In-house Finite Element Program Research Articles

Electric-thermal-mechanics modeling for in-process phenomena during micro resistance spot welding spark plug of Pt and Inconel600

The spark plug is one of the important components in the gasoline engine's combustion chamber. To reduce vehicle emissions, the platinum spark plug is selected due to its good performance. Due to the high productivity of resistance spot welding (RSW), a micro-scale RSW process is employed to assemble the platinum tip to Inconel600 part in the production of spark plugs. In order to understand the electric-thermal-mechanics phenomena during micro resistance spot welding spark plug for controlling the welding quality and saving electric energy, a three-dimensional simulation model and the in-house finite element program JWRIAN-RSW3D were developed. The potential history and upper electrode displacement results were verified with experiments. Numerical case studies were made to investigate the influence magnitude of welding current on the electric-thermal-mechanics phenomena. The developed model reveals inside phenomena to clearly understand the welding mechanism for potential, current density, temperature, electrode displacement and their distribution/history as well as the molten zone. The comprehensive phenomena of maximum temperature distribution on both base metals and Inconel600 were clarified using a top perspective, revealing differences in distribution on the contact surface between horizontal and vertical sections. To achieve a complete welding joint, the molten zone on the contact area is required carefully in order to facilitate the bonding of both base metals. Based on simulation results for three welding conditions, the alternating current at the magnitude of 1.2 kA with the welding time of 0.1 s is recommended to obtain the welded joint with minimized energy consumption in production.

Advances on kinematically exact rod models for thin-walled open-section members: Consistent warping function and nonlinear constitutive equation

This work proposes two advances on kinematically exact rod models for thin-walled open section members: (i) an explicit analytical expression for the cross-section warping function, including both primary and secondary warping for arbitrary section geometries, and (ii) a nonlinear elastic constitutive equation with all higher-order strain terms included, suitable for truly finite strains. By not neglecting any of the strain terms at the constitutive level, full bending, compression and torsional strain couplings are enabled. This improves the model performance in capturing buckling phenomena and describing the developed post-critical configurations. Since the stress-resultants end up with elaborate expressions, numerical rather than analytical integration over the cross-section is preferred for their computation, which explains the need for knowing a priori the warping function (and its directional derivatives) in the entire cross-section, including in the thickness direction. The advances are implemented in a 7-DOF (3 displacements, 3 rotations and one warping intensity) rod model available in an in-house finite element program. Validation is performed using existing results from the literature as well as solutions obtained with shell models from a commercial software. The proposed advances proved to fix pathological behavior of previous rod models in both torsional and lateral–torsional buckling problems, as well as numerical convergence issues in developed post-critical configurations.

Steady-State Thermal Analysis of Functionally Graded Rotating Disks Using Finite Element and Analytical Methods

A steady-state thermal analysis for a hollow and axisymmetric functionally graded (FG) rotating disk with a uniform thickness was performed in this study. In the studied FG disk, metal and ceramic materials were considered for the inner and outer surfaces, respectively, when the material properties varied along the radial direction but not through material thickness variations. A power law distribution was employed to represent the material properties. Three different methods were used to present the temperature distribution along the radial direction of the FG disk, namely (1) an in-house finite element (FE) program, (2) the ANSYS parametric design language (APDL), and (3) an analytical solution. Furthermore, the in-house FE program presented the thermal stress and thermal strain of the FG disk. The weighted residual method in the FEM was used to present the temperature distribution when the material properties along an element are varying in contrast with using a commercial finite element software when the material properties are constant within an element to simulate FGMs. The accuracy of the in-house FE program was tested, and it was shown that the temperature distributions obtained by using the abovementioned methods were exactly the same. A parametric material gradation study was performed to understand the effects on the temperature, thermal strain, and stress. The material gradation was found to have a significant effect in this regard. The in-house finite element program enables one to perform a post-processing analysis in a more efficient and convenient manner than that through simulations in a finite element software program such as ANSYS. Lastly, this in-house code can be used to perform an optimization analysis to minimize the thermal strain and stress while the stiffness of the plate is maintained when the material properties within an element vary.

