Kinetics Of Damage Accumulation Research Articles

Stochastic cluster dynamics method for simulations of multispecies irradiation damage accumulation

Accurate modeling of irradiation damage processes is important to predict materials performance in nuclear environments. The mean-field rate theory (RT) approach has been and remains the standard method for calculations of the kinetics of damage accumulation under irradiation. Despite its many advantages, when using RT, very large numbers of ordinary differential equations (ODEs) need to be solved if one is interested in the kinetics of complex defect populations containing defect clusters made up of constituent defect species of different types, e.g. He, H, O, alloying impurities, etc. Here we present a stochastic variant of RT, which we term stochastic cluster dynamics (SCD), intended as an alternative to the standard ODE-based implementation. SCD obviates the need to solve the exceedingly large sets of ODEs and relies instead on sparse stochastic sampling from the underlying kinetic Master Equation. The new method evolves an integer-valued defect population in a finite material volume. In this paper we describe the general ideas behind the SCD method, give essential details of our numerical implementation and present SCD simulations that verify the new method against standard RT implementations on two well characterized material models. We then apply the method to simulate triple beam irradiation experiments of heavy Fe ions, He, and H on model ferritic alloys up to a dose of 1 dpa.

Studies on damage accumulation kinetics in a metal under cyclic loading in the multiaxial stress state

Results of experimental investigations of deformation behavior for 10GN2MFA steel under cyclic loading in the multiaxial stress state are presented. The effect of a stress state on homogeneity factor variations that represents a measure of metal damage is shown.

Simulation of the elementary damage accumulation kinetics in loaded materials

The evolution of an ensemble of elementary-damage clusters is considered using a probabilistic cellular automaton, and the characteristics of the time series of the number of elementary damages and the number of elementary-damage clusters are studied. The transition of the autocorrelation function of the time series of the number of elementary damages to a negative-correlation region is shown to correspond to the transition of the evolution of an ensemble of clusters to the stage of coalescence. The autocorrelation function of the time series of the number of elementary damages agrees qualitatively with the experimental behavior of the autocorrelation functions of the number of electromagnetic- and light-emission pulses in loaded materials.

The kinetics of damage accumulation in heat-resistant steels under different loading conditions

The investigation results are presented for the kinetics of damage accumulation and the process of deformation in a heat-resistant steel 10GN2MFA for different loading conditions under complex stress state.

Study of the kinetics of damage accumulation in loaded materials based on impulse electromagnetic and photon emission

The kinetic characteristics for the random process of elementary damage accumulation are compared with the corresponding kinetic characteristics for the processes of impulse electromagnetic and light emission of loaded materials in simulation by the probabilistic cellular automation. It is established that transition of the temporal autocorrelation functions for the number of emission impulses to the region of negative correlations can be considered as a precursor of the transition of the loaded material to the irreversible failure.

Meso and macroscopic considerations about damage accumulation processes

Meso (effect of grain size) and macroscopic (effect of sample dimension) considerations about damage accumulation processes are discussed. Although both factors may significantly influence damage accumulation kinetics, they are not taken into account in most of currently used models. The role of meso and macroscopic factors may be explained in the framework of a recently developed model of damage accumulation (Multi-Step Damage Accumulation – MSDA), which assumes that the damage build-up can be regarded as a sequence of structural transformations triggered by the destabilization of the current structure of a crystal induced by radiation damage.

A study of deformation and damage accumulation processes in 10GN2MFa steel under low-cycle loading

The paper presents results of the experimental investigation of deformation behavior and damage accumulation kinetics in a heat-resistant reactor pressure vessel steel at high stress levels under stress-controlled (pulsating), low-cycle loading up to 104 cycles. Hardness measurements have been performed upon various operating time periods under elastoplastic deformation. It has been found that hardness and strength of the steel exhibit qualitatively different behaviors throughout the lifetime. The damage accumulation process in steels under static and cyclic loadings has been studied by means of the LM-hardness method. The curves of Weibull homogeneity coefficient vs. cycling stress and accumulated strains are obtained.

