Plastic Layer Research Articles

An Evaluation of a Marginal Land’s Geological Engineering Properties in Borikiri Sandfill, Port Harcourt Nigeria

Aim: The aim of this study was to assess the geological engineering properties of a marginal land in Borikiri Sandfill, Port Harcourt, Nigeria, using both field and laboratory investigations.
 Study Design: The study design involved the drilling of 4 boreholes and standard penetration tests to determine the soil profile and index properties such as particle size analysis, atterberg limits, and moisture content. Consolidation and triaxial tests were also performed to determine the values of the coefficients of permeability (k), volume compressibility (Mv), and consolidation (Cv).
 Place and Duration of Study: The Study was conducted in Borikiri Sandfill, Port Harcourt between February and May 2020.
 Methods: This study's methodology included field research, laboratory analysis, and testing. Drilling and conventional penetration tests were used to assess the soil profile. Laboratory tests such as particle size analysis, atterberg limits, and moisture content were used to determine the index characteristics. The values of permeability (k), volume compressibility (Mv), and consolidation (Cv) were also determined using triaxial and consolidation tests.
 Results: The results of the study showed that the soil profile consists of five stratigraphic sequences, with a top organic silty layer followed by a sandy layer, a dark plastic layer, a dark silty clayey sand, and a well-graded sand. The clays had an average Liquid limit (LL) of 45% and a Plastic Limit (PL) value of 23%. The values of k, Mv, and Cv were determined to be 2.1 x 10-7 m/s, 1.8 x 10-4–2.5 x 10-4 m2/MN, and 3.8 m2/yr, respectively. The average bearing capacity values at 2.5 m and 4.5 m depths were determined to be 186.39 kPa and 278.71 kPa, respectively. Settlement values were calculated empirically for immediate and consolidation settlement, with immediate settlement being high at 25.85 mm and consolidated settlement being 7.53mm. T50 and T90 values were also determined to be 1.32 and 4.52 years, respectively.
 Conclusion: It is recommended that a shallow foundation, down to the first layer, can be used for any light construction on the marginal land in Borikiri Sandfill, Port Harcourt, Nigeria. The values of k, Mv, and Cv also indicate that the soil is relatively compressible, which should be taken into account in any design or construction activities.

Polarized light diffuse reflectance FT-NIR MEMS spectrometer enabling the detection of powder samples through a thin plastic layer.

Polarized scattered light Fourier transform infrared (FTIR) spectroscopy is used for measuring the absorbance of highly scattering materials overcoming the multiple scattering effect. It has been reported for in vivo for biomedical applications and in-field for agricultural and for environmental monitoring. In this paper, we report a polarized light microelectromechanical system (MEMS)-based FTIR in the extended near infrared (NIR) that utilizes a bistate polarizer in a diffuse reflectance measurement setup. The spectrometer is capable of distinguishing between single backscattering from the uppermost layer and multiple scattering from the deep layers. The spectrometer has a spectral resolution of 64c m -1 (about 16nm at a wavelength of 1550nm) and operates in the spectral range of 4347c m -1 to 7692c m -1 (1300nm to 2300nm). The technique implies de-embedding of the MEMS spectrometer polarization response by normalizing its effect; this is applied on three different samples: milk powder, sugar, and flour in plastic bags. The technique is examined on different scattering size particles. The scattering particles diameter's range is expected to vary from 10µm to 400µm. The absorbance spectra of the samples are extracted and compared to the direct diffuse reflectance measurements of the samples, showing good agreement. By using the proposed technique, the calculated error for the flour was decreased from 43.2% to 2.9% at 1935nm wavelength. The wavelength error dependence is also reduced.

Statistical Analysis of the Effective Friction Angle of Sand Tailings from Germano Dam

Tailings dam accidents emphasize the importance of an adequate understanding of the strength parameters of tailings to improve the efficiency and effectiveness of the design, construction, and operation of such structures. Usually, the tailings strength is addressed in a deterministic manner. However, a statistical approach would better represent their behavior due to its inherent heterogeneity. The literature about tailings strength distribution is relatively rare or superficial, which impairs the probabilistic analyses which are essential for risk management. Therefore, this article focuses on the probability density function (PDF) of the effective friction angle (ϕ′) of iron ore tailings from the reservoir of Germano dam, Mariana, Brazil, based on data from publicly available CPTu tests. The influence of the relative density (Dr), and the presence of plastic layers amidst the sand tailings on the strength of the sand are also discussed herein. Several correlations were employed to estimate ϕ’ and Dr. According to the results, the presence of plastic layers influences the estimated properties, and the relative density has a log-normal distribution. The effective friction angle, on the other hand, presents a normal distribution.

