Static Stress Research Articles

Shear Stress Induces Morphology Changes in Human Lung Microvascular Endothelial Cells via Calcium Influx

Introduction: The pulmonary vascular endothelium is in contact with laminar blood flow, resulting in a physiologic degree of shear stress exerted on endothelial cells (ECs). In vitro cell culture of ECs is typically performed under static conditions, leading to underappreciation of the impact of shear stress. Calcium signaling is among the most ubiquitous cell signaling mechanisms, and changes in intracellular calcium concentration ([Ca2+]i) have been linked to shear stress. The impact of shear stress on human lung microvascular endothelial cell (hLMVEC) morphology and cell signaling is not well described. We hypothesized that hLMVECs exposed to shear stress would undergo Ca2+-dependent morphologic changes. Methods: The effect of shear stress on [Ca2+]i was first tested using ratiometric measurement. Early passage (p≤8) primary hLMVECs from three unique donor lots were plated in gelatin-coated Ibidi 0.2 uM depth plates for 16 h, then incubated with the calcium indicator Fura-2 AM for 1 h. Measurement of [Ca2+]i was obtained over 15 minutes under static and physiologic shear stress (0 and 12 dyn/cm2, respectively), using validated flow rates from the Ibidi system. Measured [Ca2+]i was compared between cells treated vehicle or an inhibitor of the mechanosensitive Ca2+-permeable channel TRPV4 (HC-067047). HC treatment was for 1 h prior to and throughout the duration of shear exposure. Morphology changes were then assessed in hLMVECs from the same three cell lots grown in standard 6-well plates; one plate kept in static culture, while another was exposed to 24 h of 12 dyn/cm2 shear stress using an orbital shaker. Treatments in each plate were control, vehicle, and HC. Representative photos of each well were taken at 0 h and at 24 h. Average ratios of shortest to longest dimensions from 30 cells/field were measured using ImageJ and compared between treatments and shear conditions. A 2-way ANOVA with post-test was used to test for statistically significant changes in morphology. Results: Shear stress increased [Ca2+]i within 15 minutes, and both baseline [Ca2+]i and observed change in response to shear stress were decreased by TRPV4 inhibition with HC. Morphologic changes were observed after exposure to shear stress on microscopic examination, with cells grown in static culture having typical cobblestone appearance and shear-adapted cells having an elongated, spindle like appearance aligned in the direction of flow. The calculated ratio (shortest to longest dimension) of all wells at 0 h was ~0.70 with no significant differences between groups. 24 h of shear stress caused a nearly 80% decrease in ratio compared to static culture in untreated cells (p<0.05), with a decrease of only 30% in HC-treated cells after 24 h of shear (p<0.05). Conclusions: Exposure to shear stress at physiological levels results in a rapid increase [Ca2+]i through mechanosensitive, Ca2+-permeable TRPV4 channels as well as notable morphologic changes to hLMVECs with prolonged exposure to shear stress that appear to be mediated in large part by TRPV4. Further investigation into the impact of shear stress on hLMVECs is warranted to elucidate biochemical pathways and other downstream functional consequences of increased [Ca2+]i. NIH-T32HL007534. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mechanical analysis for deepwater drilling riser system with structural parameters uncertainty

Uncertain structural parameters increase the mechanical failure risk of the drilling riser system. The effect of uncertain structural parameters on the mechanical characteristics of the drilling riser system is unclear. Therefore, the mechanical characteristics of the drilling riser system with structural parameter uncertainty are analyzed. A mechanical model with uncertain structural parameters is established based on the basic analysis model and the local average theory. The basic analysis model takes into account the combined effects of platform motion, tensioner, riser string, and marine environment. The local average theory is suitable for situations where there is a lack of uncertainty information. A solution approach is proposed using the second-order central perturbation method and the Newmark-β method. The solution method reduces the load by simplifying degrees of freedom and random variables. The correctness of the solution method is verified using the Monte Carlo method. The analysis results indicate that uncertain structural parameters significantly affect the static response, while the dynamic response is less affected. The failure risk due to static axial stress and static shear stress is heightened by uncertain structural parameters. The failure risk arising from static shear stress at the bottom of the riser system experiences a significant increase.

