空间结构增强铜基复合材料的摩擦磨损特征

为实现铜基复合材料性能的有效调控,采用激光选区熔化成形制备了单元尺寸分别为5.00、3.75、2.75、1.75和0.75 mm的18Ni300空间结构增强体,然后在挤压铸造条件获得了具有不同增强体分布的18Ni300空间结构增强铜基复合材料. 研究了复合材料的微观组织、硬度、摩擦磨损性能和磨损表面形貌. 结果表明:随着空间结构单元尺寸的减小,复合材料增强体体积分数不断增加,硬度和耐磨性提高. 结构单元尺寸为0.75 mm时,复合材料增强体体积分数为13.35%,硬度达到HBW120,为铜基体硬度的1.71倍;载荷40 N、线速度0.75 m/s、磨损时间25 min 条件下的体积磨损量为35.4 mm3,比铜基体磨损量降低58%. 由于增强体的作用,复合材料的磨损机制由纯铜的黏着磨损转变为磨粒磨损.      

TNT空爆载荷下WELDOX 700E钢变形行为研究

以WELDOX 700E钢为研究对象,研究了8 mm钢在6 kg球形TNT空爆载荷、12 mm钢在10 kg球形TNT空爆载荷下的抗爆轰变形行为,结合ABAQUS模拟计算软件建立了WELDOX 700E钢抗爆轰变形模拟计算模型。结果表明:材料强度是影响WELDOX 700E钢抗爆轰变形行为的关键因素之一,高强度WELDOX 700E钢在球形TNT空爆载荷条件下呈现均匀的拱形变形。在6 kg球形TNT空爆载荷下,8 mm WELDOX 700E钢板中点的最大动态位移为144 mm,永久挠度为124 mm,回弹为21 mm;在10 kg球形TNT空爆载荷下,12 mm WELDOX 700E钢板中点的最大动态位移为166 mm,永久挠度为143 mm,回弹为23 mm。在不考虑实验工装整体偏移的条件下,球形TNT空爆载荷下钢的抗爆轰变形模拟计算结果可准确反映WELDOX 700E钢的抗爆轰变形行为。WELDOX 700E钢在抗爆轰形变过程中存在显著的厚度减薄现象并伴随一定的应变硬化行为,应变硬化行为主要为WELDOX 700E钢马氏体晶粒内部位错増殖的表现,8 mm和12 mm WELDOX 700E钢中心区域的位错密度较边部分别增加80.31%和151.76%。     

高密度B炸药的燃烧转爆轰实验研究

采用电探针及压力传感器测试技术对密度为1.597 g/cm3的固体B炸药（TNT/RDX=40/60）的燃烧转爆轰性能进行研究。实验结果表明,在较强的约束条件下（45号钢管,内径20 mm,外径64 mm,长500 mm）,B炸药形成了DDT现象,诱导爆轰距离为295~310 mm。     

EFFECT OF Z-PINS＇ DIAMETER, SPACING AND OVERLAP LENGTH ON CONNECTING PERFORMANCE OF CMC SINGLE LAP JOINT

The effect of through-thickness reinforcement by composite pins （Z-pins） on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite （CMC） is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, （a） the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; （b） the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins＇ diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins＇ diameter and spacing are 0.4 mm, 5 mm, respectively.     

On the mechanism by which nose bluntness suppresses second-mode instability

A physical mechanism by which nose bluntness suppresses second-mode instability is proposed.Considered are 7 degree half-angle straight cones with nose bluntness radii of 0.15 mm, 3.556 mm,5 mm, 9.525 mm, 12.7 mm and 25.4 mm at tunnel conditions relevant to the AFOSR-Notre Dame Large Mach 6 Quiet Tunnel. It is shown that second-mode suppression is achieved via entropy layer modulation of the basic state density gradient. A weakening of the density gradient disrupts the acoustic resonance necessary to sustain second-mode growth. These results are consistent with the thermoacoustic interpretation which posits that second-mode instability can be modeled as thermoacoustic resonance of acoustic energy trapped within an acoustic impedance well.Furthermore, the generalized inflection point criterion of Lees and Lin is applied to develop a criterion for the existence of second-mode instability based on the strength of the basic state density gradient.     

