Methodology of physical mesomechanics as a basis for model construction in computer-aided design of materials

Conclusions The basic theses concerning the methodology of physical mesomechanics considered in this review show that a deformable solid can be represented as a microlevel system of self-consistent deformation structural elements of different scales. The law of scale invariance allows us to describe the behavior of very different materials under different loading conditions based on the element base for the scale levels of a deformable solid. The motion of volume structural elements of the deformation is described by the equations of mechanics (mesolevel and macrolevel), accommodation processes within the SEDs and on their boundaries — dislocation theory (microlevel). We have formulated an algorithm for construction of models for such multilevel systems which can be used in computer-aided design of materials. Examples of the classification of different structural materials have been presented based on the proposed algorithm.This work was done with the support of the Russian Foundation for Basic Research, Project No. 9301-16498.Institute of Physics of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 6–25, November, 1995.     

Role of local nanostructural states in plastic deformation and fracture of solids

The paper substantiates the concept of physical mesomechanics that the basis for nonlinear behavior of solids under plastic deformation and fracture is the formation of nanostructural states in local highly nonequilibrium zones. Their structural transformations and two-phase decay govern the generation of strain-induced defects and cracks. Nonlinear wave mechanisms of nanostructural states influence on plastic deformation and fracture are discussed.     

Scale invariance of plastic deformation of the planar and crystal subsystems of solids under superplastic conditions

The theory of structural transformations in the planar sybsystem (surface layers and internal interfaces) of solids under plastic deformation is developed. The theory is based on a consideration for local curvature of the crystal lattice, with new structural states arising in its interstices, responsible for plastic distortion. To satisfy the superplastic condition, such high-rate mechanisms should develop in both planar and 3D crystal subsystems. In a translation-invariant crystal, this condition is met by concentration fluctuations. The multiscale criterion of superplasticity is formulated based on the scale invariance of plastic deformation of the planar and crystal subsystems in a deformable solid. Beyond the criterion, superplasticity passes to the creep mode with restricted plasticity of the material.     

Mesomechanics of plastic deformation and fracture of partially crystalline polyethylene

From the standpoint of physical mesomechanics, we have investigated plastic deformation mechanisms and the mechanical properties of partially crystalline polyethylene. We show that from the very beginning, plastic deformation occurs at the mesoscopic level. Fracture is preceded by fragmentation of the material. The observed stages of the process of plastic deformation of polyethylene are qualitatively similar to the stages of this process for metallic materials. The effect of electron bombardment on the mechanical properties of polyethylene is explained by the size reduction in the mesoscopic substructure formed on plastic deformation. Tomsk Polytechnical University. Zhilin University, People’s Republic of China. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 48–53, January, 1997.     

Problems of the mesomechanics of strength and plasticity of nanostructured materials

The results of the investigations performed in collaboration with our co-workers are reviewed and used to formulate a conceptual framework of the physical mesomechanics of nanostructured materials. Low plasticity of materials of this kind is associated with suppression of the microscale deformation due to the motion of dislocations and with development of meso- and macroscale localized-deformation bands. For an optimum combination of strains at the micro- and mesoscale levels, formation of a nanocrystalline structure provides high strength and plastic properties of the materials. Strain localization at the macroscale level impairs the strength and plasticity of nanostructured materials.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 4–17, August, 2004.     

Origin of Elastic–Plastic Deformation Invariant

We consider the autowave mechanism of evolution of a localized plastic deformation of crystalline solids of different origins. It is found that localization of the plastic flow is determined by the relation between elastic and plastic phenomena in deforming materials. It is shown that the main parameter of deformation processes is the elastic–plastic deformation invariant, viz., a dimensionless quantity connecting quantitatively the parameters of elastic waves and self-sustained waves (autowaves) of localized plastic deformation. The correctness of this statement is verified for metals, alkali-halide crystals, and rocks. The physical origin of the invariant is explained on the basis of thermodynamic considerations.     

非晶力学流变的自组织临界行为

非晶材料是由液体快冷冻结而成的结构无序的亚稳态固体.在受力条件下,非晶材料表现出独特和复杂的流变行为,具有跨尺度的高度时空不均匀特征,并在一定条件下表现出自组织临界行为,和自然界以及物理系统中许多复杂体系的动力学行为相似.本文结合作者近年来在非晶合金流变行为方面的研究结果,对非晶材料流变的研究进展和物理机制的认识进行介绍,包括非晶材料流变的跨尺度特征、表征和微观结构机制,以及近年来发现的非晶力学流变的自组织临界行为、物理机制等.最后,对非晶材料流变行为研究中亟需解决的问题进行了总结和展望.     

