泥质盐岩单轴蠕变寿命研究

岩石流变力学的研究中，蠕变寿命是一个重要问题.由于长期蠕变试验资料的缺乏，难以估计蠕变破坏时间.该文进行了泥质盐岩单轴全应力 应变压缩试验，并采用陈氏加载法进行了单轴蠕变试验.对蠕变曲线进行了处理，获得了不同应力水平下的蠕变曲线簇，进而得到了等时应力-应变曲线簇.通过拟合分析，建立了等时应力-应变曲线割线模量随时间变化关系模型和等时应力 应变曲线的数学模型.对等时应力 应变曲线与全应力-应变曲线之间的关系进行了分析，获得了蠕变破坏强度和破坏应变分别与蠕变寿命之间的数学表达式.该文研究成果可以估计泥质盐岩的蠕变寿命、长期强度、长期模量、蠕变破坏线和蠕变终止线，对相关岩石流变寿命的估计具有借鉴意义.     

反映混凝土单边效应的弹塑性损伤本构模型及应用

为了尽可能有效和准确地描述混凝土材料的非线性力学特性,在研究国内外混凝土损伤本构模型的基础上,基于连续介质损伤力学和不可逆热力学的理论框架,采用统一强度理论作为屈服破坏准则,分别定义拉、压双标量损伤来考虑材料的拉、压迥异特性,同时引入反向加载影响因子以修正拉压交替循环加载时材料的单边效应,以及多轴应力状态下拉、压损伤累积的相互影响,最终采用显式积分算法建立了一种改进的混凝土弹塑性损伤本构模型.不同素混凝土加载试验模拟结果初步验证了建议模型的有效性,而通过对含I型裂缝的混凝土简支梁试验进行数值分析,结果表明,所得的荷载 挠度曲线与试验结果吻合良好,进一步检验了模型应用于结构非线性分析的有效性.     

下分层不同层位千米钻孔稳定性研究

抽采钻孔的稳定性影响到抽采工程效果的好坏.采动作用下,位于底板下方不同层位千米钻孔的加卸载路径不同.为得到采动作用对不同层位钻孔稳定性的影响,分析了底板不同层位钻孔加卸载路径,依据该路径,设计十种数值模拟计算方案,对底板钻孔在不同速率加卸载、变速加卸载两种方式下的破坏范围、孔壁位移进行了分析,得到了加卸载结束后各方案对应的塑性区分布范围及加卸载过程中孔壁位移曲线.依据数值计算得到的卸载速率与形变恢复滞后性的关系,建立了考虑卸载速率变化的钻孔周边切应力计算模型.研究结果表明:加载速率对钻孔周边的破坏范围几乎不产生影响;卸载过程中,钻孔周边破坏范围与初始卸载应力及卸载速率相关,在进行底板顺层抽采钻孔布置时需综合考虑布孔位置处的应力值及卸载速率.     

正交各向异性圆柱体在轴压作用下的应力场

基于材料体积不可压假设,对轴向压缩作用下圆柱试件在加载面内的环向和径向应力分布进行理论分析,计算结果表明:当试件材料本构为正交各向异性时,环向和径向应力分布为半径的幂函数形式;试件材料为横观各向同性时,环向和径向应力为半径的二次函数.在圆柱试件轴线上环向和径向应力相等,且均具有最大值;试件圆周边界上径向应力为0,环向应力具有极小值.通过最大拉伸应变破坏理论对试件环向应变进行分析,获得了产生环向拉伸破坏时的临界轴向载荷;并采用Hill-蔡强度理论对试件圆周边界上计算得到的应力参量进行描述,得到了轴压作用下圆柱试件的Hill-蔡强度理论表达式,其不仅取决于轴向应力和试件材料的基本力学性能,还与试件轴向变形的应变率及应变率随时间的变化率相关.     

水库淡水冰剪切强度试验研究

对红旗泡水库淡水冰开展了剪切强度系列试验,累计得到236个试样的剪切强度数据.分析了剪切强度随温度、剪切应变速率以及加载方向的变化规律.通过试验结果得到剪切强度随剪切应变速率的变化规律,利用统计分析得出峰值剪切强度与冰温度的试验关系.同时分析了水库冰各向异性特点,产生不同加载方向下剪切强度的差异.     

