铝氢脆破坏微观机制的分子动力学研究

采用分子动力学方法模拟了铝单晶、双晶及其含氢模型在拉伸条件下的力学特性。根据模拟结果,讨论了氢导致铝材料脆化破坏的微观机理。研究表明:铝单晶、双晶中的氢降低了铝的抗拉强度,且力学性能随氢含量的升高而降低;应力条件下晶体内部的氢原子会产生偏聚和富集,在富集处铝原子更易发生位错,产生空穴,诱发脆断;和同等条件下的铝单晶相比,铝双晶对氢脆破坏更为敏感。     

SiC／Ti-153复合材料界面与性能研究

对带(B4C C)涂层的SiC纤维增强Ti-153复合材料的界面反应进行热力学分析,并对界面反应层做能谱成分分析及X-射线衍射结构分析.结果表明,界面反应层为TiC,TiB2和TiB相的组合物.采用不同的热压工艺制备复合材料并分别进行拉伸实验及扫面电镜观察,从而得出不同界面结合状态与拉伸性能之间的关系.对经不同时间的热处理具有不同界面反应层厚度的复合材料进行拉伸实验,结果表明,随着反应层厚度的增加复合材料性能下降.     

Cross-Scale Coupling Within Rolled-Up MHD-Scale Vortices and Its Effect on Large Scale Plasma Mixing Across the Magnetospheric Boundary

Kelvin-Helmholtz Instability (KHI) is an MHD-scale instability that grows in a velocity shear layer such as the low-latitude boundary layer of the magnetosphere. KHI is driven unstable when a velocity shear is strong enough to overcome the stabilization effect of magnetic field. When the shear is significantly strong, vortices in the nonlinear stage of KHI is so rolled-up as to situate magnetospheric plasma outward of the magnetosheath plasma and vice versa. The big question is if such highly rolled-up vortices contribute significantly to the plasma transport across the boundary and to the filling of the plasma sheet by cool magnetosheath component, which is observed under northward Interplanetary Magnetic Field (IMF) condition. Here we review our recent results from two-fluid simulations of MHD-scale KHI with finite electron inertia taken into account. The results indicate that there is coupling between the MHD-scale dynamics and electron-scale dynamics in the rolled-up stage of the vortices. While the details differ depending on the initial magnetic geometry, the general conclusion is that there is significant modification of the MHD-scale vortex flow pattern via coupling to the micro-physics. The kick-back from the parasitic micro-physics enhances highly the potential for large-scale plasma mixing of the parent MHD-scale vortices, which is prohibited by definition in ideal-MHD. We also review our recent 3-D MHD simulation results indicating that KHI vortex can indeed roll-up in the magnetotail-flank situation despite the strong stabilization by the lobe magnetic field. These results encouraged us to search for evidence of rolled-up vortices in the Cluster formation flying observations. As reviewed in this paper, a nice event was found during northward IMF interval. This interval is when the plasma transport via large scale reconnection becomes less efficient. The finding supports the argument that KHI is playing some role in transporting solar wind into the magnetosphere when the normal mode of transport cannot dominate.     

干涉配合紧固件孔的弹塑性工程分析

本文根据厚壁筒概念,以平面应变、有限边界情况和理想塑性材料的假定,对铆接或螺接干涉配合紧固件孔边的应力场进行了弹塑性工程分析,给出了便于分析使用的计算弹性配合的极限干涉量,塑性配合的塑性区半径,弹、塑性区内的径向和周向应力分布等参数方程式,这些参数和参数方程式对紧固件孔的疲劳设计和生产工艺都具有十分重要的意义。 应用分析说明了铆距和耳片外边界半径对所得结果的影响,以及平面应变和理想塑性材料与平面应力和幕强化塑性材料假定对于孔边应力分布的影响。     

