Values Of Plastic Deformation Research Articles

Wear Rate, Tribo-Corrosion, and Plastic Deformation Values of Co-Cr-Mo Alloy in Ringer Lactate Solution.

This study investigates the tribocorrosion performance of a cast Co-Cr-Mo alloy prepared using casting and electromagnetic stirring (EMS) at specific frequencies. The tribocorrosion behaviour of the alloy was evaluated when exposed to Ringer's lactate solution to optimize the EMS parameters and improve its properties. The research focuses on biomedical implant applications and explores how EMS affects alloy wear and corrosion resistance. As did the friction coefficient and wear volume, the wear rate of samples produced with EMS frequencies of 75 Hz and 150 Hz decreased. These improvements are attributed to the ability of EMS to refine grain size and homogenize the microstructure, thereby increasing the resistance to tribocorrosion. Techniques such as scanning electron microscopy (SEM) and profilometry were used for surface and wear analysis, while mechanical properties were evaluated through instrumented indentation tests. The findings confirm that EMS improves the alloy's durability and tribocorrosion resistance, making it highly suitable for demanding biomedical applications such as joint replacements. This highlights the importance of advanced manufacturing techniques in optimizing biomedical alloys for simulated body conditions.

Structural Performance of Bolted Lateral Connections in Steel Beams under Bending Using the Component-Based Finite Element Method

Structures must provide strength, stability, and stiffness to buildings and at the same time be efficient. This study addressed the effect of design elements and parameters on the strength of bolted lateral connections in steel beams under bending using the component-based finite element method. The variables evaluated were plate thickness, horizontal and vertical spacing between bolts, and geometric arrangement of bolts. Finite element software was used to evaluate the stress state of the junction plate, its plastic deformation, and bolt shear. A sensitivity analysis was performed to determine which bolt arrangements result in safer and more efficient designs using the same components. Stress distribution within the junction plate and plastic deformation values were used to evaluate the structural performance of the joints according to EuroCode 3. The results showed that placing bolts near the edge of a plate affected the bolts’ utilization, especially with thinner plates. Additionally, introducing an offset between central and outer bolt rows is not recommended as it worsened the stress distribution and the structural performance.

Numerical model of aneurysm formation in vascular grafts

Background. Using numerical modeling to study biomechanics of implantable devices for cardiovascular healthcare can help specialists understand underlying mechanisms of clinical complications caused by these devices.Aim: To describe the results of numerical modeling of aneurysm formation in vascular grafts based on the simulation of degradation of their mechanical properties.Material and Methods. The simulation was carried out using a three-dimensional computer model obtained by high-resolution computed tomography of the vascular graft “KemAngioProtez” (CJSC “NeoKor”, Russia). Using the 3D model obtained with a specialized script in the Abaqus/CAE environment (Dassault systems, USA), we have simulated the decrease in the elastic modulus (from 100 to 10%) with post-threshold stresses in the material and the accumulation of plastic strain.Results. Undergoing 150 loading cycles, the vascular wall in the model swelled up to 0.7 mm in the radial direction, and its mechanical properties degraded significantly (by 90% compared to baseline) due to prolonged pressure exposure. The value of maximum plastic deformation was 0.55%.Conclusion. Numerical modeling of graft mechanical properties degradation can assist in qualitative and quantitative assessment of the areas of aneurysm formation. The method makes it possible to visualize the swelling areas and can be used as a valuable tool to complement the existing approaches to studying vascular grafts, and biografts in particular.

Tensile properties of GH4169 superalloy for smooth and notch specimens determined by tests and simulation

Tensile mechanical tests of GH4169 superalloy were performed for smooth and notch specimens at room temperature. Moreover, a finite element method (FEM) was employed by an Abaqus simulation software to provide the tensile test processes during elastic and plastic deformation. Comparing the experimental measurements with the simulation and analysis results, it was found that the [Formula: see text] value decreased with increasing [Formula: see text] value, and the [Formula: see text] value of smooth and notched specimens were close to the [Formula: see text] value of both elastic deformation and plastic deformation. Reasonable explanations were also provided for the stress concentration factor [Formula: see text] and strain concentration factor [Formula: see text].

