Full 3D Finite Element Analysis Research Articles

A multiscale strategy for assessing the micro-scale stress distribution in the matrix of textile composites

In this work, a multiscale strategy for estimating the local stress fields in the matrix of woven composites is presented. This is a fundamental tool for predicting the static and fatigue bundle crack initiation. The strategy adopts first an analytical model to estimate the average stresses in the bundles at the meso-scale. These are used as an input for 2D Finite Element (FE) analyses on representative volume elements to calculate the local stress fields in the matrix at the micro-scale. In particular, the cumulative distribution function of the local stress components in the matrix are predicted. From that, the average stresses in a control volume of the matrix are obtained, to be used for assessing the crack initiation in off-axis bundles. The entire strategy is validated experimentally, in terms of elastic properties, and numerically, in terms of average bundle stresses and local stress fields obtained through full 3D FE analyses.

Finite element analysis on titanium-tantalum lattice structures fabricated using selective laser melting

In this study, Finite Element Analysis (FEA) is used to study the mechanical properties of titanium-tantalum (TiTa) alloy lattice structures fabricated using selective laser melting (SLM) in previous literature. Based on the actual measured dimension of the experiment samples, the geometry is reproduced and analyzed in ANSYS using two different approaches (beam model, full-3D model). The mechanical properties, such as elastic modulus and yield strength, are then predicted using the two ANSYS models and compared to the experiment results. It is found that both beam model and full-3D model can predict the elastic modulus of the fabricated TiTa parts with high accuracy. However, for yield strength, the predictions from beam model and full-3D model are around 50 % and 65 % in average lower than the experimental data respectively. Finally, in order to validate the design parameter, e.g. porosity levels, the mechanical properties of the lattice structures with porosity from 50 % to 90 % are studied using full-3D FEA model and the results are found to follow the Gibson-Ashby model.

Contact analysis of laminated structures including transverse shear and stretching

This work presents contact problems of laminated structures via the Carrera Unified Formulation (CUF). The modeling approach makes use of higher-order 1D elements accounting for transverse shear and stretching. The current work considers normal, frictionless contact based on a node-to-node formulation, and the penalty approach to enforce the contact constraints. Numerical assessments compare classical beam theories, higher-order CUF, and 3D finite element models regarding solution accuracy, computational size, and time required for the analysis. The results show the validity of Layer-Wise CUF models to capture both global and local deformations accurately, which is a shortcoming of classical beam theories, and require at least an order of magnitude fewer degrees of freedom and computational time than a full 3D finite element analysis. Particularly relevant are the accurate distributions of transverse shear stress and stretching along the thickness in the perspective of failure analyses.

A global-local approach for the elastoplastic analysis of compact and thin-walled structures via refined models

A computationally efficient framework has been developed for the elastoplastic analysis of compact and thin-walled structures using a combination of global-local techniques and refined beam models. The theory of the Carrera Unified Formulation (CUF) and its application to physically nonlinear problems are discussed. Higher-order models derived using Taylor and Lagrange expansions have been used to model the structure, and the elastoplastic behavior is described by a von Mises constitutive model with isotropic work hardening. Comparisons are made between classical and higher-order models regarding the deformations in the nonlinear regime, which highlight the capabilities of the latter in accurately predicting the elastoplastic behavior. The concept of global-local analysis is introduced, and two versions are presented - the first where physical nonlinearity is considered for both the global and local analyses, and the second where nonlinearity is considered only for the local analysis. The second version results in reasonably accurate results compared to a full 3D finite element analysis, with a twofold reduction in the number of degrees of freedom.

Design and Integrity Evaluation of a Finned-Tube Sodium-to-Air Heat Exchanger in a Sodium Test Facility

