Kinetics Of Damage Accumulation Research Articles

Method of quantitative assessment of changes in “critical” levels of elastic-strength parameters of epoxy polymers in the process of natural climatic aging

The method for quantitative analysis of the kinetics of damage accumulation in the structure of series of polymer samples at stretching is proposed. The proposed approach is to calculate the fractality indices of time series by means of a minimum coverage method, followed by a failure frequency analysis, while increasing the levels of applied stresses and relative deformations. Epoxy polymer based on ED-20 resin hardened by Etal-1460 hardener, was selected as the object of the study. The results of the study of changes in elastic-strength indicators and levels of “critical” stresses and relative elongation in the stretching of epoxy polymer during the natural climate impact are presented.

Effective method of evaluating the level of material damage under different loading conditions

The article analyses the known experimental results of the assessment of the level of damage of structural materials of various grades under the conditions of long-term, cyclic, static loading, and lubricated friction. The structural changes that occur in the materials during loading have been shown with correlate to the changes in the statistical scattering characteristics of the hardness measurement results. This enables prediction of the kinetics of damage accumulation in materials during operation and, therefore, prediction of their service life. This approach is relevant for the development of methods for the assessment of the current condition and residual life of structures in the railway and other transport industries. It is proposed to use this methodology to evaluate the level of damage to the microstructure of materials in the contact zone and its impact on the tribological characteristics of metal friction pairs. A new method is proposed for the performance assessment of lubricating compositions based on industrial lubricants that contain nano-additives of different chemical compositions for higher wear resistance of heavy-loaded steel friction pairs. The method is based on the joint analysis of the experimental data on the wear kinetics, variation of the relative hardness, and level of damage in the surface layers of the metal friction pairs. The structural damage of the materials in the contact zone is determined by employing the statistical parameters of scattering of the hardness values. The methodology has been approved for steel friction pairs where lubricants based on industrial oil and on nano-additives of copper, magnesium alloy, graphite, and two grades of medium-carbon steels, are used.

Численное моделирование цунами оползневого типа

The article proposes mathematical models and stable numerical algorithms for solving problems of deformation and flow of water-saturated porous materials. This class of problems arises in many engineering and applied fields, from field development to biomechanics. Of particular interest are the problems of the collapse of the banks of rivers, lakes and bays of the seas due to their catastrophic impact on possible consequences, for example, blocking the riverbed, the occurrence of a tsunami on the water surface of a reservoir, etc. For the mathematical description of the stress-strain state of saturated porous media, the Biot theory of three-dimensional consolidation is used, supplemented by the kinetics of damage accumulation in the medium and the Drucker-Prager yield conditions. After the formation of the main yield surface (or crack) in the material at the moment of the beginning of the collapse, its rheological properties are presented in the form of a Bingham model with a mathematical description similar to the Navier-Stokes equations with effective viscosity. A characteristic hydrodynamic feature of the problem under consideration is the presence of a free surface. Numerical modeling of the considered problems is carried out by the finite element method. The evolution of the free surface and the occurrence of a tsunami generated by a landslide are investigated.

MODELING OF INTELIGENT SOFTWARE FOR THE DIAGNOSIS AND MONITORING OF SHIP POWER PLANT COMPONENTS USING MARKOV CHAINS

The reliability and serviceability of metal structures depends on the quality of control over the technical condition and mechanical properties of materials in accordance with international standards. However, in the course of operation, deviations from the normative values of material properties occur due to the uncertain nature and magnitude of the loads, which necessitates periodic shutdowns of the equipment for the purpose of diagnostics. Uninterrupted operation of elements of power equipment of marine vessels depends on the quality of control of their technical condition by physical diagnostic methods. The most effective method of reducing operating costs and increasing the reliability of equipment is maintenance based on interactive monitoring of its condition, detection of malfunctions and forecasting of energy equipment parameters. This makes the tasks of control, diagnosis and forecasting of energy equipment parameters particularly relevant. At the same time, the use of various diagnostic methods does not allow taking into account all the features of real operating conditions. This problem is especially acute in conditions of various extreme situations and peak loads, which cannot be taken into account. Probabilistic methods, in particular Markov chains, are a promising area of research. The system of intelligent diagnostics and monitoring of ship power plant turbochargers using Markov chains is presented. The novelty of the developed methodology lies in replacing discrete time intervals of the diagnostic process with a sequence of states of technical objects. In this formulation, Markov chains represent a synthetic property that accumulates diverse factors. Randomization of stochastic diagnostic and monitoring processes of ship power plant components enables an increase in reliability of equipment under severe operating conditions. The results of calculations of digitalization of experimental data, calculations of transition matrices and construction of an orgraph allowing to study the kinetics of damage accumulation in real time are presented.