On the correlation between processing parameters, plastic deformation, and mechanical property in hard machining of H13 steel

Hard machining, as one of the sustainable manufacturing technologies, tends to introduce highly coupled thermomechanical loads into the machined surface layer, which causes materials to suffer from severe plastic deformation underneath and, thus, the alteration of the mechanical properties. In this paper, a systemic investigation was performed on the correlation of processing parameters, plastic deformation, and mechanical properties of machined surface layer for hardened H13 steel, where the cutting parameters and tool micro-geometry are varied. The plastic deformation layer was composed of an amorphous structure and plastically deformed grain. Compared to cutting parameters, edge micro-geometry significantly influences the depth of the plastic deformation layer. The automated ball indentation (ABI) technique was utilized to evaluate the mechanical properties of the machined surface layers. Finally, the relationship between processing parameters, depth of plastic deformation, and mechanical properties was revealed. The experimental findings provide a solid foundation for processing parameter selection to improve the functional performance of manufactured components.

Caspian Elegies

Caspian Elegies Layli Shirani (bio) for Ali First Elegy When we were kids, we found Paradise in the dewy Hyrcanian forests and moody, sentient waters of the Caspian seashore. You handsome, a bit serious, dimple-chinned with a drooping lower lip; me scrawny, messy, eager to keep up. Every family has its own unique geometry. Where I was inconsistent, changeful, rebellious, you were steady, committed, argumentative: a Euclidean vector conferring, upholding, the symmetry and harmony that bound us together. Host to endless hectares of shalizar, our Caspian region has always favored the Mehr varietal: the rice that stretches and gives more of itself after a good salty soaking. Our people prize quality over yield. The cultivation of rice is a delicate process involving rice buds—shaltooks—gestating safe and warm and away from any inclemency for a whole year before being plunged in saltwater and gently stirred, allowing the heavier, heartier seeds to announce themselves by sinking to the bottom. The shalikars rinse the more viable seeds, place them in semi-full gunny sacks and submerge them in fresh water, allowing the seeds to swell in size before laying them out to sprout. You would think the surviving seeds are now ready to begin their separate journeys, but they are not. [End Page 69] Picture our homeland as it is often described: in the shape of a cat. Now see its scruff and there we are, in the middle . . . in Vanoosh village, Nowshahr County, Mazandaran Province, on the wrong side of the highway from the seashore, in a modest villa surrounded, saturated, by damp, green shalizar. A cradle. Think: nobody worried about us crossing the busy Nowshahr-Mahmudabad Road during our daily treks to and from the darya, or how often we young shaltooks ventured into those turbulent waters, unaccompanied and unseen. How free we were. I had my big brother next to me. I had you. Iranian shalikars practice the seedling method of cultivation. Every shalizar has a khazaneh—an enclosed area either adjacent to or on the land itself—where the seeds are released into water at least three centimeters deep. Often the khazaneh is covered with a layer of plastic at night to protect the babes from aberrant drops in temperature or other calamities. Here they will germinate, grow tentative roots, begin their adolescence. Once, on our way back to the villa for lunch, you were running ahead of me through a narrow passageway, and the next thing I knew your face was swarmed by attacking bees. I don’t remember which side of the highway we were on, but we sprinted, eyes half-shut and screaming until we reached Mom, who was nearby at the villa if not on the land itself. In the khazaneh, when the plants become teenagers, the shalikars withhold water for three weeks and then flood them, tricking the young seedlings into believing they are ready to separate from the earth. They emerge, quivering, their fledgling roots intact for nearby transplantation. And they are yet a long way from becoming the grains presently soaking in a bowl on my kitchen counter here in California—continents away from their birthplace—resting beneath a watery western salt cap. Suppose I were to tell you that I have never stopped trying to return to that place where danger and separation were neither thoughts nor words, and safety and comfort were always nearby if not on the land itself ? Where the best part of eating balaal by the roadside in Vanoosh was not so much the grilled corn but the process of receiving it by the cob’s end with a bit of newspaper wrapped around and dunking it into a communal saltwater [End Page 70] bucket that was blackened . . . with bits of char, ash, and rootlike filaments. Suppose I were to tell you that my body rejected its transplant, that the distance was too far, the soil too alien. That my roots are still flooded, still seeking familiar earth.1 Second Elegy In one of my earliest memories, we are in Princeton, our leafy anchor to this country. I am scared of the neighbor’s dog who barks whenever we walk past. You grip my...