Pengaruh Penambahan Filler Al2O3 dan TiO2 pada Resin Polyester terhadap Sifat Fisik dan Mekanik

Polyester composites have been developed to have high strength and light density, but the fracture occurs due to very little plastic deformation or low strain values, pre-failure detection is difficult in these composites due to the rapid propagation of cracks in the composite system. To increase the strength and delay failure, the addition of filler in the form of Al2O3 and TiO2 particles is carried out. The use of particles as fillers in polymer composite materials is increasingly being developed. In this study, Al2O3 and TiO2 particles (0%, 2%, 4%, 6%, 8%, 10% vol.) were added in polyester matrix BQIN EX 157. by casting method; the liquid homogeneous mixture was carefully poured into a simple mould to be air dried. The composites were cut to serve as specimens for density test, mechanical tests such as tensile and compressive tests. The results showed a density of 1.23 g/cm3, a maximum strength of 47 MPa for 2% additional Al2O3 filler, (tensile, decreasing ̴11%) and 120 MPa (compressive) for a maximum of 2% additional Al2O3 (compressive, decreasing ̴3%) with TiO2 filler. The decrease in strength was caused by uneven particle dispersion, voids and agglomeration that occurred during the casting process.

Approaches to Control Crazing Deformation of PHA-Based Biopolymeric Blends.

The mechanical behavior of polymer materials is heavily influenced by a phenomenon known as crazing. Crazing is a precursor to damage and leads to the formation of cracks as it grows in both thickness and tip size. The current research employs an in situ SEM method to investigate the initiation and progression of crazing in all-biopolymeric blends based on Polyhydroxyalkanoates (PHAs). To this end, two chemically different grades of PHA, namely poly(hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV), were melt-blended with polybutyrate adipate terephthalate (PBAT). The obtained morphologies of blends, the droplet/fibrillar matrix, were highly influenced by the plasticity of the matrices as well as the content of the minor phase. Increasing the concentration of PBAT from 15 to 30 wt.% resulted in the brittle to ductile transition. It changed the mechanism of plastic deformation from single craze-cracking to homogeneous and heterogeneous intensified crazing for PHB and PHBHV matrices, respectively. Homogeneous tensile crazes formed perpendicularly to the draw direction at the initial stages of deformation, transformed into shear crazes characterized by oblique edge propagation for the PHBHV/PBAT blend. Such angled crazes suggested that the displacement might be caused by shear localized deformation. The crazes' strength and the time to failure increased with the minor phase fibers. These fibers, aligned with the tensile direction and spanning the width of the crazes, were in the order of a few micrometers in diameter depending on the concentration. The network of fibrillar PBAT provided additional integrity for larger plastic deformation values. This study elucidates the mechanism of crazing in PHA blends and provides strategies for controlling it.

Neural network modeling of rutting performance for sustainable asphalt mixtures modified by industrial waste alumina

Considerable efforts have been devoted to developing a sustainable approach to road construction. The use of recycled concrete aggregate (RCA) obtained from construction-demolished concrete as a substitute for natural aggregate (NA) has increased interest. However, the inferior performance of the resulting RCA mixtures requires adding other improvement materials. To build on the few existing works in this area, the present study investigated the role of waste alumina (Al) as a reinforcement agent when added at rates of 1 %, 2 %, and 3 % by mixture weight. The experimental program consisted of volumetric properties analysis accompanying the Marshall test, dynamic creep test, and wheel tracking test. This study revealed that RCA-mixtures reached their typical Marshall and volumetric properties at 4.5 % binder content recording an increasing increment of 10 % compared to NA-mixtures which needed only 4.1 % binder content. Overall, all the utilized Al dosages improved the rutting resistance; optimally, 2 % of Al decreased the rutting depth by 26 %. This dosage also increased the index of plastic deformation, resilient modulus, and flow number values by 30 %, 16 %, and 23 %, respectively. The artificial neural network statistical technique produced a robust model (R 2 = 0.995) correlating the performed tests’ outcomes with rutting values.

