Showing papers in "Strength of Materials in 2020"
TL;DR: In this paper, a mathematical model of the formation of stress and strain fields during electrodynamic treatment, which is based on the motion of an elastoplastic medium, does not take into account the effect of ECPs on dynamic relaxation processes.
Abstract: The development of energy-efficient methods of controlling the stress state of metallic materials and welded joints is topical for modern production. One of such methods is electrodynamic treatment (EDT). It is based on the passage of electric current pulses (ECP) through the metal, time-synchronized with an impact load initiated by electrodynamic forces. In this case, an electrodynamic deformation process and a process of formation of elastic strain waves occur simultaneously in the material being treated; they are defined as “electrodynamic impact”, the result of which is a local stress relaxation in the metal. The developed mathematical model of the formation of stress and strain fields during EDT, which is based on the motion of an elastoplastic medium, does not take into account the effect of ECPs on dynamic relaxation processes. A computational and experimental assessment of the effect of ECPs, which is based on the experimental assessment of the stress state and microindentation of AMg6 aluminum alloy plates after EDT without and with the passage of ECPs through the metal being treated, has been performed by the mathematical modeling of the EDT process taking into account microindentation results. The passage of ECPs contributes to an increase in tensile plastic strains and hence to an increase in residual compressive stresses (provided that the specimens to be treated are rigidly fixed). The reliability of the procedure has been confirmed by the results of evaluating the distribution of residual welding stresses in AMg6 alloy butt joints after EDT.
12 citations
TL;DR: In this article, the temperature influence on the structural and mechanical properties of AISI 420 stainless steel is studied, and the material was examined with nanoindentation, macrohardness, scanning electron microscopy, light microscopy and X-ray diffraction.
Abstract: The temperature influence on the structural and mechanical properties of AISI 420 stainless steel is studied. The iron-based alloy underwent normalizing at three temperatures 975, 1025, and 1075°C for 1 h, followed by annealing at temperatures ranging from 250 to 650°C for 2 h. At both treatment stages, steel is air-cooled. The material was examined with nanoindentation, macrohardness, scanning electron microscopy, light microscopy, and X-ray diffraction. For each normalizing temperature, the two stages of the mechanical behavior were observed. At the first stage, in which macrohardness and nanohardness decrease slightly over temperature range of 250–450°C, and the second one is characterized by a significant loss of these mechanical properties corresponding to 550 and 650°C temperatures. At the microstructural level, softening of AISI 420 steel occurs due to dissociation of large cementite into smaller spheroids.
10 citations
TL;DR: In this article, the assembly of a ship-to-shore portal crane after 33 years of service was studied on the possible loss of the initial brittle fracture resistance level by rolled steel sheets.
Abstract: The assemblies of a ship-to-shore portal crane after 33 years of service were studied on the possible loss of the initial brittle fracture resistance level by rolled steel sheets. Strain gauge measurements were used to predict the level of operating stresses. The latter and a decrease in the Charpy impact strength were established to be distinctly related. Transverse specimens are shown to generally exhibit a lower impact strength level as compared to that of the longitudinal ones. The differences in the brittle fracture resistance of specimens, differently oriented with respect to the stamping direction, are revealed to be growing with the metal degradation level. This level along the stamped fibers is demonstrated to increase with a decrease in the sheet thickness, which can be explained by the effect of aggressive marine environment as a factor of metal hydrogenation.
10 citations
TL;DR: In this paper, a priori estimates of the maximum permissible value of free swelling and damaging dose for steel under various irradiation temperatures were given for 08Kh18N10T steel.
Abstract: The paper provides results of the study of correctness of the mathematical model that includes the influence of stresses on irradiation-induced swelling of metal in the problems of elastic-plastic deformation mechanics. The present-day approaches to modeling irradiation-induced swelling, which take into account a damaging dose, irradiation temperature, and the effect of the stress state on the swelling deformation, are discussed. The constitutive equations that describe the elasticplastic deformation processes allowing for the influence of a stress mode on the irradiation-induced swelling in metal are put forward. Analysis of these equations has made it possible to find the conditions that ensure correctness of the plasticity equations considered and to make a lower-bound estimate of the maximum permissible value of free swelling and irradiation dose. A priori estimates of the maximum permissible value of free swelling and damaging dose are given for 08Kh18N10T steel under various irradiation temperatures. In the practice of strength design such estimates are needed at the stage of problem formulation in order to analyze adequacy of input data, for they enable one to assess a prior the possibility of solving the problem for a given temperature and irradiation dose. The boundary-value problem that describes non-isothermal processes of elasticplastic deformation including swelling strains has been defined in the form of a nonlinear operator equation. Based on the findings regarding the correctness of the constitutive equations, we have established the existence and uniqueness of the generalized solution and its continuous dependence on applied loads, thermal strains and swelling strains. The convergence of the method of elasticity solutions and the method of variable elasticity parameters has been studied as applied to a thermoplasticity problem including irradiation-induced swelling strains.
