Loading Boundary Conditions Research Articles

Generalized photo-thermo-microstretch elastic solid semiconductor medium due to the excitation process

A novel model in the photo-thermoelasticity theory with microstretch properties is studied. The plasma-elastic-thermal plane waves are propagated in a linear isotropic generalized photo-thermo-microstretch elastic semiconductor solid medium. The photothermal excitation occurs in the context of the microinertia of the microelement process during two-dimensional (2D) deformation. The harmonic wave techniques are used to get the solutions for the basic variables. The analytical solution of the main physical fields; carrier intensity, normal displacement components, temperature, stress load force, microstress and tangential coupled stress can be obtained. Some graphics illustrated when using the plasma, thermal and mechanical load boundary conditions are applied at the outer free surface of the elastic medium. Some semiconductor materials, as silicon (Si) and Germanium (Ge), are used to make the numerical simulation and some comparisons in different thermal memories are made. The main physical variables with new parameters are discussed theoretically and shown graphically.

Aerodynamic analysis and structural integrity for optimal performance of sweeping and spanning morphing unmanned air vehicles

An optimized morphing unmanned aerial vehicle capable of sweeping and spanning its wings is proposed and analyzed aerodynamically and structurally in order to examine and improve its efficiency, flight transition analysis, and structural integrity. The lift to drag ratio of five different flight modes of the drone is examined using the Pollhamus lift theory to evaluate the aerodynamic performance during the transition phases. To verify Pollhamus lift theory in the determination of the aerodynamic loads for the four configurations of the morphing unmanned system, namely, fully compressed, fully expanded, fully swept, and fully expanded and swept, 3D panel and Vortex Lattice Methods are used. In order to improve the structural stability during the transition phase of the flight, a finite element analysis is conducted to approximate pressures on the wings of the unmanned system under a load and specific boundary conditions. The information from the finite element simulations is then utilized to determine the number of support rods needed for structural stability and the ideal positions of the rods. The vibratory qualities of the wings are also analyzed through modal and transient analyses. According to the results of the modal analysis, because of the low natural frequency of the wing, there is a strong possibility of flutter and a vibratory response due to the aerodynamic force and disturbances. The transient analysis demonstrates that the stress waves propagating through the wings, due to an excitation force, tend to localize around the circumference of the support rods.

Удовлетворение критериев прочности модельного перекрытия из ПКМ с учетом нелинейности заполнителя при различных характерах нагружения

This study compares different strength criteria in static loading simulation of a polymeric-composite grillage for different loading scenarios, boundary conditions and models of physical material behaviour. The paper discusses a detailed, structurally similar model of grillage made up by three-layered parts taking into account contact interaction (not the joint one) at the boundaries of bearing layers and the filler, with consideration of physically linear and nonlinear model of filler behaviour. The study applies volume-shell FE idealization. The loading (distributed and local)is simulated as per a step-wise procedure until the selected failure criteria are met, i.e. until limit loads (according to various hypotheses) are achieved. The paper gives examples of limit load calculations and their respective states of grillage for different variants of bearing circuit fastening and different loading types. The study yielded the fields of stress-strain parameters and the four principal complex failure criteria. The study discusses the effect of overall grillage compliance, as well as the effect of local (i.e. not affecting the compliant areas of the flooring) and distributed loading upon the limit state pattern of the structure and the level of its bearing capacity. It also estimates the effect of soft non-linearity of the filler upon limit stress-strain state pattern and limit load level, as well as upon the localization of «triggering» zones for non-dimensional criteria.

Nonlocal elasticity theory for lateral stability analysis of tapered thin-walled nanobeams with axially varying materials

The lateral-torsional buckling behavior of functionally graded (FG) non-local beams with a tapered I-section is here investigated using an innovative methodology. The material properties are supposed to vary continuously along the longitudinal direction according to a homogenization procedure, based on a power-law function, whereas the nanobeam is modeled within the framework of a Vlasov thin-walled beam theory. The flexural-torsional governing equations of the problem are derived based on the Eringen's nonlocal elasticity theory and the energy method. The system of lateral stability equations is, thus, reduced to a fourth-order differential equation in terms of the twist angle by uncoupling the equilibrium differential equations. The buckling loads are finally determined using the differential quadrature method (DQM), which is here applied as numerical tool to solve directly the differential equations of the problem in a strong form. A systematic investigation checks for the influence of some parameters such as the power-law index, tapering ratios, loading height parameter, boundary conditions and non-local parameter, on the lateral stability resistance of the tapered I-nanobeams. The numerical outcomes of this paper can be used as benchmarks for further studies on nanoscale tapered thin-walled beams.

