羟基明显减少,在空气中的吸潮性大大降低,圆柱体在空气中的径向收缩率从30%降至3%。     

钢纤维高强混凝土材料的气体炮试验研究

采用一级气炮设备对C100钢纤维混凝土进行了高应变率冲击压缩实验,对一维应变状态下的混凝土冲击特性进行了分析.试验中采用锰铜压力计测量得到了混凝土中不同拉格朗日位置处的压力波形,利用拉格朗日分析得到了应力应变曲线,冲击波峰值随传播距离而衰减,在钢纤维混凝土中衰减较慢.分析探讨了钢纤维对混凝土的增强作用.     

二氧化硅气凝胶辐射特性反演方法研究

建立了基于光谱半球反射率和光谱半球透过率的二氧化硅气凝胶样品辐射特性参数的反演方法。采用离散坐标法、四通量法、二通量法计算了二氧化硅气凝胶样品内辐射传输问题,反演了样品的光谱辐射特性参数。结果表明,离散坐标法和四通量法反演结果几乎一致,二通量法反演结果小于离散坐标法和四通量法反演结果,而且误差较大,对于高孔隙率的二氧化硅气凝胶,界面反射对反演结果的影响很小,可以忽略。本文的研究工作对二氧化硅气凝胶辐射换热特性具有理论指导意义。     

多层介质对应力波传播特性影响分析

 通过在气炮上进行多层介质的低速冲击实验及相应的数值计算，分析了不同组成的多层介质对应力波传播特性的影响。结果表明：多层介质中的泡沫材料不仅能够改变应力波的幅值与作用时间，而且具有显著的吸能效果，引起应力波在传播过程中在各层介质中能量与动量分配的改变。通过对泡沫铝和泡沫混凝土两种软材料在多层介质中作用的比较表明，在低速冲击的实验条件下，含泡沫混凝土的多层介质具有较好的削波作用，含泡沫铝的多层介质具有较好的吸能性能。     

激光驱动冲击波在铝-金阻抗匹配靶中的传播稳定性

 针对神光Ⅱ第九路激光条件,利用1维JB程序和多台阶靶技术对冲击波在铝 金阻抗匹配靶中的传播稳定性进行了理论和实验研究,实验结果与理论结果基本吻合。结果表明,激光驱动冲击波在铝 金阻抗匹配靶中传播时,高阻抗待测材料金中的冲击波稳定传播最大距离急剧减小。因此,在进行铝-金阻抗匹配靶物理参数设计时,应保证高阻抗材料金台阶厚度满足冲击波传播稳定性,然后再按照阻抗匹配实验中两种材料的冲击波速度比来确定低阻抗标准材料铝的台阶厚度。根据神光Ⅱ第九路激光条件,铝-金阻抗匹配靶中铝基底厚度选取为30 μm左右较好,金台阶和铝台阶厚度应分别小于10 μm和17 μm。     

强激光使铝靶层裂的模拟实验研究

 激光引起的冲击波可能使得靶材料层裂断裂，这个现象取决于光束的功率密度、脉冲持续时间、靶的厚度和靶材料的性能参数。用气炮驱动的平板撞击实验和概念模拟分析了极短持续时间的三角形压缩应力击波在LY-12铝靶中的传播衰减和层裂强度的时间相关性，根据气炮模拟实验结果，估计了厚度小于2 mm的LY-12铝靶产生层裂所需的激光功率密度和能量密度的阈值条件。     

爆炸载荷下舱内泡沫铝夹芯结构的动响应特性

为探索爆炸载荷下舱内夹芯复合结构的动态响应特性与防护效能,采用小尺度舱室结构模型实验,结合有限元数值分析,开展了不同爆炸距离下舱内双层泡沫铝夹芯结构的动响应特性和变形模式研究。分析了不同爆距下舱内爆炸载荷的作用过程和时空分布特性,讨论了在初始冲击波、初始冲击波叠加各壁面二次反射波和舱内爆炸准静态压力3种载荷下泡沫铝夹芯结构的变形模式。爆炸载荷下舱室壁板承受的载荷依次为初始冲击波、各壁面二次反射波和准静态气压。炸药在靠近舱室一端处起爆时,初始冲击波在近端壁的局部效应明显,在远端壁的作用范围更大,与舱室中心爆炸相比,其爆轰产物波动次数更少。泡沫铝夹芯结构的变形过程可分为泡沫芯层压缩、局部凸起变形和整体挠曲变形3个阶段,对应迎爆面板局部凸起叠加整体挠曲大变形、局部凸起叠加整体挠曲大变形和整体挠曲大变形3种变形模式。     