Development and testing of knife-plate connected steel panel dampers

Steel panel dampers (SPDs), consisting of the inelastic panel and elastic connecting segments, have been widely used in steel building structures commonly with brace- or stub-column-type configurations, especially in high seismic regions. The elastic connecting segments of stub-column-type SPDs were usually significantly enlarged to ensure their elasticity under the associated extreme loads of the inelastic panel. With the aim of improving the structural efficiency and ductility capability of SPDs, a novel design, named as knife-plate-connected SPD (KSPD), was proposed in the study. The proposed KSPD consisted of one steel panel and two boundary-columns on the horizontal sides with pinned column ends, which were achieved by knife-plate details, connecting to the framing systems. The designed configuration of KSPDs potentially reduced the aspect ratio of the steel panels for easily achieving shear yielding while remaining the stud-column appearance, and mitigated the deformation amplification of the steel panels usually occurred in conventional stub-column-type SPDs. Five full-scale KSPD specimens with various configurations of the panel stiffeners have been experimentally examined and compared under cyclic loadings including fatigue cycles. The feasibility of the KSPD design was experimentally validated, and the developed KSPDs were verified to achieve stable energy dissipation and significant ductility of approximate ten and cumulative plastic deformation (CPD) value up to 796. For the design purpose of the members, the width-to-thickness limits of the steel panel were established to prevent panel buckling and the sub-panel edge fracture upon the test results, respectively, and a design inequality of the knife plates upon strengths was developed to prevent the fracture of the knife plate. Finally, the design suggestions of the proposed KSPD were summarized upon the experimental results and findings of the study.

Monitoring interactions through molecular dynamics simulations: effect of calcium carbonate on the mechanical properties of cellulose composites

This study describes the preparation and characterization of full atomistic models of amorphous cellulose and calcium carbonate (CaCO3) nanocomposite to assess its mechanical properties within and beyond the elastic limit via molecular dynamics simulations. The interactions by hydrogen bond and conformation of the cellulose molecules from the assessment of torsional angles were specifically monitored during the tensile stretching simulations to get deep understanding of the possible structural changes produced in the material during the deformation. On the one hand, the results showed a favorable interaction of the cellulose matrix with the calcium carbonate nanoparticle, with the electrostatic contribution being dominant over the van der Waals component. The determined mechanical elastic constants indicated that the inclusion of the CaCO3 nanoparticle provided an increase on the rigidity of the composite system of 15%, 18% and 19% in the Young, shear or bulk modulus, respectively. On the other hand, using extension and compression simulations, the recovery capacity of the material systems was also assessed in terms of plastic deformation. The elastoplastic behavior was observed for either the neat or the CaCO3 nanocomposite, with an elastic limit around 2.5%. The results also showed that the presence of the CaCO3 nanoparticle produced higher values of plastic deformation in the composite material compared to the neat cellulose system and thus decreased the flexibility of the material. A hysteresis mechanism was identified together with irreversible conformational changes on the cellulose molecules which would explain the plastic deformation observed on the cellulosic systems. It was concluded that the higher plastic deformations observed in the nanocomposite system would be a result of the disruption of the network of hydrogen bonds and the associated decrease on the number of possible interactions.Graphical

DEFORMATION-HARDENING FIBER COMPOSITES: DEFINITION, PRINCIPLES OF PREPARATION AND PROSPECTS OF APPLICATION

The article presents the results of a study of the effect of microfiber based on high - density polyethylene and polybenzoxazole on the axial stretching of fibrocomposites. The definition of the phenomenon of deformation hardening of a hydration hardening fibrocomposite is proposed. Characteristic deformation diagrams of various fiber - reinforced composites are obtained and analyzed. The ranges of values of deformation hardening and plastic deformation are determined, as well as the factors that determine these characteristics are stated. From a practical point of view the increase of the resistance of fibrocomposite while maintaining its integrity in conditions of high values of plastic deformations opens up the possibility of using such materials for repairing damaged superstructures and ceilings, durable (heat and bio - resistant) sealing of joints of precast reinforced concrete structures.

