Cyclic Crack Resistance Research Articles

Determination of the residual life of the pipe metal under conditions of corrosion fatigue

This paper presents a method for calculating the residual metal life of pipelines with crack-like defects. The results of corrosion and fatigue tests of ordinary grade structural steel VSt3sp, widely used in the oil and gas industry, are presented. The work carried out studies on the effect of cathodic polarization on the cyclic crack resistance of VSt3sp steel under the influence of a carbonate-bicarbonate medium.

Влияние толщины и состава верхнего слоя двухслойного покрытия на циклическую трещиностойкость и работоспособность твёрдосплавного режущего инструмента

The results of studies on the effect of the thickness and composition of the upper layer of two-layer coatings on the cyclic crack resistance and operability of a carbide cutting tool are presented. It is shown that the dependence of cyclic crack resistance and the durability period of a carbide cutting tool on the thickness of the upper layer is extreme, and their maximum values are observed at the same thickness of the upper layer. Varying the thickness of the top layer within 2-6 microns leads to a change in the durability period from 10% to 30%.

PROPOSALS FOR IMPROVING DSTU B B.2.6210: 2016

The analysis of the normative document DSTU B В.2.6210: 2016 on the assessment of the technical condition of steel building structures, which are in operation. In particular, the document does not address the analysis of degradation processes. Does not consider monitoring impacts and loads. Does not consider the calculation of steel structures for cyclic crack resistance, the calculation of structures on the resistance to brittle fracture. The document does not address the definition of a residual resource. Does not consider the issues of reasonable reassignment and extension of the life of steel structures. Defects of the document are determined. References are given to scientific publications in which: the classification of loads, influences, aggressive operating environments, classification of degradation mechanisms is given, methods for determining the mechanisms of the degradation of steels and structures are presented; Methods for calculating strength reserves; Methods for determining the residual longevity, residual and reassigned resource of steel structures are described.

Исследование циклической трещиностойкости стали литых несущих деталей грузовых вагонов

Purpose: Carrying out complex experimental studies of cyclic crack resistance of molten steel which is used for load-bearing parts of freight wagon running systems with kinetic diagram building for fatigue failure. Methods: Method of mechanical testing of molten steel samples under cyclic loading conditions was applied, the method makes it possible to obtain quantitative estimates of stuff ability to resist fatigue failure on the stage of fatigue crack development (testing on cyclic crack resistance). To study the surface of fatigue failure, relief micrographic analysis was used. To study molten steel elemental composition and the mechanisms of fatigue crack development, X-ray micro-spectral analysis was used on fatigue failure various stages. Results: The results of the research of cyclic crack resistance of 20 GL molten steel, which is used for load-bearing parts of freight cars, are presented. Fatigue failure kinetic diagram has been built, detailed micrographic analysis of fatigue failure surface has been carried out and elemental composition of non-metallic inclusions has been studied. Practical significance: Based on the research results, it is possible to assess the performance of 20 GL steel with cracks and to predict survivability. The results obtained make it possible to improve the methods of resource projection of molten bearing parts for freight wagon running systems in order to increase their operational reliability. The research results are used by enterprises - manufacturers of molten parts to control technology stability and to improve product quality.

Study of cyclic crack resistance and efficiency of cutting tool with single- and multilayer coatings based on niobium nitride

The results of studies on the effect of single- and multi-layer coatings based on niobium nitride on their cyclic crack resistance and efficiency of carbide cutting tools are presented. It is shown that the use of these coatings can significantly increase the operating time of the cutting tool before their destruction due to cracking. At the same time, the greatest effect is achieved when using multilayer coatings with a lower heat-protective layer of niobium nitride.

Strength and fracture mechanism of nanostructured metal materials for medical applications

In this paper we study titanium Grade4, magnesium alloy Mg-Zn-Ca, corrosion-resistant austenitic steel 08Kh18N9 for medical applications. The mechanical properties in tension, torsional strength, and cyclic crack resistance under different types of loading of steels are investigated. The results are compared for two states of steels: the initial coarse-grained (CG) state and ultrafine-grained (UFG) state produced by severe plastic deformation processing via equal-cannel angular pressing (ECAP). It is demonstrated that the ultrafine-grained materials have essentially better strength and lower sensitivity to cyclic overloads. It is concluded that all the studied UFG materials are more promising compared to CG ones for the manufacture of medical devices for various purposes, which experience various static and cyclic loads during operation.

