Mechanical Stress Distribution Research Articles

Numerical simulation and mathematical modeling of biomechanical stress distribution in poroelastic tumor tissue via magnetic field and bio-ferro-fluid

Based on scientific evidence, it seems that bio-magnetic systems can change the process of cancer cell death by affecting the distribution of pressure and mechanical stress in the tumor tissue. Already most of the research has been done experimentally and few mathematical modeling and numerical simulations have been done to investigate the relationship between the magnetic parameters and the mechanical stress of the tumor tissue. This is despite the fact that in order to be able to make new equipment with the help of medical engineering methods, it is definitely necessary that the mathematics governing the problem and changes in the effective magnetic parameters (such as the shape of the magnetic source, magnetic flux density, magnetic source distance and ferro-fluid volume fraction) should be studied as much as possible. In this research, using numerical simulation and mathematical modeling, four common geometrical shapes (rectangular and circular) of the static magnetic field source were used to investigate the relationship between the change of the effective magnetic parameters and the mechanical stress created in the tumor tissue. The results of this research showed that when the magnetic flux density and ferro-fluid volume fraction and also the distance between the magnet and the tissue are kept constant, as well as without spending any extra energy, for a rectangular magnet, just by changing the way the source is placed on the tissue, the average biomechanical stress inside the tumor tissue causes a 25% change. Also, for a circular magnet, just by doubling the radius of the magnet, the average biomechanical stress inside the tumor tissue causes a 73% change.

On a Method for Calculating Bending and Shear Vibrations of a Porous Piezoelement in the Low-Frequency Region

Introduction. Devices for collecting and storing energy from the external environment are low-power sources of electric energy that are actively used. The autonomous devices for monitoring the damaged condition of various structures include them as well. The working element of these devices is a piezoelectric generator (PEG) — a converter of mechanical energy into electrical energy. The design of PEG is associated with the preliminary construction of their mathematical and computer models, with the help of which the calculation and optimization of structures is carried out. One of the ways to model and calculate PEG is to develop approximate calculation methods based on applied theories. The applied theories for calculating bending vibrations of multilayer piezoactive plates are known and previously developed in the literature. However, in the scientific literature there is not enough information about bending and shear vibrations as a tool for improving the efficiency of engineering calculations of the described structures. The objective of this work was to develop an applied method for calculating bending and shear vibrations of piezoceramic plates, including porous ones.Materials and Methods. Piezoceramics PZT-4, including porous ones, were used as the piezoactive material of the plate. When using porous ceramics, the rigidity of the structure decreased to a greater extent than the piezoelectric modules, which made it possible to obtain a more effective PEG under mechanical action. The mathematical formulation was carried out within the framework of the linear theory of electroelasticity with plate polarization in thickness. The sides of the plate were electrodated, the right side was fixed, and a smooth contact in the vertical wall was set on the left side. Steady-state vibrations of the plate were caused by pressure on the front surfaces of the plate or the difference in electrical potentials at the electrodes. To calculate the characteristics of PEG, the authors proposed an applied theory based on hypotheses about the distribution of characteristics of the stress-strain state and the electric field.Results. Transverse vibrations of a piezoceramic plate in the low-frequency region (below the first bending-shear resonance) were studied. Due to the fact that the mathematical formulation was considered within the framework of the linear theory of elasticity, the problem was divided into the sum of two. The first one took into account the mechanical effect: a distributed load and a transverse force at the left end acted on the front surfaces of the plate, and the potentials at the electrodes were zero. In the second task, there were no mechanical loads, but the potential difference was set at the electrodes. Based on hypotheses about the distribution of deformations, mechanical stresses and electric potential, both problems were reduced to a system of ordinary differential equations and boundary conditions. Comparison with the results of calculations by the finite element method in the ACELAN package showed the adequacy of the proposed applied theory in the low-frequency region.Discussion and Conclusion. Since the formulation of the problem was considered in the linear theory of electroelasticity, and the low-frequency region was studied, the work succeeded in dividing the problem of bending-shear vibrations of a porous piezoceramic plate into two: bending — with mechanical action at zero potentials, and shear — when setting the potential difference and zero mechanical action. The corresponding hypotheses about bending and shear were used. Two systems of ordinary differential equations and boundary conditions, which were solved analytically without the use of “heavy” finite element packages, were constructed. To compare the results and confirm the adequacy of the proposed method, the finite element modeling of such tasks was carried out in a specialized ACELAN package. The comparison showed that the error in determining displacements and electric potential when using this approach, in the case of setting mechanical loads and potential differences, did not exceed 6%. The method developed in the paper can be applied in the design of piezoelectric generators for energy storage in the low-frequency region.

