Commercial Finite Element Analysis Code Research Articles

Effect of Film-Induced Stress on Mechanical Properties at Stress Corrosion Cracking Tip

Oxide film rupture theory has become one of the most popular models to quantitatively predict the stress corrosion cracking (SCC) rate at crack tip of nickel-based alloys in high temperature and high pressure environments, and stress intensity factor has become an important parameter to measure the stress corrosion cracking rate. In order to further understand the fracture mechanism of the oxide film and the driving force of crack growth, film-induced stress intensity factor was proposed. To understand the effect of film-induced stress intensity factor on the micro-mechanical state at the tip of EAC (environmentally assisted cracking), the stress-strain in the base metal at the EAC tip was simulated and discussed using a commercial finite element analysis code. And then the effect of film-induced stress intensity factor on Mises stress, equivalent plastic strain, tensile stress, tensile strain and tensile plastic strain gradient of crack tip was obtained, which provides a parameter to improve the quantitative predication accuracy of EAC growth rate of nickel-based alloys and austenitic stainless steels in the important structures of nuclear power plants. Therefore the oxide film rupture theory was improved.

Parametric Evaluation of SiC/SiC Composite Cladding with UO2 Fuel for LWR Applications: Fuel Rod Interactions and Impact of Nonuniform Power Profile in Fuel Rod

SiC/SiC composites are candidates for accident tolerant fuel cladding in light water reactors. In the extreme nuclear reactor environment, SiC-based fuel cladding will be exposed to neutron damage, significant heat flux, and a corrosive environment. To ensure reliable and safe operation of accident tolerant fuel cladding concepts such as SiC-based materials, it is important to assess thermo-mechanical performance under in-reactor conditions including irradiation and realistic temperature distributions. The effect of non-uniform dimensional changes caused by neutron irradiation with spatially varying temperatures, along with the closing of the fuel–cladding gap, on the stress development in the cladding over the course of irradiation were evaluated. The effect of non-uniform circumferential power profile in the fuel rod on the mechanical performance of the cladding is also evaluated. These analyses have been performed using the BISON fuel performance modeling code and the commercial finite element analysis code Abaqus. A constitutive model is constructed and solved numerically to predict the stress distribution in the cladding under normal operating conditions. The dependence of dimensions and thermophysical properties on irradiation dose and temperature has been incorporated into the models. Initial scoping results from parametric analyses provide time varying stress distributions in the cladding as well as the interaction of fuel rod with the cladding under different conditions of initial fuel rod-cladding gap and linear heat rate. It is found that a non-uniform circumferential power profile in the fuel rod may cause significant lateral bowing in the cladding, and motivates further analysis and evaluation.

Modeling of elasto-viscoplastic behavior for polyurethane foam under various strain rates and temperatures

The polyurethane foam (PUF) is one of the most widely used composite materials in industrial and biomedical fields. It is frequently adopted in a wide range of environmental conditions, i.e., from static to dynamic compressive loads, and from cryogenic to high temperatures. Under these various environments, the PUF shows an elasto-viscoplastic behavior including three stages of material characteristics, namely, linear elasticity, a plateau with stress drop, and densification. Hence, the establishment of material model as well as the identification of material characteristics is the key of design and fabrication for PUF-based structures. In the present study, the strain rate- and the temperature-dependent elasto-viscoplastic behavior of polyurethane foam (PUF) which is extensively used in various fields and environments was computationally estimated under static/dynamic compression and the low/high temperature. To depict the three stages of material characteristics such as linear elasticity, a plateau with stress drop, and densification under uniaxial compression numerically, a Frank-Brockman type plastic multiplier and a Zairi type hardening-softening internal stress state variable were introduced. Then, the constitutive model was transformed as an implicit form using algorithmic tangential stiffness (ATS) method and was programmed as a user-defined material subroutine of commercial finite element analysis (FEA) code, namely, ABAQUS UMAT. Through the developed material subroutine, the strain rate- and the temperature-dependent static and dynamic stress-strain behaviors were numerically assessed. In addition, the change of material constants such as elastic modulus, yield stress, and hardening and softening control parameters was investigated quantitatively, and the polynomial multiple regression models were suggested. Consequently, the calculated results considerably correspond to experimental results, and through some supplements, accuracy can be improved. On using the proposed numerical method with some revision, it might be possible to anticipate the nonlinear behavior of the unknown material in various strain rate and temperature environment.

