考虑非达西渗流的成层地基一维固结半解析解

在土中渗流遵从Hansbo非达西渗流的前提下,考虑实际工程中的变荷载,利用解析与数值相结合的半解析方法,对成层地基一维固结问题进行数值求解。将基于Hansbo非达西渗流的双层地基一维固结半解析解与相应的差分数值解进行对比,验证了半解析方法计算基于Hansbo非达西渗流下成层地基一维固结问题的可靠性。最后,对某三层地基考虑Hansbo非达西渗流的一维固结实例进行计算分析,结果表明：基于Hansbo非达西渗流下成层地基的沉降发展速率与超孔隙水压力的消散速率是不一致的。     

埋置移动荷载作用下成层饱和地基的动力响应

利用Fourier变换和传递反射矩阵法（TRM法）研究了成层饱和地基在埋置移动荷载作用下的动力响应。土体被假设为完全饱和的多孔弹性介质并且服从Biot多孔弹性波动方程,用修正粘滞阻尼模型来描述土体的粘弹性行为,采用TRM法来考虑饱和地基的成层性,利用Fourier变换和Fourier逆变换得到了埋置移动荷载作用下饱和地基动力响应积分形式解答。当饱和成层地基退化单层饱和地基时,该文解与已有解能很好的吻合。最后,通过数值计算分析了埋置荷载深度﹑荷载速度、荷载频率及软硬夹层对动力响应的影响。     

周期荷载下半透水边界饱和地基的固结

在Terzaghi一维固结假设的基础上，分析了半透水边界饱和土层在周期荷载作用下有效应力比的变化规律。通过基本方程，结合初边值条件，利用Laplace变换，得到了随时间任意变化荷载作用下的有效应力解。通过典型算例，结合编制的数值Laplace逆变换程序，对几种常见的荷载作用下的情况进行了讨论，研究了参数的影响。通常所研究的透水或不透水边界条件只是本文的特例。本文的结论可以用于指导工程实践。     

轴对称荷载下多层地基的Boit固结及其变形

本文用Laplace变换、Hankel变换以及矩阵递推规律分别建立了轴对称荷载下单层以及多层地基Biot固结的初始函数表达式。根据表达式推导得到Biot固结引起的竖向变形计算式,此式仅用一个广义积分表达,很容易用数值积分求解。不论地基土层数多少,只要求解一个三元一次代数方程就能得到多层地基固结变形计算式。本文导出的计算式能计算轴对称荷载下多层地基地表任意位置的竖向变形。不但能解决荷载作用于地基表面的Boussinesq问题,而且能解决荷载作用地基内部的Mindlin问题。     

瑞利波作用下成层地基中单桩横向振动分析

采用文克勒地基梁模型建立了成层地基中桩土相互作用的粘弹性模型,并利用现有的成层地基中的瑞利波弥散曲线解析解,通过解析法建立了瑞利波作用下多层介质中的桩体横向位移计算公式。在此基础上通过计算实例分析发现,无量纲频率α0、桩土相对刚度比Ep/Es、桩顶约束条件是影响桩体横向位移变化规律的主要因素,随着无量纲频率、桩土相对刚度比的增大,桩土分离的现象逐渐变得显著,桩顶约束的出现也会引起相同的结果。     

双面半透水边界饱和土层在循环荷载作用下一维粘弹性固结解析解

研究了在循环荷载作用下考虑土的流变特性时具有双面半透水边界的饱和粘土层的一维固结问题,根据瞬时加载条件下的解,通过积分的方法,得到了循环荷载条件下的解析解.并且根据解析解的结果,通过电算程序作出了几个主要影响因素对固结过程的影响曲线图,经过分析得出了一些重要的结论.     

双面半透水边界饱和土层在循环荷载作用下的一维粘弹性固结解析解

研究了在循环荷载作用下考虑土的流变特性时具有双面半透水边界的饱和粘土层的一维固结问题,根据瞬时加载条件下的解,通过积分的方法,得到了循环荷载条件下的解析解。并且根据解析解的结果,通过电算程序作出了几个主要影响因素对固结过程的影响曲线图,经过分析得出了一些重要的结论。     