Marine shaft optimization using surrogate models and multi-objective optimization

This paper aims to obtain an application software using Ansys software in which a static, dynamic, and modal analysis for the power transmission of ships is presented. The objective functions of this research are maximum static stress, maximum dynamic stress, shaft mass, and modal shaft frequency analysis. A complete, comprehensive, and generalizable model for metal shaft types is presented. Then, using the kriging response surface and multi-objective genetic algorithm (NSGA II), these goals are optimized simultaneously. In this research, the optimization parameters are geometric parameters of the shaft design, including the position of the supports and the inner and outer diameters of the shaft. As a result of this optimization, the shaft's maximum static and dynamic stresses are reduced by 36% and 42%, respectively. The shaft's mass, which is one of the most critical factors during the shaft and its vibrations, is reduced by about 9%. In this regard, the first natural frequency of the optimized shaft increased by about 28.5% compared to the initial shaft.

Coal burst mechanism in large-scale panel under extra-thick key strata

Extra-thick key strata (ETKS) are a key factor causing coal bursts. In this study, field monitoring, physical and numerical modelling, and theoretical analysis were comprehensively adopted to investigate the effect of ETKS on the static and dynamic stress and its impact on coal bursts. Firstly, the coal bursts and the stability of ETKS were investigated. The roof strata structure and the mining-induced stress in a large scale panel under ETKS were analyzed. Then, the coal burst mechanism under ETKS is discussed. The results show that when the panel reaches the 4th and 5th longwall faces, the inferior ETKS and the main ETKS break, respectively, and large-scale cantilever-articulated structures involving the ETKS are formed. This moment, the overburden load is transferred downwards massively, and the coal seam becomes overstressed and accumulates massive elastic energy. Meanwhile, the collaborative collapse of multiple strata in the large cantilever-articulated structures causes the sudden release of elastic energy and high-energy seismicity, which exerts strong dynamic disturbances on the overstressed coal mass and leads to coal burst. Finally, strategies for coal burst control under ETKS including deep-hole pre-splitting blasting and panel size optimization are proposed and validated.

Detecting normal and cancer skin cells via glycosylation and adhesion signatures: A path to enhanced microfluidic phenotyping

Recruiting circulating cells based on interactions between surface receptors and corresponding ligands holds promise for capturing cells with specific adhesive properties. Our study investigates the adhesion of skin cells to specific lectins, particularly focusing on advancements in lectin-based biosensors with diagnostic potential. We explore whether we can successfully capture normal skin (melanocytes and keratinocytes) and melanoma (WM35, WM115, WM266-4) cells in a low-shear flow environment by coating surfaces with lectins. Specifically, we coated surfaces with Dolichos biflorus (DBA) and Maackia Amurensis (MAL) lectins, which were used to detect and capture specific skin cells from the flow of cell mixture. Alterations in glycan expression (confirmed by fluorescent microscopy) demonstrated that DBA binds predominantly to normal skin cells, while MAL interacts strongly with melanoma cells. Assessing adhesion under static and dynamic low-shear stress conditions (up to 30 mPa) underscores the reliability of DBA and MAL as markers for discriminating specific cell type. Melanocytes and keratinocytes adhere to DBA-coated surfaces, while melanoma cells prefer MAL-coated surfaces. A comprehensive analysis encompassing cell shape, cytoskeleton, and focal adhesions shows the independence of our approach from the inherent characteristics of cells, thus demonstrating its robustness. Our results carry practical implications for lectin-biosensor designs, emphasizing the significance of glycan-based discrimination of pathologically altered cells. Combined with microfluidics, it demonstrates the value of cell adhesion as a discriminant of cancer-related changes, with potential applications spanning diagnostics, therapeutic interventions, and advanced biomedical technologies.