A high-temperature design and an integrity evaluation for a finned-tube sodium-to-air heat exchanger (FHX) in a sodium test facility were conducted based on full 3D finite-element analyses, and comparisons of the design codes were made. A model FHX has been installed in a sodium test facility of sodium thermal-hydraulic experiment loop for finned-tube sodium-to-air heat exchanger (SELFA) for simulating the thermal hydraulic behavior of the FHX unit in the prototype Gen IV sodium-cooled fast reactor (PGSFR). For the design evaluations, ASME Section VIII Div. 2 has been applied for the FHX as a whole. For parts of the FHX operating in the creep regime, nuclear grade elevated temperature design (ETD) codes of ASME Section III Subsection NH and RCC-MRx were additionally applied to evaluate the integrity against creep-fatigue damage. For parts of the FHX operating at low temperature, ASME Section III Subsection NB was applied additionally to evaluate the integrity upon load-controlled stresses and fatigue. The integrity of the FHX was confirmed based on the design evaluations as per the design codes. Code comparisons were made in terms of the chemical compositions, material properties, and conservatism. The conservatism was quantified and compared at the critical low temperature location between ASME Section VIII Div. 2 and ASME-NB, and at the critical high-temperature location between ASME-NH and RCC-MRx.

소듐 시험루프 내 고온 압력용기의 크리프-피로 건전성 평가

본 연구에서는 한국원자력연구원 내에 설치될 예정인 소듐시험 시설인 SELFA(Sodium Thermalhydraulic Experiment Loop for Finned-tube Sodium-to-Air heat exchanger) 내에서 정상상태 가동온도가 510°C의 고온 압력용기인 팽창탱크에 대해 고온 건전성 평가를 수행하였다. 팽창탱크에 대해 3 차원 유한요소 해석에 기초하여 고온설계 기술기준인 ASME Section III Subsection NH 와 프랑스의 RCC-MRx 코드를 따라 크리프-피로 손상평가를 수행하였다. 평가결과 팽창탱크는 크리프-피로 설계 과도 하중 하에서 구조적 건전성을 유지하는 것으로 나타났다. 316L 스테인리스강 재질의 동 압력용기에 대해 정량적 코드 비교 분석을 수행하였다.

In-service life estimation of damaged gas pipelines: Full-scale experiments and finite element analyses

Statistical analysis reveals that mechanical damage is the first cause of incidents on gas transmission pipelines. They can be created by third party activities such as excavator tooth impact or by interaction between the pipe and rocks. To manage the damaged pipeline safely without useless cost, there is a need to investigate the mechanical behaviour of dented pipelines under a varying internal pressure. The purpose of this study is to characterize the stress and strain field around defects in pipes submitted to cyclic pressure loadings in order to estimate their residual lifetime. Full 3D finite element analyses of the denting process followed by cyclic loading are performed. Full-scale experiments on dented sections are planned.

Impact of overhead excavation on an existing shield tunnel : field monitoring and a full 3D finite element analysis

Impact of overhead excavation on an existing shield tunnel : field monitoring and a full 3D finite element analysis

High temperature design of finned-tube sodium-to-air heat exchanger in a sodium test loop

A sodium test loop called ‘SELFA’ (sodium thermal-hydraulic experiment loop for finned-tube sodium-to-air heat exchanger) for simulating thermal hydraulic behavior of the FHX (finned-tube sodium-to-air heat exchanger) unit in a Korean prototype sodium-cooled fast reactor is planned to be constructed at KAERI (Korea Atomic Energy Research Institute). In this study, the elevated temperature design for a model FHX and creep–fatigue damage evaluation have been conducted for the model according to the design codes of ASME section III subsection NH and RCC-MRx based on full 3D finite element analyses. Design optimization for the finned-tubes and tube arrangements in the scaled-down FHX has been performed. The materials of the FHX and piping systems are austenitic stainless steel type 316. The design temperature of the SELFA test loop is 600°C and the design pressure is 1MPa. The damage evaluation results have shown that no creep–fatigue damage occurs in the present design of the FHX under the intended test conditions.

소듐냉각고속로 붕괴열교환기의 고온 설계 및 건전성 평가

In this study, high temperature design and creep-fatigue damage evaluation of a decay heat exchanger (DHX) in the decay heat removal systems of a sodium-cooled fast reactor (SFR) have been performed. Detail design and 3D finite element analysis have been conducted for the DHXs to be installed in active and passive decay heat removal systems in Korean Generation IV SFR, and the DHX installed in the STELLA-1(Sodium integral effect test loop for safety simulation and assessment) at KAERI (Korea Atomic Energy Research Institute). Evaluations of creep-fatigue damage based on full 3D finite element analyses were conducted for the two Mod.9Cr-1Mo steel heat exchangers according to the elevated temperature design codes of ASME Section III Subsection NH and RCC-MR code. Code comparisons were made based on the creep-fatigue damage evaluation and issues on conservatisms of the design codes were discussed.

