Static Behavior Research Articles

Bending of bidirectional functionally graded nonlocal stress-driven beam

This paper provides a comprehensive analysis, using nonlocal stress-driven integral theory, of the static behavior of a nanoscale beam of bidirectionally graded materials. After a brief explanation of the mathematical formulation of BDFGMs, the work done and strain energy expressions derived from the displacement field are discussed. Variational formulations and Hamilton's principle are used to develop the equilibrium equation. An analytical development of the nonlocal kernel for stress-driven integral theory and formulated governing equation which was nondimensionalized later. Explicit equations for displacement and moment are obtained by solving this equation using the Laplace transformation. Three different boundary conditions are examined, and differences in the maximum displacement with respect to the nonlocal parameter and the two material FGM parameters are displayed both visually and in table form. The results exhibit excellent agreement and provide a standard for further research when they are closely compared to the existing numerical data. This work contributes to the knowledge of BDFGMs under nonlocal effects generated by stress-driven integral theory and offers solutions that have been confirmed for further investigation.

Nonlinear thermo-mechanical static stability analysis of FG-TPMS shallow spherical shells

An analytical solution for the nonlinear static stability problem of functionally graded triply periodic minimal surface (FG-TPMS) shallow spherical shells is studied in the current research for the first time. Three common TPMS structures including Primitive (P), Gyroid (G), and I-graph and Wrapped Package-graph (IWP) with three models of functionally graded porosity distribution along the thickness are considered. The shallow spherical shells (shallow SSs) are subjected to combined thermo-mechanical loadings and rested on a nonlinear elastic foundation. The fundamental formulas are expressed based on the higher-order shear deformation theory (HSDT) and von Kármán's geometrical nonlinearities. Employing the Ritz energy minimization method, the explicit relationship between load and deflection is derived. Subsequently, the static stability behavior of FG-TPMS shallow SSs is investigated. Numerical illustrations are investigated to show the superior thermo-mechanical load-carrying performance of the FG-TPMS SSs compared to corresponding isotropic structures of the same weight. The significant effects of geometric parameters, nonlinear elastic foundation parameters, and the type of FG-TPMS structures on the nonlinear static stability behavior of shallow SSs are further considered.

A modified quasi-3D theory and mixed beam element method for static behaviour analysis of functionally graded beams

This paper develops a modified quasi-3D theory and the mixed beam element model for static analysis of functionally graded beams. The modified quasi-3D theory encompasses two innovations. Firstly, the accurate distribution of transverse shear stress is derived from the differential equilibrium equation that describes the relationship between stresses, rather than the traditional one derived from geometric relations and constitutive equations. Secondly, the effect of distributed loads associated with transverse stretching deformation, a factor typically overlooked in the existing quasi-3D theory-based beam models, is involved. In the development of beam finite element model, the mixed variational principle is firstly utilized to formulate the model of a quasi-3D theory-based beam element, where generalized displacements and internal forces are treated as two types of independent field quantities. Two numerical examples are conducted to investigate the validity and accuracy of the proposed theory and beam element. Numerical results indicate that the proposed mixed beam element can accurately predict the stress distributions over the cross-section and produce accurate displacement solutions. Meanwhile, it is noted that the effect of distributed loads related to the transverse stretching deformation should be correctly considered in the analysis of functionally graded beams based on quasi-3D theory.

Understanding Degradation Mechanisms in PEM Water Electrolysis Under Dynamic and Static Operating Conditions

