旋转尾翼弹箭极限圆锥运动稳定判据

为获得旋转尾翼弹箭极限圆锥运动稳定判据,针对现有理论方法的不足,提出了改进理论模型。该模型通过对弹箭在准圆运动状态下的振幅平面方程进行泰勒展开,从而充分考虑幅值变化对振幅平面方程中根号项取值的影响;在此基础上,根据不同参数取值情况,对其非零奇点的存在性和稳定性进行分析,导出了弹箭在非线性静力矩和非线性马格努斯力矩作用下形成稳定极限圆锥运动的解析判据,并给出两条仅与攻角方程初始参数相关的综合判据条件J₁>0和J₂>0;以某型旋转尾翼弹箭气动及结构特征参数为例,对所得理论判据进行了验证。研究结果表明,给出的稳定极限圆锥运动形成判据,与现有理论结果相比,更为全面且明确,利用所得判据条件,可方便准确地对弹箭极限圆锥运动特性进行分析判断。     

膨胀型防火涂层膨胀尺寸非线性传热模型

膨胀型防火涂层在膨胀过程中孔隙存在的对流传热和辐射传热会降低涂层的防火性能。考虑到孔隙之间存在涂层分解产生的气体,因此通过理想气体状态方程,描述了涂层在不同升温条件下的膨胀行为。建立了以膨胀尺寸为输出项,并考虑孔隙对有效导热系数增强作用的有限元传热模型,探究不同厚度的涂层在不同升温环境下的防火性能。结果表明：膨胀尺寸模型能够较为准确地预测涂层在不同温度场下的膨胀行为,涂层最大膨胀率随干膜厚度增大而减小;基于膨胀尺寸和多孔有效导热系数的有限元传热模型模拟的钢管温度变化与试验结果吻合较好;膨胀型防火涂层在高升温速率环境中能够明显延缓钢管升温,并降低其最大受火温度;不同升温环境中,涂层的防火能力和厚度呈非线性变化。     

定向反射膨胀装置作用特性研究

为实现冲击波尽量小的高效后坐,提出了定向反射膨胀原理,设计了相应的装置。运用一维准定常气体动力学理论,建立了气体动力学模型,根据实际情况选定模型参数进行数值分析,得到了装置减后坐效率及弹丸炮口初速等理论分析结果; 根据理论分析结果确定了实验装置的基本参数,设计实验并在某30 mm口径的火炮上进行定向反射膨胀装置的实验验证。实验测试结果表明,理论分析结果与实验测试结果基本一致,验证了定向反射膨胀装置作用特性研究的正确性,为定向反射膨胀原理及装置的继续研究打下了基础。     

Hydraulic fracturing pressure of concentric double-layered cylinder in cohesive soil

This study aims to investigate hydrofracturing in double-layered soil through theoretical and experimental analysis, as multilayered soils where the difference in mechanical properties exists are generally encountered in practical engineering. First, an analytical solution for fracturing pressure in two different concentric regions of soil was presented based on the cavity expansion theory. Then, several triaxial hydraulic fracturing tests were carried out to validate the analytical solution. The comparison between the experimental and analytical results indicates the remarkable accuracy of the derived formula, and the following conclusions were also obtained. First, there is a linear relationship between the fracturing pressure and confining pressure in concentric double-layered cohesive soil. Second, when the internal-layer soil is softer than the external-layer soil, the presence of internal soil on the fracturing pressure approximately brings the weakening effect, and the greater strength distinction between the two layers, the greater the weakening effect. Third, when the internal-layer soil is harder than the external-layer soil, the existence of the internal-layer soil has a strengthening effect on the fracturing pressure regardless of the proportion of internal-layer soil. Moreover, the influence of strength distinction between the two layers on the fracturing pressure is significant when the proportion of internal-layer soil is less than half, while it’s limited when the proportion is more than half. The proposed solution is potentially useful for geotechnical problems involving aspects of cohesive soil layering in a composite formation.     

Effect of Cold Expansion on High Cycle Fatigue of 7A85 Aluminum Alloy Straight Lugs

提出采用孔挤压方法来提高7A85铝合金直耳片的高周疲劳性能。孔挤压后耳片孔壁的显微组织、显微硬度和残余应力的测试结果表明孔挤压后孔壁处形成了大约150 μm 的塑性变形层。塑性变形层内,显微硬度较高,存在残余压应力,且晶粒在平行于挤压棒运动方向上被拉长,垂直于挤压棒运动方向上被压缩。高周疲劳测试结果表明,孔挤压后的耳片疲劳寿命和疲劳强度均得到了较大的提高。通过对比孔挤压与未孔挤压耳片的疲劳源区和裂纹扩展形貌,分析了孔挤压提高7A85铝合金耳片疲劳性能的内在机理     

New filler metal systems for the brazing of titanium alloys

It’s well known welding takes the leading role in development of titanium structures. However, in number of cases technological processes of brazing are more appropriate and, sometimes, being the single possible, in particular, during production of multilayer thin-wall structures. It should be noted that brazing filler metals of Ti-Cu-Ni, Ti-Zr-Cu-Ni, Zr-Ti-Ni and Cu-Zr-Ti systems in a form of plastic foils, as well as in powder form are mainly used in world practice for brazing of titanium alloys. Present work provides the results of complex investigations of brazing filler metals of Ti-Zr-Fe, Ti-Zr-Mn and Ti-Zr-Co systems using differential thermal analysis, light and scanning microscopy, X-ray microspectrum analysis. Data on melting ranges of pilot alloys were obtained, and liquidus surfaces of given systems using simplex-lattice method were build. Brazing filler metals covering brazing temperature range of current structural titanium materials based on solid solutions as well as intermetallics were proposed. Structure, chemical inhomogeniety and strength characteristics of brazed joints were studied. It is determined that brazing of solid solution based alloys (OT4, VT6) using indicated brazing filler metals ensures strength characteristics of joints, which are not inferior to that obtained with application of known brazing filler metals even if they are received at lower brazing temperature.     

MgO/SiO_2摩尔比对金刚石砂轮用陶瓷结合剂性能的影响

研究了Na-B-Al-Si-O系陶瓷结合剂中MgO/SiO2摩尔比对其性能的影响。研究表明,随着MgO/SiO2摩尔比从0.09增加到0.35,结合剂的耐火度从800℃降低到725℃,热膨胀系数先减小后增大,但MgO的加入能有效控制结合剂热膨胀系数只在小范围内变化。制备的砂轮试样抗折强度最高值达到95MPa,利用所研究的结合剂制备的砂轮比市售砂轮使用寿命提高25%。研究结果证明:减少碱金属氧化物含量、增大碱土金属氧化物含量是获得低耐火度、低热膨胀系数结合剂的一种有效方法。     

钉/孔摩擦对复合材料机械连接强度的影响研究

建立了复合材料层合板单钉连接强度分析的三维模型,模型考虑了螺栓-孔接触面的摩擦效应。研究结果表明,在各个铺层中,随着摩擦系数的增大,周向应力和径向应力减小。螺栓-孔接触面摩擦系数对复合材料的拉压强度和剪切强度有较大影响,在一定范围内增加摩擦系数将会提高接头的极限破坏载荷。