Hydro-Mechanically Coupled Numerical Modelling on Vibratory Open-Ended Pile Driving in Saturated Sand

Vibratory pile diving with resonance-free technique is an advanced construction approach that can play an important part in underground engineering. This paper aims to propose a numerical model for this construction approach, which commonly involves soils below the groundwater table. Such simulations are still challenging tasks as dynamic analyses considering hydro-mechanical interactions are very complicated. Several simulations have been performed by constructing a user-defined element in the finite element code ABAQUS or developing an inhouse finite-element program for this issue. These simulations have some limitations and pay less attention to open-ended piles. This paper presents a way to simulate the vibratory open-ended pile driving in saturated sand using the finite difference code FLAC3D. The model computation efficiency is increased around 67 times by the density scaling method and this method has little effect on the numerical stability. The proposed model can generally replicate the pore pressure results of a model test. The maximum excess pore pressures are predicted with a percent error of 2–22%, and these maximums occur near the pile toe. The excess pore pressure of an observation point slowly decreases after the pile toe passes the point. This work could provide an efficient and effective method for simulating vibratory open-ended pile driving in saturated sand.

Finite Element Analysis to Determine Stiffness, Strength, and Energy Dissipation of U-Shaped Steel Damper under Quasi-Static Loading

In seismic areas, the application of structural dampers becomes compulsory in the design of buildings. There are various types of dampers, such as viscous elastic dampers, viscous fluid dampers, friction dampers, tune mass dampers, yielding/ metallic dampers, and magnetic dampers. All damper systems are designed to protect structural integrities, control damages, prevent injuries by absorbing earthquake energy, and reduce deformation. This paper is a part of research investigating the behaviour of the U-shaped steel damper (as one type of metallic damper) that can be applied to the buildings in seismic areas. The dampers are used as connections between the roof and supporting structure, with the two general purposes. The first is to control the displacement of roof under an earthquake, and the second is to absorb seismic energy through the plasticity of some parts in dampers. If a strong earthquake occurs, the plasticity will absorb the seismic energy; therefore, heavy damage could be avoided from the roof’s mainframes. In this paper, several models of U-shaped steel dampers are introduced. Several parameters, such as elastic stiffness, maximum strength, and energy dissipation, are determined under two conditions. Firstly, static analysis of the proposed damper under variation of U-steel plate configurations, searching the model with more significant energy dissipation. Secondly, static analysis of the unsymmetrical and symmetrical damper under different loading directions. An in-house finite element program that involves both geometrical and material nonlinearities is developed as a problem solver. A quasi-static lateral loading is given to each model until one cycle of the hysteresis curve is reached (in the displacement range between -20 mm to +20 mm). The above parameters are calculated from the hysteresis curve. From the results, the behaviour of the U-steel damper can be described as follows. Firstly, increasing the energy dissipation in the lateral direction can be done by increasing the lateral stiffness of the damper. However, it can reduce the maximum elastic deformation of the damper. Secondly, under the random direction of loading, a symmetrical shape can increase the energy dissipation of the damper.

Fully-coupled electro-magneto-elastic behavior of unidirectional multiphased composites via finite-volume homogenization