Features of Mechanical Properties and Residual Stress Distribution in Butt Joint of HSB690-SM355 Dissimilar Steel

Features of Mechanical Properties and Residual Stress Distribution in Butt Joint of HSB690-SM355 Dissimilar Steel

FEM Analysis And Design Optimization Of The Piston

The workings of an engine rely on the piston rod and/or connecting rod to transmit the force of the expanding gas in the cylinder to the crankshaft. Because of its critical role in engines, the piston is subject to inertial stresses and cyclic gas pressure, which may lead to fatigue damage in the form of side wear, fractures in the piston head or crown, and other issues. According to the research, the top of the piston experiences the highest level of stress, which is a major contributor to fatigue failure. This study uses finite element analysis to illustrate the stress distribution on an internal combustion engine's piston. It is the CAD and CAE programs that carry out the FEA. Examining and analyzing the distribution of thermal and mechanical stresses on the piston under real-world engine conditions during combustion is the primary focus. Predicting the component's critical area and greater stress using finite element analysis is also detailed in the paper. Created a structural model of a piston using CATIA software. We ran simulations and stress analyses with the help of ANSYS V14.5.

Biomechanical evaluation of a modified intramedullary nail for the treatment of unstable femoral trochanteric fractures

BackgroundThe Proximal Femoral Nail Antirotation (PFNA) device is the most commonly used implant to fix unstable femoral trochanteric fractures (UFTFs), but it has a relatively high incidence of complications. Due to this factor, the modified intramedullary nail (MIN) was created to treat patients with UFTFs. The aim was to exhibit the MIN and make a comparison with PFNA and InterTAN using biomechanical methods. MethodsAn adult UFTF model was developed using Mimics software. The PFNA, InterTAN nail, and MIN models were drawn referring to the corresponding parameters and installed in the fracture models. Vertical, anteroposterior (AP) bending, and torsion loads of the femoral head were set in advance and loaded onto the fracture models. The value of maximal displacement and von Mises stress was evaluated via finite element analysis (FEA). ResultsThe MIN model had smaller values for maximal displacement than that of the PFNA model, and the increase in displacement was less pronounced for the MIN compared to PFNA under increasing vertical loads. For the indicator of von Mises stress, the MIN model showed lower stress compared with the PFNA model in vertical loads ranging from 300 N to 2100 N. Except for the maximal stress at implants under AP bending loads, the MIN demonstrated the most superior biomechanical properties under AP bending and torsional loads. ConclusionThe MIN offered obvious advantages in terms of mechanical stability and stress distribution among the three studied implants, providing a promising implant option for patients with UFTFs.