冲击波作用下铝的等效剪切模量

提出了冲击波作用下通过测量沿着准弹性卸载过程纵波波速与体波波速得到等效剪切模量的方法,应用该方法对LY12铝在20—70 GPa冲击压力下的等效剪切模量进行了测量.实验结果表明,等效剪切模量随应力线性减少直至反向屈服时为零,而初始卸载时的等效剪切模量可以由修正的Steinberg-Cochran-Guinan模型进行描述.应用得到的等效剪切模量进行了初步数值模拟,计算结果与实验测量的粒子速度剖面符合很好,重现了准弹性卸载到塑性卸载的光滑过渡. 关键词： 等效剪切模量 波速 准弹性卸载 冲击波 铝     

高强混凝土气体炮试验与高压状态方程研究

采用一级气炮加载技术和锰铜压力计测试技术, 对C100混凝土在一维应变条件下的冲击特性进行了实验测量和分析. 基于锰铜压力计测量的压力波形, 通过拉格朗日分析得到了各拉氏位置的相关物理量, 实测压力波形显示: 不同位置处的压力波形在迅速上升至峰值后均随时间逐渐衰减, 而冲击波峰值又随传播距离而衰减,于是将损伤引入状态方程, 再从这些物理量出发, 得到了多项式形式Grüneisen型状态方程中的各项系数.     

密度渐变多层碳气凝胶靶型的制备

 以间苯二酚-甲醛为原料,结合自制活动式微模具成型工艺制备不同厚度和密度的碳气凝胶薄片,采用密度为10 mg·cm^-3的SiO₂溶胶为“粘合剂”,获得单元薄片厚度在100～580 μm,密度在50～400 mg·cm^-3范围内变化的5层密度渐变碳气凝胶靶型。重点研究了该特殊靶型内部C/SiO₂气凝胶层间界面情况。采用场发射扫描电镜（FESEM）,X射线相衬成像仪等对靶型整体结构及碳气凝胶单元薄片表面和内部微观结构进行了表征。结果表明：胶粘层SiO₂气凝胶厚度约为15 μm,厚度一致,远小于碳气凝胶层厚度且与碳气凝胶薄片的胶粘程度较好,界面平整,靶结构均匀。     

Formation of a shock wave in aerogel irradiated with a high-current pulsed electron beam

The propagation of pressure jumps excited by a high-current pulsed electron beam in SiO₂ aerogels with density ranging from 0.025 to 0.25 g/cm³ is investigated using a laser differential interferometer and optical methods. Spallation on the back side of the aerogel targets is observed and the velocity of the spallation fragments is measured. The expansion velocity of the aerogel in the direction of the electron beam is determined. The parameters of the shock adiabat are established in a wide range of aerogel porosities. The depth of the energy-deposition zone of the electron beam is determined experimentally as a function of the aerogel density in the range from 0.015 to 0.25 g/cm³. A model describing highly porous materials which reflects the fractal properties of highly porous aerogels is developed on the basis of the experimental data. Numerical calculations of the observed phenomena are performed. Zh. Tekh. Fiz. 69, 18–25 (December 1999)     

Numerical study of shock wave entry and propagation in a microchannel

The entry of a shock wave with the Mach number M_is = 2.03 into a microchannel and its further propagation is numerically studied with the use of kinetic and continuum approaches. Numerical simulations on the basis of the Navier ?? Stokes equations and the Direct Simulation Monte Carlo method are performed for different Knudsen numbers Kn = 8·10^?3 and 8·10^?2 based on the microchannel half-height. At the Knudsen number Kn = 8·10^?3, amplification of the shock wave after its entry into the microchannel is observed. Further downstream, the shock wave is attenuated, which is in qualitative agreement with experimental data. It is demonstrated that results predicted by a quasi-one-dimensional model (which ignores viscosity and heat conduction) of shock wave propagation over a channel with an abrupt change in the area agrees with results of numerical simulations on the basis of the Euler equations. In both cases, shock wave acceleration (amplification) after its entry into the microchannel is observed. At the Knudsen number Kn = 8·10^?2, the influence of the entrance shape on shock wave propagation over the microchannel is examined. Intense attenuation of the shock wave is observed in three cases: channel with sudden contraction, junction of two channels with an additional thin separating plate, and rounded junction in the form of a sector with an angle of 90° (quarter of a circumference). It is shown that the microchannel entrance shape can affect further propagation of the shock wave. The wave has the highest velocity in the case with a rounded entrance.     