9 citations
TL;DR: In this paper, the Vlasov-Pasternak two-parameter elastic bed model was used to simulate the stress state of the bonding layer of the adhesive layer. And the problem was reduced to a system of ordinary differential equations in displacements and rotation angles of bearing layers.
Abstract: A new mathematical model of adhesive joint was developed and experimentally validated, in which the Vlasov–Pasternak two-parameter elastic bed model was used to simulate the stress state of the bonding layer. According to this elastic model, the adhesive layer was regarded as a membrane located in the middle of the adhesive layer thickness, between which and the bearing layers there were elastic elements. The outer bearing layers were regarded as beams in the Timoshenko approximation. The tangential stresses were considered to be constant across the thickness of the adhesive layer, and the normal (cleavage) stresses to be variable. This approach allows one to describe different types of boundary conditions for tangential stresses in the adhesive layer at the ends of the adhesive line, viz.: there are no tangential stresses at the edge of the adhesive joint if there are no adhesive spews, or the tangential stresses reach a maximum at the edge of the adhesive line if these spews exist. The problem was reduced to a system of ordinary differential equations in displacements and rotation angles of bearing layers. The system was solved by the matrix method. It was found that the sagging of the adhesive greatly reduced the maximum cleavage stresses in the adhesive layer. Tensile tests of adhesive lap-jointed metal rods were carried out. The proposed model was used to evaluate the strength criterion of the adhesive layer. It was shown that the best approximation of calculated and experimental data was provided by the maximum principal stress criterion. The proposed approach can be used to solve joint design problems.
9 citations
TL;DR: In this paper, the residual stresses and deformation in terms of the thermoelastoplastic theory were simulated with the finite element method using ANSYS 13.0 software for a 5A06 aluminum alloy plate after welding.
Abstract: The residual stresses and deformation, in terms of the thermoelastoplastic theory, were simulated with the finite element method using ANSYS 13.0 software for a 5A06 aluminum alloy plate after welding. The butt joint thickness of the plate was 6 mm. A 3D thermomechanical model of the plate was constructed. The dimensions and distribution of residual stresses in the welded structure should be analyzed after simulation. Appropriate welding technologies were chosen to control welding residual stresses and deformation. The efficient production of an aluminum alloy for the welded structures will be provided.
8 citations
TL;DR: In this article, the LM-hardness method is used to assess the damage rate of structural elements by in-service scratching of structure element surfaces and employing portable instruments for its implementation, which can provide the rapid analysis of damage of a structural element to be diagnosed, continuous measurement of axial displacements of the embedded scratching tip, moving over the surface of this element, and statistical processing of experimental data for Weibull homogeneity coefficient computations.
Abstract: The procedure for the material damage assessment by the LM-hardness method, consisting of the in-service scratching of structure element surfaces and employing portable instruments for its implementation, is described. These instruments can provide the rapid analysis of damage of a structural element to be diagnosed, continuous measurement of axial displacements of the embedded scratching tip, moving over the surface of this element, systematization, and statistical processing of experimental data for Weibull homogeneity coefficient computations. The latter results derived via the LM-hardness method are used to assess the damage rate of the material. The advantage of these instruments is their high accuracy and performance in measuring a large number of axial displacements of the tip necessary for statistical processing as well as actual testing on vertical, ceiling, and inclined surfaces of structural elements.
8 citations
TL;DR: In this paper, closed-cell aluminum foams of varying porosities (65-75%) were produced through the stir casting technique using TiH2 (1 wt%) as a foaming agent.
Abstract: In the present study, closed-cell aluminum foams of varying porosities (65–75%) were produced through the stir casting technique using TiH2 (1 wt.%) as a foaming agent. Under the uniaxial compressive loading, the compressive stress-strain responses of these foams were examined. The finite element (FE) models of the foam were elaborated using the ABAQUS FE simulation software and realized via the ABAQUS Explicit solver. Within the test domain, the experimental results were compared with the FE-predicted ones for the same porosities and both yielded similar stress-strain responses. The energy absorption capacity, yield stress, and densification strain values of AFs obtained through FE simulation were in good agreement with the experimental results, while the predicted plateau stress values differed from the latter by no more than 4–5%.