The effective and localized electro-magneto-elastic behavior of periodic unidirectional composites is investigated in this work. Instead of adopting the classical micromechanics models or variational principle-based finite-element (FE) techniques, the finite-volume direct averaging micromechanics (FVDAM) is extended to fulfill this task by incorporating fully-coupled electro-magneto-elastic constitutive relations. Consistent with the mathematical homogenization theories, the mechanical displacements and electric/magnetic potentials are partitioned using two-scale expansion involving the macroscopic and fluctuating contributions. The generalized local stiffness matrices are constructed explicitly by relating the surface-averaged tractions, electric displacements, and magnetic inductions to the surface-averaged mechanical displacements and electric/magnetic potentials, followed which the continuity and periodic boundary conditions are applied. The homogenized coefficients and localized stress, electric/magnetic field distributions are validated extensively against the exact generalized Eshelby solution and an in-house FE program, as well as the experimental measurements, where perfect agreements are observed for all cases. The efficiency and convergence of the proposed multiphysics FVDAM (MFVDAM) are tested by comparing the execution time and localized fields as a function of mesh discretization, with the multiphysics FE (MFEM) results as references. Besides, the MFVDAM is encapsulated into the particle swarm optimization algorithm to deduce the optimal fiber volume fraction at which maximum magnetoelectric coupling effect may occur in the composite system with piezomagnetic ceramics reinforced with piezoelectric unidirectional fibers.

A computationally efficient locking free numerical framework for modeling visco-hyperelastic dielectric elastomers

In this paper, we present a finite element formulation for simulating the electromechanical behavior of nonlinear visco-hyperelastic dielectric elastomers undergoing isochoric finite strain deformations. The incompressible nature of dielectric elastomer results in the problem of volumetric locking. In order to alleviate this problem various techniques, such as selective reduce integration method, F-bar method, and mixed formulation have been used. In the present numerical framework, we treat this problem by adapting the computationally efficient J-bar method. This method of alleviating locking is based on the assumption of the dependence of volumetric density function only on the smoothed volumetric part of the multiplicatively decomposed deformation gradient. A staggered solution algorithm is used for solving the coupled nonlinear equations by decoupling displacement and electric potential fields. The present formulation is implemented into an in-house finite element program. Firstly, the finite element implementation of the proposed formulation is validated and demonstrated by investigating the effect of viscosity parameter on the electromechanical phenomenon of homogeneously deforming dielectric elastomers, i.e., voltage driven creep and pull-in instability. Further, for an in-homogeneously deforming bi-layered bending actuator, the computational efficiency of the proposed J-bar method employed in conjunction with the staggered solution approach is established over the conventional F-bar and multi-field formulations used with the monolithic solution scheme. Finally, we utilize the proposed formulation for investigating the effect of visco-elasticity on the electromechanical response of complex dielectric elastomeric actuators involving inhomogeneous deformations such as, bilayer bending actuators, grippers, and buckling pumps, when subjected to monotonic and constant electrical loads.

A numerical framework for modeling anisotropic dielectric elastomers

This paper reports a finite element based numerical framework for simulating the electromechanical behavior of nonlinear anisotropic dielectric elastomer actuators at finite strains. Based on the existing models for incompressible anisotropic neo-Hookean hyperelastic solids and ideal dielectric elastomers, a theory of anisotropic dielectric elastomers is outlined. The analytical expressions are derived for the tangent moduli of the anisotropic materials. A computationally efficient staggered solution algorithm is presented for solving the coupled nonlinear equations by decoupling displacement and electric potential fields. Selective reduced integration technique is used for alleviating the volumetric locking due to material incompressibility. The model is implemented into an in-house finite element program. We first validate the accuracy of the finite element implementation by considering the cases of homogeneous deformation, with a particular emphasis on the electromechanical instability. Subsequently we demonstrate the utility of the proposed numerical framework by analyzing two representative cases (bending and buckling actuators) involving inhomogeneous deformations. In both the cases, anisotropy in the mechanical properties of the elastomer is found to have a favorable influence on the actuation performance. Finally, for various mesh sizes, a comparison of the computation time required by the monolithic solution approach and the proposed staggered approach is presented to highlight the computational efficacy of the latter.

