Theoretical model of the anisotropy of low-cycle deformability of glass-fiber reinforced plastics

Conclusion A theoretical model is suggested for the anisotropy of low-cycle deformability of glass plastics determined by the anisotropy of the deformational properties of the material in short-term static tension (compression). The effect of the anisotropy of cyclic loss of strength of the deformational properties is taken into account by the introduction of the characterizing function which is taken to be independent of the mechanical properties of the material and of the conditions of low-cycle loading.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 437–442, May–June, 1985.     

页岩储层各向异性对水平井坍塌压力的影响

为揭示层理页岩强度各向异性对水平井井壁坍塌压力的影响规律,对取自四川盆地龙马溪组页岩钻井不同层理角度的岩芯,通过岩芯观测、偏光显微镜、扫描电镜试验分别从宏观和微观角度研究了页岩层理特征,并基于单轴抗压强度研究了页岩强度各向异性特征.层理结构发育导致页岩呈现出显著的各向异性特征,粗略地将页岩视为各向同性体及简单采用Mohr-Coulomb准则作为破坏判据,使得预测的维持井壁稳定的坍塌压力不能满足安全钻井的需要.该文在研究层理地层岩石力学特性的基础上,采用横观各向同性地层井周应力分析模型,研究了弹性模量及地应力各向异性比对井周应力的影响;并结合考虑中间主应力的Mogi-Coulomb判据,分析了井壁坍塌压力对弹性模量E和Poisson(泊松)比ν各向异性比值变化的敏感性.实例分析结果表明:弹性模量和水平地应力各向异性比值的变化会对井周应力产生较大影响;Poisson比各向异性对井壁坍塌压力没有明显影响,而弹性模量比值的变化对井壁坍塌压力影响较大;横观各向同性地层中井壁坍塌压力与储层水平和垂直方向的硬脆性强弱关系有关,弹性力学参数各向异性既有可能利于井壁稳定,也可能更易导致井壁的剪切破坏;在实际工程中应根据储层岩石水平和垂直方向的硬脆性强弱关系,确定安全钻井液密度窗口.该结果对现场施工具有很好的指导意义.     

Numerical characteristics of the degree of anisotropy of the mechanical properties of materials

Conclusions 1. A unique procedure for determination of the numerical characteristics of the degree of anisotropy of the strength and deformation properties of materials is proposed.2. The concepts of the deformability surface and the anisotropy surface of the deformability permit representing graphically the deformation properties of materials.3. The system of integral characteristics of the mechanical properties of materials opens up new possibilities in connection with the analysis and optimization of different reinforcement schemes.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 601–609, July–August, 1978.     

Anisotropy of the elastic and strength properties of reinforced plastics

The method and results of experimental investigation of anisotropy of the elastic and strength properties of reinforced plastics are discussed. A method of determining the mechanical characteristics in different directions on tubular test pieces is proposed. A special testing machine is described. It is shown that determining the strength and elastic properties of reinforced materials in directions other than the directions of reinforcing on flat test pieces cut mechanically leads to distorted results.Mekhanika Polimerov, Vol. 3, No. 3, pp. 461–466, 1967     

Dispersed failure of an anisotropic flywheel

Based on a hereditary damage model of solids, the strength of a cylindrically anisotropic flywheel is calculated. By using a failure criterion, the location and time of initial failure is determined in relation to an anisotropy parameter, for which the ratio of rigidities in the tangential and radial directions is taken. The process of dispersed failure depends on the expansion intensity of the damaged zone. The boundary of the zone is the failure front, whose equations of motion are obtained in the cases of absence and presence of a residual strength for the material behind the failure front. In the second case, the damaged material is modeled by an isotropic elastic medium with considerably reduced values of strength and rigidity characteristics, and variations in the pressure on the failure front are also determined. Graphs of the radial coordinate of failure front as a function of time are constructed and analyzed for different values of the anisotropy parameter, the degree of residual strength and density behind the failure front, and proportions of geometrical sizes of the flywheel. The critical failure times are found. A system of restrictions on the values of mechanical and geometrical parameters is revealed which makes possible the realization of the process of dispersed failure investigated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 1, pp. 93–108, January–February, 2005.     

Deformability and strength of compact bone tissue during tensioning

The deformability and strength characteristics of compact bone tissue of human tibia during tensioning along all three main anisotropy axes was determined experimentally. The character of change in the secant moduli of elasticity and specific energies of deformation during the loading process were studied. A correlation was established between the mechanical characteristics and the biochemical composition of the bone tissue.     

A complex approach to evaluation of the strain-strength properties in stretching of KMU-8 carbon-filled construction plastic

Conclusion The detailed study of the mechanical properties of KMU-8 CFRP in stretching characterizes it as a construction material with high anisotropy of the elastic and strength properties. The accurate determination of the properties of the monolayer allows subsequently calculating the elastic characteristics based on the theory of laminated plastics with a precision sufficient for engineering and construction calculations. The calculated strengths should be estimated with consideration of the specific features of strain and failure of the carbon-filled plastic.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 488–499, July–August, 1993.     

Stark–Wannier ladders and cubic exponential sums

Given a one-dimensional Stark–Wannier operator, we study the reflection coefficient and its poles in the lower half of the complex plane far from the real axis. In particular, the reflection coefficient is described asymptotically in terms of regularized infinite cubic exponential sums.     

反射系数的线性最小均方误差估计

从地震记录信号中获取反射系数对岩性分析和寻找储油(气)地层构造是非常重要的,本文对非白噪型反射系数的反褶积模型方法进行了探讨,给出了一个获取反射系数的估计方法.     