含共线分布多裂纹板的剩余强度

采用各向异性体平面弹性理论中的复势方法，应用保角映射技术和Faber级数展开，导出在任意载荷作用下多裂纹板应力场的级数解，引入当量屈服应力修正裂尖塑性区，并利用Swift韧带屈服准则建立舍共线分布多裂纹结构的剩余强度分析模型，计算结果与试验结果吻合较好。文中还讨论了各裂纹参数对结构剩余强度的影响。计算结果表明，本文以当量屈服应力代替材料屈服应力，避免了复杂的弹塑性分析，思路简单有效。便于工程应用。     

NiTi形状记忆合金的拉伸实验与物理模型

根据NiTi丝的拉伸实验结果,基于滞后元方法,建立了拉伸状态下应力-应变曲线的唯象物理模型,并进行了数值模拟。研究结果表明(1)SMA丝在马氏体相变,特别是R相变时出现一系列物理、力学性质的异常变化,其应力-应变关系呈现高度非线性;(2)在NiTi丝断裂之前没有明显的屈服现象;(3)物理模型的数值模拟结果与实验结果吻合较好。     

纤维表面处理对单向C/SiC复合材料拉伸强度的影响

为改善纤维与基体的界面结合状态,提高C/SiC复合材料力学性能,对炭纤维采用1800℃高温处理、CVI沉积热解炭以及两者联合作用3种方法进行纤维表面处理,研究了表面处理对C/SiC单向复合材料力学性能的影响。结果表明,经过1800℃处理后的纤维表面粗糙度变大,表面沟槽加深,复合材料的拉伸强度是未经表面处理纤维复合材料拉伸强度的2.4倍;纤维表面沉积热解炭后表面粗糙度减弱,其拉伸强度是未经表面处理纤维复合材料的3.1倍;两者联合作用时纤维表面光滑,拉伸强度最高,达708 MPa。     

轧制NiMnFeGa高温形状记忆合金的微观结构及拉伸力学性能

 采用包套热轧的方法,将Ni56Mn17Fe8Ga19和Ni56Mn15Fe10Ga19合金铸锭成功轧制为均匀板材,研究了其微观组织结构、相变特性和拉伸力学性能等。结果显示,轧制后合金的晶粒和γ相变得细碎,且沿着轧制方向伸长分布,其逆马氏体相变温度下降,相变滞后减小;轧制态合金的抗拉强度和延伸率分别超过500 MPa和2%,热处理后,强度降低而延伸率上升。     

Effects of RRA Treatments on Microstructures and Properties of a New High-strength Aluminum-Lithium Alloy-2A97

A new high strength 2A97 Al-Cu-Li-X alloy was subjected to triple-aging of retrogression and re-aging treatments (RRA). Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and tensile tests were used to investigate the effects of RRA treatment on the microstructures and properties. DSC test reveals the reversion temperature range of the strengthening δ' (Al3Li)phase. The results show that the microstructure consists of δ' (Al3Li) phase, T1 (Al2CuLi) phase and θ"/θ'(Al2Cu) phase for 2A97 alloy treated by a triple-aging ora retrogression and re-aging treatment in the following order: (1) at 165 ℃×30 min, (2) at 220 ℃ or 240 ℃×15 min, (3) at 165 ℃×24 h. The plastic deformation, incorporated into the treatment after secondary high temperature aging, promotes the T1 precipitation during final re-aging. The tensile properties of the alloy treated by the retrogression and re-aging treatment reach the peak level of alloy single-aged at 165 ℃ in T6 temper.     

On Nonlinear-Evolution of C-type Instability in Nonparallel Boundary Layers

The process of evolution, especially that of nonlinear evolution, of C-type instability of laminar-turbulent flow transition in nonparallel boundary layers are studied by means of a newly developed method called parabolic stability equations （PSE）. Initial conditions, which are very important for the nonlinear problem, are investigated by computing initial solution of the harmonic waves, modifying the mean-flow-distortion, and giving initial value of TS wave and its subharmonic waves at initial station by solving linear PSE. A numerical method with high-order accuracy are developed in the text, the key normalization conditions in the PSE are satisfied, and nonlinear PSE are solved efficiently and implemented stably by the spatial marching. It has been shown that the computed process of nonlinear evolution of C-type instability in Blasius boundary layer is in good agreement with the experimental results.