Constitutive behavior and microstructural evolution in hot deformed 2297 Al-Li alloy

The microstructural evolution mechanism and constitutive behavior of 2297 Al-Li alloy were studied via thermal compression test with the constant strain rates of 0.001–1 s⁻¹ and the deformation temperatures ranging from 623 to 773 K. To verify the predictable ability of diverse constitutive models under different stress states, the hot compression experiments with stress triaxiality varying from −0.33 to 0.46 were conducted. The microstructures of the deformed specimens under diverse deformation conditions are probed to reveal the mechanism of hot deformation behavior. The experimental results indicate that the work-hardening and dynamic softening are competitive during the hot compression process, and the dynamic softening is more obvious under low deformation temperature and high strain rate. The microstructural analysis manifests that the dynamic recovery gets predominant at high deformation temperature to produce fine grains. Meanwhile, the dynamic recrystallization becomes more dominant as the strain rate decreases, which is sensitive to the stress triaxiality. In addition, both the modified Johnson-Cook model and strain-compensated Arrhenius-type function are suitable for describing the flow behavior of 2297 alloy, while the latter reveals a more accurate prediction. However, the predictability of the two kinds of models is worsened with the transformation of stress triaxiality, and the validity of the Arrhenius-type model is restricted by high stress triaxiality.     

刀具刚度对钛合金超薄侧壁加工变形的影响

以控制钛合金超薄结构件的加工变形、获得良好的表面加工质量为目标,基于薄壁零件加工变形理论模型与铣削加工试验,研究分析了刀具刚度对钛合金超薄侧壁结构加工受力变形及表面粗糙度的影响。通过对比分析刚度刀具铣削钛合金超薄侧壁结构时的加工尺寸精度、表面粗糙度以及切削力,发现合理增加刀具刚度可以有效改善超薄壁结构的加工尺寸精度及表面质量。     

基于修正Rife算法的脉冲回波相参积累算法

针对目标径向运动导致回波在波门内出现距离走动的情况,提出了一种针对径向匀速运动目标回波信号长时间相参积累的方法。该方法根据傅里叶变换的时移性质——不同时刻回波频谱相关序列的频率包含了各回波到达的时间延迟,通过修正Rife算法估计此时间延迟,最终确定并补偿各个回波的距离走动分量。仿真结果表明:提出的方法可以有效补偿各回波间的距离走动;信噪比低至-6dB时,算法的性能即可达到最优;补偿后积累信号的信噪比可以达到理想积累情况下的93%。     

A comprehensive numerical model examining the thermal performance of airships

A novel computational model for analyzing the airship’s transient thermal performance under different environmental conditions was developed. Radiative heat transfer and natural convection inside the airship were modeled using the control volume method. The Semi-Implicit Method aiming at the Pressure-Linked Equations algorithm was adopted to solve the control equations. Such approach was able to take into account the solar irradiative heat flux, the infrared radiation at different locations, and the convection both inside and outside the airship. The simulation results, showing the detailed distributions of temperature and velocity on the envelope and inside the airship, were in good agreement with the experimental measurements. The influences of solar position and material radiative properties on temperature distribution, as well as natural convective flow inside airship, were further simulated and discussed.     

分子定向及引起的收缩与变形

基于分子定向是塑料凝固时出现的特有现象。探讨、分析分子定向产生的机理以及分子定向所带来的不良后果，为提高塑料制件的质量提供了有参考价值的理论依据。     

基坑开挖的试验研究与Plaxis结果的比较讨论

基坑开挖与支护是一个三维空间问题。我国对软土深基坑支护工程的研究已取得一些成果，但对非饱和土地区的深基坑支护工程而言，由于非饱和土中存在负孔隙水压力(基质吸力)，使得其与饱和土在性状上有显著的不同。因而软土深基坑支护工程的许多成功经验不适用于非饱和土。对非饱和土基坑开挖的研究，尚存在许多问题有待解决，其中最主要的问题是挡墙上土压力的分布及变形。采用国际先进的Plaxis程序，将计算结果与室内大型模型试验结果进行对比分析，得出挡墙上土压力的分布及变形规律，以期完善土压力理论。     

双S弯喷管的流固耦合特性研究

为了明晰S弯喷管的流固耦合特性,数值模拟了流固耦合作用下双S弯收敛喷管的结构变形特征及其内/外流特性。结果表明：S弯喷管的圆转方弯曲构型产生了非均匀的流场分布,并增强了结构的弹性特征,它们通过交换气动载荷与变形位移数据形成了S弯喷管流固耦合的作用机理。在气动载荷作用下,S弯喷管沿Y向的最大变形位移为25.3mm,它位于喷管出口上壁面的中心位置。当喷管的结构变形稳定时,第二弯转弯处下壁面的气流加速至局部超音速,壁面静压大幅降低;第一弯下游上壁面附近形成了气流分离区;喷管出口喷流沿轴向向上偏转。流固耦合作用导致S弯喷管的流量系数减小0.6%,推力系数降低1.8%。矩形截面与弯曲构型是影响S弯喷管流固耦合特性的主要几何特征,其中矩形截面能够显著增大喷管的变形位移;S形弯曲构型虽然能够有效抑制变形特征,但它导致喷管多个区域出现变形,喷管的结构变形分布变得更加复杂。     

计及摩擦的有限变形碟形弹簧薄膜解

应用Ｔｉｍｏｓｈｅｎｋｏ ＳＰ的刚性截面假设，分析了单片碟形弹簧在大变形情况下计及摩擦与滑动的载荷－位移关系，并对有导杆与无导杆，计摩擦与不计摩擦等不同情况下的载荷－位移曲线作了对比分析，在此基础上对重复加载时摩擦力的损耗（滞后功）进行了计算和讨论，这对连接件的抗疲劳设计将会起有益的作用。     

具有初始弯曲的转子系统的振动特性

具有初始弯曲的转子系统的振动特性与不平衡响应相比,既有相似之处,又存在独有的特点.从转子动力学理论出发,建立了适合工程应用的多自由度分析模型,给出了分析方法,并通过一实际转子系统的计算分析,阐述了其动力学特点.     

变形工艺对Ti-3Al-5Mo-5V动态压缩变形的影响

采用显微组织分析和工艺试验相结合的方法系统分析了变形工艺对Ti-3A l-5Mo-5V钛合金动态压缩变形行为的影响规律。结果表明,变形速率和变形量影响着合金动态变形局部化的程度(剪切带的宽度)和变形过程中出现的剪切带的类型,动态变形后剪切带区域的硬度与其他位置的硬度差异较大,这种差异可以通过变形后适当的后续退火处理来消除。