An anisotropic cyclic plasticity, creep and fatigue predictive tool for unfilled polymers

Resistance to Low Cycle Fatigue (LCF) as well as High Cycle Fatigue (HCF) of polymers and Polymer Matrix Composites (PMC) depends on various loading modes, frequency, temperature, aging, and environmental effects. On the other hand, fatigue, plasticity, and creep deformation mechanisms are history dependent phenomena, and in order to account for their interactions a coupled computational platform is required. Cyclic behavior of polymers and PMCs have been extensively explored experimentally, but a rational fatigue failure model that would be anchored in the microstructure and would allow for coupling between fatigue, creep and plasticity through the lifetime is lacking. This work aims at developing an anisotropic coupled cyclic plasticity, creep and fatigue life predictive technique in which a Continuum Damage Mechanics (CDM) framework is utilized to link microscale LCF and HCF damage mechanisms, i.e. microcracking and microvoiding, to the macroscale fatigue failure. This task is accomplished through a top-down multiscale CDM approach, in which microscale damage laws are calibrated with respect to the macroscale fatigue failure data. Cyclic plasticity and creep models are also incorporated to capture anisotropic inelastic behaviors of Polymer and PMC systems. The developed framework is implemented into a commercial Finite Element Analysis (FEA) code, viz. ABAQUS, through user-defined coding. The FEA model represents an isotropic polymer or homogenized PMC system in which various factors that affect fatigue behavior are studied. A cyclic jump method is also utilized to reduce the computational cost of the proposed coupled computational approach. The performance of the developed computational platform has been examined through numerical studies and comparison to experimental data. The developed fatigue life predictive tool may be utilized by engineers for lifetime prognosis and to improve the performance of Polymer and PMC structures.

Electroelastic fields for a piezoelectric threading dislocation in various growth orientations of gallium nitride

Abstract Linear piezoelectric formulations were employed to analytically evaluate the electroelastic fields generated by a single threading edge/screw dislocation in piezoelectric gallium nitride (GaN) thin film. All possible growth orientations, namely c -plane (polar), a - and m -planes (non-polar), and ( 11 2 ¯ 2 ) -plane (semi-polar) of GaN layers were considered for the analysis. Single piezoelectric threading edge and screw dislocations were also modeled by a commercial finite element analysis code, ABAQUS 6.14. The edge dislocation was modeled by invoking one-dimensional thermal strain analogy to effectively introduce an extra plane of atoms. The screw dislocation was modeled by creating a slip in opposite surfaces by applying opposite displacements of magnitude equal to half the Burgers vector parallel to the direction of the dislocation line. We also evaluated the Peach-Kohler force acting on a piezoelectric dislocation as well as the material force calculated by the J -integral. The effects of piezoelectricity and the line charge on electroelastic fields induced by a single dislocation were investigated for various growth orientations. We also evaluated the role of spontaneous polarization along c -direction in the presence of electroelastic fields generated by the dislocation. These results can be utilized in studying the influence of piezoelectric strains and electrical fields on the optoelectronic performance of GaN-based devices in the presence of dislocations. They can also be helpful in understanding the mechanics of misfit dislocations that form between the substrate and the film.