交错式扇贝阻尼密封动力特性研究

建立交错式扇贝阻尼密封三维数值分析模型,基于动网格及多频椭圆涡动模型研究密封动力特性沿轴向分布规律,计算分析错开角度(α=0°、11.25°、22.5°、33.75°)与密封腔深度(h=2.8、3.3、3.8和4.3 mm)对密封动力特性的影响. 结果表明:上游腔室(C1~C4)具有较大的正直接刚度和有效阻尼,对抑制转子涡动、提升系统稳定性的贡献相对较大. 相对并列式(α=0°)结构,交错式扇贝阻尼密封流体周向速度较小、湍流耗散增加,系统稳定性提升,同时密封泄漏量降低. 错开角度为33.75°时的有效阻尼约为0°时的111%~121%;错开角度为22.5°时的泄漏量相较于0°时约降低了2.11%. 有效阻尼随密封腔深度减小而增大,密封腔深度为2.8 mm时的有效阻尼约为4.3 mm时的146%~211%;密封泄漏量随密封腔深度增大而降低,密封腔深度为4.3 mm时的泄漏量相较于2.8 mm时降低了约3.73%.      

Investigation into Electromechanical Properties of Biocompatible Chitosan-Based Ionic Actuator

Ionic actuators have attracted much attention due to their remarkably large strain under low-voltage stimulation. Here, we investigate a highly biocompatible ionic polymer actuator, which consists of multi-walled carbon nanotube (MCNT) film as a double electrode layer and an electrolyte layer equipped with chitosan polymer skeleton and ionic liquid. As a result, with the thickness increase of the electrolyte layer and the electrode layer, the membrane capacitance values are obviously improved, which are 0.01 F (membrane thickness of 1.3 mm) and 0.4 F (0.25 mm). The blocking force and its response speed show peak values of 5.75 mN (1.1 mm) and 5.1 mN (0.25 mm), while reverse increases for the displacement and its response speed are observed, which present maximum values of 10.3 mm (0.3 mm) and 13.3 mm (0.15 mm). Furthermore, for various thicknesses of the electrode layers under applied direct current of 5 V, the generated strain of 0.15 mm thickness (59%) is 4.92 times greater than that of the 0.25 mm thickness. This is against the strain difference on the electrode surface due to the growing stiffness of the electrode layer. Additionally, from the experiments of the electromechanical energy efficiency of various electrode layers and electrolyte layers, our actuator exhibits excellent electromechanical energy efficiency under a high electrical conductivity of the electrode layer, which enhance the specific electromechanical energy up to 9.95%.     

Evaporation flow pattern and heat transfer of R-22 and R-134a in small diameter tubes

The flow patterns and heat transfer coefficients of R-22 and R-134a during evaporation in small diameter tubes were investigated experimentally. The evaporation flow patterns of R-22 and R-134a were observed in Pyrex sight glass tubes with 2 and 8 mm diameter tube, and heat transfer coefficients were measured in smooth and horizontal copper tubes with 1.77, 3.36 and 5.35 mm diameter tube, respectively. In the flow patterns during evaporation process, the annular flows in 2 mm glass tube occurred at a relatively lower vapor quality compared to 8 mm glass tube. The flow patterns in 2 mm glass tube did not agree with the Mandhane’s flow pattern maps. The evaporation heat transfer coefficients in the small diameter tubes (d _i  < 6 mm) were observed to be strongly affected by tube diameters, and to differ from those in the large diameter tubes. The heat transfer coefficients of 1.77 mm tube were higher than those of 3.36 mm and 5.35 mm tube. Most of the existing correlations failed to predict the evaporation heat transfer coefficient in small diameter tubes. Therefore, based on the experimental data, the new correlation is proposed to predict the evaporation heat transfer coefficients of R-22 and R-134a in small diameter tubes.     