Impact Simulation of Straight Tube Heat Exchanger Subject to Cross-Flow

Heat exchangers have been among the most troublesome components of both nuclear power and chemical process plants. Heat exchanger tubes are supported at intermediate points by support plates. Flow- induced vibration of tube can cause it to impact or rub against a support plate or against adjacent tubes and can result in tube fretting wear. Simulation of heat exchanger tube/ support dynamic interaction is presented. The tube/ support interaction parameters, ‘RMS Impact force’ and ‘Contact ratio’ are studied. These are significant inputs to predict fretting wear limited life of the heat exchanger tubes. An algorithm includes equilibrium iteration and variable time stepping based on convergence criteria is implemented in an in-house finite element program. The tool is validated solving documented premature failure case of shell and tube type heat exchanger.

A new finite element for thick laminates and sandwich structures using a generalized and unified plate theory

SummaryThe contribution of this work is the implementation of a new elastic solution method for thick laminated composites and sandwich structures based on a generalized unified formulation using finite elements. A quadrilateral four‐node element was developed and evaluated using an in‐house finite element program. The C‐1 continuity requirements are fulfilled for the transversal displacement field variable. This method is tagged as Caliri's generalized formulation. The results employing the proposed solution method yielded coherent results with deviations as low as 0.05% for a static simply supported symmetric laminate and 0.5% for the modal analyses of a soft core sandwich structure. Copyright © 2016 John Wiley & Sons, Ltd.

Prediction of flow patterns during silo discharges using a finite element approach and its preliminary experimental verification

Obtaining a reliable discharge of particulate solids from a storage silo is a prerequisite to securing operational adequacy in solids handling processes. If a silo is poorly designed, an unreliable interrupted discharge often occurs. In this study, an in-house finite element (FE) program was modified to predict the particulate solids flow patterns during discharges from silos, and the effect of a double-cone insert on such flow patterns. In FE modeling, a Eulerian approach was adopted with an assumption of steady-state flow—a state that greatly facilitated investigations on the effects of double-cone inserts on the flow of particulate solids. Predictions were carried out on whether the discharge was in mass flow or funnel flow, associated with the inclination angle of the silo's hopper. Predicted results were in agreement with the Jenike Chart, and proved that an upper lateral pressure ratio value gave a better critical hopper half angle to achieve mass flow (EN 1991-4, 2006). The shape and size of the stagnant zone were further discussed to address the flow channel boundary between the flowing and static solids if the discharge was in a funnel pattern. Results also showed the effects of a double-cone insert on the flow patterns which converted silos from funnel flow to mass flow up to a certain hopper inclination angle and would improve the flow pattern even for shallower angles. Experiments were carried out to verify some of the predicted results. Some qualitative comparisons were made between the predicted results and experimental measurements, which indicated that further efforts are needed in predicting the shape of the stagnant zone (flow channel boundary) during funnel flow discharges.

Anisotropic hyperelastic behavior of soft biological tissues

Constitutive laws are fundamental to the studies of the mechanically dominated clinical interventions involving soft biological tissues which show a highly anisotropic hyperelastic mechanical properties. The purpose of this paper was to develop an improved constitutive law based on the Holzapfel–Gasser–Ogden's model: to replace the isotropic part with Gent constitutive law so as to model the noncollagenous matrix of the media due to its generality and capability to reproduce the Neo-Hookean model. This model is implemented into an in-house finite element program. A uniaxial tension test is considered to study the influence of material parameter in Gent model and which represents the angle between the collagen fibers and the circumferential direction. A simulation of an adventitial strip specimen under tension is performed to show the applicability of this constitutive law.

속도의존성 결정소성 모델 기반의 유한요소해석을 통한 BCC 금속의 변형 집합조직 예측

In the current study, a rate-dependent crystal plasticity finite element method (CPFEM) was used to simulate flow stress behavior and texture evolution of a body-centered cubic (BCC) crystalline material during plastic deformation at room temperature. To account for crystallographic slip and rotation, a rate-dependent crystal constitutive law with a hardening model was incorporated into an in-house finite element program, CAMPform3D. Microstructural heterogeneity and anisotropy were handled by assigning a crystallographic orientation to each integration point of the element and determining the stiffness matrix of the individual crystal. Uniaxial tensile tests of single crystals with different crystallographic orientations were simulated to determine the material parameters in the hardening model. The texture evolution during four different deformation modes - uniaxial tension, uniaxial compression, channel die compression, and simple shear deformation - was investigated based on the comparison with experimental data available in the literature.