Preparation of microfluidics device from PMMA for liposome synthesis

Microfluidics has emerged in recent years as a technology that has advantages and is well suited for studying chemistry, biology, and physics at the microscale. A common material which has been widely use to fabricate the microfluidic system is thermoplastic materials. The method of fabricating microfluidic devices has been growing because of advantages such as high-quality feature replication, inexpensiveness, and ease of use. However, the major barrier to the utilization of thermoplastics is the lack of bonding methods for different plastic layers to close the microchannels. Therefore, this study focused on fabricating a microfluidic device on poly(methyl methacrylate) (PMMA) plates by laser engraving. The bonding technique for plastic layers has relied on the application of small amounts of ethanol with conditions of low temperatures (100 ⁰C), and relatively low pressures (5 tons) for 2 minutes. With this technique, the microfluidic device is created to operate stably, without leakage or cracking even under high pressure. The microfluidic device was applied to synthesize liposomes with a 5:1 ratio of syringe pump velocity between water and lipid solution. The size of liposomes after synthesis is 109.64 ± 4.62 nm (mean ± sd) and the PDI is in accordance with standard conditions (PDI < 0.200).

Comparison of Physical Properties and Degradation of Polylactic Acid and Polypropylene Facemask Layer

The current 3-ply facemasks are produced mostly using polypropylene (PP) as the main plastic layer that is a non-biodegradable polymer. The objective of this study was to fabricate a polylactic acid (PLA) layer, a biodegradable polymer, using the electrospinning process. Comparison on the degradation trend of PLA layer and PP layer obtained from commercial 3-ply face mask (CFM) layer in seawater, river water, soil, and compost environment for a total of 60 days was observed. Results showed that the electrospinning method can produce PLA layers with similar thickness with current CFM layer, narrow distribution of fiber diameter, and slightly dense surface morphology comparable to the CFM. Synthesized PLA fiber layer shows 68.6%, 39.8%, and 415.7% improvement in tensile strength, Young’s modulus, and elongation at break, respectively, compared to CFM samples. Meanwhile, for the degradation study, PLA samples show more significant changes on its morphology corresponding to the degradation process that occurred on its fibers in the seawater, river water, and soil environment, whereas for the weight change study, only the soil environment shows significant changes after 45 days. In contrast, CFM samples did not show any significant changes corresponding to degradation activity.

Effects of the oversized microplastic pollution layer on soil aggregates and organic carbon at different soil depths

Soil aggregates (SAs) are the main site for soil organic carbon (SOC) fixation, and land plastic pollution is increasingly causing many soil problems. The effects of plastic on SAs and SOC seem to be significant, but there is still a lack of relevant research. This study investigated the effects of the “plastic contamination layer” (PCL) formed by the microplastic precursors (namely, oversized microplastics (OMPs)) on the content and properties of SAs of different particle sizes at different soil depths. The results showed that the PCL had an effect on SAs of different sizes at different depths: Compared with the control group, PCL mainly increased the content of SAs in 0–5 cm soil depth, about 28.08 mg macroaggregates, 13.79 mg microaggregates and 59.82 mg silt and clay aggregates per gram of soil. The presence of the PCL mainly down-regulates the organic carbon (OC) content in 0–5 cm macroaggregates, which is about 9.59 g/kg, the OC content in 10–20 cm microaggregates, which is about 16.41 g/kg, and the OC content in 0–5 cm silt and clay aggregates, which is about 4.16 g /kg, downregulated the expression of the key carbon metabolism genes (CMGs) coxL, and inhibited the contribution of the potential CMGs host bacteria Sphaerimonospora and Bacteroides to soil organic matter. This paper emphasizes that the presence of PCL reduced SOC sequestration.