Analysis of Mechanical Stress on Fowler-Nordheim Tunneling for Program Operation in 3D NAND Flash Memory

This study investigated the relationship between mechanical stress and program efficiency in three-dimensional (3D) NAND flash memory devices. A stacked memory array transistor (SMArT) 3D NAND flash structure was modeled using a technology computer-aided design (TCAD) simulation. The mechanical stress distribution in the device depended on the deposition temperature (TD) of the constituent material. In particular, the TD of tungsten (TD,W) dominated the mechanical stress. The tensile stress on the polycrystalline silicon (poly-Si) channel increased as the TD,W decreased, and the compressive stress on the tunneling oxide (Tox) decreased. Consequently, the barrier height between Tox and poly-Si, and the effective electron mass decreased as the electric field in the Tox increased. These changes significantly increased the Fowler-Nordheim (FN) tunneling process and program efficiency, indicating the crucial performance of 3D NAND flash. Moreover, the mechanical stress caused by the differences in TD,W improved the program efficiency at a lower program voltage (VPGM). Therefore, a change in the mechanical stress based on decreasing TD,W improved the program efficiency through a higher FN tunneling process.

Finite Element Analysis for Degenerative Cervical Myelopathy: Scoping Review of the Current Findings and Design Approaches, Including Recommendations on the Choice of Material Properties.

Degenerative cervical myelopathy (DCM) is a slow-motion spinal cord injury caused via chronic mechanical loading by spinal degenerative changes. A range of different degenerative changes can occur. Finite element analysis (FEA) can predict the distribution of mechanical stress and strain on the spinal cord to help understand the implications of any mechanical loading. One of the critical assumptions for FEA is the behavior of each anatomical element under loading (ie, its material properties). This scoping review aims to undertake a structured process to select the most appropriate material properties for use in DCM FEA. In doing so, it also provides an overview of existing modeling approaches in spinal cord disease and clinical insights into DCM. We conducted a scoping review using qualitative synthesis. Observational studies that discussed the use of FEA models involving the spinal cord in either health or disease (including DCM) were eligible for inclusion in the review. We followed the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) guidelines. The MEDLINE and Embase databases were searched to September 1, 2021. This was supplemented with citation searching to retrieve the literature used to define material properties. Duplicate title and abstract screening and data extraction were performed. The quality of evidence was appraised using the quality assessment tool we developed, adapted from the Newcastle-Ottawa Scale, and shortlisted with respect to DCM material properties, with a final recommendation provided. A qualitative synthesis of the literature is presented according to the Synthesis Without Meta-Analysis reporting guidelines. A total of 60 papers were included: 41 (68%) "FEA articles" and 19 (32%) "source articles." Most FEA articles (33/41, 80%) modeled the gray matter and white matter separately, with models typically based on tabulated data or, less frequently, a hyperelastic Ogden variant or linear elastic function. Of the 19 source articles, 14 (74%) were identified as describing the material properties of the spinal cord, of which 3 (21%) were considered most relevant to DCM. Of the 41 FEA articles, 15 (37%) focused on DCM, of which 9 (60%) focused on ossification of the posterior longitudinal ligament. Our aggregated results of DCM FEA indicate that spinal cord loading is influenced by the pattern of degenerative changes, with decompression alone (eg, laminectomy) sufficient to address this as opposed to decompression combined with other procedures (eg, laminectomy and fusion). FEA is a promising technique for exploring the pathobiology of DCM and informing clinical care. This review describes a structured approach to help future investigators deploy FEA for DCM. However, there are limitations to these recommendations and wider uncertainties. It is likely that these will need to be overcome to support the clinical translation of FEA to DCM.

Flower-like carbon spheres formed by self-assembly of nitrogen-doped porous nanoribbons to boost SnS2 nanosheets for advanced lithium storage

SnS2 is a two-dimensional layered material with high theoretical capacity, but its further application in lithium-ion batteries is limited by problems such as low intrinsic conductivity and dramatic volume expansion during lithiation process. Therefore, SnS2 nanosheets were designed to anchor in the interlayer nanospaces of flower-like carbon spheres self-assembled from nitrogen-doped porous carbon nanoribbons (SnS2/N-FC). Nitrogen-doped porous nanoribbons facilitated the uniform distribution of SnS2 nanosheets in the interlayer nanospaces of the flower-like carbon spheres, establishing a face-to-face interaction with the nanoribbons and the SnS2 nanosheets. This composite structure enhances the transfer of electrons between the components. In addition, the integration of spherical flower-like electrodes with the reserved interlayer nanospaces provided a buffering space for volume expansion which ensured an even distribution of mechanical stress. As a result, SnS2/N-FC exhibited a high reversible specific capacity of 1322.3 mAh g−1 after 200 cycles at 0.1 A g−1, with the capacity kept growing to 1329.4 mAh g−1 after 1000 cycles at 1 A g−1. This study introduces a novel approach for the design of anode materials which demonstrate excellent lithium storage.