Development of rails of a new category for use in particularly harsh operating conditions

Introduction. In the conditions of an annual increase in load stress on the roads of the Eastern Polygon, an effective technical solution to the problem of an increased number of rolling stock derailments due to rail breakage is the creation of rails for cold climate conditions with increased hardness to increase wear resistance and contact endurance with simultaneously high values of impact strength. Such a set of properties can be achieved by using separate heating for quenching and cooling with a quenching medium with a high cooling capacity. Rails manufactured using this technology will belong to a new category. In this regard, the purpose of this work was to create a new category of rails for their use in particularly harsh operating conditions.Materials and methods. In this paper the effect of separate induction heating before differentiated quenching with compressed air of controlled humidity on the microstructure and mechanical properties (hardness, mechanical properties during tensile and impact tests, endurance limit, cyclic crack resistance) of rails of type R65 was investigated.The results of the study. A comparative analysis of the results obtained with similar indicators for rails of the DT350, DT350NN and DT370IK categories according to GOST R 51685-2013 was carried out. Studies of the chemical composition, mechanical properties, hardness on the rolling surface of the rail head and cross-section, as well as the microstructure of the rails of the experimental batch showed compliance with the requirements of GOST R 51685-2013 for rails of categories DT350, DT370IK, DT350NN.Discussion and conclusion. It is shown that as a result of the application of differentiated thermal hardening of the rail using compressed air of controlled humidity as a quenching medium, a new category of DTO350NN rails was obtained, characterized by a favorable combination of strength properties, plasticity characteristics and brittle fracture resistance indicators. Rails of the new category can be recommended for use in particularly severe operating conditions (in curved sections of the track of a small radius at low temperatures), including on the roads of the Eastern Polygon.

Applications of preloading pressure on expansive subgrade treated with nano-geopolymer binder for cyclic crack resistance

Applications of preloading pressure on expansive subgrade treated with nano-geopolymer binder for cyclic crack resistance

Strength and Fracture Mechanism of an Ultrafine-Grained Austenitic Steel for Medical Applications.

In this paper, we study the corrosion-resistant austenitic steel Fe-0.02C-18Cr-8Ni for medical applications. The microstructure and mechanical properties (tensile mechanical properties, torsional strength, impact toughness, and static and cyclic crack resistance) under different types of loading of the steel are investigated. The results are compared for the two states of the steel: the initial (coarse-grained) state and the ultrafine-grained state produced by severe plastic deformation processing via equal-channel angular pressing. It is demonstrated that the ultrafine-grained steel 0.08C-18Cr-9Ni has essentially better properties and is very promising for the manufacture of medical products for various applications that experience various static and cyclic loads during operation.

Investigation of the fatigue crack growth rate in heatresistant nickel alloys

The results of tests on the FCGR (fatigue crack growth rate) of compact specimens of eccentric tension using a crack opening (COD) sensor under conditions of an asymmetric loading cycleR=0.1 at room and elevated temperatures are presented. The relationship between the conditions of force loading of preliminary growth of the initial fatigue crack is considered. The values of the effective stress intensity factor Keffwere obtained, which is an important estimate for interpreting the observed character of crack growth. A comparison of the properties of the cyclic crack resistance of the VZh175-ID alloy with the properties of foreign analogues Rene 88DT, Inconel 625 SLM and domestic ones - EP741NP, EK151-ID is presented. The influence of the test temperature on the growth rate is shown. The hypothesis about the linear dependence of the parameters of the Paris equation is tested.

EVALUATION OF CHARACTERISTICS OF RESISTANCE OF PROPAGATION OF CORROSION- FATIGUE CRACKS OF LONG-TERM OPERATED DRILL PIPES

The aim of the proposed article is to determine the patterns of the corrosion-fatigue cracks in long-term operational metal elements of drill strings (steel 45, 36G2S, 40HN) when drilling wells in corrosive environments (drilling fluid "Biocar", potassium polymer mud and on the air). Based on the obtained results of experimental studies, diagrams of cyclic corrosion crack resistance for the studied systems "metal - medium" were drawn. The cyclic crack resistance characteristics of long-used metals of drill string elements are determined - the values of constants (C and n) in power dependence of Paris, as well as the values of threshold and critical stress intensity factory. The influence of drilling mud of the corrosion crack resistance of the investigated metals of drill string elements was estimated quantitatively. In particular, in the environment of drilling mud "Biocar" the process of corrosion-fatigue crack development in the studied metals of the elements of drill strings is not significantly, in the range of 1-5%, differs from the development of fatigue crack on the air. Whereas in the potassium polymer drilling mud media, the rate of corrosion-fatigue cracks development in the investigated metals of the drill strings elements significantly, in the range of 15-35%, differs from the development of fatigue cracks on the air. It is established that under the influence of working loads the process of the corrosion-fatigue crack development in long-operated elements of drilling string is accelerated by more than 10% in the media of the potassium polymeric drilling mud than in the environment of drilling mud "Biocar".