基于坐标平移法的正常固结非饱和土三剪弹塑性本构模型

采用单应力变量法和双应力变量法建立了非饱和土的三剪统一强度准则,在此基础上用坐标平移法分别推导了相应的破坏应力比.将所得破坏应力比与非饱和土修正Cambridge模型进行结合,分别建立了单应力变量及双应力变量下的正常固结非饱和土三剪弹塑性本构模型,并对其做了ABAQUS二次开发.以南昌非饱和重塑红土为研究对象,分别对其做了非饱和土三轴固结排水试验验证、真三轴固结排水试验模拟,并研究了中间主应力影响系数b和基质吸力s对重力式挡土墙计算模型的影响.计算结果表明:所提的2种本构模型在三轴固结排水试验中均能很好地描述正常固结非饱和土的变形特性,且双应力变量下采用坐标平移法的模拟结果相对更为接近真实试验结果;在真三轴固结排水试验模拟中,采用双应力变量法相对单应力变量法所得偏应力和体应变偏大,随着中间主应力影响系数b增大,2种本构模型的偏应力和体应变也会随之增大;双应力变量下的重力式挡土墙计算模型更为稳定,随着中间主应力影响系数b或基质吸力s的增大,挡土墙模型土体位移相应减小,而墙后土体强度及稳定性相应增大.     

缓慢扩展裂纹尖端的各向异性塑性应力场

在裂纹尖端的理想塑性应力分量都只是θ的函数的条件下,利用平衡方程、Hill各向异性屈服条件及卸载应力应变关系,我们导出了缓慢定常扩展平面应变裂纹和反平面应变裂纹的尖端的各向异性塑性应力场的一般解析表达式.将这些一般解析表达式用于具体裂纹,我们就得到缓慢定常扩展Ⅰ型和Ⅲ型裂纹尖端的各向异性塑性应力场的解析表达式.对于各向同性塑性材料,缓慢扩展裂纹尖端的各向异性塑性应力场就变成理想塑性应力场.     

高温合金GH4169的失效特性及失效模型研究

对GH4169高温合金开展了不同应力三轴度（-0.33~0.33）、不同应变率（0.001~5 000 s-1）、不同温度（293~1 073 K）条件下的材料性能试验.基于Johnson-Cook失效模型的框架,研究了Johnson-Cook(JC)失效模型及已有文献提出的修改形式中应力三轴度项拟合结果的不确定性及应变率对失效应变的线性关系描述局限性问题,通过提出的特定参数确定方法与耦合应力三轴度的应变率效应指数函数,建立了一种唯象修正的失效模型.基于GH4169高温合金的试验结果,标定了修正的失效模型与JC模型中各个参数.结果表明:在不同应力三轴度下,GH4169的失效应变表现出不同的应变率效应;与传统的JC模型相比,修正的失效模型更能够较好地描述GH4169的失效行为;同时能够保证失效应变的非负性.     

基于裂纹尖端二阶弹性解的断裂过程区尺度

基于Westergaard应力函数裂纹尖端二阶弹性解,推导了裂纹尖端微裂区的轮廓线和特征尺寸的解析表达式;采用幂函数模型描述的拉应变软化模型,确定了在最大拉应力强度理论和最大拉应变强度理论下断裂过程区（FPZ）临界值的解析表达式;将基于Westergaard应力函数一阶弹性解及二阶弹性解、Muskhelishvili应力函数和Duan-Nakagawa模型确定的FPZ临界值进行了比较．结果表明裂纹尖端微裂区和FPZ临界值随着Poisson比的减小而增加并逐渐趋近于应用最大拉应力强度理论确定的结果;二阶弹性解确定的裂纹尖端微裂区和FPZ临界值大于一阶弹性解的值;FPZ临界值随着拉应变软化指数的增加而增加;二阶弹性解确定的FPZ临界值的精度远高于一阶弹性解确定的值.     