Finite element stress analysis and topological optimization of a commercial aircraft seat structure

In recent years, the Finite Element Method (FEM) has emerged as a cornerstone in the field of seating design, particularly within the aircraft industry. Over the past decade, significant advancements in Finite Element (FE) analysis techniques have revolutionized the seat industry, enabling the creation of safer and more cost-effective seat designs. The accuracy of FE analysis plays a pivotal role in this transformation. In the process of constructing a reliable finite element model, the selection and precise manipulation of key parameters are paramount. These crucial parameters encompass element size, time scale, analysis type, and material model. Properly defining and implementing these parameters ensures that the FE model produces accurate results, closely mirroring real-world performance. Verification of Finite Element Analysis (FEA) results is commonly accomplished through experimental methods. Notably, when the parameters are appropriately integrated into the modelling process, FE analysis outcomes closely align with experimental results. This study aims to leverage the power of FEM in performing static stress analysis and topology optimization of aircraft seats using the SOLIDWORKS commercial finite element platform. By simulating loading conditions, this research calculates static stresses and displacements experienced by the aircraft seat. Through a comprehensive topology optimization study, the weight of the airplane seat is remarkably reduced by up to 30%, while still prioritizing passenger safety. The success of this optimization showcases the potential for substantial weight savings in aircraft seat design without compromising safety standards.

Effect of TGF-β3 on wound healing of bone cell monolayer in static and hydrodynamic shear stress conditions.

Wound healing is characterized as a complicated and sophisticated biological process through which tissue heals and repairs itself after injury. However, the normal wound healing process relies on different growth factors as well as the presence of an accurate cytokine level to ensure appropriate cellular responses. In the case of wound healing, the effects of various growth factors have been studied, but the effects of transforming growth factor beta (TGF-β) on wound healing have been found to be more significant because of its broad spectrum of impacts on healing the wounded tissues or skins. In the current study, the impact of TGF-β3 in bone cells' wound healing was examined in vitro. Furthermore, the activities and characteristics of TGF-β3, as well as those of related growth factors throughout this wound healing process, were studied under hydrodynamic shear stress conditions as well as static conditions of cultured bone cells. We demonstrated that a positive outcome of TGF-β3 treatment was found after 24 h under a static condition, while TGF-β3 treatment was found to be effective under a dynamic condition for wound closure. In the case of the dynamic condition, a full wound closure was obtained after 18 h in both the control and TGF-β3 treatment, while in the case of static conditions, wounds were found to remain open, even after 24 h, for both the control and TGF-β3 treatment. Additionally, in the static condition, the wound closure rate with TGF-β3 treatment was found to be quicker than that of the control flask, which implies that wound healing can be postponed in the static condition. In the dynamic condition, the wound healing process became more rapid in a cultured cell environment. The synergistic effect of TGF-β3 and hydrodynamic shear stress conditions had a positive impact on increasing wound healing and improving the rate of wound closure.

Airway stability in sleep apnea: Assessing continuous positive airway pressure efficiency

Obstructive Sleep Apnea Syndrome (OSAS) disrupts millions of lives with its burden of airway obstruction during sleep. Continuous Positive Airway Pressure (CPAP) therapy has been scrutinized for its biomechanical impact on the respiratory tract. This study leverages computational fluid dynamics to investigate CPAP's effects at 9 cm H2O (882.6 Pa) on the computed-tomography-based nasal-to-14-generation full respiratory tract model compared to ambient conditions, focusing on static pressure, airflow velocity, and shear stress. Our findings reveal that CPAP significantly increases static pressure, enhancing airway patency without adverse changes in airflow velocity or harmful shear stress on lung tissue, challenging prior concerns about its safety. Notably, the larynx experiences the highest shear stress due to its narrow anatomy, yet CPAP therapy overall supports airway walls against collapse. This investigation highlights CPAP's critical role in OSAS treatment, offering reassurance about its safety and efficacy. By clarifying CPAP therapy's physiological impacts, our study contributes vital insights for optimizing OSAS management strategies, affirming CPAP's benefit in maintaining open airways with minimal tissue strain.