7 citations
TL;DR: In this paper, a numerical simulation model for the first layer deposition with the smoothed particle hydrodynamics method was constructed and implemented in an LS-DYNA commercial complex.
Abstract: The additive friction stir process provides a new approach to additive manufacturing by depositing and coating of a variety of similar and dissimilar materials with imparting them exceptional mechanical properties. During this process, the filler material can be deposited layer-by-layer on the substrate effected by heat and plastic deformation due to friction between the filler rod and substrate. For understanding complex physics of this advanced process, a numerical simulation model for the first layer deposition with the smoothed particle hydrodynamics method was constructed and implemented in an LS-DYNA commercial complex. The temperature distribution, material deposition, deformation and stress state were evaluated on the basis of simulation results. The Vickers hardness distribution was also measured in the experiment to verify the stress distribution. A higher stress observed on the top layer of deposition and Vickers hardness appeared to be similar characteristics due to the relationship between stress and hardness.
6 citations
TL;DR: In this article, the experimental and theoretical investigation on ultimate strength of cold-formed steel built-up square stub columns under axial compression was described. And the reliability analysis was carried out to evaluate the appropriateness of the design standards.
Abstract: This paper describes the experimental and theoretical investigation on ultimate strength of cold-formed steel built-up square stub columns under axial compression. In total, fifteen stub columns were tested by varying the cross-sectional dimensions of specimens. Local buckling, distortion, and interaction of these buckling modes were observed. The strengths obtained from the experiment are compared to the design strengths calculated using the effective width method, which is a direct strength method in the North American Specification for cold-formed steel structures. It was observed that the effective width method conservatively predicted the strength of specimens. The reliability analysis was carried out to evaluate the appropriateness of the design standards.
6 citations
TL;DR: In this paper, the impact of different materials and application methods on the stress effect in CAD/CAM applied endocrowns was evaluated using finite elemental analysis (FEA).
Abstract: Computer-aided design/manufacturing (CAD/CAM) endocrowns are commonly applied to strengthen endodontically treated teeth with too much tissue loss. Monolithic or multilayer structures may be used for this purpose. Restorations made with multilayering technique may mimic natural teeth better. The purpose of this finite elemental analysis (FEA) research was to appraise the impact of different materials and application methods on the stress effect in CAD/CAM applied endocrowns. A 3-dimensional mathematical model simulating an endodontically treated mandibular first molar was modeled. The sample was then modified to imitate the ceramic endocrown applied molar tooth. Three FEA models were then created from this main model to simulate the following endocrown structures: 1: lithium disilicate reinforced glass ceramic, 2: monolithic zirconia, 3: multi-layered glass ceramic and glass-fiber endocrown (the core structure was composed of glass-fiber while the crown is prepared by glass ceramic). The SolidWorks/CosmosWorks programs were used as structural analysis programs. The materials used in the study were accepted as homogeneous and isotropic. A 300 N load was applied to the occlusal surfaces of the restored teeth. The results of the study are presented according to the von Mises criteria. The von Mises stresses recorded at the cavity base were 0.417–0.7, 0.6–0.85, and 0.083–0.25 MPa, respectively. The multilayering technique reduced stresses as compared to the other two different designs and materials and showed similar stress distributions with the natural tooth model. Models simulating teeth with a zirconia endocrown showed the highest stresses. The multilayering technique using fiber-reinforced glass ceramic as a core and glass ceramic as a crown reduced the stresses and showed stress distributions similar to natural teeth. This technique can be used to create biomimetic restorations with a core material, which mimics dentin (glass-fiber reinforced ceramic) and crown material, which mimics enamel (glass ceramic).
TL;DR: In this paper, the effect of different sizes of cavities on uniaxial compression strength of concrete columns was investigated based on the experiment and numerical simulation (particle flow code).
Abstract: The concrete compression strength is an effective characteristics among other properties of practical significance. Although coring testing on such members as columns is not recommended. But sometimes, for determining the concrete strength in the column, this method should be applied to the reinforced concrete one. Coring in a reinforced concrete column creates a cylindrical cavity in it, which has an apparently negative effect on the bearing capacity of the structural member. The effect of different sizes of cavities on uniaxial compression strength of concrete was investigated based on the experiment and numerical simulation (particle flow code). The results of the experiments show that the cavities have a great influence on the uniaxial compression strength. For example, if the cavity volume is calculated about 14% of the sample volume, it can reduce of the uniaxial compression strength down to 58%. If the cavity diameter is 60% of the sample width, the strength can go down to 74%.