Mathematical modelling of thermal stresses of induction surface hardening in axi-symmetric formulation

The paper presents the original general model of induction surface hardening based upon analysis of coupled electromagnetic, thermal, mechanical and metallurgical phenomena. The distribution of mechanical strains and stresses in surface layers of steel materials subjected to induction hardening is determined. This distribution is not caused only by the thermoelastic processes, but often, it is also influenced by plastic deformations of the exposed layers and transformation of particular levels of steel. An illustrative example shows the methodology of solution for an axi-symmetric configuration.

Mechanical responses and stress distribution of rock-like specimen containing a spherical defect under uniaxial compression

Spherical defect is often seen in rock material, and the size and position of the defect seriously affect the stability of rock mass. In this study, a locating device for preparing spherical defects was designed. A series of uniaxial compression tests and simulations were conducted to study the influence of the defect size and location on the mechanical, micro-cracking, failure characteristics, and stress distribution of the sample containing a spherical defect. The results indicate that the uniaxial compressive strength (UCS) and Young’s modulus both decrease with increasing defect size. The location variation of the same-sized spherical defect has a significant influence on the UCS but hardly influences Young’s modulus. The closer the defect is to the boundary, the lower the UCS is. The acoustic emission (AE) monitoring results indicate that the damage point aggregates and expands around the defect, forming a failure surface in the later stage of specimen loading. The failure modes of the specimen are divided into tensile failure, shear failure, and tensile-shear failure. Laboratory test results match well with the numerical simulation results obtained through the PFC3D program. The numerical stress monitoring results indicate that there is significant stress concentration near the defect. And the concentrated stress at the defect boundary drops before the the model reaches its peak stress, which can be used to predict the failure of the defected rock mass. The research findings could supply a certain reference for stability analysis and control of rock material containing similar types of defects.

FEM Analysis on Thermo-mechanical behavior and experimental validation of Al20Cr20Fe25Ni25Mn10 High Entropy Alloy during Spark Plasma Sintering

High entropy alloy developed with spark plasma sintering was modelled with COMSOL Multiphysics. This focus at examining the effect of spark plasma sintering fabrication parameters on thermal and mechanical stress distribution in the sintered Al20Cr20Fe25Ni25Mn10 high entropy alloy (HEA). And to achieve this, a fully thermal-electrical-mechanical integrated and dynamic finite element model (FEM) was adopted. The simulation utilised the optimal parameters employed in the laboratory to produce the samples. The geometry for the modelling was 2D axisymmetric as the parameters were based on temperature-dependent characteristics noting that only the sintered sample was modelled and simulated in order not to simplify the modelling. The FEM maintained constant sintering temperature, pressure, and heating rate but concentrated on the impact of residence durations. To verify the simulation results, morphological alterations and densification validation tests were conducted. The microstructural characterization of the sintered sample demonstrated the relationship between the stress distribution and computational temperature found in the current FEM. Noting good particle-to-particle necking. From the model, results showed that the sintered sample at different points depicted a yield stress far greater than the von Mises stress with least thermal stress at 30 MPa. This validate that the developed sample is mechanically stable based on the factor of safety failure criterion and design. However, the study recommend that further work should be conducted considering different sintering pressure of variation 10 to 30 MPa.