Hydrogen production by electrolysis has great potential to enable a decarbonized economy, although further effort is needed to decrease its cost to meet ambitious targets, such as the US Department of Energy Hydrogen Earthshot goal of $1/kgH2.1 Achieving such low hydrogen production costs using polymer electrolyte membrane water electrolysis (PEMWE) will require decreasing the cost of input electricity while lowering capital costs through thrifting of iridium and other measures. An important opportunity to lower costs is the use of inexpensive intermittent electricity, either directly sourced from renewables or from grid leveling. However, previous studies have shown that dynamic cycling can accelerate degradation, especially when combined with low iridium catalyst loadings.2 It is therefore necessary to further understand the relevant degradation mechanisms, mitigation strategies, and implications for water electrolysis deployment.Here we present the results of investigations to understand the degradation mechanisms in PEMWEs under dynamic and static operating conditions. This presentation will discuss the attribution of voltage degradation observed during long-term, constant-current operation as well as comparison of the degradation observed under cycled and static test conditions, with select results illustrated in Figure 1. This includes experiments designed to understand the transition between static and dynamic degradation behavior, differences in the degradation mechanisms, and opportunities for mitigation of dynamic degradation. We will further present investigations into the impacts of porous transport layer-catalyst layer interactions on anode catalyst degradation. Finally, we will discuss the implications of these results for guiding research priorities in PEMWE and developing operational and materials-based mitigation strategies.Citations: Energy.gov https://www.energy.gov/eere/fuelcells/hydrogen-shot.S. M. Alia, S. Stariha, and R. L. Borup, J. Electrochem. Soc., 166, F1164–F1172 (2019). Figure 1: Voltage over time profiles for durability tests comparing different current densities and cycle/hold protocols. All tests use anode/cathode catalyst loadings of 0.4 mgIrcm-2/0.1 mgPtcm-2 and a Nafion N115 membrane, operating at 80°C. Figure 1

Nanocomposites with cylindrical/rectangular/spherical/ellipsoidal reinforcements: Generalized continuum mechanics

Nanocomposites can show different properties according to the type of reinforcements they have. In this article, a model for the study of nanocomposites is examined, which is able to examine all nanocomposites with elliptical, cylindrical, spherical and rectangular reinforcements. Also, in this model, unlike some other models, the effects of interphase section are included. The results obtained from this model are compared with the results of experimental tests. Also, in present research, instead of classical continuum theories, generalized continuum mechanics is used and combined with above model to present more accurate model for studying nanocomposites. After estimating the material properties of nanocomposites, the static and dynamics behaviors of them are also studied and the influences of various parameters such as volume fraction of interphase section, geometrical shapes of reinforcements, volume fraction of fibers, gradient parameter, nonlocality and magnetic field are investigated on the results.

An Experimental Investigation on the Effects of Temperature and Confining Pressure on the Static and Dynamic Behaviors of Shale Rocks

Abstract To better understand the associated thermal and mechanical effects on the elastic behaviors of shale rocks, we examine the shale rocks at reservoir stress (static) and elastic conditions (dynamic) at varying temperature (25–110°C) and pressure (5–55 MPa) conditions through coupling dynamic–static experimental measurements. The results illustrate that the shale’s P- and S-wave velocities increase with the increasing confining pressure but decrease with the elevated temperature. For the pressure history, ultrasonic P-wave velocities upon hydrostatic unloading are slightly larger than the loading ones, whereas S-wave velocities are almost overlapping together. Meanwhile, the temperature elevation causes much less velocity reduction at a higher confining pressure than lower confining pressure. The measured data demonstrate that the static bulk modulus is more sensitive to the confining pressure than the dynamic bulk modulus. Moreover, with the elevated temperature, the dynamic bulk moduli separate by showing a decreasing trend in either hydrostatic loading or unloading. The loading–unloading cycle shows that the static bulk moduli present values approaching the dynamic ones at all temperature levels when the confining pressure is initially unloaded from the maximum pressure. Both static and dynamic bulk moduli decrease with the continued unloading, with more decrement for the static bulk modulus. The coupling effects of the pressure and temperature on the static and elastic properties of shale samples imply that, in the practical shale reservoir characterization process, temperature and pressure influences should be considered to characterize the relation of dynamic and static properties of shale rocks. The laboratory investigations on shales imply that the relation of dynamic and static properties is pressure dependent mainly due to the intrinsic behavior of fracture, soft pore, and microstructure in the rock frame.

Tunability of Sb2Se3 phase change material for multi-domain optoelectronics

Phase change materials play an essential role in the development of tuneable optics by overcoming the limitations possessed by conventional optics due to their static behaviour. Due to their non-volatile nature, chalcogenide materials attained attention beyond other phase change materials. Antimony-based chalcogenides are promising due to low absorption loss, optimal refractive index change, and compatibility with silicon integration. This study optimises near-stoichiometric sputtered Sb2Se3 thin films and investigates their compositional, physical, and optical properties change by thermal, optical, and electrical stimuli. We further extend the investigation to the induced intermediate states in the Sb2Se3 thin film for multi-bit operation for tunable photonics and phase-change memory with a current switching ratio of 104 during a phase transition. The findings are integral to the realisation of high-capacity optical switches and routers, displays with larger colour distribution, and photonic memories with high computational capabilities.