Mechanical characteristics of H-shaped shear panel damper fabricated by SPHC steel according to stiffener reinforcement and stud support installation

In this study, cyclic loading tests were conducted at a constant deformation amplitude to investigate the mechanical characteristics of an H-shaped shear panel damper (HSPD)1HSPD: H-shaped shear panel damper; FE: Finite element.1 fabricated with the use of SHPC steel. Two experimental conditions were established according to the test parameters for the damper unit and damper system (damper supported by studs). For each experimental condition, two types of HSPDs were applied according to the presence or absence of stiffener reinforcement. The experimental results of the damper supported by studs showed that the elastoplastic behavior of the damper part was similar to that of the damper unit. Additionally, it was shown that the stud maintained its elastic state until the end of the test. Furthermore, it was found that when the damper was reinforced with a stiffener, the plastic deformation capacity of the damper was improved significantly compared with the case in which the stiffener was not reinforced. The effect of the stiffener reinforcement was also investigated based on nonlinear finite element analysis. The plastic strain distribution of the HSPD panel was evaluated based on the analyzed results that tracked the load–deformation relationship of the experimental results. As a result, the HSPD panel part was segmented by the stiffener and the width-to-thickness ratio was reduced so that the distribution of the plastic deformation values in the panel was relatively stable, and the deformation in the out-of-plane direction could be suppressed. The results showed that the shear buckling for the same shear deformation could be delayed according to the effect of the width-to-thickness ratio of the panel which was reduced by the reinforcement of the stiffener.

Determination of the strain rate effect in electromagnetic forming processes

Effect of strain rate, quantity of plastic deformation and temperature of material on characteristics of material at electromagnetic forming is considered. It is shown that strength characteristics increase with growth of strain rate, and the plasticity increases with an increase in the value of plastic deformation and temperature. The variant of writing of the constitutive equation considering these changes is offered, and its use in calculations can significantly increase efficiency of calculations of operations of electromagnetic forming.

The Influence of Cutting Parameters on Plastic Deformation and Chip Compression during the Turning of C45 Medium Carbon Steel and 62SiMnCr4 Tool Steel.

The paper deals with the issue of cutting zone and chip compression. The aim was to analyse the microstructure transverse section of the cutting zone on a metallographic cut, due to determined values of chip compression and plastic deformation, which affect the cutting process efficiency. The tested cutting tool material was coated with cemented carbide. The selected workpiece materials were C45 medium carbon steel of ISO grade and 62SiMnCr4 tool steel of ISO (W.Nr. 1.2101) grade. In the experiments, a DMG CTX alpha 500 turning centre was used. The cutting speed and feed were varied, and the depth of the cut was kept constant during the turning. The plastic deformation and chip compression determine the efficiency of the cutting process. The higher compression requires more work to perform the process and, therefore, it requires more energy for doing so. With the increase of the cutting speed, the deformation for C45 steel is decreased. The rapid deformation reduction was observed when the cutting speed was increased from 145 m/min to 180 m/min. Generally, deformation is decreasing with the increase of the feed. Only at a cutting speed of 145 m/min was the deformation elevation observed, when the feed was increased from 0.4 mm to 0.6 mm. During the turning of the 62SiMnCr4 tool steel we observed an error value at a cutting speed of 145 m/min and a feed of 0.4 mm was the middle cutting parameter. However, feed dependence was clear: With an increase of the feed, the plastic deformation was decreasing. This decreasing was more rapid with the increasing of the cutting speed. Besides plastic deformation, there was analysed chip compression as well. With the increasing of the cutting speed, there was a decrease of the chip compression. Due to a lack of information in the area of the chip compression and the plastic deformation in the cutting process, we decided to investigate the cutting zone for the turning of tool steels 62SiMnCr4, which was compared with the reference steel C45. The results could be applied to increase the efficiency of the process and improvement of the surface integrity.