Damage of materials under proportional loading

The work is devoted to the study of material damage during elasto-plastic proportional loading, in particular, the influence of two loading mechanisms, detachment and shear, is taken into account. These mechanisms include viscous, brittle, and visco-brittle modes of failure. The accumulation of scattered damage is considered as a multi-scale and multi-stage phenomenon that occurs during proportional loading at the micro- and meso-levels of the destruction of the metal structural material. As part of the study, a quantitative assessment of the degradation of the physical and mechanical properties of materials was performed, in particular, changes in the modulus of elasticity E and G, and the definition of equivalent damage arising from an elastoplastic proportional load is proposed. Experimental data on the kinetics of damage accumulation on 12X18N10T steel samples, which were subjected to axial load (tension), shear (torsion) and proportional load with the stiffness parameter of the stress state K = 0.5 before failure, are considered. The work compares experimental results with theoretical data, damage accumulation. The obtained conclusions contribute to a deeper understanding of the mechanisms of destruction of materials under the action of a proportional load, and can also find practical application in the design and assessment of the load-bearing capacity of structural elements.

Surface treatments and substrate-coating interface effects on damage accumulation kinetics in hard-coated WC-Co hardmetals under cyclic multi-axial high-temperature loading

Coated hardmetals are commonly used tool materials for metal cutting applications. For these applications, the substrate- and the coating surface qualities are improved by grinding, polishing, or blasting. The focus of the current work was to study the influence of different combinations of substrate-coating surface processing techniques on the induced damage in Al2O3/TiCN hard-coated WC-12 wt% hardmetal substrates and the depth to which the damage reaches into the substrate. The substrate and coating surfaces were prepared by grinding, polishing, dry blasting, wet blasting, or remaining in the deposited state. Investigations were performed using cyclic indentation with a novel ball-in-cone test method in a vacuum at 700 °C, under conditions that imitate the combined shear-compression loads that occur at the cutting edges of metal cutting tools. Additionally, finite element simulations were performed to characterize the stress state arising during ball-in-cone testing. The kinetics of defect formation and accumulation in the hardmetal substrate as a function of the loading situation during the ball-in-cone test will also be discussed. The defects that formed in the substrate during cyclic loading were studied using scanning electron microscopy in cross-sections prepared by focused ion beam milling. A larger increase in defect frequency was observed for rougher coating surfaces and substrate-coating interfaces than for smoother ones. Furthermore, 6 μm thick coatings exhibited a higher defect frequency after cyclic loading than 15 μm thick coatings. Most of the observed defects were in the nm-size range close to the substrate-coating interfaces and tended to have increased in size after cyclic loading. The ball-in-cone test set-up enables the study of the damage mechanisms in coated hardmetal substrates with different treatments prior to and after deposition under tunable milling-like stress and temperature conditions.

Calculation of Life Characteristics for Structural Alloys under the Mutual Influence of Fatigue and Long-Term Strength