Numerical Analysis on Fatigue Behavior of Plain Concrete and Alkali-activated Concrete

Abstract Alkali-activated concrete (AAC) has recently gained a lot of potential to become one of the most recommended sustainable replacements for Ordinary Portland cement concrete (OPCC). In the present investigation, an attempt has been made to study the static and fatigue flexural behavior of AAC compared to that of OPCC by using numerical modeling FEA software, ABAQUS. The nonlinear behavior of the stress-strain curve of the concrete has been studied using the concrete damage plasticity (CDP) model. A 2D notched beam was modelled using plane stress condition and three-point bending tests were performed under monotonic loading to obtain the static behavior of concrete. The result obtained has been utilized to fix the loading range for cyclic loads in fatigue analysis and at different loading frequencies. The load-CMOD curves and load-deflection curves were obtained for both static and fatigue loading, and the number of cycles to failure during fatigue. From the results, it has been observed that the Ordinary Portland cement concrete specimens sustain more load than that of Alkali-activated concrete under monotonic loading. However, AAC has shown more resistance to fatigue than that of the OPCC and the frequency of loading significantly influences the fatigue performance.

Numerical Study on Static and Fatigue Behavior of Alkali-Activated Fly Ash Concrete Modelled using Concrete Damage Plasticity (CDP) Model

Abstract Alkali-activated concretes (AAC) are considered as an alternative to Portland cement concretes because of their much lower carbon emissions. To study its characteristics is of utmost importance. In the present research, an attempt is made to create a numerical model to analyze the static and fatigue flexural behavior of alkali-activated fly ash concrete (FC) and compare them with ordinary Portland cement concrete (PCC). Three-point bending tests are simulated for the monotonic load to obtain the static behavior of a 2D notched rectangular beam. A 2D beam specimen of size 262.5 mm x 75 mm, with a notch of size 15 mm x 3 mm was provided at the bottom middle. Fly ash-based alkali-activated concrete (FC) and corresponding PCC of similar strength are modeled in ABAQUS CAE using the concrete damage plasticity (CDP) model. The ultimate loads, maximum deflection, and CMOD for each of them were obtained from the history output manager. The results of monotonic tests are utilized for creating a sinusoidal load cycle for fatigue tests with various loading frequencies and stress ratios. Different structural responses are examined under the fatigue test. The results showed that FC performs better than PCC under static and fatigue tests. Fatigue performance of both FC and PCC is influenced by the frequency of loading and fatigue life increases at higher frequencies. It is also found that stress reversal negatively impacts the fatigue life of both FC and PCC.

Mechanical behavior and seismic control performance of a metallic torsional damper for flexible structures

The use of metallic dampers is an effective way to reduce seismic responses and dissipate excessive vibration energy for civil structures. Conventional metallic dampers employed energy dissipation by plastic deformation under bending or shear modes are hard to design, and may cause uniform distribution of stress in the metallic components. In this paper, employing the high plastic deformation capacity of aluminum materials, a metallic torsional damper using a gear and rack device (MTDGRD) is proposed to enhance the control effectiveness for the structural response reduction under earthquakes. The static mechanical behavior and energy dissipation of aluminum metallic components under torsional deformation are experimentally studied. Moreover, the configuration and working principle of the proposed damper are introduced. The dynamic behavior of the proposed damper is experimentally studied. For precise modeling in simulations, the elastic-plastic theory of torsional deformation is used to derive the mechanical model of the proposed damper and the model accuracy is validated by experimental data. Finally, numerical simulations under different seismic ground motions controlled by a proposed MTDGRD are compared to that controlled by a conventional tuned mass damper (TMD) for a 10-floor flexible structure. The results show that aluminum 6061# of the energy dissipation capacity is higher than aluminum 1060#. The dynamical tests show that the loading frequency and operational cycles have very limited effect on mechanical behavior and energy consumption capacity of the MTDGRD. The proposed dynamic mechanical model of the MTDGRD has considerable accuracy in numerical simulations and seismic control simulations show the better performance of the proposed damper in reducing structural displacement responses than the conventional TMD with a mass ratio of 0.5 %.

