Healing of Cracks in Anisotropic Bodies

Materials Science - We obtain the solution of a plane problem of the theory of elasticity on the phenomenon of “healing” of a crack in an anisotropic body. By using the model of...     

Healing of Shear Cracks in Anisotropic Bodies

Materials Science - We solve the plane problem of the theory of elasticity of anisotropic bodies with transverse shear cracks “healed” by the injection technologies, which is reduced to...     

A Crack Emanating from a Wedge In Dissimilar Anisotropic Materials Under Antiplane Shear

A crack in a composite wedge consisting of two dissimilar anisotropic materials under concentrated antiplane loads is analyzed. The problem of a crack in an isotropic composite wedge is solved first by using the Mellin transform and the Wiener-Hopf method. Using a linear transformation of the original composite wedge into an isotropic composite wedge consisting of dissimilar isotropic materials, the antiplane displacement and stresses for the anisotropic composite wedge are obtained from the solution for the transformed wedge. The stress intensity factor for the crack in the original anisotropic composite wedge is obtained from the solution of the crack in the transformed wedge. Special attention is given to the asymptotic problem of a wedge crack in an anisotropic bimaterial. Numerical computations are carried out to obtain the energy release rate for various apex angles and anisotropic parameters as a function of crack angle.     

Strain Measurement for Anisotropic Bodies

The latest advances have been used in strain measurement in a method of determining the mechanical characteristics of pipelines, which often behave as anisotropic bodies, and a method is given for determining the states of strain in them under compound loading.     

Deformation Fracture Criterion for Bodies with V-Notches under Symmetric Loading

The limiting equilibrium of bodies with V-notches is extensively studied by using the force fracture criterion according to which the stress intensity factor at the notch tip is equal to its critical value. In this case, the critical stress intensity factor depends on the opening angle of the V-notch. By using the solution of the problem of plastic strips in a plate with V-notch, we develop a deformation fracture criterion based on the use of standard characteristics of the material and independent of the geometry of the specimen.     

Dynamic Stresses in Structurally Anisotropic Bodies

We obtain practical expressions for the correct evaluation of dynamic stresses by using the polarization-optical method in structurally anisotropic media. It is shown that the influence of anisotropy on the character of wave fields of stresses in the subsurface zone manifests itself as a 1.28-fold increase (as compared with the isotropic case) in the stresses _k formed on the contour in the case where a plane P-wave falls on the free boundary of the plate which coincides with the principal axis of orthotropy E _max. If the P-wave falls on the free boundary in the direction of orthotropy E _min, then the values of the contour stresses _k in the anisotropic plate are close to the corresponding values obtained for the isotropic plate.     

Heat and Mass Transfer in Anisotropic Bodies

This review is aimed, on the one hand, at attracting the researchers' attention to the problems associated with heat transfer in anisotropic bodies and, on the other hand, at analyzing the scanty experience in investigating the heat transfer in anisotropic bodies that has been accumulated over the last 30 years. We treat conjugate heat transfer between boundary layers and anisotropic bodies, and heat transfer under conditions of simultaneous reciprocal influence of anisotropic thermal conductivity and anisotropic filtration upon film cooling of bodies with anisotropic properties. New effects are revealed during simulation of conjugate heat transfer; the law of nonlinear filtration in anisotropic bodies is identified; and the effect of individual components and of the orientation of the principal axes of thermal conductivity and penetrability tensors on stationary temperature fields and on the distribution of components of the filtration rate is investigated. The results of analytical investigation of heat transfer in anisotropic bodies enables one, under conditions of lack of adequate information, to exactly simulate nonstationary temperature in simplest anisotropic bodies, which may be used as test results. A number of recommendations are formulated for implementation of heat shielding of anisotropic bodies under conditions of their aerogasdynamic heating.     

Crack Growth in Rolling Bodies under the Conditions of Dry Friction and Wetting

Within the framework of a two-dimensional mathematical model, we study the development of a surface macrocrack in the course of unidirectional rolling under the conditions of dry friction and wetting. The damaged body in a rolling couple is modeled by an elastic half plane with an edge cut (crack) and the action of the counterbody is simulated by the translational motion of Hertzian contact forces along the boundary of the half plane with taking into account the friction forces. We compute the crack-growth paths depending on the coefficient of contact friction between the bodies and the orientation and length of the crack. The numerical calculations are performed by the step-by-step method based on the use of the singular integral equations of the theory of elasticity for bodies with curvilinear cracks and the criterion of generalized opening. It is shown that, for high coefficients of friction between the bodies of the rolling couple (f = 0.20–40; dry friction), a branch propagates from the original fatigue shear macrocrack into the bulk of the material of the driven body. In the case of low friction coefficients (f < 0.20; wetting), a branch mainly propagates along the boundary of the body in the direction of motion of the counterbody. We propose an explanation of the mechanism of development of burrow-type defects often encountered in railroad rails.     