A new constitutive model for simulation of softening, plateau, and densification phenomena for trabecular bone under compression

A new type of constitutive model and its computational implementation procedure for the simulation of a trabecular bone are proposed in the present study. A yield surface-independent Frank–Brockman elasto-viscoplastic model is introduced to express the nonlinear material behavior such as softening beyond yield point, plateau, and densification under compressive loads. In particular, the hardening- and softening-dominant material functions are introduced and adopted in the plastic multiplier to describe each nonlinear material behavior separately. In addition, the elasto-viscoplastic model is transformed into an implicit type discrete model, and is programmed as a user-defined material subroutine in commercial finite element analysis code. In particular, the consistent tangent modulus method is proposed to improve the computational convergence and to save computational time during finite element analysis. Through the developed material library, the nonlinear stress–strain relationship is analyzed qualitatively and quantitatively, and the simulation results are compared with the results of compression test on the trabecular bone to validate the proposed constitutive model, computational method, and material library.

Micro-mechanical State at Tip of Environmentally Assisted Cracking in Nickel-based Alloy

Nickel-based alloys and austenitic stainless steels are widely used in the structures of primary circuit of nuclear power plants. Environmentally assisted cracking (EAC) of these materials is one of the most significant potential safety hazards in the primary circuit of nuclear power plants. Researches show that EAC in nickel-based alloy is a process of oxide film rupture and reform at the tip of EAC in the high temperature water environment of nuclear power plants. To understand the micro-mechanical state at the tip of EAC, the stress-strain in the oxide film and the base metal at the EAC tip was simulated and discussed using a commercial finite element analysis code, which provides a foundation to improve the quantitative predication accuracy of EAC growth rate of nickel-based alloys and austenitic stainless steels in the important structures of nuclear power plants.

Analysis of Dynamic Fracture Parameters in Functionally Graded Material Plates with Cracks by Graded Finite Element Method and Virtual Crack Closure Technique

Based on the finite element software ABAQUS and graded element method, we developed a dummy node fracture element, wrote the user subroutines UMAT and UEL, and solved the energy release rate component of functionally graded material (FGM) plates with cracks. An interface element tailored for the virtual crack closure technique (VCCT) was applied. Fixed cracks and moving cracks under dynamic loads were simulated. The results were compared to other VCCT-based analyses. With the implementation of a crack speed function within the element, it can be easily expanded to the cases of varying crack velocities, without convergence difficulty for all cases. Neither singular element nor collapsed element was required. Therefore, due to its simplicity, the VCCT interface element is a potential tool for engineers to conduct dynamic fracture analysis in conjunction with commercial finite element analysis codes.

Estimation of Stress Corrosion Cracking Growth Behavior Under Weld Residual Stress in the Bottom of a Reactor Pressure Vessel by Finite Element Analysis

A method for evaluating crack growth by repeatedly modeling and analyzing the transitional crack shapes is developed for a general computing environment in which a commercial finite element preprocessor and analysis code are used. The proposed method calculates stress intensity factors (SIFs) by finite element analysis (FEA) by directly distributing estimated weld residual stress obtained from noncracked components on the crack surface on the basis of the superposition principle. In present case, to specify a nonuniform residual stress distribution, a subroutine for a commercial FEA code (ABAQUS) was developed. Arbitrary crack shapes during the crack propagation were expressed by applying the submodeling technique which allowed arbitrary crack shapes to be meshed. The sequence of steps in the proposed method was designed to make it possible to consider complicated stress distributions, such as weld residual stress, and to express arbitrary crack shapes. The applicability of the proposed FEA based method was verified by comparing the result of a stress corrosion cracking (SCC) growth analysis results of a flat plate obtained with the proposed method and with the ASME code procedure. As an application example, the SCC growth behavior of a crack at the bottom of a nuclear reactor pressure vessel (RPV) involving a dissimilar metal weld and a unique geometry was evaluated by the proposed method. The evaluation results were compared with results obtained using a conventional method, i.e., the influence function method (IFM). Since both sets of results were in reasonable agreement, it was concluded that IFM can be applied to this case. Previously, it was difficult to assess the applicability of conventional methods, such as the code procedure and IFM, to a complicated problem because of the existence of complicated residual stress fields, dissimilar metals, and the complicated crack shapes involved. The proposed method using FEA allows the applicability of conventional methods to complicated crack growth evaluations to be assessed.