Effect the hot deformation on austenite structure of the carbon steel

Purpose. Determination influence temperature and degree of hot plastic deformation carbon steel on the development secondary recrystallization of the austenite. M ethodology. The carbon steels with a concentration of carbon by 0.55 and 0.65%, which correspond to the maximum and minimum values within the brand composition for all-rolled railway wheels, were used as material for the research. The number of other chemical elements met requirements of the documentation for railway wheels. The samples for research had the form of cylinders with a diameter of 20 and a height of 40 mm. Different degrees of plastic deformation were obtained during compression with a deformation rate of 10-3 s-1. Chamber-type electric heating furnaces were used to heat the samples to temperatures of the hot pressing. When heating samples, measures are taken to prevent oxidation and a local decrease concentration of the carbon atoms on their surfaces. After heat treatment of the samples and mechanical preparation of the surface, detection of the structure of austenite was carried out using of the etching based on a mixture of solutions hydrochloric and picric acids. The structure of the steels was investigated under a light microscope. The size of the austenite grain was determined by the methods of quantitative metallographic. Findings. The study structure of the carbon steel determined that under conditions of increasing the annealing temperature, the occurrence of structural heterogeneity of the austenite is caused by a change at mechanism of the development secondary recrystallization. Starting from 10% of hot pressing, in proportion to the degree of plastic deformation, development secondary recrystallization by the mechanism of movement of the large-angle boundaries leads to grinding of the austenite grain and the formation of a homogeneous structure. At degrees of hot deformation less than 10%, the density of dislocations is not enough to form a nucleus for the development secondary recrystallization by the mechanism of movement of the large-angle boundaries. As a result, recombination of the dislocations in grains of hot deformed austenite will occur much faster, which will lead to the separation of grains into fragments. Their size will be determined by the density of dislocations introduced during hot pressing. Disorientation angles between fragments have intermediate values between boundaries with large disorientation angles and subboundaries, which determines their low mobility. For such a structure, development of the secondary recrystallization in austenite will occur by the mechanism of grain boundary dissolution. As a result, there is significant heterogeneity structure of the austenite, which is determined by the difference in sizes between neighboring grains up to several times. Originality. Depending on the conditions of hot pressing of the carbon steel, the value of plastic deformation is determined, which separates development the secondary recrystallization of the austenite by qualitatively different mechanisms. At a low value of hot deformation, when the density of dislocations is not sufficient for the formation of a nucleus of the secondary recrystallization by the mechanism movement of the large-angle boundaries, the growth austenite grains occurs by the mechanism of dissolution of the grain boundaries. Practical value. Determining effect temperature and degree of hot plastic deformation on the mechanism of the development secondary recrystallization will allow to the optimize tenology crimping the blank of the all-rolled railway wheel.

МОДЕЛЮВАННЯ ПОВЕДІНКИ ЛОКАЛЬНО НАВАНТАЖЕНОЇ ПОЛОСИ З ПСЕВДО-ПРУЖНО-ПЛАСТИЧНОГО МАТЕРІАЛУ ПРИ ВЕЛИКИХ ПЛАСТИЧНИХ ДЕФОРМАЦІЯХ