High temperature design and damage evaluation of a helical type sodium-to-air heat exchanger in a sodium-cooled fast reactor

A high temperature design and creep-fatigue damage evaluation for a helical type sodium-to-air heat exchanger (AHX) in a 600MWe sodium-cooled fast reactor (SFR) has been conducted. The AHX is a safety-grade component in a passive decay heat removal (DHR) system. Safe and reliable decay heat removal is one of the most important tasks in the successful design of a sodium-cooled fast reactor. Therefore, independent, diverse and redundant DHR systems incorporating both passive and active mechanisms have been employed in the demonstration SFR developed by Korea Atomic Energy Research Institute (KAERI). One of the key DHR components is sodium-to-air heat exchanger, which has a helically coiled tube arrangements. A creep-fatigue damage evaluation has been performed according to the elevated temperature design codes of ASME Subsection NH and RCC-MRx based on a full 3D finite element analysis. The integrity of the heat exchangers under creep-fatigue loading was confirmed and code comparisons were made as well.

Elastic sectional stress analysis of variable section piers subjected to three-dimensional loads

The elastic stress analysis of beam-column structures of uniaxial symmetrical variable cross-sections is developed using an extension of Euler–Bernoulli beam theory. The applied loads are general considering axial (P), flexure (Mx–My), shear (Vx–Vy), and torsion (T). Three-dimensional analytical solutions for normal and shear stresses are derived using sectional analysis with warping functions for variable boundaries in elevation. The differential equations of equilibrium and deformations are accounting for the variations in the geometrical properties of the cross-section and related boundary conditions. The strong form solution is then written in a weak form that is implemented in a 2D sectional finite element (FE) code assuming linear normal stress distribution. Three application examples are presented to validate the proposed sectional approach and illustrate its accuracy by comparing with results from full 3D FE analyses: (a) a slender rectangular section pier with a sloped boundary, (b) a bulk rectangular section buttress with unsymmetrical slopes, and (c) a pier (squat wall) for a hydraulic structure. When the assumption of linear distribution for normal flexural stress is satisfied, the proposed sectional approach produces results within 1% of 3D FE with much reduced computational efforts. For bulk and squat walls the stress field distribution are very similar to 3D FE while the stress intensity shows some variations. This is of major practical significance because the proposed approach allows performing first a series of simplified yet acceptable sectional analyses in safety assessment of the three-dimensional type of structures considered herein.

An Evaluation of Creep-Fatigue Damage for the Prototype Process Heat Exchanger of the NHDD Plant

A process heat exchanger (PHE) transfers the heat generated from a nuclear reactor to a sulfur-iodine hydrogen production system in the Nuclear Hydrogen Development and Demonstration, and was subjected to very high temperature up to 950°C. An evaluation of creep-fatigue damage, for a prototype PHE, has been carried out from finite element analysis with the full three dimensional model of the PHE. The inlet temperature in the primary side of the PHE was 950°C with an internal pressure of 7 MPa, while the inlet temperature in the secondary side of the PHE is 500°C with internal pressure of 4 MPa. The candidate materials of the PHE were Alloy 617 and Hastelloy X. In this study, only the Alloy 617 was considered because the high temperature design code is available only for Alloy 617. Using the full 3D finite element analysis on the PHE model, creep-fatigue damage evaluation at very high temperature was carried out, according to the ASME Draft Code Case for Alloy 617, and technical issues in the Draft Code Case were raised.

A General Cuboidal Element for Three-Dimensional Thermal Modelling

This paper presents a lumped parameter approach for three-dimensional (3D) thermal modelling based upon the use of general 3D elements which are formulated to accurately cater for internal heat generation. Commonly used thermal networks tend not to account for an internal heat generation that is essential for accurate temperature predictions. In contrast, the general element proposed in this paper includes the internal heat generation as well as a material thermal anisotropy. To validate the technique, thermal models of an inductor using the equivalent circuit method based around a general cuboidal element and a full 3D finite element analysis was constructed and analyzed. The calculated results from the cuboidal element method show good agreement with the FEM predictions.

