原状Q_2黄土三轴剪切细观结构演化定量研究

基于非饱和原状Q2黄土CT-三轴剪切试验得到的结构演化清晰的CT图像及CT数据,提出利用CT数随偏应力的关系确定屈服应力的新方法。基于CT数定义了结构性参数和结构演化变量;分析了结构演化变量与净围压和吸力的关系,相对于应变(包括偏应变和体应变),当吸力相同时,净围压越大,结构演化变量值越大;当净围压相同时,吸力越大,结构演化变量值越小。建立了非饱和原状Q2黄土三轴剪切过程的结构演化方程,该方程为结构演化变量与偏应变和体应变的关系,能同时反映净围压和吸力等对结构演化的影响。利用提出的结构演化方程对试验数据进行拟合,拟合结果较理想。

原状Q_3黄土在加载和湿陷过程中细观结构动态演化的CT–三轴试验研究

为了揭示原状Q3黄土在加载和湿陷过程中的细观结构变化,将湿陷三轴仪与医用CT机相配套,进行了一系列控制吸力的CT-三轴湿陷试验,不仅得到了加载过程和湿陷过程中的宏观反应曲线,而且得到了相对应的CT扫描图像。结果表明:原状湿陷性黄土具有较强的初始结构性;加载过程中,较大的孔洞先扩展后闭合,小孔洞逐渐闭合;湿陷过程中,大部分孔洞逐渐闭合且断面的密度分布趋于均匀;湿陷过程中大孔洞闭合与否取决于浸水时的应力状态。通过宏细观试验资料的分析,确定了原状湿陷性黄土的结构屈服应力,提出了一个基于CT数均值的结构性参数,分别定义了加载和湿陷过程中的结构损伤变量,研究了它们的变化规律,建立了结构损伤演化方程。

膨胀土在湿干循环和三轴浸水过程中细观结构变化的试验研究

为研究膨胀土裂隙的产生及闭合规律,对重塑膨胀土进行了无约束条件下的3次湿干循环试验;再对湿干循环后的裂隙膨胀土进行了控制围压和偏应力为常数的CT–三轴浸水试验。研究结果表明:无约束条件下的膨胀土试样增湿和干燥都能引发裂隙的产生和闭合;在三轴浸水试验中,裂隙均趋于闭合,而闭合程度与应力状态有关;浸水过程中,试样体积变化可分为3个阶段,体积首先减小,接着因湿胀作用逐渐增大,尔后又因膨胀力释放和模量降低而减小;定义了结构修复参数,提出了三轴浸水过程中的土样结构修复演化方程。

原状Q2黄土CT-三轴浸水试验研究

利用后勤工程学院研制的CT-多功能土工三轴仪，研究非饱和原状Q2黄土三轴浸水变形特性，并在浸水过程中利用CT技术对内部结构的变化进行无损的量测，得到内部结构演化的CT图像和相应的CT数据，从细观上解释了三轴浸水过程。基于CT数据定义结构性参数和结构演化变量；分析浸水过程中结构演化变量与净围压、偏应力和吸力的关系，浸水前的固结净围压、偏应力和吸力越大，浸水过程中结构演化越快。建立非饱和原状Q2黄土三轴浸水过程的结构演化方程，该方程为结构演化变量与偏应变、体应变和饱和度增量的关系，能同时反映净围压、偏应力和吸力等对结构演化的影响。利用提出的结构演化方程对试验数据进行拟合，拟合结果较理想。CT技术使土的细观结构研究达到定量阶段，为建立土的结构演化方程和结构性本构模型提供了试验基础。

Phase-field study on competition precipitation process of Ni-Al-V alloy

With microscopic phase-field kinetic model, atomic-scale computer simulation program for the precipitation sequence and microstructure evolution of the ordered intermetallic compound γ＇ and θ in ternary Ni75AlxV25-x alloy were studied. The simulation results show that Al concentration has important effects on the precipitation sequence. When Al concentration in Ni75AlxV25-x alloy is low, 0（Ni3V） ordered phase will be firstly precipitated, followed by γ＇（Ni3Al） ordered phase. With Al concentration increasing, θ and γ＇ ordered phases are simultaneously precipitated. With A1 concentration further increasing, γ＇ ordered phase is firstly precipitated, followed by θ ordered phase. There is a competition relationship between θ and γ＇ ordered phases during growth and coarsening process. No matter which first precipitates, θ ordered phase always occupies advantage in the competition process of coarsening, thus, the microstructure with preferred orientation is formed.

A New Liouville Integrable Hamiltonian System

With the help of a Lie algebra, an isospectral Lax pair is introduced for which a new Liouville integrable hierarchy of evolution equations is generated. Its Hamiltonian structure is also worked out by use of the quadratic-form identity.

Some Evolution Hierarchies Derived from Self-dual Yang-Mills Equations

We develop in this paper a new method to construct two explicit Lie algebras E and F. By using a loop algebra E of the Lie algebra E and the reduced self-dual Yang-Mills equations, we obtain an expanding integrable model of the Giachetti-Johnson （G J） hierarchy whose Hamiltonian structure can also be derived by using the trace identity. This provides a much simplier construction method in comparing with the tedious variational identity approach. Furthermore, the nonlinear integrable coupling of the GJ hierarchy is readily obtained by introducing the Lie algebra gN. As an application, we apply the loop algebra E of the Lie algebra E to obtain a kind of expanding integrable model of the Kaup-Newell （KN） hierarchy which, consisting of two arbitrary parameters a and β, can be reduced to two nonlinear evolution equations. In addition, we use a loop algebra F of the Lie algebra F to obtain an expanding integrable model of the BT hierarchy whose Hamiltonian structure is the same as using the trace identity. Finally, we deduce five integrable systems in R3 based on the self-dual Yang-Mills equations, which include Poisson structures, irregular lines, and the reduced equations.

A New CKP Hierarchy with Two Generalized Time Series and Its Reduction

A new C-type subhierarchy for KP hierarchy with two new time series γn and σk （ （Tn,crk ）-CKPH）, which consists of γn-flow, σk-flow and mixed γn and σk evolution equations of eigenfunctions, is proposed. The zero-curvature representation for the （γn, σk ）-CKPH is derived. The reduction and constrained flows of （γn, σk ）-CKPH are studied.

Stochastic response analysis of damaged elastic beams

Great progress has been made in study on dynamic behavior of the damaged structures subject to deterministic excitation.The stochastic response analysis of the damaged structures,however,has not yet attracted people's attention.Taking the damaged elastic beams for example,the analysis procedure for stochastic response of the damaged structures subject to stochastic excitations is investigated in this paper.First,the damage constitutive relations and the corresponding damage evolution equation of one-dimensional elastic structures are briefly discussed.Second,the stochastic dynamic equation with respect to transverse displacement of the damaged elastic beams is deduced.The finite difference method and Newmark method are adopted to solve the stochastic partially-differential equation and corresponding boundary conditions.The stochastic response characteristic,damage evolution law,the effect of noise intensity on damage evolution and the first-passage time of damage are discussed in detail.The present work extends the research field of damaged structures,and the proposed procedure can be generalized to analyze the dynamic behavior of more complex structures,such as damaged plates and shells.