The Crystal Eye X and gamma-ray detector for space missions

Crystal Eye idea comes from the analysis of two gravitational waves events: GW170817 and GW190425. Both events were referred to neutron star mergers. In the first case Fermi-GBM and INTEGRAL claimed the detection of a short Gamma Ray Burst (GRB 170817A) and in order to follow up and target the GW electromagnetic counterparts, a huge effort has been made by other satellites and ground-based experiments. In the second case, only INTEGRAL claimed the detection of a faint GRB (GRB 190425) while Fermi satellite was in Earth occultation. Crystal Eye is a space-based X and γ ray all-sky monitor sensitive in the 10 keV - 30 MeV energy range. In its baseline configuration, it consists of a hemisphere, made by 112 pixels, with a wide (about 6 sr) field of view (FOV), a full sky coverage and a very large effective area (6 times Fermi-GBM at 1 MeV) in the energy range of interest. Given the pixel structure – a two-layer crystal scintillator and a plastic scintillator veto layer – and the hemispherical design, Crystal Eye concentrate the pointing capability of a γ-ray telescope and the sky coverage of an all-sky monitor in a single detector. Moreover, the use of Silicon Photomultiplier (SiPM) at the place of traditional PMs, besides being a challenge for their qualification for space missions, allows a more compact and less power-consuming design. A Crystal Eye pathfinder has been designed and realized to be tested in view of the mission on the Space Rider by ESA. The prototype is made by 4 pixels. The mission is aimed at testing in the space environment the LYSO crystals, the MPPC-arrays and the DAQ board.

Research on the Effect of Pearlite Lamellar Spacing on Rolling Contact Wear Behavior of U75V Rail Steel

The damage mode of U75V rail steel in application is determined by its rolling wear behavior. In this paper, the pearlite microstructure of U75V steel is characterized to investigate the relationship between wear and fatigue behavior. The results show that, with decreasing of pearlite lamellar spacing, the wear resistance of the steel increases and the contact fatigue resistance decreases. The spacing decreasing causes the change of the wear mechanism from abrasive wear to adhesive wear, as well as the damage mode from wear damage to fatigue damage. The smaller the pearlite lamellar spacing is, the stronger the deformation of the cementite lamellar is. The thin cementite lamellar is hardly broken in the rolling friction to pile up a large number of dislocations in the ferrite matrix and the work hardening degree was improved. So, the plastic deformation layer is difficult to remove, and fatigue cracks are easy to initiate and extend to the interior of the material.

Process-performance-prediction integration for fatigue life improvement technologies: An implementation in cold expansion of hole structures

In this work, the process-performance-prediction integration (3P integration) is developed to improve the fatigue life and reveal the strengthening mechanisms of holed structures after a novel cold expansion process (CEP), where a specific dual-scale modelling approach is proposed to refine the close-loop system. In macro-scale simulation, the cyclic deformation behavior is addressed by an isotropic constitutive model, where the residual stress distribution extracted from CEP simulation is set as initial stress field. The local deformation histories in weak region calculated from the macro-scale simulation are supplied to micro-scale simulation as boundary conditions. The micro-scale simulation solves the local damage evolution of holed structures after CEP by using a modified crystal plasticity theory that grain size effect is considered. Excellent agreements between experimental data and predicted results in terms of fatigue life and damage mechanisms prove the robustness and accuracy of the proposed dual-scale modelling approach. Finally, a feedback link in 3P integration is established by the proposed approach combined with different residual stresses and plastic layers. The significant fatigue life improvement is mainly ascribed to residual stress, while plastic layer plays a synergistic role in life performance.

Ultrasonic constitutive model and its application in ultrasonic vibration-assisted milling Ti3Al intermetallics