Transient stress and deformation analysis of a shear deformable FG rotating cylindrical shell made of AL-SIC subjected to thermo-mechanical loading.

ABSTRACT Transient stress and deformation analysis of a functionally graded rotating cylinder made of Al-Sic with short length under thermal and mechanical loads is studied in this paper. It is assumed that the cylinder is located on a friction bed and is subjected to an external torque. The material property is assumed to be variable along the radial direction based on volume fraction distribution. Thermal conductivity equation with time parameter is solved to obtain temperature distribution by Finite Difference Method. First-order shear deformation theory is used to derive kinematic relations. The governing equations are derived using minimum total potential energy and Euler relations. These governing equations are solved using the method of Eigenvalue and Eigenvector. The physical and loading boundary conditions are applied to obtain unknown coefficients. As the main result of this paper, it is concluded that the radial displacement is uniform at the middle of a cylindrical shell and is decreased to zero with an increase of axial coordinate.

Studies on large deflection of geometrically nonlinear corrugated structures

This manuscript proposes an iterative scheme for geometrically large deflection analysis of corrugated structures using the nonlinear shooting method. The corrugated structure is modeled by discretizing it in several corrugated units. The solution of each unit is obtained assuming it to be consistering of several beam elements. Finally, the deflection of a corrugated structure is calculated assembling the deflection of each of the corrugated units. The formulation has been extended to various boundary conditions (fixed–fixed and fixed–hinged) and loading conditions (point loads and uniformly distributed load). This shows the versatility of the methods in solving various problems. Furthermore, two prototypes of the corrugated structure are fabricated using aluminum and carbon fiber reinforced polymer (CFRP) laminate, and a moment actuation test is performed. The deflections of these prototypes obtained using the proposed iterative scheme are compared with the numerical model and validated with experiments, and results are found to be in good agreement.

Numerical analysis of porous blank die forging in the die with the implementation of active friction forces

The paper provides the results of simulating the hot die forging of porous powder preforms with active friction forces applied along the lateral surface of the deformable blank by means of internal cohesion in the die-material system. The study covers the evolution of relative density distribution over the blank cross section at different stages of deformation, stress-strain state and total strain force while varying the loading boundary conditions by changing the initial compression force applied to elastic elements that prevent the die from displacement. It is shown that active friction forces acting on the periphery of the forging adjacent to the die inner side result in areas with a significantly higher deformation intensity compared to deformations in the center of the blank volume. At the same time, the volume of the high deformation intensity area and maximum values of deformation increase with a decrease in the spring initial compression force and, accordingly, with an increase in the die displacement value during deformation. Automatic die displacement due to internal cohesion in the die-deformable material system leads to a decrease in the total deformation force, and with a decrease in the die displacement value during deformation, the deformation force increases.

Analytical solutions to the advection-diffusion equation with Atangana-Baleanu time-fractional derivative and a concentrated loading

In this communication we have studied well known physical process of two-dimensional advection–diffusion phenomena. The advection–diffusion equation is time-fractionalized by exploiting Atangana-Baleanu fractional derivative operator. This fractionalization is achieved in the generalized constitutive equation of the mass flux density vector. The fractionalized two-dimensional advection–diffusion equation turns out to be a two-dimensional nonlinear fractional partial differential equation. This partial differential equation is considered under the hypothesis of an initial concentrated loading and Robin type boundary conditions. The analytical expression of the solution is determined for this boundary value problem by employing the integral transforms method, namely, the Laplace transform, sine-Fourier transform and finite sine–cosine Fourier transform. The effects of fractional parameter α on the concentration obtained from the analytical solution, for various parameters of interest, are illustrated graphically with the help of software Mathcad. The graphs illustrate that the memory effects are remarkable for small values of time and ordinary for large values of the time.