Study of the polymer material fracture process by the acoustic emission method

The studies of the mechanics of the damage of the polymer materials are now extending beyond the question of the load-carrying capability of the articles, constructions, and structures. The control of the damage processes and the knowledge of their relationships are of tremendous importance for engineering and technology in the various industrial fields. For example, the service life of the constructions and structures can be increased by slowing the growth of the cracks, while in the machining of the materials, conversely, it is often advisable to reduce the strength of the material that is being worked. The studies of Kudinov, Poduraev, and Kabaldin [1‐ 3] have shown that the damage of the material is a necessary part of the cutting process. The commonality of the materials damage and cutting processes has been established, specifically the realization of both processes either by the development of the elastoplastic deformation to the critical state or by the formation and growth of the cracks, i.e., the realization of brittle fracture in the microvolumes of the material. Thus, we can represent the working of the various materials, and the polymers in particular, by cutting as a version of a controllable damage process that is accompanied by the dynamic action of the tool cutting edges on the workpiece surface. Considering the foregoing and the fact that the polymer materials have an ensemble of specific properties that is different from the behavior of the metals and alloys in mechanical working by cutting, it is important to study the polymer materials damage mechanism with the use of the modern methods. The study of the kinetics of damage accumulation in the deformation and fracture process has considerable theoretical and practical importance: this study will make it possible to establish the mechanism of the damage of the material in each stage of the deformation process, and determine the influence of the various damage conditions. It is known [4, 5] that tension is the most dangerous form of the stress state of the polymer materials. The tests of the materials are most often performed in tension, since this type of deformation can be realized in nearly the pure form, in contrast with the compression, shearing, and torsional deformations. Therefore the mechanical characteristics that are determined in tension are the primary basic data for the calculations of the strength of the parts and structures that are made of the polymer materials. At the present time the acoustic emission method, based on the analysis of the parameters of the elastic acoustic emission (AE) waves, is used effectively to study the deformation and failure mechanisms of the solid bodies [6]. This method makes it possible to gather a considerable amount of information on the physical processes taking place in the structure of the material, and to evaluate quantitatively the degree of the damage accumulation and the mechanism of the structural changes. The parameters of the AE method that are most informative and are traditionally used include the following: the peak amplitude of the AE signals, the overall signal count, the count rate, and the overall energy of the signals. The peak amplitude of the signals is the energetic index of the level of the damage of the material. The amplitude distribution of the AE pulses can be used to evaluate the type of deformation in the specific loading conditions. The overall signal count is the information on the integral level of the damage of the object in the course of some external action, including the increase of the length of the defect and the change of its area. The signal count rate (the intensity of the pulses) reflects the rate of the development of the damage of the material at the given moment of time. The overall energy of the AE signals is the area below the envelope of the electric signal. It is generally proportional to the dimensions of the cracks that form under load. The studies were performed on the standard flat specimens with the use of the ALA TOO IMASH 20‐ 75 universal testing system as the loading device. The specimens for the tests of the polymer materials were fabricated in the form of double-end blades with 3 × 2 mm rectangular section in the working zone. The loading curve was recorded with the use of the tensile testing system recorder. Along with the loading curve, the AE signals were recorded continuously with the use

Damage accumulation stages in a low-carbon steel during uniaxial tension

The kinetics of damage accumulation during tension of a low-carbon steel with an edge notch has been studied by acoustic emission, ultrasonic attenuation, and replicas. The criteria of damage, fracture mechanics, percolation, and fractal dimension are estimated and used to distinguish the stages of fracture.

Kinetics of scattered fracture in structural metals under elastoplastic deformation

The paper presents a procedure whereby the damage accumulation kinetics in structural materials, such as steel 45, stainless steel 12Kh18N10T, aluminum alloy D16T, and titanium alloy VT22, under elastoplastic deformation is studied based on variation parameters of elastic modulus and resistivity. For complex stress conditions, a continuum model for damage accumulation is proposed which relates the damage parameter to the intensity of accumulated plastic strains. The data calculated by the proposed continuum model are compared to the experimental findings of the investigation of the damage accumulation kinetics for some structural metals.

Damage accumulation in ion-irradiated ceramics

The radiation damage induced by energetic ions is one of the basic problems related to ion implantation technology. Each incoming ion creates a huge number of defects, so that high irradiation fluences eventually lead to complete amorphization of the material. Despite the obvious importance of this process, theoretical descriptions of the kinetics of radiation damage accumulation are still incomplete and limited to single-step processes only. In the present paper, we propose a new approach for the description of the radiation damage build-up in crystals, which is based on the concept of subsequent destabilization of the crystalline phases. We compare the presented model to experimental results of damage accumulation kinetics measured for SiC, ZrO 2 and MgAl 2O 4, i.e. cases when one, two or three stages of defects accumulation were observed.

Kinetics of damage accumulation in sheet materials under biaxial deformation along nonlinear trajectories

We study elastoplastic deformation of a sheet material subjected to loading along curved trajectories in a two-dimensional deformation space. The influence of the deformation trajectory parameters on the damage accumulation process in a sheet material is established. It is demonstrated that express assessment of crack growth resistance of material can be performed by using a hardness scatter parameter.

Simulation of damage accumulation kinetics with a probabilistic cellular automaton

The kinetics of damage accumulation and the evolution of damage clusters in loaded materials are simulated with a probabilistic cellular automaton controlled by three probabilities, namely, by the probabilities of free-cell occupation, cluster perimeter growth, and coalescence of clusters separated by a critical distance. The automaton algorithm is realized with Microsoft Visual Basic 6.0 as a single-document Windows application connected with Microsoft Excel, which is used as an automaton client to save and process output data. The operation of the automaton is illustrated by the example of the kinetics of damage accumulation and the evolution of a damage cluster structure compared for two simulation scenarios.

Procedure for the evaluation of the accumulation of defects in metallic structural materials under complex elastoplastic loading

Within framework of the continual fracture mechanics, we describe the engineering approach to the assessment of scattered microdamage accumulation kinetics in metallic materials under elastoplastic loading conditions in case of plane stressed state. Automatized experimental stand and the respective investigation technique are discussed. The stand has been developed based on modification of the UME-10T electromechanic test machine. State-of-the-art computer technologies and microprocessing hardware are incorporated in the stand automation. We present the technique of experimental assessment of damage accumulation kinetics in metallic structural materials under complex elastoplastic loading conditions with account of two different fracture (cleavage and shear) processes, which technique is based on measuring the specific electric resistance of the specimen.