TL;DR: In this paper, mechanically defibrillated CNF reinforced epoxy resin matrix (Epoxy-CNF) composites with various CNF volume fraction were fabricated, and their tensile modulus and ultimate strength were deteriorated by the CNF slurry addition, while the fracture elongation was increased.
Abstract: Cellulose nanofiber (CNF) is one of natural fibers, and its Young modulus and tensile strength have been estimated close to 140 GPa and at least 2–3 GPa, respectively. As the homogeneous dispersion method of CNF in polymer matrix, the chemical modification of the CNF surface or solvent exchange process are often used. However, the environmental load of these processes is large, and the chemically modified CNF is expensive. In this study, mechanically defibrillated CNF reinforced epoxy resin matrix (Epoxy-CNF) composites with various CNF volume fraction were fabricated. Their tensile modulus and ultimate strength of the epoxy composites were deteriorated by the CNF slurry addition, while the fracture elongation was increased. This can be attributed to the interaction of epoxy and water, concentration of microvoids, and CNF agglomeration. Thus, the reduced water content in Epoxy-CNF composites improves their tensile properties.
TL;DR: In this article, the authors present the results of computer simulation of the stress-strain state of a thin-walled spherical shell with an elliptical opening and the surrounding reinforcing inclusion of another material.
Abstract: The authors present the results of computer simulation of the stress-strain state of a thin-walled spherical shell with an elliptical opening and the surrounding reinforcing inclusion of another material. The effect of geometric and mechanical parameters of inclusions on the stress distribution around the opening and deformation of the shell under uniform internal pressure are investigated. The issue of stress concentration in modern leading fields of technology and industry, namely, in mechanical engineering, rocket, and space, is quite topical since it is associated with the reliability and durability of the designed structures or their elements. Stress concentrators can occur due to imperfections in the materials’ structure (cavities, cracks, foreign inclusions, etc.) or technological and structural necessity (openings, cutouts, leaks). Shell structures are used as load-carrying structures in many fields of engineering. They combine high strength with low weight, which contributes to their reliability and safety during operation. In most cases, shells in real structures have simple geometric surfaces (shells of rotation). Complex structures are usually a combination of such shells. It is important to investigate the effect of local stress concentrators as openings (considering inclusions) on the stress-strain state of shells. The methods of stress concentration reduction should be outlined. The authors performed a finite element analysis of the effect of reinforcements modeled by inclusions made of the different materials as compared with the shell material having an opening on the parameters of its stress-strain state. Such investigations are crucial for the design and optimization of the structures in many engineering fields.
TL;DR: In this paper, the effect of hydrogen on the strength, ductility, short-term and long-term static crack resistance of four KhN43MBTYu (EP-915VD) alloy modifications with different heat treatment modes and chemical composition has been studied.
Abstract: The effect of hydrogen at a pressure of up to 35 MPa and a content of up to 29 ppm on the strength, ductility, short-term and long-term static crack resistance of four KhN43MBTYu (EP-915VD) alloy modifications with different heat treatment modes and chemical composition has been studied. It has been found that the critical stress intensity factor KIc in the presence of hydrogen, just as the ductility characteristics of smooth specimens, depends on the deformation rate, reaching minimum values at rates of less than 0.1 mm/min. The fracture toughness decreases under the action of hydrogen by a factor of 2.5, and the plane strain state occurs at a much smaller specimen thickness. An optimal combination of high strength, ductility, short- and long-term static crack resistance in air and hydrogen has been achieved in a fine-grained alloy with low carbon and sulfur content. Based on the results of long-term static crack resistance tests at the predetermined maximum fatigue test duration of 300 h, the invariant characteristics of crack resistance, the threshold values of stress intensity factor in hydrogen, have been determined, which vary from 23 to 48 MPa ∙ m1 / 2 depending on the alloy heat treatment mode.
TL;DR: In this paper, the residual stresses in hot-extruded Al-6061 rods with different cross-sectional reduction were investigated using the contour method, which provided a twodimensional map of residual stresses.