Relation between the Hurst Exponent and the Efficiency of Self-organization of a Deformable System

We have established the degree of self-organization of a system under plastic deformation at different scale levels. Using fractal analysis, we have determined the Hurst exponent and correlation lengths in the region of formation of a corrugated (wrinkled) structure in [111] nickel single crystals under compression. This has made it possible to single out two (micro-and meso-) levels of self-organization in the deformable system. A qualitative relation between the values of the Hurst exponent and the stages of the stress–strain curve has been established.     

Application of aluminum foil for “strain sensing” at fatigue damage evaluation of carbon fiber composite

Surface layer of a loaded solid is an individual structural level of deformation that was shown numerously within concept of physical mesomechanics.This gives rise to advance in its deformation development under loading as well as allows using this phenomenon to sense the strain induced structure changes.It is of specific importance for composite materials since they are highly heterogeneous while estimating their mechanical state is a topical applied problem.Fatigue tests of carbon fiber composite specimens were carried out for cyclic deformation estimation with the use of strain sensors made of thin(80μm)aluminum foil glued to the specimen’s surface.The surface images were captured by DSLR camera mounted onto an optical microscope.Strain relief to form during cyclic loading was numerically estimated using different parameters:dispersion,mean square error,universal image quality index,fractal dimension and energy of Fourier spectrum.The results are discussed in view of deformation mismatch in thin foil and bulk specimen and are offered to be applied for the development of Structural Health Monitoring(SHM)approach.     

Wave velocities in shock-compressed cubic and hexagonal single crystals above the elastic limit

When solids are subjected to high-pressure shock-wave loading, multiple stress waves propagate with velocities dependent upon the elastic and inelastic compressibilities of the solid. The present paper shows that the inelastic or plastic waves in cubic and hexagonal single crystals do not necessarily propagate with the bulk sound speed as they do in isotropic elastic-plastic solids. This result is a consequence of anisotropy in the plastic deformation which depends on the slip plane orientation in the crystal and has important consequences with regard to the determination of compressibilities from shock-wave data. In particular, for wave propagation in the <110> directions of cubic crystals the departure from the bulk velocity can be significant (5–25 per cent). For wave propagation normal to the c-axis in hexagonal crystals, the plastic wave velocity also differs from the bulk sound speed (10–25 per cent). Plastic wave velocities are tabulated for a number of cubic crystals on the basis of the various slip systems common to these materials. The calculated velocities are then compared with experimental data on shock-loaded single-crystal aluminum and sodium chloride.     

Relaxation waves in plastic deformation

Conclusion Experimental study of distortion fields of plastically deformed solids performed on a wide range of materials including fine- and coarse-grain body- and face-centered polycrystals, as well as amorphous alloys reveals that in these materials plastic deformation develops in the form of waves having translational and rotational components. This fact is in accordance with the currently developed theory of a turbulent mechanical field, which also has translational and rotational components.The plastic deformation waves are observable at a macroscopic structural level, and their spatial period (wavelength) is determined by the dimensions of the deformed object and dimensions of the basic structural elements (for a polycrystal, the grain size). The propagation rate of these waves is significantly less than the characteristic propagation rate of an elastic excitation and the velocity of previously described plastic waves which are produced by shock deformation, which latter speed is determined by the hardening coefficient.The character of plasticity waves depends on the form of the material's deformation curve, and on the stage of the hardening curve. The distribution of plastic distortion components changes especially significantly in prefailure regions, which allows detection of the latter long before formation of a macroscopic crack. The role of rotations in forming the failure process has been established.A synergetic interpretation of plasticity wave formation has been proposed, based on synchronization of relaxation acts occurring at stress concentrators during the deformation process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 19–35, February, 1990.     

Analysis of near weld stress field based on strain measurement and physical mesomechanics

Stresses induced by welding are analyzed from the viewpoint of material deformation behavior. Strain gages are used to measure the residual stresses, and electronic speckle-pattern interferometry is used to analyze the response of the welded work to external force. A tensile load is applied to a butt-welded, thin-plate steel specimen, and the resultant strain field is analyzed with the electronic speckle-pattern interferometry. Comparison is made with the case of a nonwelded specimen of the same material and dimension. The analysis indicates that the residual stress due to welding makes the normal strain due to the external tensile load asymmetric. The asymmetry enhances shear and rotational modes of deformation, generating stress concentration at a point away from the weld where the residual stress is substantially negligible. The observed features are discussed based on physical mesomechanics. Analysis reveals plastic deformation like behavior in the response of the welded specimen to the external force.     