层状地基一维固结电阻网法解答

考虑层状地基一维固结问题的复杂性,现有解答较为繁杂同时不便应用。该文基于Liebmann 电阻网原理,推导了初始孔压沿深度任意分布、荷载随时间任意变化作用下的孔压、平均固结度的解答。该解对于各种复杂条件均具有统一的矩阵表达式,便于编程计算和工程应用。通过与精确解的比较论证了该文方法的有效性。最后,对三层地基一维固结问题进行了分析和讨论。     

成层地基中倾斜荷载桩改进有限杆单元法研究

传统有限杆单元法不能考虑倾斜偏心荷载下基桩的P-Δ效应,假定桩身位移为三次幂函数,结合倾斜偏心荷载下单桩受力微分方程确定的桩身弯矩、剪力与桩身水平位移关系,导得具有简洁形式、计入P-Δ效应的杆单元刚度方程,进而得到改进的有限杆单元方法,并给列出了用该法进行成层地基中倾斜偏心荷载、桩自重、水平分布荷载、竖向分布荷载和竖向分散集中荷载综合作用下并考虑桩身倾斜影响基桩内力位移分析的具体计算步骤。结合某工程实例,对上述方法进行了验证。最后对影响倾斜荷载桩的主要因素如埋深、桩材、基桩自由长度、桩身倾斜度、竖向荷载偏心矩以及荷载倾角等对基桩受力特性影响进行了分析,获得了一些定性的结论。     

路堤荷载下横观各向同性地基固结特性参数分析

采用各向异性弹性有限元法,系统分析了弹性各向异性参数特别是水平方向上的参数(水平向模量Eh,水平向泊松比νhh和剪切模量Ghv)取值对路堤荷载作用下地基固结特性的影响,包括地基中心沉降、地基水平位移、地基中的孔压消散以及平均固结度。研究结果表明:Eh的变化对路堤的沉降(特别是固结沉降)、路基的瞬时水平位移、孔压生成和消散以及总体平均固结度的影响显著;νhh的变化对路堤的固结沉降有显著影响;Ghv的变化对路堤的沉降、水平位移影响显著,而对孔压、总体平均固结度结果基本没有影响。     

高饱和土固结及饱和度对土体固结的影响

以Terzaghi土体固结理论和Biot固结理论为基础,按饱和度不同的分类,研究了高饱和土固结机理及过程,深入分析了高饱和土饱和度变化对孔隙流体压缩性的影响,以及由此影响到高饱和土的固结全过程。     

Asymmetry Behaviour between Tension and Compression for Prestrained Materials under Cyclic Loading

The prestrained metals show substantial asymmetry between tension and compression in addition tothe softening under cyclic loading, thus the cyclic creep takes place at a load-control test. The soft-ening reflects the decrease in density of dislocation and total internal stress, and the creep implies theasymmetry in back stress between tension and compression, The mechanical behaviour of the soft-ening is similar for materials with different slip modes, but their features of creep differ significantly.The creep of planar slip Cu-Zn alloy exhibits“explosively”, while that of wavy slip Cu and low car-bon steel occurs continuously and slowly. The explanation of creep behaviour via the internal dislo-cation structure was presented in this paper. According to asymmetw behaviour, it can be concludedthat the internal processes of softehing also strongly depend on the slip mode. In addition, underhigh stress amplitude the opposite asymmetries take place for Cu and Cu-Zn alloy, it indicates thatasymmetric back stresses developed in pretension have been eliminated even though the density andthe configuration of dislocations have not reached equilibrium.     

A Device for the Synchronization of Cyclic Heating with Low-Cycle Mechanical Loading

We describe a device for cyclic heating of laboratory specimens in the same or opposite phases with low-cycle mechanical loading in a standard low-cycle testing machine. We develop a special phase shifter capable of compensating for the delay of the phases of heating of the specimen relative to the phases of its mechanical loading. It is also possible to control the phase shift between cyclic heating and mechanical loading.     