Rheological study of methane gas hydrates in the presence of micron-sized sand particles

Natural gas hydrates, intricate crystalline structures formed by water molecules and small gas molecules, have emerged as a significant and globally impactful clean energy resource. However, their commercial exploitation faces challenges, particularly operational disruptions caused by sand-related blockages. Understanding the rheological properties of hydrate slurry, especially in the presence of micron-sized sand particles, is imperative for ensuring the flow assurance of subsea hydrate exploitation. This study extensively investigates the rheological properties of sand-containing hydrate slurries. The findings reveal that these slurries exhibit non-Newtonian fluid characteristics, including yield stress, thixotropy, and shear-thinning behavior. Solid-like elastic features are observed in sand-containing hydrate slurries before yielding, transitioning to viscous behavior after yielding. Even with a minimal amount of sand, both static yield stress and yield strain experience substantial changes, correlating with the increase in sand concentration. The research conclusively establishes the thixotropic nature of sand–hydrate slurries, where the viscosity decay rate is directly influenced by the shear rate. These insights aim to contribute comprehensively to the development of effective flow assurance strategies, ensuring the safe and stable operation of subsea hydrate exploitation.

Design of rose thorn biomimetic micro-protrusion for metals and CFRTP easily disassembled joining

This study focuses on the joining techniques for metals and carbon fiber reinforced thermoplastic (CFRTP) to address the pursuit of lightweight vehicles and high recycling efficiency. The innovative concept of ‘easy-disassembly joining’ is introduced for the first time, aiming for robust joint strength and efficient disassembly/recycling of end-of-life vehicles. Inspired by rose thorn morphology and natural performances, bionic micro-protrusions are explored as intermediate structures to facilitate the easy disassembly joining between metals and CFRTP. The primary focus of the study revolves around the design strategy of micro-protrusions inspired by rose thorns. The objective is to identify the most effective micro-protrusion shapes by understanding the interplay of its geometrical parameters, including base shape, apex position, profile curvature, and stress distribution under diverse loads. Utilizing static stress numerical simulations, the study conclusively identifies an elliptical base shape with the apex positioned slightly above the right edge of the structure. The outer profile adopts a circular arc, and the inner profile follows a conical curve. This configuration effectively mitigates stress concentration at the bottom, which interfaces with the metal substrate and the smaller areas around the apex. This research introduces an innovative concept for metal-CFRTP joining and applies bionic principles in engineering solutions. By promoting lightweight and sustainable structures through enhanced disassembly efficiency, it contributes to groundbreaking advancements in the field.

Influence of perforation on static characteristics of the enclosing corrugated panel under the wind action

The application of the enclosing panels with perforation in construction practice for protective structures is economic advantageous due to reduction of financial costs for their production, transportation and installation. But influence of perforation on static and dynamic characteristics of the enclosing panels was not enough investigated. With the purpose of wind protection of the buildings and structures at the Ukrainian Antarctic station „Akademik Vernadsky” static stress and stability analyses of the protective structure were executed in according with the first and second groups of limit states of State building regulations of Ukraine. The protective structure as the enclosing corrugated steel panel and supporting columns was appeared. In the article the results of numeral research of the stress strain state and stability of the corrugated panel are presented. The panel width and height were accepted permanent, and a panel thickness was explored and accepted according to requirements for its stiffness, strength and stability. The four corrugations in the form of trapezoids are located along the panel height. Perforation of the panel in the form of round holes with a radius of 12.5 mm was presented. Two finite element models of the corrugated panel using the software NASTRAN were built. The corrugated panel without perforation model as a collection of rectangular shell finite elements with six degrees of freedom at the node was modeled. This model contained 35161 finite elements and 32540 nodes. The finite element model of the enclosing corrugated panel with perforation contained 383043 triangular shell finite elements with six degrees of freedom at the node and 211609 nodes. Boundary conditions were imposed on the modal nodes along the height on both sides of the corrugated panel in the form of fixing, taking into account its rigid attachment to the columns. Wind action on the enclosing panel was presented as uniform distributed static load, the limit calculation values of which were got according to State building regulations of Ukraine and statistical data of wind at the Ukrainian Antarctic station. The main attention was given to research of influence of perforation on the corrugated panel equivalent stresses and displacements, critical values of wind load and form of loss of corrugated panel stability. Computational procedures of static stress and stability analyses of software NASTRAN were applied.

