Plastic FE Analysis Research Articles

Disclination-Based Crystal Plasticity FE Analysis for Influence of Kink Formation and Grain Size on Material Strength in Dual-Phase Mg Alloy with LPSO Phase

Disclination-Based Crystal Plasticity FE Analysis for Influence of Kink Formation and Grain Size on Material Strength in Dual-Phase Mg Alloy with LPSO Phase

Computational investigation on transient thermal tensioning for mitigation of welding induced buckling by elastic FE method

Transient thermal tensioning (TTT) as an in-process technique is extensively used to mitigate welding induced buckling during the fabrication of thin plate welded structures, which drastically influences dimensional accuracy and manufacturing costs due to post-straightening work. In this study, the processes with conventional welding (CW) and TTT technique during the butt welding with thin plates were investigated by elastic FE method based on welding inherent deformation theory. In detail, thermal elastic plastic (TEP) FE analysis for the butt welded joint was validated, while the computed welding induced buckling and residual stress during CW process were in good agreement with experimental results. Then, TTT technique was implemented with above TEP FE analysis; it consists of two additional heat sources, which were symmetrically distributed and offset 150 mm with respect to the welding line. Moreover, the influence of energy intensity Q for additional heat sources on welding induced buckling mitigation was numerically examined. Elastic FE analyses during CW and TTT processes were carried out with welding inherent deformation evaluated by results of TEP FE analysis. The comparison between elastic FE analysis and TEP FE analysis suggests that the developed elastic FE analysis can accurately and efficiently represent welding distortion during CW and TTT processes with less than 5 % error. There is an appropriate interval of energy intensity Q during TTT process, which can significantly decrease relative displacement Urelative in the butt welded joint by up to 89.1 %. Furthermore, the reduction of tendon force and transverse inherent bending is the primary reason for welding buckling distortion mitigation during TTT process, and the decrease of tendon force is more critical.

結晶相の形状不均一性を考慮した結晶性ポリマの寸法依存性に関する分子鎖塑性FEM解析

Crystalline polymers may show different deformation responses depending on size of crystalline phase with respect to that of specimen. In the previous report, experimental stress-strain curves are numerically reproduced by the molecular chain plasticity FE analysis using a unit cell with hexagonal crystalline phases. However, there are some problems that the shape of crystalline phase in the unit cell is not always 6-fold symmetrical in the actual two-dimensional cross section of PP and the effect of the shape heterogeneity of crystalline phases on deformation responses has not been clarified. In the present report, the authors change the shape of some crystalline phase in the unit cell from hexagon to square and attempt to conduct the molecular chain plasticity FE analysis for amorphous phase and crystal plasticity FE analysis for crystalline one. Furthermore, the effect of shape heterogeneity of crystalline phases on deformation responses is investigated by comparing the results for unit cells with different heterogeneity.

Computational analysis of welding radial deformation of typical pressure cylindrical shell with ring stiffener

We report on the evaluation of the radial deformation caused by the welding process on a typical pressure cylindrical shell with ring stiffeners. Welding experiments on butt and fillet welding were conducted beforehand, and temperature-dependent material properties were considered. The out-of-plane welding distortion and residual stress were measured using a three-coordinate measuring machine and X-ray diffraction, respectively. Effective thermal elastic plastic FE analysis based on parallel computation technology was performed to examine the mechanical behaviors. Computed results were validated by comparison with experimental measurements. Welding inherent deformations of the examined butt and fillet joints were then evaluated by integrating computed plastic strains. The elastic FE analysis, with welding inherent deformation as mechanical loading, was employed to examine the dimensional variation of the considered pressure cylindrical shell. The influence of ring stiffener on welding radial deformation was also discussed. Moreover, the application of welding sequence modification and inverse deformation was numerically examined with the proposed elastic FE analysis to reduce the welding radial deformation and enhance the fabrication accuracy. • Thermal and mechanical behaviors of welding experiments were holistically examined with advanced measurement approach. • TEP FE analysis was employed to represent welding response, and computed results have good agreement with measurement. • Ring stiffener has significant influence on dimensional accuracy by elastic FE analysis with welding inherent deformation. • Welding sequence and inverse deformation have significant effect to prevent radial deformation of pressure cylindrical shell.