The processes of degradation of the initial strength properties of polycrystalline structural alloys are considered under mechanisms that combine low-cycle fatigue and long-term strength of the material. From the point of view of mechanics of damaged medium (MDM) and fracture mechanics (FM), a mathematical model that describes the processes of cyclic viscoplastic deformation and damage accumulation in structural alloys under multiaxial disproportionate modes of combined thermomechanical loading has been developed. The model consists of three interrelated components: relations that determine the cyclic viscoplastic behavior of the material by taking into account the dependence on the fracture process; evolutionary equations describing the kinetics of damage accumulation; criterion of the strength of the damaged material. The viscoplasticity model is based on the idea of the existence of plasticity and creep surfaces in stress space and the principle of gradient vectors of plastic and creep strain rates to the corresponding surface at the loading point. This form of the equations of state reflects the main effects of cyclic viscoplastic deformation of the material for arbitrary complex loading trajectories. The form of kinetic equations for damage accumulation is based on the introduction of a scalar damage parameter and on energy principles. It also takes into account the main effects of the formation, growth and merging of microdefects under arbitrary complex modes of combined thermomechanical loading. A joint form of the evolutionary equation for damage accumulation in the areas of low-cycle fatigue and long-term strength of the material is proposed. As a criterion for the strength of a damaged material, the condition for reaching a critical value is used. The material parameters and scalar functions included in the constitutive relations of the MDM mathematical model are obtained. The results of numerical simulation of the processes of deformation and damage accumulation in structural alloys under the mutual influence of low-cycle fatigue and long-term strength of the material are presented. The results of comparison of calculated and experimental data show that the proposed MDM model qualitatively and with the accuracy necessary for practical calculations quantitatively describes the durability of materials under the mutual influence of low-cycle fatigue and long-term strength of the material.

Criterion of damageability of structural materials

The work considers the quantitative assessment of the accumulation of scattered damage as a multi-scale and multi-stage phenomenon under elastic-plastic loading, which leads to the degradation of the physical and mechanical properties of structural materials, which is expressed in the change of the modulus of elasticity G and E. The paper proposes a criterion of damage, containing the effect of damage on the service life of the structure under an external complex load. The physics of the process of kinetics of damage accumulation suggests a factor of structural changes as a result of loosening of the material under load for separation and shearing of the representative element in the most loaded section.

EVALUATION OF RESOURCE CHARACTERISTICS OF POWER EQUIPMENT PARTS UNDER THERMAL CYCLIC LOADING

The problem of assessing the strength and resource of critical engineering facilities, the operational properties of which are characterized by multiparametric non-stationary thermo-mechanical effects, is discussed. The main degradation mechanisms of structural materials (metals and their alloys) characteristic of such objects are considered. The basic requirements for mathematical models of these processes are formulated. A mathematical model describing the processes of thermoplastic deformation and accumulation of fatigue damage during degradation of the material by the mechanism of thermal fatigue has been developed from the position of mechanics of the damaged medium (MPS). The IPU model consists of three interrelated parts: relations that determine the cyclic thermoplastic behavior of the material, taking into account the dependence on the destruction process; equations describing the kinetics of fatigue damage accumulation; strength criteria of the damaged material. The variant of the defining relations of thermoplasticity is based on the idea of the yield surface and the principle of gradiency of the velocity vector of plastic deformations to the yield surface at the loading point. This version of the equations of state reflects the main effects of the process of cyclic thermoplastic deformation of the material for arbitrary complex trajectories of combined thermomechanical loading. The variant of kinetic equations of fatigue damage accumulation is based on the introduction of a scalar damage parameter, is based on energy principles and takes into account the main effects of formation, growth and fusion of microdefects under arbitrary complex loading conditions. As a criterion of the strength of the damaged material, the condition of reaching the critical value of the damage value is used. To assess the degree of reliability and determine the limits of applicability of the developed defining ratios of MPS, calculations of the processes of thermoplastic deformation and accumulation of fatigue damage were carried out and the numerical results obtained were compared with the data of field experiments on the example of a specific applied problem. A numerical analysis of the characteristic features of the thermal fatigue durability of a compact sample with stress concentrators simulating the operation of parts in the nozzle box of a steam turbine of a nuclear power plant (NPP) is carried out. The results of calculations of fatigue damage accumulation processes during thermal pulsations are compared with experimental data. It is shown that the developed MPS model qualitatively and with the accuracy necessary for engineering calculations quantitatively describes experimental data and can be effectively used to assess the thermocyclic fatigue durability of structures with multiaxial disproportionate paths of combined thermomechanical loading.