Determination of the maximum mechanical stresses in the insulating material around a defect with a high dielectric permittivity in an electrostatic field

Introduction. All insulating macrohomogeneous solid materials change shape under the influence of an electric field. Problem. The presence of minor defects changes the distribution of an electric field and causes a significant concentration of mechanical stresses in a given section of the material, which, under certain circumstances, can cause partial or complete destruction of this material. Goal. The purpose of the work is to determine maximum mechanical stresses according to the von Mises criterion in insulating materials around defects with ionized air and water in an electrostatic field. Also, to analyze the influence of the following parameters on the indicated stresses: the location of the defect, the orientation angle of the semi-major axis of the defect cross-section, the ratio of semi-major and semi-minor axes, elastic and dielectric properties of the insulating material and the defect. Methodology. The study is based on the interrelated equations of electrostatics and structural mechanics for an isotropic piecewise homogeneous medium. The solution of these equations is obtained by the finite element method. Results. Graphs of dependences of maximum mechanical stresses on the ratio of semi-major and semi-minor axes of the ellipsoidal cross-section of the defect have been obtained. The minimum ratio of the greatest stresses in the insulating materials around the surface cracks and pores for ionized air has been 9.3 times for the maximum ratio of major and minor semi-axes of the cross-section of the defect considered in the work, which is 10. For a water defect, the similar ratio has been 2...5.6 times, increasing when the relative dielectric permittivity of the insulating material changes from 7 to 2. When Young’s modulus of the insulating material increases from 1 MPa to 100 GPa, the angles of the inclination of the linearized dependences of maximum mechanical stresses around bounded pores with ionized air (water) to the axis of the ratio of major and minor semi-axes of the defect cross-section have been increased by 35.9° (58.0°) and 18.6° (20.1°) at orientations of major semi-axes at angles of 0° and 45°, respectively. Originality. The numerical-field mathematical two-dimensional model has been developed for the first time, which consists of sequentially solved equations of electrostatics and structural mechanics, for the determination of the distribution of mechanical stresses in an insulating material with a liquid or gaseous defect. It has been established for the first time that the ratio of the elastic properties of the insulating material and the defect determines the angle of the inclination of the linearized dependence of the maximum mechanical stress to the axis of the ratio of major and minor semi-axes of the defect cross-section. Practical value. The types of defects that contribute to the aging of insulation materials under the combined action of an electric field and a stress field to the greatest extent have been established.

Microscale Simulation of Carbon Support Structure Degradation in Polymer Electrolyte Fuel Cell

Understanding the mechanism of Polymer electrolyte fuel cell (PEFC) degradation plays an important role in improving fuel cell performance and durability. For the PEFC system, the structure of catalyst layers (CLs) is the critical component that determines cell performance. The PEFC degradation due to the reduction of carbon on the CLs has been investigated in previous studies [1]. In our past studies, we focused on the actual heterogeneous porous structure of catalyst layer. From these results, it was found that mass transport performance of oxygen and proton in heterogeneous porous catalyst layer, which consists of carbon support, ionomer and void space, is much lower than that of theoretical prediction in homogeneous porous media [2-5]. In addition, it depends on the structure of carbon black, the coating structure of ionomer and the local distribution of these materials. Thus, it is important to understand and to predict the carbon support structure change by degradation because this structural degradation strongly affect the mass transport performance. In this work, the effect of CLs porous carbon support degradation on cell performance is investigated by microscale simulation.The CLs structures, consisting of porous carbon, ionomer, and Pt, are created by our previous study multi-block method [2,6]. In our simulation, we focus on studying the effect of CLs' beginning-of-life (BOL) and end-of-life (EOL) structure in the degradation process. The CLs creation procedure is illustrated in Fig. 1. Firstly, CLs structure are created by packing CB and covered ionomer and Pt. The amount of ionomer and Pt are assumed as constant during the degradation process. Therefore, the amount of carbon is reduced in EOL structure. In this study, various CLs structures with decreasing of carbon volume are constructed. Furthermore, the mechanical stress distribution under compression condition was simulated in each structure to understand the effect of framework of carbon on local porosity in catalyst layer. The effect of carbon corrosion in CLs is investigated by calculating the cell performance of PEFC of each CLs structure by ORR mass transport and electrochemical reaction calculation with our previous method [6].The cell performance is significantly decreased by reducing carbon. The degradation mechanism of PFEC is explained by degradation of not only effective surface area but also the porous structure change which affect oxygen diffusion performance. Moreover, compared with BOL structure the apparant thickness of covered ionomer layer is higher in EOL structures because of carbon corrosion and constancy of ionomer. Hence, the higher oxygen diffusion resistance in secondary pore and ionomer layer occur in CLs degradation structures. The effect of this dynamic structure change on cell output performance will be reported in this presentation.Acknowledgements:This research was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, grant number P20003-20001327-0.