Disclination-Based Crystal Plasticity FE Analysis for Influence of Ridge-shaped Kink Band on Work Hardening of Dual-phase LPSO/Mg Alloy in Lording and Reverse Lordiong

Disclination-Based Crystal Plasticity FE Analysis for Influence of Ridge-shaped Kink Band on Work Hardening of Dual-phase LPSO/Mg Alloy in Lording and Reverse Lordiong

Uncertainty-quantified parametrically homogenized constitutive models (UQ-PHCMs) for dual-phase \u03b1/\u03b2 titanium alloys

This paper develops an uncertainty-quantified parametrically homogenized constitutive model (UQ-PHCM) for dual-phase α/β titanium alloys such as Ti6242S. Their microstructures are characterized by primary α-grains consisting of hcp crystals and transformed β-grains consisting of alternating laths of α (hcp) and β (bcc) phases. The PHCMs bridge length-scales through explicit microstructural representation in structure-scale constitutive models. The forms of equations are chosen to reflect fundamental deformation characteristics such as anisotropy, length-scale dependent flow stresses, tension-compression asymmetry, strain-rate dependency, and cyclic hardening under reversed loading conditions. Constitutive coefficients are functions of representative aggregated microstructural parameters or RAMPs that represent distributions of crystallographic orientation and morphology. The functional forms are determined by machine learning tools operating on a data-set generated by crystal plasticity FE analysis. For the dual phase alloys, an equivalent PHCM is developed from a weighted averaging rule to obtain the equivalent material response from individual PHCM responses of primary α and transformed β phases. The PHCMs are readily incorporated in FE codes like ABAQUS through user-defined material modeling windows such as UMAT. Significantly reduced number of solution variables in the PHCM simulations compared to micromechanical models, make them several orders of magnitude more efficient, but with comparable accuracy. Bayesian inference along with a Taylor-expansion based uncertainty propagation method is employed to quantify and propagate different uncertainties in PHCM such as model reduction error, data sparsity error and microstructural uncertainty. Numerical examples demonstrate the accuracy of PHCM and the relative importance of different sources of uncertainty.

Effect of sequence and stiffener shape on welding distortion of stiffened panel

Welding is extensively used in industries for the assembly of different products including ships, automobiles, trains, bridges etc. Welding distortion is usually a source of dimensional imprecision in assembly and higher manufacturing costs. So, it is of crucial importance to predict and minimize welding-induced distortion by improving the quality of the welded structure. The purpose of this research is to reduce the distortion in large ship panels. The study uses two methods. First, distortion prediction by thermal elastic plastic FE analysis is employed to estimate the inherent deformations of different SM490A steel welded joints. Then, the welding process of a large ship panel is elastically analyzed on the basis of the theory of inherent strains. The elastic analysis reveals some distortions on the edge and inside of the panel. The distortions can be minimized by changing welding sequence of panel stiffeners to symmetrical welding of type B and changing shape to L-stiffener as well as changing stiffener material to the SM570.

Development of new ηpl, β and limit load equations to evaluate fracture parameters of pre-cracked small punch test specimens