Abstract: In this study, residual stresses in hot-extruded Al-6061 rods with different cross-sectional reduction were investigated using the contour method. The contour method was used to provide a twodimensional map of residual stresses. The residual stresses were evaluated along the radius of the rods with different cross-sectional reduction before and after annealing heat treatment, and the uncertainty of the contour method was estimated. The results indicate that in the extruded rods with high reduction of diameter, tensile residual stresses are generated in the rod core, which are balanced along the rod radius by compressive residual stresses at the surface. A decrease in the cross-sectional reduction or the rod diameter increase results in rise of residual stresses. The annealing heat treatment reduces residual stresses and creates a symmetrical balance between tensile and compressive residual stresses. The countour method application revealed that maximum and minimum uncertainties occurred at the rod center and perimeter, while the latter one had a greater effect on the residual stress estimation results.
TL;DR: In this paper, an ion-plasma thermocyclic nitriding technology was used for the treatment of specimens of ChS70VI heat-resistant alloy to study its effect on fatigue resistance characteristics.
Abstract: The paper considers one of the topical problems of the targeted control of the properties of the material of products in the zones under critical loads, which lead to their failure or loss of performance. The processes for the diffusion saturation of the surface layers of parts (chemical heat treatment) are an effective method for the strengthening treatment of parts of complex geometric shape. The ion-plasma thermocyclic nitriding technology developed by the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine is used for the treatment of specimens of ChS70VI heat-resistant alloy to study its effect on fatigue resistance characteristics. A technology for the ion-plasma thermocyclic nitriding of the surface of specimens and its conditions are presented. In the ion-plasma thermocyclic nitriding technology, heating is effected through glow discharge energy. In this case, the electrical power consumption is greatly reduced (by a factor of ~10) compared with similar chemical heat treatments. Micrographic investigations to determine the surface layer characteristics of specimens after ion-plasma thermocyclic nitriding are presented. The depth distributions of alloying and saturating elements in the specimen were obtained. The micrographic investigations showed that a fairly homogeneous layer 3 μm deep, uniformly distributed over the specimen surface, was formed after treatment by ion-plasma thermocyclic nitriding. To assess the influence of the above technological treatment of specimens, fatigue tests of these specimens and speciments in the initial state were carried out. It was shown that due to the strengthened layer formed on the test surface of specimens, the process of scattered damage accumulation under cyclic loading slows down, and the fatigue resistance characteristics improve: the endurance limit of specimens at the number of cycles to failure N = 107 cycles after technological treatment is 32% higher than that of specimens in the initial state.
TL;DR: In this article, the static and dynamic modulus of a cold recycled emulsified asphalt mixture was tested in a series of experiments on cement and asphalt contents, loading frequency, and temperature.
Abstract: The design of the pavement structure can make use of moduli to predict its performance during a preset lifetime. It is essential to study static and dynamic moduli characteristics. The static modulus was derived from the compression rebound modulus of the hot-mixed asphalt. The dynamic modulus was checked against a simple performance tester. The modulus of a cold recycled emulsified asphalt mixture was tested in a series of experiments on cement contents, emulsified asphalt contents, loading frequency, and temperature. The results show that high cement and asphalt contents resulted in a lower compression rebound modulus. The dynamic modulus maximum is reached at a 2% cement content. The dynamic modulus also increases with the loading frequency. This increase is observed during the early period. When the frequency increased to 10 Hz, an increase in the dynamic modulus becomes linear, and its rate gradually decreases.
TL;DR: In this article, Mixtures of hard ceramic particles, namely, molybdenum disulphide (MoS2) and graphite particles (PC), were sprayed with a high-pressure inert gas onto the surface of AISI52100 bearing steel, forming the lubricant film.
Abstract: Bearings, as a key part of a vehicle transmission system, were extensively studied to improve their abrasion resistance and fatigue life. Mixtures of hard ceramic particles, namely, molybdenum disulphide (MoS2) and graphite particles (PC), were sprayed with a high-pressure inert gas onto the surface of AISI52100 bearing steel, forming the lubricant film. The morphology and phase composition of the protective layer were examined using confocal laser scanning microscopy, surface roughness tester, X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The changes in surface microhardness were evaluated with a microhardness tester. The friction factor and anti-wear properties of the lubricant layer were assessed with an SRV-IV microvibration tester. The solid lubricant is shown to effectively reduce the friction factor. The surface modification gave a twofold increase in extreme pressure 14% reduction in the friction factor, and 20% enhancement in microhardness. This study offers a practical method to enhance the bearing surface strength for a vehicle transmission system.
TL;DR: In this article, the effect of the notch dimension, residual stress, and stress ratio on the fatigue strength was discussed, and the main conclusion is that the impact damage-induced reduction of the injury severity depends on the ratio between notch depth and notch radius.