Permeability Evolution of Two-Dimensional Fracture Networks During Shear Under Constant Normal Stiffness Boundary Conditions

The permeability evolution of fractal-based two-dimensional discrete fracture networks (DFNs) during shearing under constant normal stiffness (CNS) boundary conditions is numerically modeled and analyzed based on a fully coupled hydromechanical (HM) model. The effects of fractal dimension, boundary normal stiffness and hydraulic pressure on the evolutions of mechanical behaviors, aperture distributions and permeability are quantitatively investigated. The results show that with increasing confining pressure from 0 to 30 MPa, the permeability decreases from the magnitude of 10−13 m2 to 10−16 m2, which is generally consistent with previous models reported in the literature. With the increment of shear displacement from 0 to 500 mm, the variations in shear stress, normal stress and normal displacement exhibit the same patterns with the conceptual model. As shear advances, the permeability evolution exhibits a three-stage behavior. In the first stage, the permeability decreases due to the compaction of fractures induced by the increasing shear stress from 0 to the peak value. In the second stage, the permeability holds almost constant values under constant normal load (CNL) boundary conditions, whereas that under CNS boundary conditions decreases by approximately one order of magnitude. Under CNS boundary conditions, although the aperture of shearing fracture increases enhancing its own permeability, the apertures of surrounding fractures are compacted due to the simultaneous increases in the normal and shear stresses, which result in the decrease in the total permeability of DFNs. When the fractal dimension increases from 1.4 to 1.5, the permeability increases following exponential functions in the early stage of shear, which fail to characterize the permeability in the residual stage due to the complex flow path distributions. At the start of shear, the ratio of permeability perpendicular to the shear direction to that parallel to shear decreases approximately from 1.0 to 0.5 and then gradually decreases from 0.5 to 0.3 in the residual stage. The hydraulic pressure tends to open up the fractures and enhances the permeability. The magnitude in permeability enhancement is of approximately the same order with the increase in the hydraulic pressure.

Cycle resolved control for HCCI engine load range expansion by combining ion current and pressure sensor

Homogeneous charge compression ignition (HCCI) offers a high potential in engine efficiency enhancement and ultra-low NOx raw emissions. However, the main difficulty in HCCI combustion is its controllability of the ignition, especially at boundary conditions. At these conditions, stochastic abnormal combustion may happen, such as incomplete combustion or knock. Traditional engine map-based control is not enough to overcome these problems. Real-time in-cylinder combustion diagnosis and cycle resolved combustion control are required. In this study, the ionization process during negative valve overlap (NVO) interval in HCCI engines is numerically studied. It is identified that the ion current can reflect the quality of fuel reforming, which has been validated in the experiments. Compared to other studies that only use a single sensor (pressure sensor or ion current sensor), here for the first time, two sensors are combined to enhance the diagnostic accuracy. Besides, for the first time, ion current during NVO is employed for control. The experiments were conducted both at light load and high load boundary conditions. For light load boundary condition, by combining two sensors, the diagnostic accuracy rate of stochastic incomplete combustion is about 91.3%, and the misjudgment rate is reduced by 30% compared to only use one of them. After the controller is activated, the standard deviations of CA50 (σCA50) and IMEP (σIMEP) are reduced by 14.6% and 11.3%, respectively. For high load boundary condition, σCA50 and σIMEP are reduced by 12.3% and 15.4% respectively. Besides, the knock intensity is reduced by 9%. Ultimately, IMEP of the minimal load is reduced from 0.23 MPa to 0.18 MPa with an extension of 22%, and IMEP of the maximum load is expanded from 0.33 MPa to 0.4 MPa with an expansion of 21%.

Laboratory investigation into effect of bolt profiles on shear behaviors of bolt-grout interface under constant normal stiffness (CNS) conditions

Abstract Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering. It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system. Previous studies have proposed some optimal rib parameters (e.g. rib spacing); unfortunately, the interface shear behaviors are generally ignored. Therefore, determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible. The load-bearing capacity and deformation capacity vary as bolt profiles differ, suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles. The aim of this study is to investigate the effects of bolt profiles (with/without ribs, rib spacing, and rib height) on the shear behaviors between the rock bolt and grout material using direct shear tests. Thereby, systematic interfacial shear tests with different bolt profiles were performed under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does, in particular at the post-yield stage. The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions, and optimize selection of rock bolts under in situ rock conditions.