Lnvestigation of the Effect of a Mechanical Stress Concentrator on the Processes of Occurrence and Development of Cracks in Structural Elements of Aviation Equipment

The purpose of the research is investigation of the patterns of crack development in structural elements of aviation equipment from a stress concentrator under the influence of a force stretching along the main axis, symmetrical alternating loads (vibrations) and combined effects in order to determine the criticality of operation of aircraft products with crack-type defects, substantiation or refutation of the need for research and operation of the processes of development of stress-strain states preceding the occurrence of a crack, in systems and complexes of periodic, preflight and operational control of the technical condition of aircraft products.Methods. Еxperimental study of the patterns of crack development from a stress concentrator in structural elements of two form factors: a cylindrical sample (GOSТ 25347-82) simulating a stringer or a load-bearing structural beam, and a plate sample (GOSТ 1497-84), simulating an aircraft skin element. Cylindrical samples were subjected to deformation caused by the kinetics of rotation, plate samples were subjected to uniaxial tensile stress and the effects of alternating loads (vibrations) individually and in combination.Results. Тhe patterns of near-surface and deep crack development, their relationship with the frequency of application of symmetric alternating loads, have been studied. Еxpressions are established for the approximate engineering calculation of the material endurance limit, fracture surface area and constant endurance with an approximation accuracy Proceedings of the Southwest State University. Series: Control, Computer Engineering, of about 0.8. For samples in the form of flat plates, a stress-strain diagram is constructed, clearly illustrating the decrease in the endurance of the material to the effects of combined loads in relation to the effects of static tensile stresses only. Тhe approximate number of residual cycles before the structural element is destroyed is estimated, taking into account the amplitude-frequency parameters of the acting vibration in the presence of a crack in the sample. Тhe estimation method using the load intensity coefficient and mathematical expressions for its calculation is given.Conclusion. /t is concluded that it is necessary to analyze the dynamics of the development of stress-strain states (fatigue) of the material as states preceding the appearance of cracks in order to carry out sufficient control of the technical condition of structural elements of aircraft products.

Predicting the bond stress–slip behavior of steel reinforcement in concrete under static and dynamic loadings by finite element, deep learning and analytical methods

This paper integrates finite element (FE) and deep learning (DL) methods to predict the bond stress–slip behavior of reinforcing bars in concrete under static and dynamic loading. A bilinear cohesive model is adopted to describe the bond stress–slip constitutive behavior between the steel reinforcement and the surrounding concrete. After calibrating the cohesive model with published experimental results, the influences of different working conditions on the bond strength between reinforcement and concrete are further investigated by performing a sensitivity analysis of critical cohesive parameters. Regarding their influences on the FE predictions, the cohesive parameters are classified as follows: damage initiation strength, fracture energy, and stiffness. It is found that a higher loading rate increases the bond strength without affecting the trend of the bond stress–displacement response. Furthermore, the FE results are extracted as the training samples for the established NARX DL model. After evaluating the static and dynamic bond stress–displacement responses predicted by the proposed NARX DL model, the Pearson correlation coefficient of 0.97 can be achieved with the FE predictions. Finally, an analytical model suitable for engineering applications is proposed, based on the observed trends, to reveal the dominant mechanisms. Work examples are provided for the loading rates of 0.01 mm/s and 5.00 mm/s. The proposed FE, DL and analytical models provide versatile tools to reasonably estimate the bond stress–slip behavior in reinforced concrete under static and dynamic loadings.

Toward static and transient stress-constrained topology optimization for shell-infill structures

This paper contributes to a stress-constrained topology optimization approach for the design of shell-infill structures. Based on the density method, we utilize the two-step filtering and projection scheme and local volume constraint for generating the shell and non-uniform infills, respectively. The topology optimization formulation is defined as a Robust Minimum Compliance problem with Volume and Stress constraints (RMCVS), where the robust method is used to eliminate undesired topological characteristics. We globalize the static and transient stress constraints through the p-norm function, and tailor material interpolation and stress relaxation schemes for both cases, respectively, to avoid numerical difficulties. Sensitivity analysis is provided, and the derivatives of the objective function and constraints with respect to the design variable fields are derived. We then validate the suggested method through several 2D and 3D benchmarks. The results illustrate that the method is robust to generate various shell-infill structures while limiting the maximum static and transient stress.