Antiplane Deformation of a Perfectly Elastoplastic Body with Rigid Rectangular Inclusion

We solve the problem of plastic exfoliation of a rigid rectangular inclusion in a perfectly elastoplastic medium loaded at infinity by shear forces parallel to the horizontal sides of the inclusion. It is assumed that plastic strains are concentrated on the boundary of the inclusion, in layers whose thickness is equal to zero starting from the vertices of the inclusion. We find the length of plastic strips and the degree of exfoliation (i.e., the jump of displacements) at the vertex of the inclusion as functions of the acting load. It is shown that the complete exfoliation of the horizontal sides of the inclusion occurs under a certain load (which increases with the width of the inclusion) but its vertical sides never exfoliate completely. We prove that the solution of the elastic problem represents the limiting case of the solution of the corresponding elastoplastic problem as the yield limit tends to infinity. By using this limit transition, we obtain the elastic solution of the analyzed problem.     

陶瓷材料裂纹愈合研究进展

分析了裂纹愈合的动力和阻力,动力来源于毛细管力和化学势差异,而阻力是裂纹面运动到平衡间距要克服的能垒和裂纹尖端位错运动需要克服的塑性变形功;综述了陶瓷材料裂纹愈合研究方法:目前所涉及的多为Al2O3、Si3N4、SiC或其复合材料的热压烧结材料,主要用维氏硬度计法获得裂纹,影响愈合效果的主要因素有化学成分与气氛、温度及时间、预制裂纹尺寸及应力等,愈合机理主要是扩散愈合和氧化反应填充愈合,并可用相应的动力学方程描述;指出今后需要解决的问题是拓宽所研究的材料体系并完善实验手段、系统研究愈合条件的影响和愈合机理.     

Three-Dimensional Ultrasonic Crack Detection in Anisotropic Materials

The scattering of probe-generated ultrasonic fields incident upon a strip-like crack in an anisotropic half-space is discussed. In the situation considered, two possibly coinciding probes are attached to the surface of the half-space. One is transmitting waves incident upon the crack and the other one is receiving the scattered waves. An electric signal response is calculated via an electromechanical reciprocity relation. For a crack far away from the probes and the surface, an approximate expression is calculated. Several numerical examples are presented for an isotropic and a transversely isotropic solid. The results are presented as A-, B-, and C-scans.     

New Discrete Model of Plastic Deformation of Solid Bodies

Materials Science - We compare the dislocation model with a new discrete model of plasticity. According to the previously proposed model, a crystal lattice with spherically symmetric potential of...     

Thermomechanical Models of Irreversible Finite Deformation of Anisotropic Solids

The proposed models for irreversible finite deformation of initially anisotropic solids are based on the hypothesis of the parameters of state, for which the authors have chosen a universal parameter (temperature) and a strain component, which is analogous to volume strains in an isotropic body and represents thermal strains of an unconstrained (stress-free) anisotropic solid. The application of this hypothesis allows the strain tensor to be resolved into a reversible and irreversible components. For irreversible processes of finite deformation of hardenable materials, the authors have proposed a deformation-type model, which makes it possible to describe a change in the type of anisotropy of initially anisotropic materials in the course of deformation. For the flow-theory-type model, the limiting state function, as given in the space of irreversible strains, allows for the experimentally observed plastic flow of anisotropic crystals under the action of hydrostatic pressure only.     

非金属材料裂纹愈合研究综述

对国外30多年以来在非金属材料裂纹愈合领域的研究结果进行了归纳总结,重点分析了对非金属材料裂纹愈合现象提出的各种解释机理及裂纹愈合过程中的形态变化,并进行了讨论。     

元胞自动机法在裂纹愈合模拟中的应用

运用元胞自动机(CA)法,通过计算机编程建立了包含内部微裂纹的元胞自动机模型,结合金属材料学基本原理和动态再结晶理论,模拟了动态再结晶条件下的裂纹愈合过程。通过研究不同因素对裂纹愈合的影响,获得了不同参数(如应变速率、应变量等)下的裂纹愈合规律,阐明了裂纹的分段愈合特征,模拟结果与现有实验研究结果相吻合。     

退火对Al2O3/SiC纳米复合材料裂纹愈合行为的影响

研究不同密度的Al2O3/SiC纳米复合材料在退火条件下的裂纹愈合行为。利用维氏压痕法引入可控的预制裂纹，通过测量退火前后材料抗弯强度的变化来表生裂纹愈合程度。当退火温度在850℃以上时，裂纹愈合效应随退火温度提高明显增强，在1150℃左右退火1h后，不同密度的试样的抗弯强度均恢复到试样的固有强度。裂纹愈合的机制主要归结于退火过程中残余应力的驰豫导致扩散键合和裂纹表面碳化硅颗粒的氧化作用。然而，过度的氧化会降低裂纹愈合的效果。     

Distribution of Stresses Near Angular Notches on an Orthotropic Elastic Plane Under Conditions of Antiplane Deformation

Materials Science - By using a solution of the antiplane eigenvalue problem of the theory of elasticity for an elastic orthotropic wedge, we construct the distribution of singular stresses and...