Assessment of cyclic crack resistance of surface hardened parts

Calculation and experimental methods for evaluating the cyclic crack resistance of materials and plain workpieces after hardening their surface layer by various technological processes are presented and argued. These methods can be used in engineering calculations to determine and designate the most effective processes for surface hardening of parts from high-strength materials and to optimize process parameters.

Experimental and numerical determination of the barrier layer effect in the composite on the crack propagation

Cyclic crack resistance tests of samples from a seven-layer metallic material obtained by the method of hot rolling were carried out. Identified features of fatigue cracks propagation. Mathematical finite element models describe the stress state at various stages of the experiment are constructed. The features of a finite thickness barrier layer effect in modeling the fatigue crack behavior are revealed.

Analysis of Propagation of Fatigue Cracks in Crane Girders

The results of analysis results of residual life of crane girders with operational defects based on numerical studies of the stress-strain state, the equations of limiting states, and the kinetic dependences of fatigue crack propagation formulated under criteria of strain and fracture mechanics are presented. A high level of wear of the fixed capital assets of engineering structures and metal constructions, as well as operation of the facilities in beyond-design-basis terms, contributes to origination of emergencies caused by damage accumulation. Crane girders operated under emergency conditions caused by the presence of fatigue cracks of different length in the most dangerous zones of the girder wall with an eccentric application of crane load are studied. According to the results of a numerical experiment, the lines of stress intensity influence at the crack tips appearing at the upper zone of the wall when different values of loading eccentricity caused by the rail displacement from the vertical axis of girder cross section were revealed. The dependence of the fatigue crack length and of the stress intensity at the crack tip on the number of load cycles of the girder is determined. To evaluating the bearing capacity of crane girders operated in emergency conditions, it is proposed to use the effective values of the stress intensity factors calculated for specific loading conditions, taking into account the structural features of the girders, the sizes of emerging fatigue cracks, and their locations in the crane girders. According to the results of analysis, the diagrams making it possible to predict the remaining residual life of crane girders with a crack are constructed. On the basis of traditional design procedures of structures for cyclic crack resistance, the calculation algorithm for individual life of crane girders which includes the obligatory analysis of the stress-strain state of the crane girder with a crack at the upper zone of the wall is formulated and implemented.

МОДЕЛИ РАЗВИТИЯ ФИЗИЧЕСКИ КОРОТКИХ И МАКРОСКОПИЧЕСКИХ ТРЕЩИН И ПРИМЕНЕНИЕ ИХ ДЛЯ БАББИТА НА ОСНОВЕ ОЛОВА

The stages of fatigue crack development are analyzed. The well-known models of physically short cracks and generalized models describing some stages are shown. A perspectivity of a statistical generalized model offered is shown. The parameters obtained of a cyclic crack resistance of tin-based babbit are presented.

CRACK RESISTANCE OF CENTRIFUGAL-CAST STEAM P I P E S MADE OF STEEL 1 5 K h l M l F

Significance of assessing the characteristics of crack resistance of centrifugal-cast (CFC) tubes made of steel 15KhlMlF is substantiated. The characteristic features of the metal under study are considered along with the methodology of crack resistance tests. Three modifications of the metal of the CFC pipes in the initial state, that differ in the degree of developed segregational heterogeneity, and two modifications of the metal with almost the same degree of structural heterogeneity, which differ in the running time as a part of the operating equipment are studied. It is shown that a decrease in the intensity of the segregational damage of the metal structure has almost no effect on the level of the strength characteristics, but is accompanied by an increase in the plastic properties and toughness of the metal. We present the results of studying crack resistance of centrifugal-cast pipes (steel 15KhlMlF) under static, cyclic and prolonged static loading in conditions of high-temperature creep. It is shown that an increase in the degree of structural heterogeneity of the CFC steel adversely affects the characteristics of static crack resistance and cyclic crack resistance as well, but to a far lesser extent and has little if any effect on the crack resistance of the CFC steel at creep. Cyclic crack resistance slightly decreases with increase of the operating time of the metal in functioning pipelines, whereas the characteristics of the prolonged static crack resistance get worse significantly. It is shown that welded joints of the CFC pipelines have a substantially lower crack resistance under creep conditions compared to the base metal. Statistical processing of the experimental data is used to get kinetic diagrams of cyclic and prolonged static crack resistance of 15X1M1F CFC-steel in creep conditions. The results of practical applications of the obtained crack resistance characteristics of the metal of the CFC pipes are demonstrated with a focus on the problems of ensuring the reliable operation of the steam pipelines of thermal power plants at the end of their service lifetime.