Ultrasonic vibration-assisted technology is widely utilized in the performance research and manufacturing process of metallic materials owing to its advantages of introducing high-frequency acoustic systems. However, the acoustic plasticity constitutive model and potential mechanism, involving Ti3Al intermetallic compounds, have not yet been clarified. Therefore, the Ultrasonic-K-M hybrid acoustic constitutive model of Ti3Al was established by considering the stress superposition, acoustic thermal softening, acoustic softening and acoustic residual hardening effects according to the dislocation density evolution theory and crystal plasticity theory. Meanwhile, the mechanical behavior of ultrasonic vibration-assisted tension (UVAT) and microstructure of ultrasonic vibration-assisted milling (UVAM) for Ti3Al was investigated. Dislocation density to be overcome from initial deformation to failure of Ti3Al was calculated in UVAT and was verified in UVAM. The results indicated that the Ultrasonic-K-M model showed a good agreement with the experimental data. There was an obviously softening phenomenon after introducing the ultrasonic energy field in the Ti3Al whole deformation region, and the degree of softening was positively correlated with amplitude. Furthermore, the maximum reduction ratio in yield strength of Ti3Al was 16 % and the maximum reduction value in ultimate tensile strength was 206.91 MPa. The elongation rose first and then fell as amplitude enlarged, but only as the vibration was applied in the whole deformation region, the elongation was always greater than 14.58 %. In addition, The UVAM process significantly reduced the dislocation density increment to be overcome for Ti3Al material removal by 1.37 times, and promoted dislocation motion and cancellation to make twisted dislocations evolve into parallel dislocations. As the amplitude increased to 4 μm, the depth of the disturbed area of the plastic deformation layer increased by a maximum of 2.5 times.

Some exact solutions of the nonlinear evolutionary equation for the spreading of a plastic layer on a plane

The problem of free spreading of a plastic layer between parallel approaching planes of tool bodies [1] is considered, which simulates the technological process of stamping thin-walled structural elements. To describe the specified flow of a thin plastic layer, A. Ilyushin proposed an effective two-dimensional mathematical model averaged over the layer thickness, to which the original three-dimensional problem of the flow of an ideally plastic body leads. The transition to a two-dimensional problem was carried out on the basis of special hypotheses proposed as a result of the analysis of the well-known Prandtl solution in the problem of upsetting a flat, in a vertical section, layer of plastic material [2]. On the contact surfaces, the condition of complete slippage of the material is assumed, and the shear stresses reach a maximum value equal to the shear yield strength of the layer material. Within the framework of this model, A. A. Ilyushin formulated a boundary value problem in a region with a moving boundary with respect to three unknown functions - contact pressure and two flow velocity components.

ИСПОЛЬЗОВАНИЕ ХАРАКТЕРИСТИК В НЕСТАЦИОНАРНЫХ ЗАДАЧАХ ПЛАСТИЧЕСКОГО ТЕЧЕНИЯ ТОНКОГО СЛОЯ ПО ПЛОСКОСТЯМ

The calculations are based on the proposed Ilyushin A.A. [1] theory of flow in a thin plastic layer enclosed between two surfaces of tool bodies approaching each other according to a given law. On contact surfaces, the classical L. Prandtl flow law is adopted [2]. To solve the proposed problem, the well-known boundary value problem in the formulation of the "ideal fluid" is used. This setting is described by nonlinear differential equations in partial derivatives of the first order with respect to the contact pressure and components of the flow velocity vector along the flow plane [3, 4]. In the general case, the desired values are complex functions that depend on the shape of the deformation zone, the value of the contact pressure at the considered point of the contact surface, the presence, composition and degree of lubrication, the roughness of the contacting surfaces, etc. [5, 6]. The paper proposes a method for solving problems of the flow of plastic layers in a new formulation. The analysis of the received result is carried out. Based on the method of characteristics, the problem of the flow of a plastic layer of material between inclined plates in a fixed circular area is solved, when its boundary is formed by grooves in one of the tool bodies, where the plastic material flows freely. Using the proposed solution, it is possible to construct the kinematics of the flow.

МОДЕЛИРОВАНИЕ И СРАВНЕНИЕ РЕЗУЛЬТАТОВ ТОЧНОГО АНАЛИТИЧЕСКОГО РЕШЕНИЯ КРАЕВОЙ ЗАДАЧИ ТЕЧЕНИЯ В ТОНКОМ СЛОЕ С ЭКСПЕРИМЕНТАЛЬНЫМИ ДАННЫМИ