New types of reinforced composite materials

The physical properties of solids determine their usefulness as structural materials. Metals have some disadvantageous characteristics which reduce their effectiveness in critical engineering applications. These limitations can be overcome by the use of certain types of fibrous reinforced composites which have become available over the last few years. However, these materials in turn have their own inherent limitations, particularly in their mode of fracture under overload conditions. In this review the basic properties of conventional fibrous composites are discussed, particular emphasis being given to physics of these failure processes.In an attempt to overcome some of these limitations a new type of fibre reinforced composite has been designed and preliminary research data on the physical properties of these systems has now been obtained. The primary reinforcing elements extend throughout the whole length of the composite but differ from others in that they do not fracture when the composite is subjected to a wide ranged of loading and deformation conditions.These characteristics are achieved because the interface between the primary reinforcing members and the rest of the composite structure is responsive to the local stress carried by the reinforcing members. This stress controlled decoupling/recoupling process is very broadly analogous to the transition between elastic and plastic deformation in metals and the physical principles underlying the design of the reinforcing members are outlined.Because the reinforcing members do not fracture any failure process is confined to the rest of the composite structure. Various interactions occur between the non-fracturing and fracturable parts of the system and these suppress crack growth in the latter, thus producing a structure possessing very considerable damage tolerance. A preliminary analysis of the basic physics of these interactions is given.Possible future developments of these materials are outlined. Also ways are discussed in which the simple analytical models, developed in the study of the fracture processes occuring these materials, amy be applied to more conventional fibrous composites.     

Mesomechanics of interface in surface-hardened and coated materials

Results of comprehensive experimental studies and numerical simulations of the plastic deformation processes involved in coated and surface-hardened materials on the mesoscopic and microscopic scale levels are presented. The effects of the processes evolving at the coating/substrate interface on the development of plastic deformation of the entire composition are shown. The data reported provide the basis for the optimization of surface-hardening and coating deposition regimes and the development of advanced materials with outstanding service properties. Institute of Strength Physics and Materials Science of the SB RAS. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, fizika, No. 3, pp. 6–26, March, 1999.     

Multiscale space-time dissipative structures in materials: Two-electron genesis of nonequilibrium electromechanical interfaces

The fundamental supra-atomic scale of nanometer attosecond processes in condensed matter creates a multiscale hierarchy of electromechanical interfaces through two-electron dissipation of energy of quantum nanoelectromechanical systems. The space-time scales of electromechanical interfaces are specified, beginning with the subatomic scale of electron Compton length λ_e, by a sequence of degrees n = 1, 2, 3,... of the fine structure constant α ^-n. The third scale, with n = 3, corresponds to quantum mesoelectromechanical 2D interfaces which form functional matrices of electromechanical energy stores and converters as active nucleation centers of fractal topological defects in adjacent crystal structure regions. The hierarchy of electromechanical interfaces creates a hierarchy of dissipative structures in mesomechanics of solids and biomimetics of soft materials.     

Damage and fracture: Review of experimental studies

This paper is a part of a review of recent (last 15 years) publications on experimental and theoretical methods and approaches for studying damage accumulation and fracture in crystalline solids. The first part of the review is devoted to the experimental studies that examine the physical mechanisms of microdamage nucleation and growth under various thermomechanical loads, physical and mechanical properties of materials, and the issues concerning the formation and growth of main cracks and transition to macrofracture. Particular attention is given to the studies of fatigue failure of various metals and alloys, particularly the features of micro- and macrodamage nucleation and growth in structures and specimens at different loading cycle parameters, and the effect of grain size, solid phase inclusions, grain boundaries, twins, etc. on damage evolution. A whole variety of modern approaches to the experimental study (including in situ studies) of specimen structure and stress-strain state is shown. Disadvantages of current experimental studies on damage and fracture are discussed, such as insufficient attention to the scale factor and determination of the representative volume for fracture analysis.     

Multiscaling of lattice curvature on friction surfaces of metallic materials as a basis of their wear mechanism

A comprehensive structural study has been performed to explore deformation and wear debris formation on friction surfaces of metallic materials. A hierarchy of structural scales of plastic deformation and failure during wear has been established. The nanoscale plays the major role in the hierarchical self-organization of multiscale debris formation processes. On this scale, bifurcational interstitial states arise in zones of local lattice curvature, with plastic distortion and motion of nonequilibrium point defects which determine the nonlinear dynamics of structure formation and wear of surface layers. Nonequilibrium vacancies on lattice sites form microporosity through the coalescence mechanism under plastic distortion. The microporosity is a precursor of meso- and macroscale plastic shearing that defines wear debris formation.