Abstract: The fatigue strength deterioration in Ti–6Al–4V specimens impacted by steel sphere was experimentally investigated. Based on the test data of Peterson’s formula and the fatigue notch factor, the relationships linking the fatigue notch factor, fatigue strength, injury notch size, and stress ratio were derived. The effect of the notch dimension, residual stress, and stress ratio on the fatigue strength is discussed. The main conclusion is that the impact damage-induced reduction of the fatigue strength depends on the ratio between notch depth and notch radius: the greater the ratio, the more pronounced the reduction. Furthermore, the greater the stress ratio, the less id the reduction. These findings have a certain reference value for blade protection design against foreign object damage, the standard-setting, and maintenance guidelines.
TL;DR: In this paper, the problem of bending fracture of common welding scrapers in actual production is under consideration, and the existing scraper structure was improved and optimized to improve the overall strength and rigidity of the scraper.
Abstract: The scraper is the core of the conveyor and its vulnerable part. The problem of bending fracture of common welding scrapers in actual production is under consideration. SolidWorks and ANSYS finite element analysis software were used to construct the three-dimensional model for simulation analysis, and the existing structure was improved and optimized. The comparison results showed: well-type stiffener contributes to improvement of the overall strength and rigidity of the scraper. Before optimization, the maximum equivalent stress on the press buckle part of the scraper was 310 MPa, and after optimization it dropped to 230 MPa, i.e., decreased by 26%, and the stress value of one side of stiffener was 170 MPa, with certain bending resistance. After optimization, the stress distribution of the scraper was uniform, with solving the problem of stress concentration. After optimization, the overall safety factor of the scraper increased by nearly 15%, improving its life. Integrity of the optimized scraper was nearly 100%, as compared to that before optimization under the same conditions, which confirmed the validity of scraper optimization.
TL;DR: In this article, a Co-Cr-Ni-W-C alloy was manufactured and cold-rolled to investigate the effect of the latter on the microstructure, precipitates, and mechanical properties.
Abstract: A Co–Cr–Ni–W–C alloy was manufactured and cold-rolled to investigate the effect of the latter. Its microstructure, precipitates, and mechanical properties are presented. An M6C carbide, Co3W intermetallic compound and α-Co matrix were selected as the main phase constituents. During cold rolling, the alloy was deformed mainly by dislocation slipping at a small reduction, but some microtwins were formed in the matrix. When the reduction increased up to 20%, grains were elongated, and twinning became the main deformation route. When the reduction reached 40%, the alloy exhibited a typical microstructure with greatly elongated grains. The intersection of twinning lamellae lead to many cell-like substructures. The appropriate reduction of the alloy was of 15–20%, while the critical reduction made up 30%. If deformation exceeds the critical rolling reduction, cracks would originate in the alloy. With an increase in the rolling reduction, the alloy ductility decreases but the strength grows.
TL;DR: In this article, a stiffness decrease scheme is proposed in which the stiffness properties of the failed element are gradually reduced resulting in redistribution of eveloping stresses on the extent of damage it accumulates.
Abstract: The finite element method is used to to study progressive failure aspects of laminar composite skewed hypar shells with straight edges employing the eight-node isoparametric element in linear and elastic ranges under uniformly distributed static loading. A stiffness decrease scheme is proposed in which the stiffness properties of the failed element are gradually reduced resulting in redistribution of eveloping stresses on the extent of damage it accumulates. Specific numerical problems of earlier investigators are solved to validate the present approach. Numerical experiments are further carried out for different parametric variations, including some complicated boundary conditions and stacking orders of practical importance to obtain the first ply and progressive failure loads. Well accepted failure criteria are used to evaluate the failure loads and its development. Progressive failure in hypar shells are examined to arrive at some conclusions useful to the practicing engineers regarding tailoring guidelines of laminar composites and planning of nondestructive test programs for their health monitoring.
TL;DR: In this paper, a system for recording the contraction of cylindrical specimens under static compression loading was developed based on the original cantilever-type extensometer and the L-Card E-440 analog-todigital converter with Power Graph software for data acquisition and pre-processing.
Abstract: A system for recording the contraction of cylindrical specimens under static compression loading was developed based on the original cantilever-type extensometer and the L-Card E-440 analog-todigital converter with Power Graph software for data acquisition and pre-processing. 26H2MF and St12T steels’ stress–strain diagrams in compression at elevated temperatures were constructed. The influence of temperature on their mechanical characteristics was established. It is shown that at elevated temperatures (200–800°C), the mechanical characteristics of St12T steel are higher than those of 26H2MF steel, while at lower temperatures (20–200°C), they are close. At elevated temperatures, St12T steel is found to exhibit a significant difference between the tensile and compressive strengths. At temperatures above 400°C, the tension-to-compression yield strength ratio sharply decreases, while for 26H2MF steel it is almost unchanged. The nature of such dependences can be attributed to the structural-phase composition of steels, which determines their resistance to elastic-plastic deformation by compression.