Many technological processes of metal forming include deformation of an elongated workpiece by approaching tools, the contact surfaces of which have shallow grooved cavities. A common special case are stamps or part of their contact surfaces, which are planes: sites for draft and some types of harvesting streams. The article is devoted to mathematical modeling of the flow of a thin metal layer over rough surfaces. The article presents the results of an analytical study of the boundary value problem of the viscoplastic flow of a thin layer of metal located between thin rough plates moving towards each other. Exact solutions based on the classical formulation in the framework of an "ideal fluid" and "viscoplastic fluid" are given. A real experiment is described for assessing the effect of shear stresses averaged over the layer thickness on the kinematics of the flow of a plastic layer. In order to assess the effect of shear stresses averaged over the layer thickness on the flow kinematics, and, in particular, near fixed boundaries, experiments were carried out and the results on settlement between converging rigid plates of a thin plastic sample bounded by fixed walls and initially having the shape of a rectangle in plan are analyzed. . The fixed walls of the tool are located along the long sides of the rectangle. Experimental regularities have been established. Spreading of samples occurs as expected, i.e., along straight streamlines parallel to the long side of the rectangle, or along the rays of a circular sector. It was found that the longitudinal displacements near the immovable walls noticeably lag behind the displacements far from the boundary, and the maximum displacements are observed on the line of symmetry of the sample with respect to the immovable walls. This fact indicates the presence of nonzero shear stresses and (velocities) of deformations in the considered flows of a thin plastic layer. Comparison of the obtained experimental and analytical simulation results allows us to evaluate the correctness of the chosen mathematical model, which can be used to describe the flows.

АППРОКСИМАЦИЯ ТЕЧЕНИЯ СЛОЯ ОГРАНИЧЕННОЙ ТОЛЩИНЫ МНОГОСВЯЗНОГО КОНТУРА СОВОКУПНОСТЬЮ ТЕЧЕНИЙ ОДНОСВЯЗНЫХ ОБЛАСТЕЙ

The calculations are based on the one proposed by A.A. Ilyushin. theory of flow in a thin plastic layer, enclosed between two surfaces of tool bodies approaching according to a given law, under the assumption that: the material of the spreading layer is ideally plastic and volumetrically incompressible; elastic deformations of the tool are small and can be neglected; on the contact surfaces of the metal layer with the tool, the classical L. Prandtl flow law is accepted. To study the characteristics of the flow, we use the well-known boundary value problem in the “ideal fluid” formulation, which is described by nonlinear first-order partial differential equations with respect to the contact pressure and components of the flow velocity vector. In the general case, the quantities under study are complex functions that depend on the shape of the deformation zone, the magnitude of the contact pressure at the considered point of the contact surface, the presence, composition and method of applying a lubricant, the roughness of the contacting surfaces and other factors. The paper proposes a method for solving problems of flow of plastic layers in a new formulation. Using the proposed mathematical apparatus, a solution algorithm and a computer model of the flow were constructed.

МОДЕЛИРОВАНИЕ ЗАДАЧИ О СВОБОДНОМ РАСТЕКАНИИ ПЛАСТИЧЕСКОГО СЛОЯ, СОСТОЯЩЕГО ИЗ РАЗНЫХ СРЕД, В ПОСТАНОВКЕ МОДЕЛИ «ИДЕАЛЬНОЙ ЖИДКОСТИ»

The approach under study is important for practical application, since is the basis of many basic plastic deformation operations associated with plastic flow in a thin layer of material deformed by rolls (longitudinal rolling, rolling) or dies (volumetric and sheet stamping), which are described by spatial mathematical models with a variety of parameters that determine the rheology of the material. Pressures are created on the contact surfaces of the processing material with the tool, which exceed the shear characteristics of the material by an order of magnitude, so that, in the initial approximation, it is possible to use the model of a hydrodynamic fluid to describe the properties of the material of the plastic layer [1, 2, 3]. As was shown earlier, sliding is observed almost along the entire contact surface, in which the contact surfaces coincide with the sliding surfaces, and the specific friction forces on them are maximum [4] and equal to the shear yield strength of the material [5, 6]. It should be noted another feature of the course of these processes, which determines the requirements for the accuracy of the final forging. It is clear that high contact pressures cause normal elastic displacements of the working surfaces of the tool, commensurate with the thickness of the plastic layer [7, 8]. We consider a plastic layer in the wedge-shaped region, composed of materials with different mechanical characteristics. the layer spreads freely between the rigid rough slabs converging in parallel. The layer under the action in the direction of the thickness of the distributed load from the side of the tool flows freely in the direction of the radii.