Nondestructive diagnostics of living trees using low frequency electric tomography

We develop and test on real objects a scientifically justified method for monitoring electric conductivity in living trees which is based on solving the inverse problem of dendrotomography. For the purpose of nondestructive diagnostics of the wood condition, we propose to determine the electric anisotropy coefficient of a living tree. We theoretically develop and experimentally confirm a technique for determining this parameter. We prove that the electric anisotropy coefficient is independent of the seasonal variations of resistivity and is determined by the system of annual rings of the tree.     

Behavior of concrete cylinders confined by carbon composite 2. Prediction of strength

The mechanical behavior of round concrete cylinders confined by a carbon-epoxy composite wrapping is analyzed concerning the increased concrete compression strength due the wrapping. It is shown that the loading trajectories in the normalized stress space fit into a single master curve for all the concrete batches and jacket thicknesses investigated. The loading paths ended at failure of the composite wrapping from the increased internal lateral pressure. The strength of the composite was determined by split-disc tests of composite rings, but the strength of composite jackets realized on concrete specimens did not reach the strength of the rings. Therefore, a coefficient of composite strength reduction was introduced. A simple formula for predicting the strength of confined concrete is derived, and a comparison with fib (fédération internationale du béton) recommendations for strength predictions is given. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 165–178, April–May, 2006.     

Technological anisotropy of chaotically reinforced glass-fiber-resin materials

The authors investigate the strength properties of chaotically reinforced glass-fiber-resin materials in compression-molded and injection-molded artifacts of complex shape and also the density, water absorption, and binder content in various zones in the artifacts. They find anisotropy to be present in the strength indices, owing to orientation of the reinforcing elements during flow of material in the mold. They determine the coefficients of anisotropy of the strength (these are defined as the ratios of the strength in the flow direction to the strength in a perpendicular direction). They suggest a method of estimating the degree of orientation of the reinforcing elements in artifacts made of nonoriented glass-fiber-resin materials.All-Union Scientific-Research Institute of Glass-Fiber-Reinforced Plastics and Glass Fiber, Moscow Region. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 507–515, May–June, 1973.     

Effect of anisotropy on the cyclic deformation and heating of SVAM-type glass-reinforced plastics

The effect of anisotropy of the mechanical properties on the cyclic deformation and heating of 1:1 and 5:1 SVAM-type glass laminates has been investigated for symmetrical tension-compression and pulsating tension and compression. It is shown that on the main part of the fatigue curve, depending on the anisotropy and the cyclic stress level, the temperature may be stabilized. At the same time, fracture is invariably accompanied, under fixed experimental conditions, by a rise in temperature to a certain value that depends only on the anisotropy property of the glass-reinforced plastic, the strain also reaching critical values that are determined by the cycle asymmetry and the anisotropy property of the material.Institute of Mathematics and Mechanics, Academy of Sciences of the Armenian SSR, Erevan. Translated from Mekhanika Polimerov, No. 5, pp. 898–903, September–October, 1971.     

Oblique wave scattering by a semi-infinite rigid dock in the presence of bottom undulations

The problem of oblique wave scattering by a semi-infinite rigid dock in the presence of varying bottom topography is investigated here using linear water wave theory. Employing a simplified perturbation analysis together with appropriate use of Green’s integral theorem, the reflection coefficient up to first order is obtained in terms of an integral involving the shape function representing the bottom topography. The zero-order reflection coefficient is obtained by using the residue calculus method of complex variable. The bottom undulations are described by sinusoidal and an exponentially decaying profile. The first order correction to the reflection coefficient is depicted graphically in a number of figures for the two shape functions characterizing the bottom undulations and appropriate conclusions are drawn.     

Inverse problem for Sturm-Liouville operators with rational reflection coefficient

In this paper we give exact formulas for the potential associated to a Sturm-Liouville equation when the reflection coefficient function is rational. The solution is given in terms of a minimal realization of the reflection coefficient function.Dedicated to the memory of M.G. Kreîn     

三斜晶体介质中三维平面波的反射

讨论三斜晶体介质半空间应力自由边界处三维平面波的传播.给出了1个寻找三维准P(qP)、准SV(qSV)和准SH(qSH)波的所有3个相速度解析表达式的方法.得出了三斜介质中qP、qSV、qSH波反射系数振幅比的三维闭式解,将其用于研究不同入射角时,对应的反射系数的数值变化,给出了不同极角和方位角时的图示.最后通过数值实例表明,与二维的情况相比较,三维各向异性对反射系数的影响更明显.     

Effects of Moisture and Stresses on the Structure and Properties of Polyester Resin

The results of a complex study of structural changes in a cured Norpol 440 polyester resin under the action of damp environment and mechanical loading are presented. A considerable effect of absorbed moisture on the structure and some characteristics of the material is revealed by using thermophysical methods and X-ray diffractometry. The joint effect of moisture and mechanical stress is estimated by investigating the creep in stationary and nonstationary moisture conditions. The anisotropy of the material structure formed during creep is evaluated from the results of dilatometric measurements. It is found that the degree of anisotropy of the material after creep accompanied by moisture sorption is higher than that after creep in the conditions of moisture equilibrium with atmosphere. It is established that the aftercure and relaxation of the residual creep deformation come to an end at heating to 80-85°C. At a further rise in temperature and repeated heating, changes in the material structure are not observed.     

Application of the method of nondestructive control to investigations of thermal characteristics of crystals

Six crystal samples were examined in the form of anisotropic half-spaces with corresponding arrangement of the directions of anisotropy. The heat sources and measurement devices for the excess temperature were moved about the surfaces of the samples in the given directions with identical velocity. The coefficient of thermal conductivity and the bulk thermal capacity of the crystals possessing straight-line anisotropy were determined.Translated from Matematiceskie Metody i Fiziko-Mekhanicheskie Polya, No. 29, pp. 12–16, 1989.