TL;DR: In this article, an elastic-plastic stress-strain analysis of a change in shape of a WWER-1000 core baffle was performed by applying up-to-date approaches of modeling the irradiation-induced swelling deformation and contact interaction conditions.
Abstract: Special features of computational assessment of dimensional change of WWER-1000 reactor core baffle during the reactor operation are discussed The paper gives results of computational analysis of a change in shape of core baffle, which was performed by applying up-to-date approaches of modeling the irradiation-induced swelling of constrained austenitic steels under the action of neutron irradiation and elevated temperatures The results have been obtained by using median and conservative values of parameters of the temperature and dose dependence of free swelling of austenitic steel Kh18N10T The authors have set out the fundamental principles of elastic-plastic stress-strain analysis of the reactor core baffle and core barrel, taking into account the irradiationinduced swelling deformation and contact interaction conditions The finite-element analysis is based on a FEM mixed scheme that ensures a continuous approximation both for displacements as well as stresses and strains, thus providing a high-accuracy determination of the stress-strain state The calculations were carried out in the two-dimensional definition for the baffle cross-section with the maximum damaging dose and irradiation temperature in the baffle height, assuming a generalized plane-strain deformation The calculated results are given for the reactor full-power operation and scheduled shutdown for re-fueling at the end of the charge life According to the calculation data, disregarding the irradiation-induced swelling deformation leads to an incorrect assessment of the change in shape of the core baffle during its operation, while the use of the accepted free swelling model gives too conservative results on the shape change, even within the designed lifetime The influence of the mean normal stress on the irradiation-induced swelling of metal makes the principal contribution to the change in shape of the core baffle During the reactor operation beyond the designed lifetime there occurs a local contact between the core baffle and the core barrel in the zone of the largest-diameter circular opening of the longitudinal cooling channel and the port channel for coolant flow between the baffle and the barrel The paper gives results of the analysis of the change in shape of the baffle in modeling of the contact conditions taking into consideration the temperature re-distribution due to deviation from the design coolant passage conditions in the zone where the baffle is in contact with the barrel In the case of using the median dependence of the free swelling, no loss of the nominal gap between the core baffle and the core barrel is observed within the designed lifetime The computational assessment using the conservative parameters of the irradiation-induced swelling leads to a distinct decrease of the gap between the core baffle and the core barrel and a local contact between them at the end of the designed lifetime The residual gap between the spacer grids of edge fuel assemblies and the baffle faces is ensured in the case of the median and conservative dependence of the irradiation-induced swelling
TL;DR: In this article, the fracture and shear removal mechanisms of SiCp were demonstrated, the conditions of siCp brittleness-ductility removal were revealed, and the SiCP/Al milling was investigated in Si-Cp fracture.
Abstract: SiCp/Al composites were machined with carbide cutting tools, the surface morphology of the materials was examined with SEM and EDXS. The SiCp removal in the aluminum matrix was studied on the basis of the brittle fracture theory. The fracture and shear removal mechanisms of SiCp were demonstrated, the conditions of SiCp brittleness-ductility removal were revealed. The SiCp/Al milling was investigated in SiCp fracture. The mathematical model of the SiCp/Al fracture force was constructed on the basis of reasonable assumptions, consideration of the contact between the hard phase of the milling tool and the workpiece material. Research on the SiCp/Al brittle fracture mechanism laid the foundation for improving the milled surface quality of a SiCp/Al composite.
TL;DR: In this article, a fractographic inspection of the fracture surface of a VT23 titanium alloy was used to detect tear dimples on the fracture surfaces of the alloy, in particular after shock and vibration loading.
Abstract: The structure nonuniformity a VT23 titanium alloy after shock and vibration loading is established to lead to larger plasticity of the material and changes in fracture mechanisms. Localization of deformation processes influences the sizes and quantitative distribution of tear dimples on the fracture surface. The approach was advanced to detect tear dimples on the fracture surface of the alloy, in particular after shock and vibration loading. The fractographic inspection was used to compute the dimple parameters, among them area, number, equivalent diameter, and visual depth. The above parameters for the conglomerates of detected dimples became the basis for statistical analysis and establishment of additional fracture mechanisms of the alloy at the microlevel. It provides the grounds the grounds for preliminary comparative evaluation of the cond of titanium alloys, modified by shock and vibration loading, using fractographic examination data.