Hydrogen assisted crack initiation and propagation in nickel-cobalt heat resistant superalloys

It has been investigated the Ni-Co alloys (obtained from powder 0.1...0.3 mm under hot gaseous (in argon) isostatic pressure (up to 300 MPa) (Ni60Co15Cr8W8Al2Mo3) (Firth Rixon Metal Ltd, Sheffield) and deformed (obtained by vacuum induced remealting) materials (Ni62Cr14Co10Mo5Nb3Al3Ti3) for gaseous turbine discs. Investigation has performed in the range of temperature 25…800°С and hydrogen pressure up to 70 MPa. By the 3D visualization of crack morphology it has been discovered the structure of fatigue crack surface and established the refer points on crack path, including the boundary between the matrix and intermetallic particles (400×200 μm), crack opening, structural elements distributions on the surface for selection of next local areas for more precision fracture surface and TEM examinations. Hydrogen influence on cyclic crack resistance parameters appears in the decreasing of loading cycles number (with amplitudes 15 MPa) in hydrogenated specimens of both alloys and increase with hydrogen concentration. At the highest hydrogen saturation regimes of Ni60Co15Cr8W8Al2Mo3 alloy (800°С, 35 MPa Н2, 36 hours, СН = 32.7 ppm) number of cycles, which necessary for crack initiation is 3 times less in comparison with specimen in initial state. At crack initiation step in hydrogenated Ni56Cr14Co15Mo5Al3Ti3 alloy it has been established that before intermetallic inclusion (400×200 μm) local stresses increased, after its passing – has decreased. By fracture surface investigation it has been found the micro cracks up to 40 μm. Thin structure of heat resistant superalloys has characterises by disperse phase agglomeration with dimensions from 5 to 30 nm and crack propagation has a jumping character with no less then 50…70 nm steps.

Specific Features of the Fatigue Fracture of Welded Joints of 34KhN2MA Steel Formed by Electrodes with Different Phase Compositions

We study the cyclic crack resistance of the metal of welded joints of 34KhN2MA thick-plate steel obtained with the help of ferritic and austenitic electrodes. It is shown that the weld metal has a higher crack resistance than the base metal only within the second part of the kinetic diagrams of fatigue fracture. In the first and third parts, the characteristics of the weld metal are worse. The results of fractographic investigations demonstrate that the decrease in the fatigue crack-growth resistance in pure austenitic welds is explained by the presence of hot cracks in the zone between the near-root metal of the welded joint and the base metal. As for the mixed ferrite-austenitic welds, the decrease in the fatigue crack-growth resistance is explained by inadmissibly large slag inclusions creating additional stress concentration and deteriorating the characteristics of cyclic crack-growth resistance.

Determination of babbit mechanical properties based on tin under static and cyclic loading

Based on the results of studies of babbitt on the basis of tin under static loading under three types of stress state, the parameters of the criterion for the equivalence of stressed states were refined and a single diagram of the babbitt deformation was obtained. It is shown that the criterion of equivalence for static loading should contain the first principal stress and stress intensity. With cyclic loading, the first main voltage can be used as a criterion. The stages of development of fatigue cracks are described and it is logical to use a statistical approach to reveal the boundary of the transition from short cracks to macrocracks, based on a significant difference in the characteristics of the dispersion of the crack speeds at these two stages. The results of experimental studies of the cyclic crack resistance of babbitt are presented and the parameters of this boundary are obtained.

Analysis of Methodological Framework for Computer Strength Justification of Steel Structures at Operating NPP Units

Over the last decade, new national regulatory documents on the design and assessment of the technical state of building structures, in particular steel ones, have been put into force in Ukraine to replace relevant former USSR regulations. The experience of applying new national regulatory documents indicates certain incorrect provisions, which can potentially cause catastrophic consequences in case of failure of steel building structures of corresponding facilities and(or) hazardous production capacities. The paper presents the analysis of Ukrainian regulations to check compliance of available methodologies for computer strength justification of steel structures. It is established that current regulatory documents of Ukraine do not contain a description of methodologies and procedures (formulae) with regard to calculations of steel structures on resistance to brittle fracture and cyclic crack resistance. The analysis of a number of publications was performed to define methods for the calculation of steel structures to check endurance, cyclic crack resistance and resistance to brittle fracture.