基于有限变形弹塑性模型模拟伪弹性合金全程变形行为

提出一个J2流的有限弹塑性本构方程来显式、全面地模拟了形状记忆合金(SMAs)在3个不同阶段加载并卸载所表现出来的应力-对数应变关系.这3个阶段包括变形完全恢复的伪弹性阶段、变形部分恢复的塑性阶段以及软化破坏阶段.该文的主要思想在于从实验数据的形函数出发,得到用形函数表达的多轴硬化函数,进而代入到本构方程,建立一个能模拟任意形状应力-对数应变关系,多轴有效的本构方程.该文方法的优势在于避免考虑微观到宏观的平均方法、相变条件等一系列复杂处理,大大减少了计算量.所得到的数值结果可以精确匹配实验数据.     

Experimental investigation of the stability of glass-reinforced plastic cylindrical shells subjected to long-term axial compression

The results of an experimental investigation of circular cylindrical glass-reinforced plastic shells under long-term axial compression are reported. The experimental method and the experimental apparatus are described. The initial irregularity functions and their evolution during loading and in time at various values of the compressive loads are investigated. The spread of the critical times at a given load level is studied together with the dependence of the critical time on the compressive load. The behavior of the shell after unloading and under alternating loading and unloading is considered. The correlation between the buckled shapes resulting from long-term compression and the initial irregularity functions is examined.Moscow Power Engineering Institute. Translated from Mekhanika Polimerov, No. 4, pp. 710–713, July–August, 1973.     

Behavior of concrete cylinders confined by a carbon composite 3. Deformability and the ultimate axial strain

Results of an experimental investigation into the mechanical properties of concrete cylinders confined by a carbon-epoxy composite wrapping are presented. It is shown that, for all the con fined con crete spec i mens tested, the loading paths in the normalized stress space follow a single master curve, what ever the concrete strength and confinement intensity. At stresses in the confined concrete exceeding the strength of plain concrete, the tangent modulus was found to depend on the slope angle of the master curve and the asymptotic value of the differential Poisson ratio (the first derivative of the lateral strain with respect to the axial one). Formulas for predicting the ultimate axial strain and the tangent modulus are derived and compared with the corresponding fib (fédération internationale du béton) recommendations. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 433–448, July–Au gust, 2006.     

Bond-slip behavior of CFRP plate-concrete interface

The paper deals with evaluation of the bond performance between a CFRP plate and concrete with respect to various compressive strengths of concrete and bond lengths of the CFRP plate as parameters. To consider stress conditions in the tensile zone of reinforced concrete (RC) structures, double-lap axial tension tests were conducted for eight specimens with CFRP plates bonded to concrete prisms. In addition, a simple linear bond-slip model for the CFRP plate/concrete joints, developed from the bond tests, was used. To verify the model proposed, a total of seven RC beams were strengthened with CFRP plates and tested in flexure employing various bond lengths, strengthening methods, and numbers of CFRP plates. A nonlinear finite-element analysis, with the bond–slip model incorporated in the DIANA program, was performed for the strengthened RC beams. Also, the results of flexural test and analytical predictions are found to be in close agreement in terms of yield and ultimate loads and ductility.     

Structural damage accumulation and stable postcritical deformation of composite materials