Calculation of Durability and Fatigue Life Parameters of Structural Alloys Using a Multilevel Model of Acoustic Emission Pulse Flow

The issues of durability and fatigue life of various structural materials occupy an important place in the operation of equipment and elements subjected to high stresses. To correctly predict its operation time, knowledge of the unique internal structure of a particular piece of operating equipment is required. To obtain such data, a multilevel model of acoustic emission signal flow is proposed in the article, which is based on the kinetic concept of strength and the selection of various stages of destruction in the kinetics of damage accumulation. The selected information, which accounts for the hypothesis of the linear summation of damage, is used in modern models for calculating fatigue life based on kinetic parameters, e.g., the activation energy of destruction and activation volume. The fracture activation energies, activation volume, destructive load, and fatigue life of various structural alloys and steels were calculated using the proposed acoustic emission model based on static test data from various scientific literature sources. For comparison, several methods of calculating kinetic parameters based on the thermal fluctuation concept of strength were used. In addition, numerical modeling was performed to select the structural lethargy coefficient from the elastic deformation zone. The results of the proposed model are in good agreement with the experimental data and allow—within the framework of more thorough tests and with a more accurate consideration of temperature—for the application of an engineering-based approach with which to evaluate the durability and residual service life of objects.

Damage accumulation and limit states under the low-cycle loading of structural softening steel

Determination and study of patterns of deformation and fracture of structural materials under cyclic loading is an important fundamental scientific problem. The kinetics of damage accumulation in softening TC (12Kh2MFA) structural steel under low-cycle loading is investigated in the paper based on the unified strain-kinetic criterion of fatigue fracture developed by the author. The damaging role of plastic and elastic strain depending on the loading (durability) is shown. Limit states and peculiarities of their occurrence during static, quasi-static, and fatigue failure are described. The force and deformation parameters determining the load-bearing capacity of the material and the nature of its exhaustion under static and cyclic loading have been established. The critical values of deformation and strength characteristics of steel under soft and hard loading are obtained. It is noted that it is reasonable to use these characteristics when modeling the stress–strain states. A method for determining the cyclic behavior of the material (hardening, softening, stabilization) by static fracture curves is proposed. The possibility of describing the kinetics of damage accumulation and limit states of softening materials by the strain-kinetic criterion of fatigue fracture is confirmed.

Determination of elastic characteristics of cement stone to predict the fatigue life of concrete

Introduction. The problem of fatigue failure of concrete is one of the least studied in computational practice. The lack of reliable data on the actual processes of accumulation of fatigue damage occurring in the structure of this material during cyclic exposure does not allow us to form a methodology for calculating concrete structures that perceive such loads. To develop the above methodology, it is proposed to use structural simulation modeling. For this purpose, mathematical models of concrete damage under the influence of cyclic loading are considered. The purpose of the study is to determine the elastic and strength characteristics of cement stone for further development of a methodology for predicting the fatigue life of concrete, taking into account the nonlinear kinetics of damage accumulation.
 
 Materials and methods. The strength limits of cement stone during bending and compression were determined by conducting a full-scale experiment on a testing machine and a hydraulic press. Elastic characteristics of cement stone were obtained as a result of static tests of cement stone samples of various shapes on the universal electromechanical system with the joint use of the digital optical system for analysis of deformation and displacement fields and the acoustic emission signal recording system.
 
 Results. During the tests of cement samples for bending and compression, the values of the corresponding bending and compression strength limits were obtained, which made it possible to confirm the design strength class of cement 32.5 N. Inhomogeneous fields of longitudinal and transverse deformations were obtained using a digital optical system to further determine the basic elastic characteristics of the material. Obtaining acoustic emission signals during the experiment made it possible to reflect the dependences of various acoustic emission parameters on time.
 
 Conclusions. The first stage of the proposed methodology for predicting the fatigue life of concrete is performed, taking into account the nonlinear kinetics of damage accumulation, as a result of which the modulus of elasticity and the Poisson’s ratio for cement stone are determined. The obtained data can be used to create a numerical model of the concrete structure, and the use of acoustic emission signals allows us to estimate the kinetics of damage accumulation in the material.