The small punch test (SPT) is an alternative method for determination of the mechanical properties when enough material is not available for conventional testing. Recently SPT specimen configuration is changed to have a crack (known as pre-cracked SPT) for more accurate determination of material fracture properties. Use of p-SPT specimens needs limit and maximum load values and geometric parameters, β and ηpl for evaluation of Stress Intensity Factor (SIF) and plastic J-integral respectively. However, general equations for these parameters are not available in the open literature. The present paper is an attempt to address this aspect of p-SPT specimens. Finite element analysis has been employed to evaluate the above parameters. Square pre-cracked specimens with crack parallel and perpendicular to the thickness direction are considered in this paper. The range of crack size a/W = 0.40–0.60 is considered for the present analysis. The load–displacement curves are extracted for both specimens using 3-D elastic–plastic FE analysis assuming elastic perfectly plastic material behaviour. Maximum load is directly obtained from the FEA load–deflection curves. The maximum load helps to assess the machine capacity to perform the SPT. Using the elastic–plastic J-integral and load–displacement data from FEA, ηpl values are calculated. Limit analysis using Plastic Work Curvature (PWC) criterion is carried out to obtain the limit loads. The geometric factor (β) is found out using elastic FE analysis for SIF calculation. Based on these FEA results, new equations have been proposed for limit load, maximum load, geometry factor (β) and ηpl for both types of p-SPT specimen configurations.

Dislocation-based crystal plasticity FE analysis for kink band formation in Mg-based LPSO phase considering higher-order stress

An FE analysis has been performed for a single crystal of long-period stacking ordered phase on the basis of the dislocation-based crystal plasticity model considering higher-order stress. The mesh dependence on the kink band formation has been discussed from the viewpoint of the strain gradient and size effect. Then, it is shown that the mesh dependence of kink deformation in the FE analysis can be removed even when the scale ratio is relatively small. Moreover, it is indicated that the disclination quadrupole structure in the kink band can be expressed qualitatively by use of the incompatibility of crystal slip.

A Study on Structural Integrity Assessment of Pipeline using Weight Function Solution

There are many Industry Code and Standard (ICS) for Structural Integrity Assessment (SIA) on welded structure with defect. The general ICSs, such as R6, BS 7910 and API 579-1/ASME FFS-1, provide equations to determine the upper bound residual stress profiles based on collections from many literatures. However, these residual stress profiles used in the SIA cause the conservative design for welded structures. In this study, the structural integrity assessment for girth weld in pipeline has been conducted based on fracture mechanics. In addition, thermo-elastic plastic FE analysis was performed for evaluating the residual stress of girth weld in pipeline. The weight function solution is used to determine the stress intensity factor using the residual stress profile obtained by the FE analysis. This approach can account for redistribution and relaxation of residual stress as the defects grow. In order to the evaluate quantitative comparison between BS 7910 and weight function solution, structural integrity assessment determining allowable crack size on cracked pipe was performed with failure assessment diagram. Key words: Structural Integrity Assessment, Welding residual stress, Weight function solution, FE analysis, Stress intensity factor

Behavior of a girth-welded duplex stainless steel pipe under external pressure

This study attempts to investigate the effects that external pressure has on the residual stress behavior in a girth-welded duplex stainless steel pipe. At first, FE simulation of the pipe girth welding is performed to identify the weld-induced residual stresses and depressions using sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Then, 3-D elastic–plastic FE analysis is carried out to evaluate the residual stress redistributions in the girth-welded pipe under external pressure. The residual stresses and plastic strains obtained from the thermo-mechanical FE simulation are employed as the initial condition for the analysis. The FE analysis results show that the hoop compressive stresses induced by the external pressure significantly alter the hoop residual stresses in the course of the mechanical loading, i.e. the hoop residual stress distributions on both surfaces of the pipe weld shift downward considerably, whilst the axial residual stresses are little affected by the superimposed external pressure.