Studies on the performances of silica aerogel electrodes for the application of supercapacitor

Silica aerogel (SiO₂ aerogel) was prepared by sol–gel method from tetraethyl orthosilicate hydrolyzation and has been characterized by scanning electron microscopy and N₂ adsorption for its surface structure, surface area, and pore-size distribution. Constant current charge–discharge technique, cyclic voltammetry, and electrochemical impedance spectrum were employed for its specific capacitance and equivalent series resistance. The results showed that the maximum specific capacitance of SiO₂ aerogel electrode in 1 M Et₄NBF₄/PC electrolyte was 62.5 F g⁻¹. In addition, the SiO₂ aerogel capacitor exhibits excellent long-term stability with no significant degradation after 500 charging and discharging cycles. Therefore, the application of high surface area SiO₂ aerogel as electrodes in supercapacitor devices is promising.     

Synthesis of Y2Si2O7:Eu nanocrystal and its optical properties

Nanocrystalline Y₂Si₂O₇:Eu phosphor with an average size about 60 nm is easily prepared using silica aerogel as raw material under ultrasonic irradiation and annealing temperature at 300-600 °C and this nanocrystalline decomposes into Y₂O₃:Eu and silica by heat treatment at 700-900 °C. The excitation broad band centered at 283 and 254 nm results from Eu³⁺ substituting for Y³⁺ in Y₂Si₂O₇ and Y₂O₃/SiO₂, respectively. Compared with Y₂O₃:Eu/SiO₂ crystalline, the PL excitation and emission peaks of Y₂Si₂O₇:Eu nanocrystalline red-shift and lead to the enhance of its luminescence intensity due to the different chemical surroundings of Eu³⁺ in above nanocrystallines. The decrease of PL intensity may be ascribed to quenching effect resulting from more defects in Y₂O₃:Eu/SiO₂ crystalline.     

氢氧爆轰波在激波管中的成长机制研究

 针对气相爆轰波成长机制研究,采用压力传感器和高速摄影技术,测试了氢氧混合气体在点火后的火焰波、前驱冲击波以及爆轰波的成长变化过程,计算了冲击波过程参数和气体状态参数,分析了火焰加速机制。实验结果表明,APX-RS型高速摄影系统可用于拍摄气相爆轰波的成长历程;氢氧爆轰波的产生是由于湍流火焰和冲击波的相互正反馈作用,导致反应区内多处发生局部爆炸,爆炸波与冲击波相互耦合,最终成长为定常爆轰波。     

ICF分解实验用双介质调制靶的研制

为了研究惯性约束聚变(ICF)实验用靶丸不同密度界面的流体力学不稳定性增长,设计并制备了聚苯乙烯(CH)/碳气凝胶(CRF),CRF/硅气凝胶(SiO2)和CH/Al三种双介质调制靶。采用溶胶-凝胶工艺制备了密度分别为250和800mg/cm3的CRF气凝胶薄片;采用激光微加工工艺分别在两种不同密度的CRF薄片和工业用纯Al箔上引入调制图形;采用旋涂工艺在Al箔和CRF薄片(250mg/cm3)的调制表面制备一层CH薄膜,得到CH/Al和CH/CRF双介质调制靶,采用溶胶-凝胶工艺在CRF薄片(800mg/cm3)表面制备一层低密度SiO2气凝胶,得到CRF/SiO2双介质调制靶。采用电子天平、扫描电子显微镜、工具显微镜和台阶仪对所制备的CH/CRF,CRF/SiO2和CH/Al三种双介质调制靶进行靶参数测量。结果表明:三种双介质调制靶层与层之间结合紧密,界面清晰,调制图形为正弦,靶参数测量准确。     

Analysis of the impedance mismatch effect in foam-solid targets compressed by laser-driven shock waves

The impedance mismatch effect in a two-layer (low density plastic foam, and solid aluminum, respectively) plane target compressed by a laser driven shock wave is considered. In such targets the ablative pressure generated by absorption of laser light in the foam layer is amplified when crossing the foam-aluminum interface. In this paper an analytical model is developed to evaluate the shock pressure in the aluminum layer as a function of the density and thickness of the foam layer and of the laser parameters. The model is in good agreement with previously published experimental results [A. Benuzzi et al., Phys. Plasmas 5, 2827 (1998)]. Received 20 January 2000 and Received in final form 16 May 2000     

多孔PMP聚合物薄膜微结构控制

将二氧化硅(SiO2)微球为模板材料分散在聚-4-甲基-1-戊烯(PMP)溶液中,通过对流自组装方法将其涂覆于基片上,经过热致相分离(TIPS)过程形成含SiO2微球模板的PMP薄膜,然后通过氢氟酸(HF)溶液腐蚀除去SiO2微球,获得了具有规则多孔结构的PMP聚合物薄膜。采用扫描电子显微镜(SEM)对含SiO2微球的PMP薄膜以及除去SiO2微球后的PMP多孔薄膜的微结构进行了表征。研究结果表明:SiO2微球在聚合物中呈有序排列,腐蚀除去SiO2微球后PMP薄膜有效复制了SiO2微球形成的有序结构,形成了有序多孔PMP薄膜。