矩形波导缝隙天线阵分析

矩形波导缝隙阵天线在机载雷达上获得广泛使用。它具有体积小、重量轻、口径效率高、宽角副瓣低等特点。文中分析了矩形波导缝隙天线阵 ,给出了方向性函数及方向图 ,编制了分析软件 ,形成了方向图数据文件供通用软件调用。

矿用防爆阻火器进气压力特性研究

本文以T400防爆发动机平板型进气阻火器为研究对象,应用Fluent软件模拟不同工况下阻火器的进气压力损失以及不同缝隙率对阻火器进气压力的影响。结果表明:不同工况下阻火器进气压力损失呈正线性关系,且工况对进气栅栏压力损失的影响较大,随着工况的不同,进气流量的增大,阻火器的进气压力损失也随之增加;缝隙率对阻火器进气压力损失影响显著且呈负相关。且不同工况下阻火器进气压力损失随缝隙率β的变化趋势趋于一致,当β<0.2时,进气压力损失变化较快,随着缝隙率β不断增大,阻火器进气压力损失变化速度趋缓,慢慢趋于稳定。

铝铁双金属石膏型铸造界面复合工艺研究

针对汽车发动机铝铁双金属缸体中铝合金基体与铸铁缸套结合不紧的问题,研究了石膏型铸造缸体成型过程中铝铁双金属界面结合工艺。采用正交试验研究了不同预热温度、不同的热浸铝温度和不同的热浸时间对铝合金缸体与缸套界面结合的影响。通过宏观和微观界面结合分析、界面缝隙率分析以及结合强度分析得到了最佳工艺参数。试验结果表明:当预热温度为350℃、热浸温度为750℃,热浸时间为300 s时,铝/铁界面结合效果最好,界面缝隙率为3.1%,结合强度达到77 MPa。

Experimental study of seepage characteristics of single rock fracture based on stress states and stress history

Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture. The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure. With the increasing in the confining pressure,the permeability of the fracture decreases,but the decreasing rate is changeing. During the unloading process,the fracture seepage velocity cannot be fully recovered to the size of the loading process. Therefore,in the unloading process of the confining pressure,the recovery of fracture permeability shows obvious hysteresis effects. The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure. In each cycle,the evolution character of the flow rate with the confining pressure remains unchanged. These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state.

Unsaturated expansive soil fissure characteristics combined with engineering behaviors

The relationship among the surface fissure ratio, moisture content, seepage coefficient and deformation modulus of field unsaturated expansive soil in Nanning, Guangxi Province, China, was obtained by a direct or indirect method. Digital images of expansive soil of the surface fissure with different moisture contents were analyzed with the binarization statistic method. In addition, the fissure fractal dimension was computed with a self-compiled program. Combined with in situ seepage and loading plate tests, the relationship among the surface fissure ratio, moisture content, seepage coefficient and deformation modulus was initially established. The surface fissure ratio and moisture content show a linear relation, ＂y=-0.019 1x＋1.028 5＂ for rufous expansive soil and ＂y=-0.07 1x＋2.610 5＂ for grey expansive soil. Soil initial seepage coefficient and surface fissure ratio show a power function relation, ＂y=1× 10^-9exp（15.472x）＂ for rufous expansive soil and ＂y=5× 10^-7exp（4.209 6x）＂ for grey expansive soil. Grey expansive soil deformation modulus and surface fissure ratio show a power fimction relation of ＂y=3.935 7exp（0.993 6x）＂. Based on the binarization and fractal dimension methods, the results show that the surface fissure statistics can depict the fissure distribution in the view of two dimensions. And the evolvement behaviors of permeability and the deformation modulus can indirectly describe the developing state of the fissure. The analysis reflects that the engineering behaviors of unsaturated expansive soil are objectively influenced by fissure.

Void Morphology in 3-D Braided Preform/phenolic Composites

Improved Resin Transfer Molding (RTM) technology and equipment were established.Void content and morphology of the 3-D braided preform/phenolic composite were investigated using different RTM processes.The results showed that void content of the vacuum and compression co-assisted RTM process was the lowest.Void morphologies of the specimen cross-section were analyzed with metallographic microscope.In traditional RTM process,the crack of cross-section was in evidence.In vacuum assisted RTM process,the void shape was divided into three categories:irregular crack,triangle,rotundity and ellipse.The most voids distributed in resin rich areas and were observed as large void based on equivalent diameter.In compression assisted RTM,vacuum and compression co-assisted RTM process,the polygonal voids mostly existed inter tows.Void size was mainly intermediate and small based equivalent diameter separately.

热效应对生物陶瓷糊剂在根管不同部位充填效果的影响

目的研究热效应对生物陶瓷糊剂结合热凝牙胶垂直加压法在根管不同部位充填效果的影响。方法将40颗单根管牙样本随机分为对照组、iRoot SP组、10 s组、20 s组,每组10颗。所有牙样本在去除牙冠后根管预备至0.04锥度。对照组行AH-plus糊剂结合热凝牙胶垂直加压充填;iRoot SP组行iRoot SP单尖充填;10 s组及20 s组使用iRoot SP单尖充填结合热凝牙胶垂直加压充填,并分别在使用热凝牙胶前以180℃分别加热10 s及20 s。使用亚甲基蓝染色法、扫描电子显微镜(SEM)观察法、牙科显微镜观察法分析充填后根管中上段和根尖1/3处的缝隙发生情况。结果对于根尖1/3处的充填,10 s组和20 s组均无明显缝隙出现,且染料侵染深度与对照组之间的差异均无统计学意义(均P>0.05)。对于根管中上段的充填,iRoot SP结合单尖充填出现缝隙的概率较高。结论短时间的高温加热不会影响iRoot SP对于根尖1/3处的封闭效果;对于根管中上段,iRoot SP单尖充填结合热凝牙胶垂直加压法的充填效果优于iRoot SP单尖法充填。