The macroscopic failure of composite materials is preceded by complex multilevel processes accompanied by accumulation and localization of damaged centers and formation of a failure cluster. Therefore, the study of these mechanisms is one of the basic problems for the mechanics of modern composite materials used in aerospace engineering. The formation of a theory of the stable postcritical deformation of the work-softening media is considered. The pseudo-plastic deformation affected by structural damage of granular composites is investigated within the framework of the considered two-level structurally phenomenological model of heterogeneous media. The stable evolution of the interconnected processes is accompanied by stress redistributions, partial or complete unloading, and strain or damage localization that are one of the main causes of implementation of the postcritical deformation stage. The numerical calculation results of inelastic deformation and failure of the periodic unidirectional fiber-reinforced composites are presented under conditions of the displacement-controlled transverse proportional loading mode. The main mechanisms of the work-softening behavior for the indicated type of materials are described in the macro-homogeneous stress-strain states. Macroscopically, the failure of heterogeneous media as a result of postcritical deformation and the loss of stability of damage accumulation depends on the stiffness of the loading system. When a deformable body is fixed on the closed surface with sufficiently but not infinitely large coefficients of stiffness, it is possible to observe the equilibrium development of the localized volumes of work-softening and damage. The constitutive equations for the work-softening isotropic, transverse isotropic, and orthotropic media are presented. The effect of the loading system on the stability of deformation, damage accumulation, and failure under monotone and nonmonotone triaxial loading was studied. The growth of failure strains with increase in stiffness of the loading system and unequal resistance of heterogeneous body are registered and investigated. A preventive unloading method is offered for the mathematical modeling of the damage accumulation during the testing of the materials on the servo-controlled systems. The displacement-controlled mode is simulated by a series of soft loading and unloading cycles. The detected phenomenon of failure where the unloading leads to stress-strain diagrams with a negative slope of the descending branch was not found either in the displacement or stress-controlled monotone loading mode.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Perm' State Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 2, pp. 234–250, March–April, 1998.     

On mathematical models of stress-strain relationship for living soft tissues

How detailed must a mathematical expression of the mechanical properties of a tissue be? The answer depends on the use intended for the constitutive equation. With the objective of application to physiology and medicine, a simplified approach is recommended. We point out that all biological tissues are composites and have complex behavior. In general, there is no "natural" state. Preconditioning is necessary to obtain repeatable experimental results. The viscoelastic properties of several tissues are examined and a unique feature is pointed out in that the stress-strain relationship in cyclic loading and unloading is not very sensitive to strain rate, and that the hysteresis loop is virtually constant for a wide range of frequencies. This is interpreted as being due to a continuously distributed spectrum of relaxation times which spread over a very wide range. This unique feature justifies the assumption of "pseudoelasticity," and the use of a pseudo strain-energy function to derive the stress-strain relationship in specific loading processes. Basic materials and tissues of higher structures may need other considerations. For example, in the lung the contribution of the surface tension between the air-liquid interface on the interalveolar septa is a major factor. The derivation of the stress-strain relationship for the lung tissue is presented.     

单轴拉伸条件下细观非均匀性岩石损伤局部化和应力应变关系分析

岩石在拉应力状态下的力学特性不同于压应力状态下的力学特性．利用细观力学理论研究了细观非均匀性岩石拉伸应力应变关系包括:线弹性阶段、非线性强化阶段、应力降阶段、应变软化阶段.模型考虑了微裂纹方位角为Weibull分布和微裂纹长度的分布密度函数为Rayleigh函数时对损伤局部化和应力应变关系的影响,分析了产生应力降和应变软化的主要原因是损伤和变形局部化.通过和实验成果对比分析验证了模型的正确性和有效性．     

Viscoelastic properties of a silica-filled styrene-butadiene rubber under uniaxial tension

A model composite — a silica-filled styrene-butadiene rubber with a various filler volume content — was tested for creep and creep recovery at different tensile load levels to evaluate the effect of viscoelasticity on the deformational properties of filled rubbers. A constitutive equation describing the diagram of equilibrium deformation of the composite in quasi-static loading was obtained from an analysis of creep test results. The equation was common for the filled rubber at different filler content. The existence of such a curve has been confirmed by experimental unloading diagrams registered in cyclic loading-unloading tests. It is shown that the phenomenological equations obtained from an analysis of creep recovery test results can be used successfully for describing the hysteresis loops of second and subsequent cycles for cyclic tests with a constant maximum stretch ratio.     

压应力状态下细观非均匀性岩石的损伤局部化和应力应变关系分析

利用摩擦弯折裂纹模型研究了受压条件下细观非均匀性岩石的损伤局部化问题和全过程应力应变关系．模型考虑了裂纹相互作用对损伤局部化和全过程应力应变关系的影响,确定了损伤局部化发生的条件,分析了产生损伤局部化的原因．研究表明全过程应力应变关系包括线弹性阶段、非线性强化阶段、应力降和应变软化阶段．通过和实验对比分析验证了模型的正确性和有效性．