Experimentally Observed Strain Distributions Near Circular Discontinuities of AA6061-T6 Extrusions During Axial Crush

An experimental investigation to determine the strain distribution and collapse behaviour for AA6061-T6 square cross-sectional extrusions with and without circular discontinuities under quasi-static axial compressive loading was completed. Three-dimensional digital image correlation (DIC) was utilized for strain assessment. In order to validate the results of the optical strain measurement system, tensile tests were first conducted employing both the DIC technique and a traditional extensometer. Strain observations from both methods were found to be very consistent prior to strain localization in the test specimen. Quasi-static axial crushing tests were then conducted. Extrusions considered for the present research had a nominal side width, wall thickness and length of 38.1 mm, 3.15 mm, and 200 mm, respectively. A centrally-located circular hole with diameter of either 14.29 mm, 10.72 mm or 7.14 mm was incorporated into the extrusion. Square tubes without any discontinuities were also considered in the experimental testing program. Testing results showed that the collapse mode of the extrusion altered from global bending to a cutting and splitting deformation mode with the presence of the circular discontinuity. Strain localization occurred near the vicinity of the holes for all specimens. For discontinuities sized 14.29 mm and 10.72 mm the location of strain localization and the initiation of material fracture was at the edge of the discontinuity while the location for extrusions with a 7.14 mm hole was found to occur at the intersection of the extrusion side walls. Maximum values of the effective strain were found to vary from approximately 60% to 100%. The region of strain localization was consistent with the location where material fracture initiated.     

巷道支护对瓦斯爆炸火焰传播速度影响的实验研究

通过对实验室中几何尺寸为80&#215;80mm钢制管道内部加装高度分别为4mm、8mm、12mm、16mm的四种螺旋环,模拟巷道支护结构对瓦斯爆炸火焰传播速度的影响。采用高精度动态数据采集分析系统,测量爆炸过程中的火焰传播速度,研究了不同高度的螺旋环对火焰传播速度的影响。结果表明：在螺旋环其他条件相同的情况下,管内瓦斯爆炸火焰传播速度随螺旋环高度、圈数增加而增加。并从理论上进行了分析,其主要原因为螺旋环高度越大、圈数越多,产生湍流度的程度亦愈大,对瓦斯爆炸火焰加速亦愈明显。试验结果对巷道支护的选择有指导意义。     

Experimental investigation on resistance characteristics in micro/mini cylinder group

Friction factors associated with forced flow of de-ionized water over staggered and in-line micro/mini cylinder group plates with 3.5 mm width and 40 mm length, which are made of micro/mini cylinders with hydraulic diameter of 0.5 mm and the heights of 1.0 mm, 0.75 mm, 0.5 mm and 0.25 mm, respectively, have been experimentally investigated over Reynolds number ranging from 25 to 800. The flux and the pressure drop between the inlet and the outlet of micro/mini cylinder group are measured and the experimental results are compared with those of convectional correlations. The investigation shows the value of fRe is approximately the constant in micro/mini cylinder group plates when the flow is purely laminar state. Except test sections with 0.25 mm cylinder height, the values of fRe for other test sections increase when Re > 100, as the results of the appearance of vortex resistance, the enhancement of stream pulse and the acceleration of stream frequency. For test section with 0.25 mm cylinder height, the values of fRe rapidly and oscillatingly increase at Re > 150 due to the influence of the scale effect, tip clearance effect and the roughness effect on the cylinder surface and bottom of micro/mini cylinder group plates. The friction factor in a staggered array is much larger than that at in-line array for micro/mini cylinder group plates and the higher the cylinder height is, the lower the friction factor becomes.     

环形液池内中等Pr数流体的浮力-热毛细对流

为了了解水平温度梯度作用时环形液池内的浮力-热毛细对流特性，利用 有限差分法进行了非稳态三维数值模拟，环形液池外壁被加热，半径为40 mm，内壁被冷却， 半径为20 mm，液池深度为3~17 mm，液池内流体为0.65cSt的硅油，其Pr数 为6.7. 模拟结果表明，当水平温度梯度较小时，流动为轴对称稳态流动，随着温度 梯度的增加，流动将会失去其稳定性，在浅的液池内(d=3mm)，转化成三维振荡 流动，在深的液池内(d≥6mm)，转化成三维稳定流动；模拟计算的 临界温差及表面温度分布图像与实验结果基本吻合.     