Fast Computation Based on an Iterative Substructure Method for Three-Dimensional Simulation of Multipass Welding

An efficient and reliable numerical analysis for three-dimensional (3D) multipass welding simulation is proposed in this paper. A fast analysis method to calculate 3D residual stress distribution in the multipass welds using the iterative substructure method (ISM) was developed and validated using other numerical analysis and measurement results. First, the analysis results by the developed method were compared with those by a conventional method using a commercial finite element analysis code. The comparisons were made for the analysis accuracy and the computational speed of the residual stress analysis in a multipass welded pipe joint. Both sets of analysis results for residual stress agreed well with each other. Furthermore, it was clarified that the developed analysis method could calculate the residual stress in a shorter computing time than the conventional analysis method. Next, the residual stress of the pipe joint computed by the developed analysis method was compared with measurement results obtained using the strain gauge method, and the good analysis accuracy was shown. Consequently, these comparisons demonstrated that the developed method for multipass welding simulation based on the ISM could calculate the residual stress distribution much faster at high analysis accuracy even when the size of the welding problems, such as for multipass welding, was large.

An efficient design sensitivity analysis using element energies for topology optimization of a frequency response problem

Abstract In this study, an efficient design sensitivity analysis (DSA) method is proposed for topology optimization of a frequency response problem. DSA of frequency response is an essential procedure for gradient-based topology optimization, which is used for noise and vibration control of structures. Traditionally, DSA of frequency response requires internal information concerning the finite element analysis (FEA) codes, such as stiffness and mass matrices, element formulation, and coordinate transformation. However, to obtain internal information on the general commercial FEA codes (e.g., MSC.NASTRAN, ANSYS, and ABAQUS), a substantial understanding of the codes and additional post-processing work is required. Furthermore, to handle modeling options (e.g., warping and offset) of complex three-dimensional (3D) built-up structures (e.g., automobile, ship, or airplane), a complicated coordinate transformation is additionally needed. In this paper, to overcome these difficulties, element energy-based DSA of a frequency response is developed using the polarization identity. In comparison with traditional DSA, the developed method is easy and efficient in terms of implementation effort because it requires only simple algebraic computations of element energies provided by commercial FEA codes. To demonstrate the validity and efficiency of the developed method, several numerical examples are solved with the commercial FEA code MSC.NASTRAN.

A temperature- and strain-rate-dependent isotropic elasto-viscoplastic model for glass-fiber-reinforced polyurethane foam

Abstract The primary aim of the present study is to provide a new constitutive model and its computational procedure for a glass-fiber-reinforced polyurethane foam (RPUF) subjected to various cryogenic temperatures and compressive loading rates. A Frank–Brockman-type isotropic elasto-viscoplastic model was introduced to describe the hardening and softening phenomena of RPUF under compressive loads. In addition, the increase of the yield strength and plateau according to the change of temperature and strain rates was demonstrated using the given constitutive model. The introduced numerical model was transformed as an implicit form and was implemented into a user-defined subroutine of commercial finite element analysis (FEA) code, i.e., ABAQUS UMAT. Based on the developed material library, the complex elasto-plastic behavior of RPUF under various cryogenic temperatures and strain rates was numerically estimated. The variation of material internal variables, such as hardening and softening control parameters, was quantitatively investigated, and the temperature- and strain-rate-dependent empirical formulae, namely, a polynomial multiple regression model, were proposed. Finally, the simulation results were compared with a series of compressive test results to validate the proposed method. On using the developed numerical method, it might be feasible to predict the unknown stress–strain behavior of RPUF under arbitrary severe environments.