Ultimate Strength Characteristics of a Ship's Deck Stiffened Plate Structure in the Presence of Camber Parabolic Curvature

The main target of this research is to identify the effects of camber parabolic curvature on the ultimate strength and behavior of stiffened plates under in-plane compression. A parametric model for the study of the problem is created. The model includes different parameters related to plate, stiffeners, and also parabolic camber curvature. Three distinct sensitivity cases are assumed. In each sensitivity case, many different models are analyzed and their ultimate strengths are obtained using an in-house finite element program. Ultimate strength and behavior of the models with different ratios of parabolic curvature are compared to each other and interpreted.

Modelling of fuel bundle vibration and the associated fretting wear in a CANDU fuel channel

In this paper a numerical model is developed to predict the vibration response of a CANDU11CANDU® is a registered trade-mark of Atomic Energy of Canada Limited (AECL). fuel bundle and the associated fretting wear in the surrounding pressure tube. Two excitation mechanisms are considered in this model: turbulence-induced excitation caused by coolant flow inside the fuel channel, and seismic excitation. For the seismic excitation, simulated accelerograms of a magnitude 6 earthquake for the eastern part of Canada are considered. These accelerograms are compatible with the 2005 national building code of Canada uniform hazard spectrum (UHS). The numerical model can be easily adapted to include the effects of fuel bundle impact during the refuelling and start-up of the reactor, and the acoustic pressure pulsations caused by the primary heat transport (PHT) pumps. The simulation is performed for a typical CANDU fuel bundle with 37 fuel elements using INDAP, which is an in-house general purpose finite element program capable of simulating the nonlinear dynamics of nuclear and power equipment subjected to fluid excitation. The clearances between the buttons of the inner fuel elements, and between the bearing pads of the outer fuel elements and the pressure tube, were measured from a typical CANDU fuel bundle. Some variability among the measured clearance values was observed. Therefore, probability density functions of the measured clearance values were established and the simulation was performed for the probabilistic distribution of the clearance values. The contact between the fuel bundle and the pressure tube is modelled using pseudo-force contact method. The results, along with the proposed modelling technique, can be used in future CANDU reactors to avoid fuel and pressure tube fretting damage due to the aforementioned excitation mechanisms.

Numerical investigations on dynamic performance of stiffened box steel bridge piers

The aim of this paper is to carry out extensive numerical investigations about the effect of various structural parameters on the dynamic performance of stiffened box steel bridge pier under a strong earthquake ground motion. The considered structural parameters are the local slenderness ratios of stiffener and stiffened wall as well as the global slenderness ratio of the pier. In the present study, all investigated piers are made of high tensile steel with high yield ratio. The non-linear time history analyses are carried out using in-house Finite Element Program DYNAPSS, recently developed by the first author. This program is verified by comparing its results with the results obtained by the general FE program. In this program, the geometrical nonlinearity is considered on the bases of Total Lagrangian formulation, while the non-linearity of structural steel material is considered through implementation of modified multisurface cyclic plasticity model by which real characteristics of high tensile steel material such as, Plateau, Massing type of Bauschinger’s effect, disappearing of Plateau and cyclic strain hardening, are accurately modeled. The results are closely examined in respect with the damage index criterion. From this study, it is found that the increase in slenderness ratios of stiffener does not only increase the damage index, but also may lead to the full collapse. Furthermore, the damage index increases with the increase of local slenderness ratio of stiffened wall and the global slenderness ratio. Also, it is found that when the loacal buckling is not the dominant eigen mode and the pier behave as a single degree of freedom, the natural period has destructive effects when it is close to predominant period of the earthquake. Finally, contour plots of damage index values are presented. These contour plots may be greatly useful for the design of stiffened box steel bridge piers, where, critical values of structural parameters corresponding to certain value of damage index could be determined.