Analytical Linearization of Aerodynamic Loads in Unsteady Vortex-Lattice Method for Nonlinear Aeroelastic Applications

This paper presents the analytical linearization of aerodynamic loads (computed with the unsteady vortex-lattice method), which is formulated as tangent matrices with respect to the kinematic states of the aerodynamic grid. The loads and their linearization are then mapped to a nonlinear structural model by means of radial-basis functions, allowing for a two-way strong interaction scheme. The structural model comprises geometrically exact beams formulated in a director-based total Lagrangian description, circumventing the need for rotational degrees of freedom. The structural model is spatially discretized into finite elements and temporally discretized with the help of an implicit scheme that identically preserves momenta and energy. The resulting nonlinear discrete equations are solved by applying Newton’s method, requiring calculating the Jacobians of the whole aeroelastic system. The correctness of the linearized loads is then shown by direct comparison with their numerical counterparts. In addition, we employ our strongly coupled aeroelastic model to investigate the nonlinear static and dynamic behavior of a suspension bridge. With this approach, we successfully investigate the numerical features of the aeroelastic system under divergence and flutter conditions.

Static behavior of FG sandwich beams under various boundary conditions using trigonometric series solutions and refined hyperbolic theory

Static behavior of FG sandwich beams under various boundary conditions using trigonometric series solutions and refined hyperbolic theory

Impact of Polymeric Composites on Static and Dynamic Behaviors of Timoshenko Beams Using Spectral and Newmark-$$\beta $$ Methods

Impact of Polymeric Composites on Static and Dynamic Behaviors of Timoshenko Beams Using Spectral and Newmark-$$\beta $$ Methods

Analysis of a passive vibration damper for high-speed superconducting magnetic bearings

Superconducting magnetic bearings (SMB) based on a combination of high temperature superconductors and permanent magnets enable the realization of self-stabilized high-speed devices with significantly reduced friction. However, external vibration might couple in the bearing resulting in large amplitude oscillations due to a resonance case. A dedicated eddy current damper (ECD) might be used to eliminate these oscillations for a stable operation. The influence of such damping elements was studied for a frictionless SMB twisting system designed to speed up the conventional ring spinning process. Therefore, conductive copper rings with different thicknesses were implemented at different positions into the bearing setup as ECD. Afterward, the SMB setup was analyzed during acceleration using an array of laser distance sensors to record the displacement of the levitating permanent magnet ring in radial and axial direction, respectively. Simultaneously, a numerical model was developed to investigate the influence of the ECDs on the dynamic and static behavior of the SMB in more detail. It was shown that the simulated damping coefficients are in good agreement with the measured values, which allows further optimization of the ECD with the developed numerical model.

Static and dynamic behaviours of a self-expanding nitinol stent real contact area within a PTFE catheter: A multiscale approach

Current research on self-expanding super-elastic nitinol stents is mainly focused on designing geometries suited to the human venous and arterial systems. This study specifically considers a patented one-piece double cross-sectional stent designed to address venous stenosis affecting the vena cava, iliac veins, and their bifurcations. Before its placement within the vein, numerous tribological challenges arise as the stent slides along the guide-wire (so-called catheter). These are mainly connected to the lack of knowledge related to (i) its frictional behaviour and (ii) the level of contact pressure linked to the unknown real contact area between the compressed stent and the polytetrafluoroethylene (PTFE) catheter.This paper describes an original multi-scale approach, based on the Persson’s contact theory, that allows determination of (i) the contact pressure, (ii) the evolution of the real contact area, and (iii) the shear stresses at the interface during the stent sliding. A topographical optimization criterion will finally be provided, enabling control of both friction and stick–slip phenomena at the stent-catheter interface.