EFFECT OF Z-PINS'' DIAMETER, SPACING AND OVERLAP LENGTH ON CONNECTING PERFORMANCE OF CMC SINGLE LAP JOINT

The effect of through-thickness reinforcement by composite pins (Z-pins) on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite (CMC) is investigated.Overlap length of the single lap joint is 15 mm,20 mm,23 mm,37 mm,and 60 mm,respectively.The experimcntal results indicate that the final failure modes of the joints can be divided into twó groups,(a) the bond-line stops debonding until crack encounters Z-pins;and then the adherends break at the location of Z-pins,when overlap length is more than 20 mm;(b) the bond-line detaches entirely and Z-pins are drawn from adherends,when overlap length is equal to 15 mm.A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints.Here,the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line.The tractions are prescribed as functions of the crack displacement,which are available in simple forms that summarize the complex deformations to a reasonable accuracy.The resulting model can be used to track the evolution of complete failure mechanisms,for example,bond-line initial delamination and ultimate failure associated with Z-pin pullout,ultimate failure of the adherends.The paper simulates connecting performance of the single lap joints with different Z-pins' diameter,spacing and overlap length;the numerical results agree with the experimental results;the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints.By numerical analysis method,the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm,when Z-pins' diameter and spacing are 0.4 ram,5 ram,respectively.     

Condensing heat transfer characteristics of hydrocarbon refrigerants in 9.52 and 12.7 mm smooth tube

Experimental results for heat transfer characteristic and pressure gradients of hydrocarbon (HC) refrigerants and R-22 during condensing inside horizontal double pipe heat exchangers are presented. The test sections which have one tube diameter of 12.70 mm with 0.86 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local condensing heat transfer coefficients of HC refrigerants were higher than that of R-22. The average condensing heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in HC refrigerants than R-22. Comparing the heat transfer coefficient of experimental results with that of other correlations, the presented results had a good agreement with most of the Cavallini’s correlations.     

光斑尺寸对K9玻璃近红外激光损伤阈值的影响

基于热弹性模型 ,用有限元法对不同光斑近红外激光辐照下K9玻璃样品中的温度和压力分布进行了计算。对厚 2mm、半径 10mm的圆片样品的计算结果表明 ,K9玻璃的损伤受表面环向拉伸应力的控制 ,光斑大小对损伤阈值有较大的影响 ,对光束总入射功率为 2 8kW的激光辐照 ,当光斑半径从 0 .4mm增加到 3mm时 ,损伤所需时间从 14ms增加到 1s。在一定光斑尺寸范围内 ,样品损伤 (表面拉伸断裂 )所需的激光功率密度在同一量级内变化 ,在更小光斑时 ,损伤时的最高温升趋于 5 6 5K。     

Subcooled pool boiling of water on a downward-facing stainless steel disk in a gap

Pool boiling is experimentally studied on a relatively large downward-facing surface with heated stainless steel disk diameters of D = 100 and 300 mm in confined space at atmospheric pressure using water as the working fluid. The bulk working fluid is subcooled. The gap size s can be adjusted to 10, 15 and 20 mm for D = 100 mm and 0.9–77 mm for D = 300 mm. We found that pool boiling under the present condition is far weaker than that occurring on an upward-facing surface. Furthermore, we found that the larger the diameter of the stainless steel plate, the weaker the pool boiling heat transfer. The heat transfer rate may be predicted by the Kutateladze correlation for s > 20 mm and by its modified form for s < 20 mm for both D = 100 and D = 300 mm. Two different typical bubble circulation motions are found. Type I motion occurs with a probability of 90.9% and type II occurs with a probability of 9.1% according to the statistical calculations. Most coalesced bubble diameters are from 90 to 100 mm for D = 100 mm and from 100 to 200 mm for D = 300 mm.     