Detailed analysis of combustion stability in a spark-assisted compression ignition engine under nearly stoichiometric and heavy EGR conditions

Extending the load range of low-temperature combustion is of priority to meet future CO2 and emission targets for reciprocating engine applications. Spark assist is a feasible solution to this challenge for mono-fuel homogeneous charge compression ignition (HCCI). This paper explains how spark-assisted compression ignition (SACI) enables ultra-low NOX targets to be met, with acceptable pressure rise rates and combustion stability, at high load boundary conditions, favourable for HCCI/SACI transition. The work provides new methods of combustion analysis which give better understanding of the mechanisms and their implementation for real-time control of SACI engines. The goals are achieved by a combination of single-cylinder engine research and high-fidelity/high-speed, model-based calculations, performed on an individual cycle basis. The results show that determining the start of the kinetic phase in SACI is possible via standard combustion indicators. The new method is two orders of magnitude faster than the commonly used spline-Wiebe approach. With real-time capability and proven correlation to temperature evolution, triggered by propagating flame, the method enables in-cycle predictive control. Additionally, it gives a deeper insight of the mechanisms underpinning the demonstrated superior performance. The study shows the capability to run SACI at indicated mean effective pressure (IMEP) of 0.5 MPa with engine-out NOX below Euro VI’s heavy-duty engine limit and with specific fuel consumption of 207 g/kWh. Importantly, pressure rise rate and variation in IMEP do not exceed 0.25 MPa/CAD and 3% respectively. Margins for critical parameters are far greater than for baseline autonomous HCCI, providing significant load extension potential.

Effects of normal stiffness on the shear behaviors and acoustic emissions of rock joints

In this study, direct shear tests were conducted on plaster joints under various boundary conditions. During shearing, the acoustic emission (AE) was measured by the PAC AE system. The damage of the asperities was evaluated based on the AE signals. The effects of the normal stiffness on the shear behavior and asperity damage were studied, and the corresponding AE characteristics were analyzed. The results show that the peak shear stress for rock joints under constant normal load boundary conditions is larger than that under the CNS boundary conditions. The shear dilation decreases as the normal stiffness increases. The AE signals are more active in the post-peak stage for the rock joints sheared under higher normal stiffness conditions. Both the AE count and AE energy rate increase with an increase in the normal stiffness. Thus, the total AE events increase with increasing normal stiffness.

Stress and deformation analysis of a connecting rod by using ANSYS

The connecting rod is the intermediate component between the piston and the crankshaft, and its primary function is to move the up and down from the piston pin to the crankshaft converting the reciprocating motion into rotary motion of the piston and crankshaft.
 This study describes a numerical analysis of connecting rod for determining the critical stress regions. During the analysis of connecting rod, loads corresponding to different engine speeds were assumed to be statically applied, and their corresponding stress and deformation values were evaluated. The power and torque values of engine were utilized to be used as the load boundary conditions in static simulation model, other parameters those of used as input values were geometric dimensions of connecting rod and its material properties.
 Numerical analyses were performed for the connecting rod made of SS 304 material. A 3D CAD model was developed for the connecting rod through the SOLIDWORKS software, then drawn solid model was transferred to the ANSYS software with Workbench module. Von mises stress and deformation analyses were evaluated under the different engine speeds with indicating that connecting rod did not failure and fractured under the applied external loads.

Comparative experimental study of fire resistance of two-way restrained and unrestrained precast concrete composite slabs

This paper presents the results of tests to investigate fire performance of two-way restrained precast concrete (PC) composite slabs under the standard ISO 834 condition. The fire tests include three specimens with different load levels and boundary conditions – with or without restraints around the edges. Tensile membrane action was observed to a moderate extent in all specimens tested, including the reference test at ambient temperature. No debonding was observed at the interface between the bottom precast slab and the top cast-in-situ composite layer for the restrained PC composite slabs, but cracks formed at the interface in the un-restrained PC composite slab. These results demonstrate much increased fire resistance due to restraint effects (195 min vs. 130 min) if the same load (195 kN) is applied, but similar fire resistance if based on load ratio (131 min and 130 min at the same load ratio of 0.42). A number of existing theoretical methods developed for calculating tensile membrane action effects of two-way concrete slabs, as well as the conventional yield line theory, are employed to calculate the load carrying capacities. They indicate that for the type of slabs investigated in this paper, the improvement due to tensile membrane action is moderate.