TL;DR: In this article, anisotropic layers of the payload fairing of the Cyclone-4M launch vehicle were modeled under the influence of impulses from pneumatic pushers during separation, and a special method for calculating the anisotropy characteristics of layers in the circumferential and meridional directions was developed.
Abstract: Dynamic processes in the payload fairing body of the Cyclone-4M launch vehicle under the influence of impulses from pneumatic pushers during separation are modeled. The complex honeycomb structure of the fairing body during modeling is replaced by a simpler composite structure, which is equivalent in mass and stiffness characteristics. Instead of a regular system of reinforcements in the composite model, anisotropic layers are introduced, the characteristics of which are determined. The number of anisotropic layers corresponds to the number of cylindrical and conical fairing sections. A special method for calculating the anisotropy characteristics of layers in the circumferential and meridional directions by the criterion of equivalent bending stiffness of the initial and modeled structures has been developed. Nonlinear relations with respect to the stiffness characteristics of anisotropic layers, which are defined by the iteration method, are obtained. The discretization of the composite model is carried out by the finite element method, while the time problem was obtained by the Wilson finite-difference method. The peculiarity of the problem is the combination of the rotational motion of the flap as a solid body and the oscillations caused by the deformations. The standard formulation for solving a dynamic problem allows us to calculate correctly the amplitudes of radial oscillations of the flap, which determine the dynamic zone of the fairing, and the stress. The characteristics of the natural oscillations of the flap were previously determined. Calculations have shown that the oscillations of the flap occur mainly with the frequency of the main tone. The calculated data for the maximum amplitudes of radial displacements are compared with the experimental values obtained during ground tests. The agreement of the results is quite satisfactory, especially for the lower flap flange, where displacements are maximum. Dynamic stresses are insignificant and do not exceed 15% of the yield stress. The task was to optimize the shape of the impulse from the pneumatic pushers to reduce the dynamic response of the flap during oscillations. Under the condition of preserving the value of the impulse required to deploy the flap during rotation, the distribution of the impulse in time, in which the maximum dynamic displacements are reduced by 1.5 times, was obtained. The change in the impulse shape can be achieved through a programmable pressure supply in the pneumatic pusher.
TL;DR: In this paper, the authors presented the indentation method for strength assessment of the welded joints in high-strength alloy steels, including base metal, heat-affected zone, and welded joint, in production after application of selected flaw detection methods as a final stage of non-destructive testing methods.
Abstract: The paper presents the indentation method for strength assessment of the welded joints in high-strength alloy steels, including base metal, heat-affected zone, and welded joint, in production after application of selected flaw detection methods as a final stage of non-destructive testing methods. Non-destructive testing methods are mainly used to detect defects, their location, size, and nature. The indentation method allows one to determine both the joint strength and the strength and dimensions of the heat-affected zone during the production process. The authors performed the comparative analysis on the hardness and strength limit of welded joints of 30Kh2CN2MFA and 28GRA alloy steels as delivered of sheet metal of 6 mm in thickness (for the production of special structures) to corroborate the method efficiency. It is shown that the Brinell hardness values obtained by the TSH-2 stationary hardness tester, ERNST Computest SC portable hardness tester, and instrumented indentation imply the same nature of the hardness distribution along the length of the specimen cut across the axis of the welded joint. The distribution nature of the strength limit values determined by the indentation method is similar to that of the Brinell HBW hardness distribution. It is established that the deviation of strength limit values determined by the indentation method did not exceed 3.7%.
TL;DR: In this paper, the authors deal with the classical and Bayesian estimations of step-stress partially accelerated life test model under type-I censoring for the inverse Weibull lifetime distribution.
Abstract: This paper deals with the classical and Bayesian estimations of step-stress partially accelerated life test model under type-I censoring for the inverse Weibull lifetime distribution. In classical estimation, the maximum likelihood estimates of the distribution parameters and the acceleration factor were obtained. In addition, approximate confidence intervals of the parameters were constructed based on the asymptotic distribution of the maximum likelihood estimators. Under Bayesian inference, besides the Lindley and Tierney–Kadane approximation posterior expectation methods, which yielded point estimates of the distribution parameters and the acceleration factors under square error loss function, we also applied the Gibbs sampling method, in order to construct credible intervals of these parameters together with their point estimates. Finally, Monte Carlo simulations were conducted to compare the performances of the above estimation methods.