Asynchronous Swarm Structural Optimization of Satellite Adapter Ring

The shape and size of a satellite adapter ring are optimized in this paper using particle swarm optimization and an in-house finite element program. For a realistic high-fidelity modeling of the adapter ring, a commercial preprocessor is used. However, optimization of a high-fidelity model inevitably involves longer computation time; therefore, parallelization is essential to shorten the total elapsed time. Furthermore, fitness evaluation time by the finite element simulation differs from case to case, which unavoidably causes idling of some of parallel computing resources. To overcome the inefficiency induced by the irregularities of individual fitness evaluation, an asynchronous parallel swarm algorithm is developed and applied to the structural optimization of the adapter ring with 19 design variables. The adapter ring’s total mass is reduced to 33.4 kg from 35.9 kg within 202 min. The asynchronous version also performs almost twice better compared with the synchronous one. The methodology proposed in this paper offers an attractive advantage for complex structural design, both in aspect of computational time and global search.

Finite Element Implementation of an Elastoplastic Constitutive Equation in the Presence of Hydrogen

Hydrogen-enhanced localized plastiticity (HELP) is recognized as a viable mechanism of hydrogen embrittlement. A possible way by which the HELP mechanism can bring about macroscopic material failure is through hydrogeninduced cracking. In this work, according to the HELP theory, a constitutive formulation for elastoplasticity model in the presence of hydrogen is presented. To model the local phenomena associated with hydrogen, the local flow stress is considered decreasing with the increasing of hydrogen concentration. Following the previous work, a new module in the open source code ADVENTURE-Solid has been developed by the authors through considering the effect of hydrogen on material softening in microscale, which equips the open source code ADVENTURE-Solid software for studying hydrogen-plasticity interactions. We then combine the ADVENTURE-Solid with an in-house advection diffusion finite element program, to analyze a transient hydrogen diffusion-elastoplastic coupling problem ahead of a crack tip. To validate the new module in the ADVENTURESolid, a set of numerical test cases are presented and discussed. Obtained results show good agreement with previous results.

A closed form solution for the uniaxial tension test of biological soft tissues

This paper concerns the modeling of biological soft tissues in the framework of anisotropic hyperelasticity. A closed form solution is proposed in the special case where uniaxial unconstrained tension loading is applied to a strip modeled by Holzapfel–Gasser–Ogden's (HGO) strain energy. The classical Cardano's formula is used to calculate the solution. This solution is investigated for different values of β which represents the angle between the collagen fibers and the circumferential direction. This study allows for the understanding of the reason why a one-to-one correspondence does not exist between the principal stretch and the fourth invariant of the right Cauchy–Green deformation tensor. It is demonstrated that the relationship becomes non-bijective when β is greater than a critical angle of 54 . 73 ∘ . The HGO model is implemented into an in-house finite element program and numerical results are in good agreement with theoretical ones.

Buckling of filament-wound composite cylinders subjected to hydrostatic pressure for underwater vehicle applications

The buckling and failure characteristics of moderately thick-walled filament-wound carbon–epoxy composite cylinders under external hydrostatic pressure were investigated through finite element analysis and testing for underwater vehicle applications. The winding angles were [±30/90]FW, [±45/90]FW and [±60/90]FW. ACOS, an in-house finite element program, successfully predicted the buckling pressure of filament-wound composite cylinders with 2 ∼ 23% deviation from the test results. The analysis and test results showed that the cylinders do not recover the initial buckling pressure after buckling and that this leads directly to the collapse. Major failure modes in the test were dominated by the helical winding angles.