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Project Number18-19-00413

Project titleDevelopment of theoretical and experimental fundamentals of the acoustodamage method for evaluating strength and durability of structural elements in the process of their manufacture and operation under conditions of extreme thermomechanical loading

Project LeadBelyaev Alexander

AffiliationPeter the Great St.Petersburg Polytechnic University,

Implementation period2018 - 2020

Research area 09 - ENGINEERING SCIENCES, 09-101 - Durability, viability, and disintegration of materials and structures

KeywordsAcoustoelasticity, acoustoplasticity, acoustodamage, acoustic anisotropy, fatigue, durability, hydrogen induced destruction, anisotropic damage, microstructural heterogeneity, finite element modeling, forecasting of service life, technical diagnostics



The development of theoretical and experimental methods of the non-destructive acoustic monitoring for strength and residual life assessment of structural elements during their manufacturing and operation activity under extreme thermomechanical conditions is an important, relevant and modern problem in new matereals development, the nuclear industry, oil and gas industry, aviation, transport and construction. Nowadays, there is no quantitative nondestructive inspection of microdamage and microdefects associated with fatigue and critical for strength accumulation of hydrogen concentration in the parts of machines and structures. Ultrasound diagnostics does not have the acceptable resolution. It does not detect microdamage including those caused by: metal fatigue, local microstructure changes, local accumulation of hydrogen, forming of microscopic zones of fatigue damage and cold working. All other methods of non-destructive testing with high resolution (acoustic emission, magnetostrictive, volumetric ray imaging), require careful calibration of measurements on samples of the same material and the same structure as the explored ones. This allows us to attribute them, rather, to qualitative methods of technical control, than to quantitative methods. The proposed method of acoustodamage considers the influence of anisotropic damage, caused by microcracking and defect forming in the surface layer and in the volume of the material, on the elastic and plastic modules as a theoretical justification for the effect of acoustic anisotropy. This influence is stronger than influence of nonlinear elasticity because the effects of nonlinear elasticity have a second-order of smallness. Thus, the method of acoustodamage is based on the impact of coarser factors than the method of acoustoelasticity. Fundamentals of methods for assessing changes in microstructure, stress-strain state and residual life assessment will be developed based on the data of the phase shift of the high-frequency acoustic waves with different polarizations for damage analysis of the wide range of materials from metals to nanoceramics, composites and geomaterials. The influence of nucleation and evolution of defects and damage, residual deformations and stresses arising as a result of plastic deformations and as a result of gradual accumulation of damage during operation on the mutual phase shift of acoustic waves will be investigated. At the same time, mechanical tests, acoustic research and measurements of the spatial-energy distribution of hydrogen will be carried out. As a result of the project, it is proposed to develop the fundamentals and to verify the new method of non-destructive testing - the method of acoustodamage of the material. This method is supposed to be turned into quantitative in the side of diagnostics and assessment of influence of accumulated plastic strain damage, fatigue and hydrogen damage on the metal strength. To do it, a whole complex of theoretical and experimental researches is planned to be performed using Russian unique devices such as ИН-5101А-00 and ИН-5101А-01. They are used to measure acoustic anisotropy. The offered project is fundamental and is situated on the edge of technologies of industrial control and mechanics of deformable solids. It will help to develop new unique methods of measuring to create materials with special properties avoid accidents and catastrophes caused by fatigue, plastic deformation, nucleation and growth of microcracks, accumulation and redistribution of hydrogen in metal.