Hygrothermal aging effect on static and fatigue behavior of three-dimensional five-directional hybrid braided composites under tension

This paper attempts to study the hygrothermal aging effect on static and fatigue behavior of carbon/glass fiber three-dimensional five-directional (3D5D) hybrid braided composites under tension. Firstly, moisture absorption tests and micro-CT scanning analysis were conducted on the composite specimens. The results show that the moisture absorption behavior follows the Fickian diffusion law well and the aging damage is dominated by matrix cracks/pores and interfacial debonding which is more severe in the braiding glass fiber yarn and surrounding regions than the axial carbon fiber yarn and surrounding regions. Then tensile tests and fatigue tests were performed on the unaged and aged composite specimens. It was found that hygrothermal aging has significant detrimental influence on the static tensile and tension-tension fatigue behavior of the composites. From experimental observations and failure analysis, it was also concluded that hygrothermal aging has impact on the failure mechanisms of the composites under both static tensile and fatigue loading owing to the extensively existed aging damage and deteriorated material properties in the aged composites.

Advances in elastomeric mount concepts for quasi-zero stiffness isolation

Quasi-zero stiffness (QZS) mounts can exploit geometric nonlinearity to minimize stiffness about an operating point which isolates vibrations from a supported source or receiver. Previous research on elastomeric QZS mounts featured 3D printed prototypes but did not consider unique material properties and fabrication artifacts that may impact the static and dynamic behavior of the mounts. Additionally, multi-axis properties and their influence on common, box-like systems supported by several mounts lacks detailed study. To overcome these limitations and improve the practicality of elastomeric QZS mechanisms, this paper discusses nonlinear stiffness, hysteresis, and fabrication issues with elastomeric materials in this context. Multi-material mount designs that improve strength and stability are considered, and their effectiveness for QZS isolation is experimentally evaluated. System-level dynamics are presented for a box-like load supported by QZS mounts. Comparisons between additive and cast materials in the fabrication of QZS mounts are discussed, and the mounts' dynamic stiffness amplification effect is examined for additive and molded materials.

Finite Element Analysis of Functionally Graded Sandwich Plates

Computational methods become a necessity at places where the fields of testing as well as lab model testing poses problems or situations demanding large number of test results at low cost. The accuracy of the computational model can be adjusted by convergence study. The present study uses finite element method for finding static behaviour of sandwich plates having functionally graded core. Power law is employed for quantification of the material properties and zig-zag theory is utilized for the analysis. Hamilton’s theorem is exploited for deriving the equation which is resolved by FEM by taking nine-node C-0 iso-parametric FE having 11 DOF/node. Aspect ratio, power law coefficient and skewness of plate are used as variables to study the bending response of the plate. Present results are found to be consistent with the published ones and new results are also presented.

Students’ behaviour analysis based on correlating thermal comfort and spatial simulations; case study of a schoolyard in Shiraz City

The significant impact of outdoor school environments on student behaviour highlights the need to study how students interact with their surroundings. This has become a central focus in recent educational research, leading scholars to use various methods to gain insight into student movement behaviour. This research introduces a novel data-driven spatial gridding technique, employing thermal comfort and space syntax evaluation through ENVI-met and depthMapX software. It validates the extracted climatic and spatial heatmaps using real-time drone footage and Python programming to map and visualize student movement patterns. The findings from the Pearson correlation analysis in the Orange Software suggest that the correlated spatial-thermal heatmap better represents students’ actual behaviour with a high correlation coefficient of 0.84 (p = 0.84). Furthermore, this study sheds light on how students’ dynamic and static behaviours are linked to the schoolyard’s thermal and spatial characteristics. In conclusion, this research innovatively combines real-time monitoring with dual-simulations to analyze student movement behaviour, providing valuable insights into specific schoolyard dynamics.

STATIC BENDING RESPONSE OF COMPOSITE PLATES RESTING ON VARIABLE ELASTIC FOUNDATIONS

This article introduces a finite element approach for examining the static bending behavior of composite plates. The method considers the variable mechanical characteristics of plates and utilizes an elastic foundation with varying stiffness values. The plate's calculation expressions and equilibrium equations are derived using the new style shear deformation theory. The article uses a mesh composed of four-node rectangular components to solve the equilibrium equation. Each node in the mesh has six degrees of freedom. The solution's dependability and convergence are confirmed by comparing it with previously published findings. Based on this premise, the study presents numerical findings that examine how various geometric factors, materials, boundary conditions, and elastic foundations affect the static bending behavior of composite panels. This research is a great resource for engineers, providing excellent guidance for the design, production, and utilization of these structures in real-world applications.