Printability and mechanical properties of 3D printing ultra-high performance concrete incorporating limestone powder

The superior mechanical properties of ultra-high performance concrete (UHPC) offer the possibility of eliminating steel reinforcement in 3D printed structures. As a kind of by-product of the limestone quarry, limestone powder (LP) can contribute to diminishing the carbon footprint and cost of 3D printing UHPC (3DP-UHPC). This study systematically investigates the effect of LP with different contents and fineness on the rheological properties, printability and mechanical properties of 3DP-UHPC. The incorporation of LP results in the decline in the static and dynamic yield stress of UHPC, which can improve the extrudability of 3DP-UHPC, but it concurrently results in a reduction in the buildability. Reducing the fineness of LP helps to improve the buildability of 3DP-UHPC. The increase in LP content enhances the flexural and compressive properties of 3DP-UHPC, mainly related to the improved compactness of particles and decrease of porosity. However, an excessive content of LP causes significant reduction in mechanical properties due to the relatively poor printability of 3DP-UHPC. In this study, 3DP-UHPC with 10 % LP exhibits the highest flexural strength and compressive strength, reaching 37.1 MPa and 153.1 MPa, respectively. This study may provide guidance for the development and utilizing of environmentally friendly 3DP-UHPC.

A parallel and performance portable implementation of a full-field crystal plasticity model

We have developed a parallel implementation of an Elasto-Viscoplastic Fast Fourier Transform-based (EVPFFT) micromechanical solver to enable computationally efficient crystal plasticity modeling for polycrystalline materials. Our primary focus lies in achieving performance portability, allowing a single EVPFFT implementation to run optimally on various homogeneous architectures, including multi-core Central Processing Units (CPUs), as well as on heterogeneous computer architectures comprising multi-core CPUs and Graphics Processing Units (GPUs) from different vendors. To accomplish this goal, we have leveraged MATAR, a C++ software library that simplifies the creation and utilization of multidimensional dense or sparse matrix and array data structures. These data structures are designed to be portable across diverse architectures through the use of Kokkos, a performance-portable library. Additionally, we have employed the Message Passing Interface (MPI) to efficiently distribute the computational workload among processors. The heFFTe (Highly Efficient FFT for Exascale) library is used to facilitate the performance portability of the fast Fourier transforms (FFTs) computation. The computational performance of EVPFFT is evaluated and presented in terms of parallel scalability and simulation runtime on different high-performance computing (HPC) architectures. The utility of the developed framework to efficiently simulate the micro-mechanical fields in polycrystalline microstructures in engineering applications is discussed. Program summaryProgram Title: EVPFFTCPC Library link to program files:https://doi.org/10.17632/2k8579fyyv.1Developer's repository link:https://github.com/lanl/FierroLicensing provisions: BSD 3-Clause LicenseProgramming language: C++External routines/libraries: MPI, Kokkos, MATAR, HeFFTe, HDF5Nature of problem: EVPFFT is a crystal plasticity code designed to compute micro-mechanical fields within a polycrystalline representative volume element (RVE) and predict the macroscale response of the RVE.Solution method: EVPFFT uses the periodic Green's function method in Fourier space to solve the field equations of static stress equilibrium in a periodic spatial domain.

Effect of hydroxypropyl methyl cellulose on coarse tailings cemented backfill: Rheology, stability, strength and microstructure

The bleeding and segregation of coarse tailings cemented backfill (CTCB) seriously affect the effect of roof-contacted filling, and may even lead to safety hazards in mining. The incorporation of hydroxypropyl methyl cellulose (HPMC) may be an effective solution, but its impact on the performance of CTCB and its underlying mechanism remains inadequately understood. This study comprehensively evaluates the rheology (static and dynamic yield stress, and plastic viscosity), stability (bleeding and permeability), strength, and microstructure of containing HPMC. In addition, the mechanism of HPMC on CTCB was further investigated. The research results show that a certain amount of HPMC (<0.1%) can significantly reduce the dynamic and static yield stress of fresh CTCB, while the plastic viscosity increases with the HPMC content. Furthermore, HPMC can significantly improve the bleeding and segregation of CTCB through association and network structure effects. Finally, HPMC delays the hydration of cement, resulting in an early strength reduction of CTCB, but it has little impact on the strength at 28 days.