Experimentation and simulation of moisture diffusion in foam-cored polyurethane sandwich structure

The moisture diffusion behavior of two-part thermoset polyurethane neat resin, woven E-glass fiber-reinforced polyurethane face sheet, closed-cell rigid polyurethane foam core and their corresponding sandwich specimens was investigated in this study. The vacuum-assisted resin transfer molding process was used to manufacture the polyurethane sandwich panels. Open-edge moisture diffusion experiment was conducted for sandwich panel and its constituents by immersing each type of samples in distilled water at room temperature for nearly seven months. Moisture diffusivities and solubility for neat resin, face sheet and foam core specimens were characterized according to the experimental analysis. The moisture diffusion behavior for closed-cell polyurethane foam was found to deviate significantly from classical Fick’s law, and a multi-stage diffusion model was thus proposed to explain this deviation using a time-dependent diffusivity scheme. A user-defined subroutine was developed to implement this scheme into the commercial finite element analysis code ABAQUS. A three-dimensional dynamic finite element model was developed to predict the moisture diffusion behavior in neat resin, face sheet, foam core and sandwich specimens. This finite element model was then validated by comparing simulation results with experimental findings.

Hashin·Puck 파손기준 기반 적층 복합재료의 섬유 및 기지파손 평가에 관한 연구

In the present study, the fiber and matrix failure of composite laminates under arbitrary biaxial stresses were evaluated based on separate mode criteria such as Hasnin and Puck theories. There is a limitation to predict the fiber-dominant and/or matrix-dominant failures under arbitrary stress states using limit criteria (maximum stress and maximum strain theories) and interactive criteria (Tsai-Hill and Tsai-Wu theories). There is little literature for failure analysis of ships and offshore composite structures considering advanced failure theories such as Hashin and Puck theories. Furthermore, there is not enough practical commercial finite element analysis (FEA) code which is basically adopted the separate mode criteria. Hence, in the present study, the user-defined subroutine of commercial FEA code ABAQUS for evaluation of fiber and matrix failures of composite structures was developed based on Hashin and Puck failure criteria. And then, the proposed subroutine was validated by comparing with a series of experimental results of carbon- and glass-implemented composite laminates to guarantee the reliability and usefulness of the developed method.

Free vibration analysis of perforated plate with square penetration pattern using equivalent material properties

Abstract In this study, the natural frequencies of the perforated square plate with a square penetration pattern are obtained as a function of ligament efficiency using the commercial finite-element analysis code ANSYS. In addition, they are used to extract the effective modulus of elasticity under an assumption of a constant Poisson's ratio. The effective modulus of elasticity of the fully perforated square plate is applied to the modal analysis of a partially perforated square plate using a homogeneous finite-element analysis model. The natural frequencies and the corresponding mode shapes of the homogeneous model are compared with the results of the detailed finite-element analysis model of the partially perforated square plate to check the validity of the effective modulus of elasticity. In addition, the theoretical method to calculate the natural frequencies of a partially perforated square plate with fixed edges is suggested according to the Rayleigh–Ritz method.

FEA Solutions for Simulating Multi-workpiece and Multi-process in Manufacturing Process of Submarine Welded Pressure Hull

To realize the numerical simulation of multi-workpiece and multi-process, two difficulties encountered in continuous finite element analysis (FEA) were brought forward firstly. Then the theoretical basis of merging measured initial residual stresses into FEA models was discussed. Based on which the mapping method of multi-model in continuous FEA was put forward. This method can be potentially used to realize such continuous FEA as manufacturing of welded submarine pressure hull by transferring the finite element analysis results between different processes and workpieces. No commercial FEA codes can give perfect solutions to these transfer processes at present. The commercial FEA code MSC.Marc was used as the FEA platform to realize simplifying analysis. Because of all the welding processes are multi-process, so the mapping method of multi-model in continuous FEA can be potential used in the welding simulation to make the calculating results be accurate.