The Transverse Shear Effect of a New Strain Based Sector Finite Elements for Plate Bending Problems

In this paper, we present the transverse shear effect on the plate bending. The element used is a sector finite element called SBSP (Strain Based Sector Plate-Kirchhoff Theory-), it used for the numerical analysis of circular thin plate bending., and it based on the strain approach. This element has four nodes and three degrees of freedom per node. Through the numerical applications with different loading cases and boundary conditions; This makes the present element robust, better suitable for computations.

Study of the Mechanics of Spatial Elastoplastic Strain and Fracture of Weld Joints of Austenite Steels

The results of calculated–experimental and numerical studies of the relative strain intensity factors in the case of semi-elliptical inclined surface cracks in the weld joints of 12Kh18N10T austenite stainless steels with the assumption of redistribution of strain and initial residual stresses under nonlinear boundary loading conditions are presented. A parametric equation for the determination of the relative strain intensity factors in the case of semi-elliptical inclined surface cracks is given. This new parametric equation allows one to evaluate the comparative survivability of the local zones of details and construction in the bulk weld joint upon elastoplastic static and low-cycle loading.

The consistency of the nonlocal strain gradient integral model in size-dependent bending analysis of beam structures

Despite the extensive applications of the nonlocal strain gradient theory to predict the size-effect of beam-like structures, the inconsistencies of its differential form have been uncovered recently. For bounded beam structures, there are additional constitutive boundary conditions should be taken into account to ensure the strict equivalence between the differential constitutive relation and the originally integral ones. Such an improvement would lead the problems to have more mandatory boundary conditions than those required, and therefore, there must be a trade-off between these boundary conditions. A strategy by omitting the higher-order (non-standard) boundary conditions has been presented recently and from which consistently size-effects can be obtained. However, it was pointed out that this treatment no longer fully meets the requirements of the energy-variational principle. In this paper, an alternative methodology by directly using the originally integral model is proposed for the first time. The advantages of such a strategy are pertinently evidenced by investigating Euler-Bernoulli curved beams made of functionally graded materials. The Laplace transform technique is applied to solve the integral constitutive equations and differential governing equations, which is an original contribution of this paper. In contrast to the differential forms, the originally integral model can satisfy energy conservation well. Meanwhile, adopting specific higher-order boundary conditions, numerical results show consistently stiffening and softening effects for all boundary edges and loading conditions.

Fish Cells, a new zero Poisson’s ratio metamaterial—part II: Elastic properties

Fish Cells as a new metamaterial with zero Poisson’s ratio in two planar directions is introduced with application in morphing aircraft skin. In order to tailor the design of this metamaterial for arbitrary loadings, equivalent elastic properties of the Fish Cells metamaterial are derived and analyzed using analytical and numerical methods. The admissible range of geometric parameters is presented and variation of elastic properties with parameters is studied. The effective elastic modulus of the metamaterial is derived analytically and verified with finite element models. The in-plane and transverse shear modulus of the metamaterial are evaluated using finite element analysis where accurate periodic boundary conditions for in-plane shear loading are investigated. The lower and upper bounds of the transverse shear modulus are derived based on strain and complementary energy relations which are verified with finite element results. As zero Poisson’s ratio behavior of the Fish Cells topology is proved, derivative geometries from this topology with zero Poisson’s ratio behavior are also presented.

Comparative analysis of a human tooth using different materials based on the finite element method

This study deals with the biomechanical analysis of a human tooth using Finite Element Method (FEM). For the analysis, a three-dimensional (3D) CAD model of the human tooth is modelled from the online available tooth scanning data in dicom format, which is processed using ITK-Snap and Meshlab software to generate a file in iges format. The tooth’s CAD model in iges format is imported in a FEM based software called Ansys. The analysis is performed using five materials namely, natural tooth material, Gold, Zirconia, Commercially Pure Titanium (CP Ti) alloy, and Ceramics. All the five considered materials are analysed for the same boundary and compressive loading conditions. The resulting stresses and deformations are compared for the different considered materials.