Kinetics of Damage Accumulation in a D16ch Alloy during Static Loading

Kinetics of Damage Accumulation in a D16ch Alloy during Static Loading

ANALYSIS OF THE MOISTURE CONTENT EFFECT ON THE SPECIFIC INDEX AND DAMAGE ACCUMULATION KINETICS IN THE STRUCTURE OF POLYMERIC MATERIALS DURING NATURAL CLIMATIC AGING

We present the results analyzing the climatic resistance of epoxy polymers obtained on the basis of a modified Etal-247 resin cured by Etal-45M under the effect of natural climatic factors in a temperate continental climate. The kinetics of damage accumulation in the structure of polymer samples under tensile loads was studied on the basis of the results obtained using the author's method. The essence of the technique was to determine the coordinates of the “critical” points of deformation curves based on the time series fractal analysis methods, recorded with a high readings frequency (0.01 s). To estimate the level of accumulated failures leading to the de-struction of samples under tensile loads, we used a parameter defined as the ratio of the number of points with a fractality index less than 0.5 to the total number of points on deformation curves (until reaching the level of “critical” tensile stresses). Time intervals of 0.16 seconds were studied with analyzed area shifted with a step of 0.01 sec. A specific index is proposed that characterizes the accumulated number of damages in the polymer sample structure per unit of its strength. Its achievement leads to the destruction of the composite under study. We have determined the moisture state effect and climatic aging duration on the damage accumulation kinetics in the polymer sample structure under tensile loads.

Zinc Prevents DNA Damage in Normal Cells but Shows Genotoxic and Cytotoxic Effects in Acute Myeloid Leukemia Cells.

Genomic instability is prevented by the DNA damage response (DDR). Micronutrients, like zinc (Zn), are cofactors of DDR proteins, and micronutrient deficiencies have been related to increased cancer risk. Acute myeloid leukemia (AML) patients commonly present Zn deficiency. Moreover, reports point to DDR defects in AML. We studied the effects of Zn in DDR modulation in AML. Cell lines of AML (HEL) and normal human lymphocytes (IMC) were cultured in standard culture, Zn depletion, and supplementation (40 μM ZnSO4) conditions and exposed to hydrogen peroxide (H2O2) or ultraviolet (UV) radiation. Chromosomal damage, cell death, and nuclear division indexes (NDI) were assessed through cytokinesis-block micronucleus assay. The phosphorylated histone H2AX (yH2AX) expression was monitored at 0 h, 1 h, and 24 h after exposure. Expression of DDR genes was evaluated by quantitative real time polymerase chain reaction (qPCR). Zn supplementation increased the genotoxicity of H2O2 and UV radiation in AML cells, induced cytotoxic and antiproliferative effects, and led to persistent yH2AX activation. In contrast, in normal lymphocytes, supplementation decreased damage rates, while Zn depletion favored damage accumulation and impaired repair kinetics. Gene expression was not affected by Zn depletion or supplementation. Zn presented a dual role in the modulation of genome damage, preventing damage accumulation in normal cells and increasing genotoxicity and cytotoxicity in AML cells.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ ДЕТАЛЕЙ АВИАЦИОННЫХ ГТД ПРИ ЦИКЛИЧЕСКОМ ДВУХЧАСТОТНОМ НАГРУЖЕНИИ