Introduction. Currently, a number of models are known to describe the thermomechanical behavior of functionally inhomogeneous materials, in particular alloys with shape memory (SPF) [3; 4]. Most of them are based on classical ideas, ie aim to directly describe the experimental data obtained on different macrosamples under simple and complex loads. However, as established in experimental studies, the behavior of the material at a point in the body in the General case may be different from the behavior of the sample as a whole [5]. In the considered problems the numerical procedure of calculation of the diagram of material which represents a curve which surrounds a family of diagrams of the material constructed for certain laws of change of speed of a front of rupture of deformations is developed. Purpose. The aim of the work is to apply a nonlinear phenomenological model, which describes the properties of alloys with shape memory and thermo-pseudo-plastic behavior (TPPM) of the material at the point to the problem of modeling a locally loaded strip of pseudo-elastic-plastic material at large plastic deformations. Compare the results of modeling in geometrically linear and nonlinear formulations for large plastic deformations. Results. The behavior of the locally loaded weakened strip of pseudo-elastic-plastic material under its non-stationary loading is modeled in the work. The authors used a nonlinear phenomenological model of the material to solve the above problem, which allows to describe a number of experimental data on different samples under different conditions. A comparison of the results obtained in geometrically linear and nonlinear formulations with large plastic deformations. Conclusion. Modeling the behavior of pseudo-elastic-plastic material with large plastic deformations requires the use of nonlinear mathematical models that could more accurately describe and predict the behavior of such a body. The behavior of the locally loaded weakened strip of pseudo-elastic-plastic material under its non-stationary loading is modeled in the work. The authors used a nonlinear phenomenological model of the material to solve the above problem, which allows to describe a number of experimental data on different samples under different conditions. A comparison of the results obtained in geometrically linear and nonlinear formulations with large plastic deformations. Numerically compared intensity fields at symmetric and asymmetric loading It is established that at plastic deformations up to 6% (small deformations) the discrepancy of results in points of localization of deformation does not exceed 5%. With increasing values of plastic deformation (more than 7%, large deformations), the discrepancy of the results can increase significantly and in the vicinity of the possible creation of the neck to reach 20%.

Mathematical model of force and deformation interaction of strip and rolls during rolling with intense plastic deformation

The operating conditions of oil and gas pipes determine strict requirements for their structure and properties, in particular, corrosion resistance. It is known that the mechanical properties and corrosion resistance of steels significantly depend on the degree of grinding of the grain and the homogeneity of the structure. One of the ways to form a fine-grained structure, increase mechanical and corrosion properties is intense plastic deformation. In order to determine the effect of intense plastic deformation on the deformation treatment of steel strips, a scheme of a simple rolling process with a blank roller was developed. The possible influence of intense plastic deformation in such a scheme on the structure of the metal required the development of a mathematical model, the purpose of which is to determine the magnitude of the true plastic deformation. Based on the results of mathematical modeling, laboratory experiment in rolling strips and determining their corrosion resistance in the proposed scheme, it is envisaged to develop an industrial installation for processing the inner surface of pipes. The mathematical model of the proposed rolling scheme with a certain value of intense plastic deformation is expected to be described in four stages. The first is to determine the force of pressing the idler roller into the material at a fixed amount of force applied to the lever of the mechanism. The second is to determine the magnitude of the pressure force of the idler roller on the rolled strip and the working roll. The third is to determine the depth of indentation of the roller in the strip at a given load in the absence of rotation of the rolls. Fourth - determining the actual and equivalent degree of deformation of the strip by a blank roller. Conclusion. Comparison of equivalent deformation roller and deformation rollers with a diameter of 180 mm with compression =0,2 мм; =1,15; =0,139 shows an order of magnitude greater deformation of the roller. The mathematical model of the offered way of rolling with intensive plastic deformation is developed, the carried-out calculations give the chance to assume considerable changes of structure of material, reduction of the sizes of grains. The latter should certainly be reflected in the change of physical and mechanical properties of the material, namely the increase of its corrosion resistance and the level of mechanical properties.

Investigation of the effects of shot overlap and rigid body assumptions on surface layer characteristics in shot peening simulation