Expected results
In the process of project implementation it is planned to obtain both fundamental scientific and practically meaningful results in three main directions: 1. Experimental research of propagation parameters variation of the incident and reflected acoustic waves with different polarization under monotonous and cyclic thermomechanical loading in case of inelastic deformation and damage accumulation; 2. Analytical and numerical investigation of acoustic environment properties with volumetric and surface damage, development of new related fatigue models, inelastic deformation, damage and hydrogen accumulation; 3. Experimental research of hydrogen redistribution with different binding energies during damage accumulation, also under cyclic thermomechanical loading. Fundamentals for quantitative non-destructive tests methods using acoustodamage will be developed for fatigue and hydrogen-induced metal damage control. It is of great importance for the operation safety of machines and structures in the oil and gas industry, civil engineering, nuclear energetics, aircraft engineering and transport sector. These results can be used in production of the machines’ parts and structures which are made of new materials and during their technical diagnostics. The world significance is determined by the fact that the phenomena of fatigue, thermal fatigue and hydrogen-induced long-term destruction don’t have an unambiguous theoretical description and in practice there are used only empirical formulas and safety factors for strength calculations. There will be developed new quantitative methods of the fatigue non-destructive tests method, initial phase of hydrogen-induced destruction evolution and metal damage. It can be applied in practice, because it will be created and tested during the project work using serial industrial equipment for technical control. This result also doesn’t have analogues, because the ultrasonic acoustic methods have not been used to determine the initial phase of failure and to assess the effect of natural, low hydrogen concentrations on fatigue strength and delayed destruction due to insufficient resolution for detection for microscopic damage. This result also doesn’t have analogues, because the influence of natural low hydrogen concentrations on fatigue strength and slow destruction has not been researched too deep. Interactive investigation of the damage accumulation process in fatigue crack front region during its growth on the basis of the acoustodamage method will make it possible to obtain patterns of the anisotropic damage accumulation during the initiation and development of macrocracks and to develop methods for monitoring and control the integrity of critical structures elements. The comparison data results on acoustic anisotropy before and after tests and high-temperature creep of the monocrystal prototype will be obtained. These investigations will make it possible to estimate the influence of the initial and acquired anisotropy related with rafting of the internal structure and plastic strains. Nonmetallic materials will be carried out which are important for power industry progress. It is planned to obtain correlation the acoustic anisotropy measurement data dependencies on the type of microporosity and cores microcracking of various oil-bearing rocks. The possibilities of applying the method of the acoustodamage to analyze nanocomposite materials, which are used in the ITER project, will be explored. Rock sample examination will make it possible to extend the method of acoustodamage to practical problems of the monitoring and controlling processes of the oil-saturated porous materials destruction that makes it possible to increase the efficiency of wells and hydrofracturing. Nonmetallic nanomaterials examination is a part of the structures’ technical diagnostics in fusion energetics. It is also planned to obtain important data for the application of the acoustodamage method in the hydrogen power engineering and for the production of semiconductors and nanocomposites. Methods of engineering finite element analysis of the stress-strain state and acoustodamage will be developed, taking into account new fatigue, inelastic deformation, accumulation of microdamage and hydrogen models. This result also has no world analogues, because the influence of hydrogen is considered by most scientists in a quasi-static formulation, without acoustic vibrations of a solid body. It is important that these engineering methods can be applied in practical calculations for strength that will allow taking into account the mutual influence of fatigue and hydrogen microdamage on the stress-strain state of the metal in advance. All these results also have important social implication. Their usage will avert disasters and technical incidents in the most important and dangerous industrial fields during accidents, in the energetics and transport sectors. Scientific results are unique, because they allow to solve the fundamental problem of acoustic vibrations coupling with the structure and damage of a material with allowance for high-cycle fatigue and the influence of a small parameter – damage and natural hydrogen concentrations that are limited by volume. Such a problem has not been posed yet, because the influence of local microstructure changes on the acoustic anisotropy was not considered. Well known physical and mechanical models of the influence of hydrogen on the structure and properties of the material are quasistationary, and known complex, nonlinear functional dependences of mechanical characteristics on hydrogen concentrations doesn’t allow it to be used during acoustic oscillations consideration. It is expected to obtain new results on continuum mechanics, acoustics and condensed matter physics. So, the project is a cross-disciplinary research, which essentially raises the fundamental importance of its results for these sciences.