Estimation of the effective length of microcracks occurring in the water-steam pipeline at cyclic operation mode of NPP steam generator

During operation of water-water reactors including KLT-40 type reactors widely used nowadays on icebreakers and floating power units (FPU), the issue of the duration of safe operation of steam generators is acute. The problem is connected with the formation of microcracks in the steam generator water and steam piping during normal operation at power, through which radioactive nitrogen 16N7 enters the steam piping, the content of which in the steam is just a sign of leakage failure of the steam generator second circuit water and steam piping. This effect, further named "leaks", was considered earlier in a number of works of the authors under conditions of cyclic operation of the steam generator water-steam mode. In the present work the main attention is paid to mathematical and physical analysis of the mechanisms causing the formation of microcracks in the steam pipeline of a steam generator arising in the steam pipeline region in which water and steam pressures are balanced, and their effective length is estimated. Calculations of temperature distribution along the steam-pipe thickness in the steam-water transition region at periodic "slamming" of this region with water are carried out. It is shown that depending on the time period of steam-water oscillations, the radial temperature distribution along the tube thickness shows a significant difference in the distribution at a constant temperature on the outer surface of the tube, and the maximum temperature difference is observed in the area of the inner surface of the tube. The distribution of mechanical stresses arising in the tube metal is characterized by a linear dependence of stresses on temperature, the maximum value of which corresponds to the maximum temperature difference characteristic of the area of the inner surface of the tube. This allows us to state that the formation of cracks starts exactly from the area of the inner surface of the tube of the steam generator in the specified transitional area of the tube.

Leaflet Mechanical Stress in Different Designs and Generations of Transcatheter Aortic Valves: An in Vitro Study

BackgroundIt is unknown whether bioprostheses used for transcatheter aortic valve implantation will have similar long-term durability as those used for surgical aortic valve replacement. Repetitive mechanical stress applied to the valve leaflets, particularly during diastole, is the main determinant of structural valve deterioration. Leaflet mechanical stress cannot be measured in vivo. The objective of this in vitro/in silico study was thus to compare the magnitude and regional distribution of leaflet mechanical stress in old vs new generations of self-expanding (SE) vs balloon expandable (BE) transcatheter heart valves (THVs). MethodsA double activation simulator was used for in vitro testing of two generations of SE THV (Medtronic CoreValve 26 mm and EVOLUT PRO 26 mm) and two generations of BE THV (Edwards SAPIEN 23 mm vs SAPIEN-3 23 mm). These THVs were implanted within a 21-mm aortic annulus. A noncontact system based on stereophotogammetry and digital image correlation with high spatial and temporal resolution (2000 img/sec) was used to visualize the valve leaflet motion and perform the three-dimensional analysis. A finite element model of the valve was developed, and the leaflet deformation obtained from the digital image correlation analysis was applied to the finite element model to calculate local leaflet mechanical stress during diastole. ResultsThe maximum von Mises leaflet stress was higher in early vs new THV generation (p < 0.05) and in BE vs SE THV (p < 0.05): early generation BE: 2.48 vs SE: 1.40 MPa; new generation BE: 1.68 vs SE: 1.07 MPa. For both types of THV, the highest values of leaflet stress were primarily observed in the upper leaflet edge near the commissures and to a lesser extent in the mid-portion of the leaflet body, which is the area where structural leaflet deterioration most often occurs in vivo. ConclusionsThe results of this in vitro/in silico study suggest that: i) Newer generations of THVs have ∼30% lower leaflet mechanical stress than the early generations; ii) For a given generation, SE THVs have lower leaflet mechanical stress than BE THVs. Further studies are needed to determine if these differences between new vs early THV generations and between SE vs BE THVs will translate into significant differences in long-term valve durability in vivo.