The problem of assessing the resource characteristics of responsible engineering facilities, taking into account the peculiarities of operational loading modes, is discussed. The processes of fatigue durability of polycrystalline structural alloys under cyclic two-frequency loading (with the combined action of mechanisms of low and multi-cycle fatigue) are considered. A mathematical model describing the processes of cyclic elastoplastic deformation and accumulation of fatigue damage in structural alloys under multiaxial disproportionate modes of combined thermomechanical loading has been developed from the modern positions of damaged medium mechanics and fracture mechanics. The model consists of three interrelated parts: relations determining the cyclic elastic-plastic behavior of the material, taking into account the dependence on the destruction process; evolutionary equations describing the kinetics of fatigue damage accumulation; criteria for the strength of the damaged material. The variant of the defining elastic-plasticity relations is based on the idea of the yield surface and the principle of gradiency of the velocity vector of plastic deformations to the yield surface at the loading point. This version of the equations of state reflects the main effects of cyclic elastic-plastic deformation of the material for arbitrary folded loading trajectories. The variant of kinetic equations of fatigue damage accumulation is based on the introduction of a scalar damage parameter, is based on energy principles and takes into account the main effects of formation, growth and fusion of microdefects under arbitrary complex cyclic loading regimes. A joint form of the evolutionary equation of fatigue damage accumulation in the areas of low- and multi-cycle fatigue is proposed. As a criterion of the strength of the damaged material, the condition of reaching the critical value of the damage value is used. The results of numerical simulation of fatigue durability of a compact sample (model of the disk deflector of the high pressure turbine of an aviation gas turbine engine) are presented with cyclic two-frequency loading. The results of the comparison of the calculated and experimental data showed that the proposed model qualitatively and with the accuracy necessary for practical calculations quantitatively describes the fatigue life of structural elements under cyclic two-frequency loading.

Kinetics of Damage of Materials under Various Regimes of Re-Changeable Loads

Kinetics of accumulation of damages in engineering objects, which work at repeated-alternating soft and hard modes of loading of details and elements of constructions of vehicles (cars, cars, railway transport, etc.). When changing the direction of the load force to the opposite in the structural material there is a phenomenon of changing the kinetics of accumulation of damage, ie the damage factor at separation and shear changes, which affects the effective stresses and service life of equipment. This effect of the factor of the influence of repeated variables on the redistribution of the kinetics of damage accumulation is considered experimentally for materials with different plastic properties

QUANTITATIVE ASSESSMENT OF THE KINETICS OF DAMAGE ACCUMULATION IN THE POLYMER MATRIX STRUCTURE UNDER FULL-SCALE CLIMATIC FACTORS AND TENSILE LOADS

Statement of the problem. In the current study we look at the change in the elastic-strength performance and kinetics of damage accumulation in epoxy polymers under tensile loads in the control state and after full-scale climatic exposure during one calendar year were studied. Damage accumulation kinetics was calculated based on the author's method using methods of fractal analysis of deformation curves for polymer materials samples under tension.Results. We proposed specific index θ to quantify the total number of damages per unit of strength,where its accumulation leads to the destruction of polymers. We obtained approximating dependences that describe the relationship between specific index θ and tensile strength of epoxy polymers.Consclusion. The study has shown that the Etal-247 epoxy resin-based polymer cured withEtal-1440 amine hardener has the most stable properties under the full-scale climatic exposure.

Damage to engineering objects during re-static alternating load modes

The paper considers the kinetics of damage accumulation in engineering facilities that operate under repeated static alternating load modes - parts and structural elements of vehicles (cars, airplanes, railways). When changing the direction of the load force in the structural material there is a phenomenon of changing the shape of micro defects, which leads to their "healing", ie the factor of damage to separation and shear changes, which affects the effective stresses and service life of equipment. This effect of defect healing is considered experimentally for materials with different plastic properties.

Model of the kinetics of aging of paint and varnish coatings of cement concrete

Information on the kinetics of aging of coatings is presented.The process of moistening was considered as one of the particular cases of aging. During incubation period there is a slight increase, and possibly a decrease in defectiveness. The duration of the incubation period is 0.2 -0.5 of the entire durability.The active stage of damage accumulation begins after the incubation period. In the active stage of accumulation of damages, significant changes occur in the structure and properties of the coating (change in color, shine , cracking, etc.).Determined that the beginning of the active stage of accumulation of lesions coincides in time with the first significant changes in the surface area of the coating. It was found that there is a correlation between the experimental data on the kinetics of damage accumulation, the degree of chalking, and surface area. It lies in the fact that the active stage of damage accumulation coincides with the beginning of chalking of coatings. An analytical dependence is proposed that makes it possible to estimate the area of the defective surface of the coating during aging. The dependence of the level of damage accumulation on the duration of tests can be described by a logistic curve (or Pearl curve)