As an important mean of shot peening (SP) research, finite element simulation has been widely and successfully employed in estimating the surface characteristic and residual stress distribution after SP treatment. In this study, the effects of shot overlap and rigid body assumptions on dimple geometry and residual stress distribution in depth were discussed via the validated ordered dimple pattern and stochastic dimple pattern SP models for quenched and tempered 42CrMo steel. The results show that shot overlap assumption has a great influence on the surface plastic deformation of peened material. The simulated value of plastic deformation is much larger than the experimental value, which results in the residual stress of the overlapping shot SP model deviating from the actual result seriously. For the prediction of the residual stress distribution, the shot must be set as an elasto-plastic body when the number of shot is large. The shot can be set as a rigid body for the aim of reducing the calculation time when the number of shots is small. In addition, the influence of material hardness on residual stress and equivalent plastic strain (PEEQ) was investigated via simulating the residual stress and PEEQ of different hardness materials treated by SP process . • It is necessary to choose the non-overlapping shot in SP simulation when the dimple geometry and residual stress distribution is predicted. • It is more accurate to choose elasto-plastic shot in SP model for the dimple geometry prediction. • The shot can be set as a rigid body when the number of shot is small.

Estimation of Local Plastic Deformation in a Bulk of Polycrystalline Materials

The article deals with the local plastic deformation analysis after cold forming. The technology of drawing seamless steel tubes was used to obtain cold-formed samples. The tubes were manufactured by a Tinius Olsen 300ST tensile tester with a 6 ° and 12 ° die drawn without and with an inner mandrel. Based on orientation size recalculated by stereology and applying Monte Carlo method a mathematical conversion model was developed. Implemented model together with surface measurements and structure characteristics were used to get the orientation to the size of the deformation. Thus, the actual (logarithmic) deformations and local stresses were determined. Comparison of experimentally measured values of the actual local plastic deformation with the deformation calculated found on the model simulation in the Deform program defined the significance of the differences assessed by means of a statistical T-test. All differences in the values of the local plastic deformation with respect to the position were evaluated as statistically insignificant and therefore the difference between the experimental calculation and the simulation is random.

Incorporation of Temperature and Plastic Strain Effects into Local Approach to Fracture.

An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect of both temperature and the plastic strain value on the crack nuclei (CN) generation rate in iron and ferritic steels is presented. It is shown how the plastic strain and temperature affect CN formation rate and, as a consequence, govern the shape of the temperature dependence of fracture toughness KJc and its scatter limits. Within the framework of the microscopic model proposed, dependences of the CN bulk density on the plastic deformation value and temperature are predicted. Convenient approximation dependences for incorporating this effect into the LA are suggested. The experimental data of reactor pressure vessel steel and cast manganese steel demonstrate that the use of these dependences enables one to predict, with sufficient accuracy, the effect of temperature on the value of fracture toughness and its scatter limits over the DBT region. It is shown that accounting for both the temperature and strain dependence of CN bulk density gives rise to the invariance of parameters of the Weibull distribution to temperature.

Influence of deformation degree of austenitic steels welded joints on structural state and internal stresses felds in weld line zone

Nowadays initial assessment of welding quality is performed by testing equipment with increased loads (high pressure) at technical devices of hazardous production facilities. Test requirements are regulated by standardized documents of the Federal Service for Environmental, Technological and Nuclear Oversight of Russia (Rostekhnadzor). Recently, along with traditional tests, a “stress test” was used – the essence of which is to load pipeline section to the yield point, followed by leak test. However, in scientifc publications there is practically no information about physical processes occurring in the base metal and in welded joints during such tests. In addition, effect of preload (deformation) on the parameters of substructure and internal stresses feld in welded joints of austenitic steels and, consequently, on the further trouble­free operation of the tested equipment was not evaluated. The paper analyzes changes in structural state and values of internal stresses in the samples of austenitic steel under the action of high loads. It substantiates the use of modulated current welding with automatic control of heat input process in molten weld pool. The admissible limits values of plastic deformation are argued when testing technical devices with high pressure for this type of steel. In order to reduce the risk of damage to austenitic steels welded joints of technical devices of hazardous industrial facilities, performed by pulsed welding with small­drop transfer, and to exclude formation of microdefects in them, high pressure tests (stress test) can be performed under loads that create deformations in metal, not exceeding 5 %. For joints welded by manual arc welding, deformations should be less than 5 %. Welded joints made by pulsed welding with large­drop transfer (with and without defects) are not recommended to be tested with high pressure.