Mechanical stress distribution over the palate by different pacifiers assessed by finite element analysis and clinical data.

The mechanical behavior of each type of pacifier on rigid structures and their various impacts on orofacial growth have yet to be discovered. The study aimed to evaluate the stress distribution over a child's palate by three types of pacifiers using finite element analysis and clinical and laboratory data. Modulus of elasticity was obtained from 30 specimens comprising 10 of each conventional (A), orthodontic (B), and breast-shaped (C) pacifiers. Tongue strength was assessed in eight 3-year-old children (kPa). A hemi-maxilla model was obtained from 2- to 3-year-old skull tomography, and the images of pacifiers A, B, and C were captured using 3D scanning. The Hypermesh® program generated a mesh of 6-node tetrahedral elements for applying forces in the X, Y, and Z directions to enable a nonlinear analysis. Pacifier B exhibited the highest values for distributed stress on the palate, followed by pacifier A. Pacifier B stimulated the maxilla forward and sideways. In contrast, pacifier A promoted a forward and upward load, favoring a more atresic palate. Pacifiers A and B tended to rotate in the sagittal plane, generating tensions in the anterior incisors and favoring the open bite. Pacifier C exhibited lateral expansion by stress induction over the mid-palatal suture with less influence on incisor inclination. Pacifiers showed different detrimental stress distributions on the palate. This information can be helpful for improving recommendations given to parents.

Effect of Extremely Cold Weather and Shrinkage Stress on Interfacial Discharge Between Epoxy and Silicone Rubber in HV Cable Terminations

Gas insulated switchgear (GIS) cable terminations have higher failure rates at low temperatures. In this study, a 110-kV full-size GIS cable termination model is developed to investigate this failure mechanism. The coupling characteristics of the thermal and mechanical stress distributions in the termination are analyzed. A pressure-controlled interfacial discharge experimental setup is established, and the partial discharge characteristics and damage features of tracking are investigated for different interface pressures. At temperatures as low as -40 °C, pressure distortion is observed at the interface between the stress cone and epoxy bushing, such that the interface pressure can drop below 0.1 MPa. The tracking at low interface pressures has a higher growth rate and fewer and finer branches than at high interface pressures. The accumulated damage area tends to develop from the epoxy resin towards the silicone rubber. As the interfacial pressure drops, the characteristics of the partial discharge change from those for internal discharge type to those for coexistence between internal discharge and surface discharge. Finally, a scheme for tracking development and damage under different interface pressures is proposed to explain the failure process for cable termination in an extremely cold environment, which is highly consistent with the characteristics of actual failure.

Evaluation of Mechanical Stress Distribution Across the Calcaneus following Calcaneal Autograft: A Finite Element Analysis