基于传递矩阵法的分层饱和土中单桩扭转动力阻抗

以分层饱和土中单桩扭转振动为研究对象,将桩周土体视为分数阶黏弹性饱和土,借助分数阶黏弹性本构模型和土体运动平衡方程、应力位移关系建立分层分数阶黏弹性饱和土层扭转振动微分方程。以两层分数阶黏弹性饱和土为例,讨论主要桩土力学参数对扭转动力阻抗影响。结果表明：下上层土体本构模型阶数比对扭转动力阻抗随频率变化曲线峰值影响较大,下上层土体剪切波速比、土层厚度比和桩土模量比对扭转动力阻抗的影响与频率有关,下上层土体液固耦合系数较小时,其对扭转动力阻抗的影响很小。     

循环载荷对裂纹扩展和持久寿命的影响

对铁基高温合金ＧＨ２１３２在各种最大试验载荷下的纯蠕变和循环蠕变寿命以及裂纹扩展断裂行征进行分析，结果表明，在裂纹扩展不同时期（σ〈σ０．２和σ〉σ０．２）循环加载对裂纹扩展的影响相反，而对最终持久寿命的影响则取决于这两种相反作用之总的效果。     

等压固结条件下湘江饱和砂土动力特性研究

在大量的动三轴试验基础上,研究了等压固结条件下湘江饱和砂土振动孔隙水压力、应力应变滞回圈以及应力路径的发展变化规律。研究结果表明:孔压发展变化过程与土体的剪胀、剪缩密切相关;孔压与轴向动应变之间的变化关系显示饱和砂土具有明显的各向异性;从孔压与滞回圈面积累积之和的关系看,孔压的增长伴随着能量的损失;对于围压较大的情形,用ExpAssoc函数进行拟合效果较好。隧振次增加应力应变滞回圈也在发生变化,第一阶段滞回圈呈倒置的帽子形,第二阶段呈菱角形状。在振动初始阶段,应力路径基本上呈倾斜的直线变化;随孔压的增加,加载和卸载两条应力路径逐渐分开,呈纺锤形。     

Dislocation Structure of VT22 Titanium Alloy in Cyclic Loading with Various Loading Frequencies

We study the dislocation structure of a Tindash;5percnt;Alndash;5percnt;V alloy upon cyclic-strength and crack-propagation resistance tests with symmetrical tensionndash;compression loading with frequencies of 100 Hz, 500 Hz, 3 kHz, and 10 kHz. The identity of the test conditions has allowed us to carry out a comparative analysis of the influence of the loading frequency on the evolution of the dislocation structure in the material main volume during the fatigue-damage accumulation and in the fracture zone during the fatigue-crack propagation. It is shown that at these two loading stages the plastic-deformation micromechanisms adapt themselves to the loading rate. In the first case, this is due to the fact that a decrease in the activity of the work of the Frankndash;Read sources in high-frequency loading is compensated for by a more pronounced deformation of the alpha;-phase as a result of the formation of stacking faults. In the second case, the high level of local stresses activates the cross sliding and the formation of a honeycomb structure in the alpha;- and beta;-phases, and the elements of this structure decrease in size with increasing loading frequency. The incompleteness of relaxation processes in high-frequency cyclic loading is offset by the deformation of boundary volumes which are initially present in the alpha;-phase of twins.     

Fatigue-Crack Propagation in Heat-Resistant Alloys under Thermomechanical Loading. Part 2. A Method of Accounting for the Influence of Thermomechanical Loading on the Material Resistance to Fatigue-Crack Growth

A method is proposed for a comprehensive consideration of the influence of thermomechanical-loading components on the variation of the fatigue-crack propagation rate. The method takes into account the variability of the values of the calculated stress intensity factors over the crack front and with the time of a thermal cycle. Experimental results obtained for alloys KhN70VMTYu (Eacute;I617) and KhN73MBTYu (Eacute;I698) are described. For two regimes of thermal cycling, near-threshold and medium sections of kinetic diagrams of fracture of these alloys are constructed.     

An Assessment of Nonlinearly Viscoelastic Constitutive Models for Cyclic Loading: The Effect of a General Loading/Unloading Rule

Predicting the unloading and/or cyclic deformation behavior of polymers is a challenge for most nonlinear viscoelastic constitutive models. Experimental data of an epoxy polymer under uniaxial loading/unloading and two other types of cyclic loadings are used to assess the predictive capabilities of three types of nonlinear viscoelastic models. A general loading/unloading criterion and a switching rule, proposed recently by the authors, are further modified and incorporated into each of the three models. For each model, predictions by both the original formulations and that incorporating the proposed loading/unloading rule are compared with the test data. It is clearly shown that such a rule is essential to correctly simulate the unloading and cyclic loading behavior of polymers. By introducing such a rule to constitutive models, the quantitative predictions can be improved, to various degrees of success, with respect to cyclic deformation features such as ratcheting under cyclic loading with a mean stress and stress relaxation under cyclic straining with a mean strain.