점소성-손상모델 기반 피로균열 진전속도 전산 평가법 개발

In this paper, computational evaluation method for fatigue crack growth rate(FCGR) based on material viscoplastic-damage model is proposed. Viscoplastic-damage model expressing material constitutive behavior of 7% nickel steel is introduced and is implemented into commercial finite element analysis(FEA) code, ABAQUS, as a user defined material subroutine(UMAT) for application in the FEA environments. Verification of developed UMAT and material parameters of material model are carried out by uniaxial tensile test simulations of 7% nickel steel. Moreover, jump-in-cycles procedure and rearrangement of critical damage are employed and also implemented to the ABAQUS UMAT for fatigue damage analysis. Typical FCGR test results such as relationship between crack length and number of cycles and relationship between  and  could be obtained from FCGR test simulation using developed UMAT and these results are compared with experimental results in order to verify of proposed computational method.

Ultrasonic wave propagation in the corner section of composite laminate structure: Numerical simulations and experiments

Two-dimensional finite element simulations and experiments are presented to examine the ultrasonic wave propagation behavior in the corner section of CFRP (carbon fiber reinforced plastics) laminate structures. The numerical model consists of a right-angle corner section of CFRP laminate immersed in water and subjected to the ultrasonic wave incidence from its inner or outer side. The anisotropic stiffness constants of the unidirectional CFRP are identified experimentally and used to model the curved laminate structure. A commercial finite element analysis code is used to compute the reflection waveforms in the pulse-echo mode, and the effect of the laminate stacking sequence and the wave incidence direction is examined. It is shown that the reflection waveforms for the wave incidence from the outer side of the corner qualitatively resemble those for the plane laminate except that the echo signals of the former are substantially weaker. The numerical simulations are shown to well reproduce the qualitative features of experimental reflection measurements performed for the corner sections of 16-ply CFRP laminate. Experimental results indicate that the porosity content of the corner section can be estimated by the amplitude ratio of the surface and the back-wall echoes when a curvature-dependent calibration relation is properly used.

Free material stiffness design of laminated composite structures using commercial finite element analysis codes

In this work optimum stiffness design of laminated composite structures is performed using the commercially available programs ANSYS and MATLAB. Within these programs a Free Material Optimization algorithm is implemented based on an optimality condition and a heuristic update scheme. The heuristic update scheme is needed because commercially available finite element analysis software is used. When using a commercial finite element analysis code it is not straight forward to implement a computationally efficient gradient based optimization algorithm. Examples considered in this work are a clamped-clamped 2D plate loaded in two load cases and a point loaded six layered 3D double curved corner hinged shell. The first example displays the effect of varying the size of patches having the same parametrization, and the second illustrates the benefit of using a layered free material parametrization. The results provide information concerning topology, material anisotropy, and the direction having the maximum stiffness. The obtained results are compared to gradient based optimization solutions using Discrete Material Optimization and Continuous Fiber Angle Optimization implemented in a research code, where full access to the finite element analysis core is granted. This comparison displays the possibility of using commercially available programs for stiffness design of laminated composite structures.

Sampling-Based RBDO of Ship Hull Structures Considering Thermo-Elasto-Plastic Residual Deformation

We present a shape optimization method using a sampling-based RBDO method linked with a commercial finite element analysis (FEA) code ANSYS, which is applicable to residual deformation problems of the ship hull structure in welding process. The programming language ANSYS Parametric Design Language (APDL) and shell elements are used for the thermo-elasto-plastic analysis. The shape of the ship hull structure is modeled using the bicubic Ferguson patch and coordinate components of vertices, tangential vectors of boundary curves are selected as design variables. The sensitivity of probabilistic constraint is calculated from the probabilistic sensitivity analysis using the score function and Monte Carlo Simulation (MCS) on the surrogate model constructed by using the Dynamic Kriging (DKG) method. The sequential quadratic programming (SQP) algorithm is used for the optimization. In two numerical examples, the suggested optimization method is applied to practical residual deformation problems in welding ship hull structures, which proves the sampling-based RBDO can be successfully utilized for obtaining a reliable optimum design in highly nonlinear multi-physics problem of thermo-elasto-plasticity.