Category: Other Introduction/Purpose: The purpose of this study was to utilize finite element analysis to evaluate progressive bone removal from the calcaneus at various angles and its effect on the mechanical stress distribution at the calcaneus, and potential increase in fracture risk. Methods: A calcaneus CT scan was imported into Autodesk Fusion360 (Autodesk, v.2.0.14569). After rendering the initial mesh body using tetrahedral elements, a copy of the calcaneus was made. A simulated force equal to the average weight of person (876N) was applied to the middle and posterior talus facets while the calcaneus was oriented in the heel strike position during gait, with constraints applied around the heel. The initial harvest site was modelled as a 6mm diameter 30mm deep cylinder. From this center point, the diameter of the harvest site was increased to 8, and 10mm, with the depth being adjusted such that there was no risk of breaching the cortex on the opposite side. For each iteration, the safety factor, stress (MPa), and strain were recorded. This was repeated at an angle of 90°, 45° and a combination of 45° and 90°. Results: The 90° model demonstrated that as the diameter of the harvest site increased, there was a reciprocal increase in stress across the calcaneus. The number of cycles to failure (fracture) for all diameters was 10^6-10^7. The 45° model demonstrated that as the diameter of the harvest site increased, there was a reciprocal increase in stress applied across the calcaneus with a corresponding decrease in stress at the harvest site. The number of cycles to failure increased from 10^3 at 6mm to 10^4-10^5 at 10mm. The combination of the 45°-90° model demonstrated that as the diameter of the harvest site increased, there was a reciprocal increase in stress applied across the calcaneus. The cycles to failures decreased as the diameter of the harvest site increased. Conclusion: This finite element analysis demonstrated that an increase in the diameter of the harvest site led to an increase in stress along the calcaneus. There was variation in the correlation between size of the diameter and the number of cycles to failure depending on the angle of the harvest. The greatest amount of stress applied at the calcaneus was with the 45°-90° model. It was determined that harvesting at an angle of 45° at 6mm produced the lowest number of cycles to failure.

A scalable PEM fuel cell model for coupled mechanical and electrochemical analysis based on an analytical approach

A key factor in the durability of proton exchange membrane fuel cells is the distribution of mechanical stresses within the membrane electrode assembly. These stresses can be reduced by optimization of the bipolar plate rib geometry, flow field design, or clamping pressure. However, these alterations have direct impact on other physical quantities such as porosity and electrical resistance, which strongly influence the cell performance. Therefore, a multi-physics simulation environment for coupled mechanical and electrochemical analysis is presented. The mechanical sub-model is based on a novel analytical approach, which, compared to FEM, reduces the computation time by a factor of up to 8, with deviations of 1–4%. The electrochemical sub-model follows a 2-dimensional FVM approach. Both sub-models are fully parameterized, scalable, modular and extensible to ensure high use-case adaptability and to allow arbitrary parametric studies and multi-criteria optimization. The simulation environment, implemented in Python, is published open access11https://git.rwth-aachen.de/markus.kohrn/IJHE2023-A-scalable-pemfc-model-for-coupled-mechanical-and-electrochemical-analysis.git..

Microstructural parameters governing the mechanical stress and conductivity of all-solid-state lithium-ion-battery cathodes

All-solid-state lithium ion batteries are considered a promising future battery concept due to their high safety and energy density. However, they might suffer from mechanical fatigue upon cycling, caused by mechanical stresses due to the volume changes of the electrode active materials constrained by solid electrolyte. Based on a reconstruction of actual microstructure of a mixed cathode (LiCoO2/Li7La3Zr2O12: LCO/LLZO) in a lab sized cell and using computer aided material design, we calculated the thermal stresses after manufacturing and the electrochemical stresses during cycling. This approach allows us intensively study the impact of microstructural parameters (grain size, solid volume fraction and relative density) on the mechanical stress distribution and conductivities, even for cases not easily manufactural in the lab. We found that the mechanical stresses and conductivities linearly depend on the solid volume fraction of LCO and are correlated to the relative density, whereas the grain sizes influenced neither the mechanical stresses nor the conductivities. We introduced a new factor Kn as a ratio of the relative interface area between solid phases and the volume fraction of the solid phase (n = LCO or LLZO) which represents the governing factor for the stresses. On the other hand, the volume fraction of LCO and LLZO are the governing factors of their electronic and ionic conductivities. This allows for a sound forecast and determination of an optimal cathode microstructure for maximum cell performance.