Surface Microstructure Refinement and Mechanical Properties of GCr15 Steels Improved During Ultrasonic Surface Rolling Processing

In this paper, ultrasonic surface rolling processing (USRP) was used to strengthen GCr15-bearing steel. A finite element three-dimensional model of USRP was established to analyze the residual compressive stress and equivalent plastic strain distribution on the bearing steel surface. The microstructure, hardness, surface roughness, and corrosion resistance before and after USRP treatment were characterized by SEM, EBSD, X-ray diffraction (XRD), and electrochemical techniques. Results indicated that USRP treatment can significantly improve the material's surface microstructure and residual compressive stress distribution and obtain a plastic strain layer of about 60μm. After USRP treatment, the Kernel Average Misorientation (KAM) increased, and the dislocation activity was more intensive, resulting in aggregation near grain boundaries, and the percentage of LAGBs increased to 38.8%. Under the combined effect of surface grain refinement, residual compressive stress, and high glossy surface, the self-corrosion current density is reduced by two orders of magnitude, and the corrosion resistance is significantly improved. This investigation suggests a solution to the bearing failure problem and has implications for understanding the deformation mechanism of ultrasonic surface rolling processing.

Image Reconstruction Analysis for Positron Emission Tomography With Heterostructured Scintillators.

The concept of structure engineering has been proposed for exploring the next generation of radiation detectors with improved performance. A TOF-PET geometry with heterostructured scintillators with a pixel size of 3.0 × 3.1 × 15 mm3 was simulated using Monte Carlo. The heterostructures consisted of alternating layers of BGO as a dense material with high stopping power and plastic (EJ232) as a fast light emitter. The detector time resolution was calculated as a function of the deposited and shared energy in both materials on an event-by-event basis. While sensitivity was reduced to 32% for 100-μm thick plastic layers and 52% for 50 μm, the coincidence time resolution (CTR) distribution improved to 204 ± 49 and 220 ± 41 ps, respectively, compared to 276 ps that we considered for bulk BGO. The complex distribution of timing resolutions was accounted for in the reconstruction. We divided the events into three groups based on their CTR and modeled them with different Gaussian TOF kernels. On an NEMA IQ phantom, the heterostructures had better contrast recovery in early iterations. On the other hand, BGO achieved a better contrast-to-noise ratio (CNR) after the 15th iteration due to the higher sensitivity. The developed simulation and reconstruction methods constitute new tools for evaluating different detector designs with complex time responses.

К ВЫБОРУ МАТЕМАТИЧЕСКОЙ МОДЕЛИ ДЛЯ КОРРЕКТНОГО РЕШЕНИЯ КРАЕВОЙ ЗАДАЧИ ТЕЧЕНИЯ ТОНКОГО СЛОЯ ПЛАСТИЧЕСКОГО МАТЕРИАЛА ПРИ СЖАТИИ ОБРАЗЦА В ВИДЕ КРУГОВОГО СЕКТОРА

The class of flow problems for a relatively thin layer of plastic metal includes most of the practical problems of rolling and forging and stamping production. With the difference that during rolling, rolling, rotary drawing and other similar processes, the deformation zone is localized, and in stamping processes, the entire volume of metal is redistributed in the cavity of the stream, flowing into its various elements, forming the necessary shape of the forging, often the shape is elongated and of small thickness. It is natural to believe that the same mathematical models can be used for the analysis of processes close in kinematics, but in different formulations. The article substantiates the choice of a mathematical model for the theoretical solution of the boundary value problem of constrained compression of a sample in the form of a circular sector based on the results of the experiment. The article presents the results of an analytical study of the boundary value problem of the viscoplastic flow of a thin layer of metal located between thin rough plates moving towards each other. Exact solutions based on the classical formulation in the framework of an "ideal fluid" and "viscoplastic fluid" are given. A real experiment is described for assessing the effect of shear stresses averaged over the layer thickness on the kinematics of the flow of a plastic layer. Comparison of the obtained experimental and analytical simulation results allows us to evaluate the correctness of the chosen mathematical model, which can be used to describe the flows. When designing and introducing into production most high-performance technological processes for processing materials by pressure, not only the numerical values of technological parameters are required, but also the prediction of the behavior of the material during loading. At present, problem-oriented software systems are available based on numerical methods for solving, for example, the finite element method (FEM), various problems of continuum mechanics (MCS). However, without the development of fundamental approaches to the formulation, schematization and analytical solution of boundary value problems, it would hardly be possible to create reliable mathematical models for modern computer systems. Therefore, the further development of theoretical approaches to solving boundary value problems of the MSS is relevant.