The 2022–2023 seismic sequence onshore South Evia, central Greece: evidence for activation of a left-lateral strike-slip fault and regional triggering of seismicity

On 29 November 2022, an earthquake of ML 5.0 (Mw 4.8) occurred onshore South Evia Island (central Greece) preceded by a ML 4.7 (Mw 4.6) event. The pattern of relocated aftershocks indicates the activation of a single, near-vertical fault segment, oriented NW-SE at shallow crustal depths (6–11 km). We suggest that both events ruptured a blind, left-lateral strike-slip fault, about 5 km southeast of village Almyropotamos. We observed that a clear foreshock activity (N=55 events) existed before the two moderate events. The impact of the static stress loading on neighboring fault planes diminishes after a distance of 7 km from the November 2022 epicenters, where the static stress falls below +0.1 bar. We further explore triggering relationships between the 29 November events and the late December 2022 moderate events (ML 4.9) that occurred about 60 km toward NW in the Psachna and Vlahia regions of central Evia. We present evidence of possible delayed dynamic triggering of the late December 2022 central Evia sequence, based on marked changes in seismicity rates and on measured peak ground velocities (PGVs) and peak dynamic strains, both exhibiting local maxima in their map distributions. The causes of the delayed triggering may be related to the well-known geothermal field in central/north Evia and the NW-SE strike of the seismic fault.

A high temperature engine materials test facility.

Gas turbine engines subject materials to extreme conditions. Their high temperature materials and co-developed coatings must survive combustion gas temperatures currently approaching 1800 °C, large thermal gradients, severe thermal shock, and static and fatigue inducing applied stresses, all the while operating in highly reactive, high-pressure, high-speed combustion gas flows containing significant partial pressures of water vapor, oxygen, and other reactive species for many tens of thousands of hours. We describe the design and development of a test facility for the study of materials under individual and combinations of test parameters similar to those experienced within legacy and future engines. A hydraulic load frame capable of applying static or cyclic tension-compression stresses up to 400 MPa to flat-dog bone-shaped test specimens is integrated within an environmental test chamber capable of sustaining gas pressures from 0.1 to 1.2 MPa (1-12 atm). An adjustable0.1-2 kW power CO2 laser whose 10.6 µm wavelength radiation is strongly absorbed by ceramic coating materials is used to heat sample surfaces to temperatures of 1800 °C and above, while rear surface air jet cooling establishes through-thickness thermal gradients. Rapid laser heating in conjunction with transiently applied front and/or rear-side air cooling is used to create hot or cold thermal shock effects. This is accompanied by the impingement of a high pressure (up to 1.3 MPa) reactive gas jet upon the sample with speeds up to 300m/s by preheating dry air, mixing it with steam to the desired humidity, heating to 850 °C, and then expanding it through a converging nozzle. Thermal imaging pyrometers measure specimen front and back surface temperature fields, while environmental test chamber view ports permit digital image correlation and strain mapping.

Numerical Study of the Strength Radial Turbomachines Based on the Use of Stainless Steel 316L

By studying various properties of materials came to the conclusion that stainless steel 316L has good properties. This material is suitable for making radial wheel turbines compared to other materials. The object of the study is a radial wheel with 10 blades manufactured by “Schiele” (Germany), which specializes in the production of units for the chemical industry and ventilation equipment. The finite element method was chosen as the basic research method for solving problems of natural and forced vibrations, static stress and studying the degree of reactivity blades radial wheels of turbomachines. It can be argued that the numerical analysis of the strength characteristics of heavily loaded turbine elements with the help of electronic computers provides a greater depth of research, the breadth of the issues covered, significantly reduces the amount of expensive experimental research, reduces the time for designing new turbines in terms of efficiency, reliability, technology and resource saving of highly loaded units. In this paper, calculations were made of the characteristics of natural frequencies, equivalent stresses, deformation and the degree of reactivity blades when using material stainless steel 316L. It is noted that this material provides the criterion of stress concentration in the wheel as low as possible and the natural frequencies of the wheel are reduced, but it does not lead to a change in the oscillation modes of this wheel. So 316L stainless steel is recommended for evaluating options in the manufacture of this radial wheel of turbomachines in the field of power, chemical and transport engineering.