3D modelling of plug failure in resistance spot welded shear-lab specimens (DP600-steel)

Ductile plug failure of resistance spot welded shear-lab specimens is studied by full 3D finite element analysis, using an elastic-viscoplastic constitutive relation that accounts for nucleation and growth of microvoids to coalescence (The Gurson model). Tensile properties and damage parameters are based on uni-axial tensile testing of the basis material, while the modelled tensile response of the shear-lab specimens is compared to experimental results for the case of a ductile failure near the heat affected zone (HAZ). A parametric study for a range of weld diameters is carried out, which makes it possible to numerically relate the weld diameter to the tensile shear force (TSF) and the associated displacement, u TSF , respectively. Main focus in the paper is on modelling the localization of plastic flow and the corresponding damage development in the vicinity of the spot weld, near the HAZ. For decreasing weld diameter, localization of plastic flow may be observed to occur in the weld nugget, introducing significant shearing. Due to these competing mechanisms a critical transition radius of the weld may be found. However, due to the limitation of the Gurson model in describing ductile failure at very low stress triaxiality, further analysis of the shear failure is omitted.

A full 3D finite element analysis of the powder injection molding filling process including slip phenomena

AbstractA full 3D finite element analysis system has been developed to simulate a Powder Injection Molding (PIM) filling process for general three‐dimensional parts. The most important features of the analysis system developed in this study are i) to incorporate the slip phenomena, the most notable rheological characteristics of PIM feedstock, into the finite element formulation based on a nonlinear penalty‐like parameter and ii) to simulate the transient flow during the filling process with a predetermined finite element mesh with the help of a volume fill factor and a melt front smoothing scheme. The treatment of the nonlinear slip boundary condition was successfully validated via a steady state pipe flow. For the purpose of comparisons, not only the numerical simulations but also experimental short‐shot experiments were performed with two 3D mold geometries using two typical materials of slip and no‐slip cases. The good agreements between the numerical and experimental results indicate that the melt front tracking scheme successfully simulates the transient filling process.

A full 3D finite element analysis using adaptive refinement and PCG solver with back interpolation

In this paper, adaptive refinement finite element analyses were carried out for full 3D problems. In order to achieve an optimal computation cost and to eliminate the effects of singular points, the adaptive refinement procedure was applied in conjunction with a back interpolation for the construction of a good initial guess for the solution of the linear equations system. The combined use of the adaptive refinement procedure, the back interpolation scheme and the preconditioned conjugate gradient (PCG) solver lead to a significant reduction in the operations for the solution of the simultaneous linear equations in the adaptive refinement analysis. In many cases the number of iterations needed by the PCG solver to reach a converged solution is independent of the number of equations in the global system. The numerical results obtained indicated that for a series of carefully designed adaptive meshes, the computational cost required to solve the linear system could be made only proportional to the number of degrees of freedom in the mesh. To our knowledge, this is the first time that the global stiffness equations in 3D stress analysis have been solved with this efficiency. The same set of numerical results also showed that, in general, the total computational cost of the adaptive refinement procedure can usually be minimized by gradually reducing the target relative error of the solution during successive refinements rather than employing a constant target relative error throughout the whole adaptive analysis.

Indentation Failure in Cross Ply Laminates, Comparison between Observations and 3D Field Solutions

A numerical as well as an experimental study of indentation damage in thick laminates is presented. Static indentation of a spherical steel ball into thick laminates, one of GFRP type and one of CFRP, is performed. The resulting fracture is in both material systems dominated by a bottom centre crack, inclined matrix cracks, accompanied by delaminations. The order of appearence is material dependent. The fracture initiates in the layer opposing the point of contact in the case of a GFRP laminate, whereas the first evidence of fracture is found in the layer nearest the loaded surface, in the case of a CFRP laminate. Full 3D finite element analyses of the elastic contact problem are performed, using a newly developed finite element specifically suited for the purpose. The numerical solutions indicate that the matrix cracking is governed by the failure criterion of maximum tensile stress perpendicular to fibres. Using this criterion the numerical solutions reveal a correlation between the ratio of moduli and the mode of failure. A low value of E, 1/E2 results in failure initiation in the lower layer, whereas a high value of El /b2 results in crack initiation and onset in the upper layers. The experimentally found divergence in terms of failure initiation between the GFRP laminate and the CFRP laminate supports this. The influence of cracks and delaminations on the overall stress distribution is studied qualitatively by inserting cavities of appropriate size and shape into the finite element model.