Fracture of crystalline iron subjected to high-rate tension. Molecular dynamics simulation

There are several descriptive levels for the fracture of the solid phase. Thermodynamic analysis provides the determination of the stability boundary for the solid phase in the negative-pressure region [1]. The propagation of cracks is described by methods of continuous mechanics [2]. When the fracture time is comparable with the duration of the loading action (e.g., in shock wave experiments), high-speed fracture is of a relaxation character and depends strongly on the kinetics of damage accumulation [3]. In view of this circumstance, problems concerning the initial stages of arising damages are of interest. The atomistic simulation methods such as molecular dynamics and the Monte Carlo method that are based on classical models of interatomic interaction allow investigations of microscopic fracture mechanisms (formation of defects, dislocations, discontinuities, propagation of cracks) for nonzero temperatures (see, e.g., [4–9]). At the same time, modern methods for the ab initio calculation of the electronic structure make it possible to precisely determine the cold curves and theoretical ultimate strength of substances (see, e.g., [10]).

Kinetic similarity of fracture processes on various scale levels

Common kinetic features of multiple fracture of metallic specimens tested at different loading conditions were studied and used for an analysis of seismic activity accompanying multiple formation of faults in the earth crust. The study revealed the similarity of basic regularities in the dynamics of seismicity before earthquake and in kinetics of damage accumulation before specimen fracture, estimated by acoustic emission and metallographic methods. The results obtained confirm the ideas of self-similarity and the hierarchical sequence of multiple fractures, and they provide a physical basis for prediction of the critical events at various scale levels.

The kinetics of steel corrosion in sea water

The kinetics of corrosion damage accumulation in stainless steels of various systems was studied using samples exposed in a model aqueous NaCl solution and in sea water. The time variation of the degree of corrosion damage corresponds to a reaction of the first order. The values of the corrosion activation energy and a parameter characterizing protective properties of a protective film on the metal surface are determined.

Application of Acoustic Emission Method to Studies of Vulnerability of TiN Coatings

The kinetics of damage accumulation in TiN coatings under various loading conditions has been investigated using spectral parameters of isolated acoustic emission pulses and their integral ow characteristics. By separating clusters plotted in the coordinates “energy–median frequency,” we have identified two types of signals corresponding to specific mechanisms of the coating fracture. Basing on distributions of such signals generated in the process of deformation, features of fractured coatings have been characterized.

Numerical Investigation of the Effect of Loading Multiaxiality and Deformation Process Parameters on the Fatigue Life of Metals

Known experimental data on the effect of loading multiaxiality and the type of deformation path on the fatigue damage accumulation process have been analyzed. In terms of the mechanics of a damaged medium, a variant of the defining relations has been developed that describes the processes of elastoplastic deformation and damage accumulation in structural materials (metals and their alloys) in the case of multiaxial nonproportional low-cycle loading paths. The damaged-medium model consists of three interrelated components: relations defining elastoplastic behavior of the material with allowance for the influence of the fracture process, equations describing the damage accumulation kinetics, and a strength criterion for damaged material. To qualitatively assess the defining relations, a numerical experiment to construct equal-damage surfaces has been carried out. The calculated data are compared with the experimental ones. The effect of the stress-state multiaxiality and the type of the deformation path on the low-cycle fatigue life of metals has been investigated. It has been shown that the developed variant of defining relations for a damaged medium reflects correctly the main effects of cyclic elastoplastic deformation and damage accumulation at a multiaxial stress-state and arbitrary material deformation paths.

Atomic displacements and defect accumulation during irradiation with energetic particles: An autobiographical review

We have been requested to prepare a rather unusual article for this special publication. The article should be not only autobiographical in nature but should also have historical perspectives and critique and should contain some element of visionary forecast. Undoubtedly, the idea is unique and challenging though may prove to be less than easy to realise! In response to this challenge, I will at least attempt to present a kind of cohesive description of the evolution of my research activities in the field of defect production, diffusion, interactions and accumulation. These activities have involved widely different irradiation conditions, extending from 1 to 225 MeV electrons, fission to fusion neutrons and 3–800 MeV protons. Over the years, I have also been involved in a variety of theoretical activities dealing with different aspects of defect production, diffusion, void/bubble nucleation, kinetics of damage accumulation and irradiation hardening and embrittlement. An overview of these activities and their main conclusions will be presented. It is somewhat surprising that even after 25 years of continuous involvement, I still find myself grappling with basically similar sorts of problems in the same field of research. In hindsight, it may appear as if all the activities that I have been involved in might have been carefully planned well in advance. The reality is, however, that «chance» and «circumstance» have actually dictated the course of events. With this experience in hand, I hesitate to venture into the lands of unknowns, and shall refrain from making visionary forecast about what future may or may not unfold in its own time!