花岗岩的加载速率效应及能量机制研究

加载速率对岩石的力学性质以及变形破坏方式具有重要的影响。基于MTS810电液伺服材料试验系统与PCI-2声发射仪对岩样进行不同加载速率作用下的单轴压缩和声发射试验。研究结果表明：（1）在各级加载速率作用下,岩样单轴压缩应力-应变曲线大致经历了压密、弹性、屈服、破坏四个阶段。岩样峰后曲线在加载速率为0.001~0.01 mm/s时出现台阶型分段跌落状,在加载速率为0.01~0.1 mm/s时呈现光滑、陡峭的连续曲线。（2）岩样峰值强度、弹性模量随加载速率的增加而增大,与加载速率对数均呈现三次多项式拟合关系。峰值应变随加载速率的增加而减小,与加载速率对数呈现线性拟合关系。（3）随着加载速率由0.001mm/s增加至0.1mm/s,岩样吸收的总应变能 具有波动性,可释放的弹性应变能 增幅60.42%,耗散应变能 降幅 66.38%, 增幅43.33%, 降幅66.67%,岩样破裂模式由拉剪破坏逐渐向张拉劈裂破坏过渡,岩样破裂块数增多。（4）加载速率为0.001~0.1 mm/s时,岩样破坏方式有所不同,但破坏为同一类损伤过程。单轴压缩状态下,能量耗散使得岩样损伤致使强度丧失,而能量释放使得岩样宏观破裂面贯通,并向着能量释放的方向张裂或弹射破坏。     

铝面板厚度对Nomex蜂窝夹层结构冲击后弯曲性能影响的试验研究

通过低速冲击试验和四点弯曲试验,研究了铝面板厚度对Nomex蜂窝夹层结构抗冲击能力和剩余强度的影响。结果表明:在冲击荷载作用下,面板发生变形的区域大小随面板厚度增加而变大,当面板厚度大于0.5mm时,变形区域直径趋于稳定;无论试件是否受到过冲击,在弯曲载荷作用下,0.2mm厚面板发生芯格内屈曲失稳,而其他厚度面板均发生格间失稳;对无冲击损伤的结构,0.2mm厚面板弯曲强度显著低于其他厚度面板;对含冲击损伤的结构,0.2mm厚面板的剩余强度百分比最高。     

7 km/s以上超高速发射技术研究进展

介绍了毫克至克量级弹丸7 km/s以上超高速发射技术的国内外研究进展,并对各发射装置的工作原理和技术要素进行了简要阐述.基于电磁驱动准等熵加载,美国ZR装置驱动25 mm×13mm×1.0mm铝飞片至46km/s速度,国内CQ系列磁驱动加载装置实现了 10mmx6mmx0.33mm铝飞片18 km/s的发射.借助于金属箔电爆炸产生高压气体驱动,美国利弗莫尔实验室100kV电炮装置驱动9.5mm×9.5 mm×0.3 mm的Kapton膜至18 km/s,国内流体物理研究所98 kJ和200 kJ电炮装置分别驱动?10 mmx0.2 mm Mylar飞片和?21 mm×0.5 mm Mylar飞片到10 km/s.基于阻抗梯度飞片技术,采用汇聚型和非汇聚型结构三级轻气炮,实现了厘米量级铝飞片和TC4钛飞片12～15 km/s速度发射.这些超高速驱动技术的发展,为空间碎片防护研究提供了坚实的技术支持.     

多级串联式超高速飞片装置实验研究

叙述了有关多级串联飞片速度的实验研究。首先做了预备实验 ,测得了2 0 0mm炸药驱动钢飞片撞击靶板时的平面范围。设计了测量多级飞片速度的实验装置 ,采用电探针方法 ,在一发实验中同时测量了三级飞片的速度。实验测得 :初级飞片速度为 4 87km/s,1mm厚次级钢飞片速度达到 7km/s ,0 .2mm厚末级钼飞片速度接近 10km/s。