位移不连续法在裂纹扩展仿真中的应用

探讨了在应用位移不连续法仿真裂纹扩展时对加载方式、裂纹扩展长度及应力强度因子计算等问题的处理方法,并据此编制了仿真程序,分析了裂纹在单向压载作用下的扩展趋势和应力变化,具有一定的工程应用价值。     

燃烧室压力对潜入式喷管喉衬热应力的影响

为了研究燃烧室压力对固体火箭发动机潜入式喷管热应力影响规律的问题,采用商业流体软件,基于压力求解器,求解了喷管纯气相的流场,确定了燃气温度、压力、壁面对流换热系数;采用有限元软件,依据流场计算的非均布壁面压力与非均布对流换热,求解了燃烧室压力为6 MPa下的潜入式喷管热结构问题;通过地面点火试验验证了仿真模型与数值方法的有效性与准确性;采用相同计算模型与数值方法,求解了在燃烧室压力为9 MPa、12 MPa下的喷管热结构问题,揭示了燃烧室压力对喉衬热应力的影响规律。结果表明:整个工作过程,喉衬环向应力最大值为103.9 MPa,位于内表面,且随时间增大,先增大后减小;喉衬环向拉应力也随时间先增大后减小;随压力增大,对流换热系数增大,喉衬温度升高,喉衬环向拉应力增大,喉衬环向压应力减小。     

Influences of different crossing types on dynamic response of underground cavern subjected to ground shock

An intersecting cavern is a common structural form used in underground engineering, and its safety and stability performance directly control the service performance of the whole project. The dynamic re-sponses of the three kinds of crossing type (+-shaped, T-shaped, L-shaped) caverns subjected to ground shock were studied by numerical simulation. The velocity plus force mode boundary setting method was proposed in the coupled static and dynamic analysis of a deep underground cavern. The results show that, among the three types of crossing caverns, the+-shaped cavern is the most significantly affected by the dynamic action, followed by T-shaped, and then L-shaped caverns. The vault settlement, straight wall deformation, vault peak particle velocity, effective plastic strain of surrounding rock, and maximum principal stress and strain at the bottom of the lining of the straight wall increase with the increase of cavern span. The vault settlement, straight wall deformation, effective plastic strain of surrounding rock, and the maximum principal stress and strain at the bottom of lining to the straight wall decrease with the increase of lateral pressure coefficient, and the peak particle velocity at the vault increases. The variation is small compared with the change of cavern span. The influence range of the underground cavern intersection is two cavern diameters from the intersection centre. The bottom of the straight wall at the intersection is the weak part. It is suggested to thicken the support locally to improve the stability of the cavern.     

Effect of friction stir processing on mechanical properties and heat transfer of TIG welded joint of AA6061 and AA7075

Tungsten inert gas (TIG) welding is the most commonly used joining process for aluminum alloy for AA6061 and AA7075 which are highly demanded in the aerospace engineering and the automobile sector, but there are some defects occur during TIG welding like micro-crack, coarse grain structure, and porosity. To improve these defects, the TIG welded joint is processed using friction stir processing (FSP). This paper presents the effect of friction stir processing on TIG welding with filler ER4043 and ER 5356 for dissimilar aluminum alloy AA6061 and AA7075. The mechanical characterization, finite element formulation and mathematical equations of heat transfer of TIG + FSP welded joints are investigated using ANSYS Fluent software by adjusting process parameters of FSP. The results show that the maximum compressive residual stress 73 MPa was obtained at the fusion zone (FZ) of the TIG weldment with filler ER4043, whereas minimum compressive residual stress 37 MPa was obtained at stir zone (SZ) of the TIG+FSP with filler 5356. The maximum heat flux 5.33 × 106 W/m2 and temperature 515 ℃ have observed at tool rotation 1600 rpm with a feed rate of 63 mm/min. These results give a satisfactory measure of confidence in the fidelity of the simulation     

自润滑弹带挤进过程中渗出油量的对比计算

从弹带的作用及特性出发, 通过数值计算和统计计算 2种方法计算了自润滑弹带挤进过程中的渗出油量,初步得出了渗出油量和行程之间的关系。这一问题的解决为自润滑弹带材料的选择提供了理论依据。通过对 2种算法的比较可知, 数值计算误差更小一些, 而统计计算对数学条件要求不太苛刻。     

大功率消磁线圈受力分析与计算

大功率消磁线圈在运行中会受到较强电磁力的作用,客观地分析和计算电磁力的大小及分布情况,是设计和建造大型消磁站的一项基础性的工作.文中从电磁场基本原理出发,应用张量理论分析、计算了大功率消磁线圈的受力情况,对于设计和建造大型消磁站具有参考作用.     

棱纹面与洛仑兹力对湍流边界层特性影响的比较

用氢气泡技术对棱纹面平板以及施加行波式洛仑兹力的平板水边界层开展流动显示实验研究,探讨棱纹面与行波式洛仑兹力影响湍流边界层相干结构的作用机理.实验结果表明,棱纹面与洛仑兹力促进了边界层由层流向湍流的转捩;而对于湍流边界层,在一定的无量纲参数范围内棱纹面与行波式洛仑兹力都能实现边界层的局部减阻,相应地湍流边界层粘性底层低速条带平均间距有所增加.     

某型飞机平尾轴疲劳断裂失效分析

采用台架试验装置对某型飞机平尾轴进行了疲劳试验,通过断口的观察分析、断口部位的金相分析、硬度检测、有限元结构应力分析,确定了平尾轴的失效模式,并对其断裂失效原因进行了分析。结果表明：平尾轴的断裂性质为疲劳断裂,裂纹源均起源于大轴简体内壁加工刀痕形成的沟槽处,变截面圆弧造成的结构应力集中和粗糙加工刀痕形成的附加应力集中是造成大轴疲劳断裂的主要原因。关键词：平尾轴;疲劳断裂;失效分析;应力集中     

全反射棱镜式激光陀螺应力检测技术研究

光学元件的装配应力和加工应力是制约高精度激光陀螺稳定工作的重要因素．考虑各向同性材料在应力作用下介电常量变化的情况,利用弹光效应和琼斯矩阵得到了复杂应力与穿过全反射棱镜的激光束偏振态改变之间的关系．通过实验,提出一种通过记录棱镜布儒斯特角反射光椭偏度配合光斑质量分析应力水平的筛选方法,对棱镜式激光陀螺装配过程中光学元件应力的早期筛查有突出作用,并设计专用工装以适应棱镜相关产品的应力检测需要．     

桅杆模型中纤绳初张力识别

桅杆有限元模型一般用实测平衡张力作为纤绳的初张力,研究表明这种做法对桅杆振动特性的影响不可忽略,有必要对有限元模型中纤绳初张力进行识别。针对实测数据可能少于、恰好或多于能确定纤绳初张力所需数目等3种情况,分别给出了纤绳初张力的识别方法,并结合算例对方法进行了验证,结果表明其方法执行效率高,提高了桅杆有限元分析的准确性。