Annotation of the results obtained in 2018
The main objective of the project is to develop the theoretical and experimental foundations of the method of acoustic damage to assess the strength and durability of structural elements in the process of their manufacture and operation. The studies were carried out in two main areas, which are acoustic and hydrogen diagnostics, both by means of experimental methods and theoretical approaches. An analysis of correlation of the results was carried out. The diagnostics of the elements of critical structures in thermonuclear power engineering was carried out by using the methods of acoustoelasticity and acoustic damage. The diagnostics was carried out on real elements made of nanostructured silicon carbide, specifically on two types of samples obtained by the industrial sintering method: on the model mirror of the light collection system of the projected ITER fusion reactor, and also on a fragment of the carrying structure of the reactor destroyed by vibration. The analysis of the obtained results confirmed the possibility of applying the method of acoustic damage to the detection of structural defects and the assessment of damage to composite structures made of nanostructured silicon carbide. Acoustic anisotropy and the spatial-energy distribution of dissolved hydrogen concentrations of samples of single-crystal materials of various crystallographic orientations subjected to cyclic effects resulting in low-cycle fatigue were studied. The performed theoretical studies covered a wide class of problems, including the consideration of fatigue cracks, and were confirmed by a finite element calculation. The study of changes in the spatial-energy distribution of dissolved hydrogen concentrations under low-cycle fatigue loading of steel samples with periodic surface modification due to mechanical processing was performed. The purpose of this part of the project was to clarify the nature of non-uniformity in the spatio-temporal distribution of hydrogen, both in depth and in length of the research object. The studies were conducted in parallel theoretically and in tests. Qualitative features were identified in order to identify the accumulation of plastic deformations and microdefects in the elements of critical structures based on the angular diagrams of acoustic anisotropy. The main goal of this part of the work was to clarify the role of factors affecting acoustic anisotropy, including anisotropy of the elastic properties of the material, active or residual stresses, plastic deformations and internal or surface defects. Analysis of the evolution of the angular diagrams of acoustic anisotropy provided additional information in determining the nature and separation of the contributions of various factors. Finite element modeling of the effect of surface microcracks on the speed of passage of ultrasonic waves in materials was carried out. This study is necessary to build a numerical counterpart of an industrial device that implements the idea of acoustoelasticity. To this end, a two-dimensional finite-element model of the passage of elastic waves initiated by a piezo-actuator was constructed in samples containing a network of microcracks in a thin surface layer, based on a two-layer heterogeneous approximation. An analytical approach was developed to describe the propagation of high-frequency waves in elastic media with a random distribution of elastic and mass characteristics in order to take into account spatial heterogeneity, microstructure, damage and microcracks within a single approach. This part of the project is dictated by the need to clarify the significance of non-ideality of the material in the results of theoretical and simulation parts of the project, made under the assumption of ideal materials. As a result of the research, the following main scientific results were obtained. The results of an experimental study of the acoustic anisotropy fields of a composite mirror of a system for collecting light from polycrystalline silicon carbide made it possible to obtain and analyze the distribution field of the main values of the damage tensor in the mirror design. A correlation was established between acoustic anisotropy, principal values of the damage tensor and dissolved hydrogen concentrations for various loading modes of standard compact single-crystal samples from nickel-based super alloys. The parameters of hydrogen transport models were obtained, which are necessary to identify the spatial parameters of damage to the samples under cyclic loading and the parameters of the bicomponent model of the material containing hydrogen, for further use in simulating the effects of acoustic damage. Mathematical models of hydrogen-containing material were developed for further use in modeling effects of acoustic damage, as well as mathematical models for calculating the main values of the damage tensor in the initially anisotropic material based on data on the propagation speeds of waves of different polarization. The dependences of acoustic anisotropy on crystallographic orientation of single-crystal samples were obtained before and after fatigue tests. Angular diagrams of acoustic anisotropy were obtained in the case of complex multi-axial stress-strain state of samples that underwent fatigue tests and in the case of step uniaxial loading of samples up to large plastic deformations and failure. The dependence of the wave propagation time on the distribution density of microcracks in a thin surface layer was established. Expressions were also obtained for the speed of passage of elastic waves in the sample material for the case of direct modeling of a network of surface cracks and for modeling their presence with a homogeneous layer with a modified shear modulus corresponding to the density of surface microcracks under consideration. As a result of solving the problem of wave propagation in an elastic medium with a random distribution of elastic and mass characteristics, expressions for the mean field and dispersion of the propagating harmonic wave for characteristic cases of inhomogeneities in materials were obtained in closed form.



1. Полянский А.М., Полянский В.А., Беляев А.К., Яковлев Ю.А. Relation of elastic properties, yield stress and ultimate strength of polycrystalline metals to their melting and evaporation parameters with account for nano and micro structure Acta Mechanica, Volume 229, Issue 12, pp. 4863–4873 (year - 2018).

2. Семенов А.С., Полянский В.А., Штукин Л.В., Третьяков Д.А. Влияние поврежденности поверхностного слоя на акустическую анизотропию Прикладная механика и техническая физика, Tом 59, №6, C. 1-10 (year - 2018).

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4. Беляев А.К., Грищенко А.И., Лобачев А.М., Полянский В.А., Третьяков Д.А. Discrete and continual approaches to the description of random microstructure of materials AIP Conference Proceedings, - (year - 2018).

5. Галяутдинова А.Р., Третьяков Д.А. Эволюция угловых диаграмм акустической анизотропии при неупругом деформировании металлов Неделя науки СПбПУ: материалы научной конференции c международным участием. Институт прикладной математики и механики, - (year - 2018).

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