A Crystal Plasticity FE Analysis Considering Mechanically Induced Martensitic Phase Transformation

A Crystal Plasticity FE Analysis Considering Mechanically Induced Martensitic Phase Transformation

FE Analysis of Buckling Behavior Caused by Welding in Thin Plates of High Tensile Strength Steel

The target of this study was to investigate buckling behavior during the entire welding process which consists of the heating and the cooling processes. For thin plate structures made of high tensile strength steel, not only residual buckling during or after cooling down but also transient buckling during heating may occur. The thermal elastic plastic FE analysis to investigate welding-induced buckling during the entire welding process is presented. Because of the high yield stress of high tensile strength steel, larger longitudinal compressive thermal stress is produced near the welding line compared with that in the case of carbon steel. Therefore, the plate may buckle due to thermal expansion, before the material nears yielding. During cooling down, the longitudinal compressive thermal stress close to the welding line disappears, and longitudinal tensile residual stress is produced due to contraction. Meanwhile, longitudinal compressive residual stress occurs far from the welding line to balance the tensile stress close to the welding line. This distribution of longitudinal residual stress would change the deformed dish shape of transient buckling into a saddle buckling type when the stress exceeds the critical buckling condition.

Influences of lumped passes on welding residual stress of a thick-walled nuclear rotor steel pipe by multipass narrow gap welding

The purpose of this study is to investigate the effect of the lumped passes simulation on the distribution of residual stresses before and after heat treatment in a thick-walled nuclear power rotor pipe with a 89-pass narrow gap welding process. The local removal blind hole method was used to measure internal residual stress of the thick-walled pipe after post weld heat treatment (PWHT). Based on the ANSYS software, a two-dimensional axisymmetric finite element model is employed. Two lumped-pass models of M-5th model (five weld beads as one lumped pass) and M-10th model (ten weld beads as one lumped pass) were developed to reduce computational cost. Based on the results in this study, the distributions of residual stresses of a thick-walled welded pipe before and after PWHT are developed. Meanwhile, the distribution of the through-wall axial residual stress along the weld center line is demonstrated to be a self-equilibrating type. In addition, the investigation results show that reasonable and reliable lumped-pass model can not only guarantee the accuracy of the simulated results, but also improve the computational efficiency in the thermo-elastic–plastic FE analysis procedure. Therefore, from the viewpoint of engineering application the developed lumped-pass computational procedure is a promising and useful method to predict residual stress of large and complex welded structures.

OS0103 LPSO型Mg多結晶合金中のキンク形成・進展に関する転位-結晶塑性FEM解析

OS0103 LPSO型Mg多結晶合金中のキンク形成・進展に関する転位-結晶塑性FEM解析

Mg基LPSO相単結晶における変形の初期方位依存性に関する転位-結晶塑性FEM解析と実験結果との比較

Mg基LPSO相単結晶における変形の初期方位依存性に関する転位-結晶塑性FEM解析と実験結果との比較

Numerical prediction and mitigation of out-of-plane welding distortion in ship panel structure by elastic FE analysis

As an application to predict and mitigate the out-of-plane welding distortion by elastic FE analysis based on the inherent deformation theory, a panel structure of a pure car carrier ship is considered. The inherent deformations of different types of welded joints included in this ship panel structure are evaluated beforehand using thermal elastic plastic FE analysis. Applying idealized boundary condition to focus on the local deformation, elastic FE analysis shows that the considered ship panel structure will buckle near the edge and only bending distortion is dominant in the internal region. In order to mitigate out-of-plane welding distortion such as buckling and bending, straightening using line heating is employed. In the internal region, only inherent bending with the same magnitude as welding induced inherent bending is applied on the opposite side of welded joints (fast moving torch). On the other hand, only in-plane inherent strain produced by line heating is introduced to the edge region to correct buckling distortion (slow moving torch). The magnitude of out-of-plane welding distortion in this ship panel structure can be minimized to an accepted level.

結晶塑性FE解析による巨視的弾性応力下の繰返し軟化挙動の考察

結晶塑性FE解析による巨視的弾性応力下の繰返し軟化挙動の考察

1418 M9基LPSO相における底面転位易動度がキング形成に及ぼす影響に関する転位 : 結晶塑性FEM解析

1418 M9基LPSO相における底面転位易動度がキング形成に及ぼす影響に関する転位 : 結晶塑性FEM解析

A Phase-Field Simulation of Nucleation from Subgrain and Grain Growth in Static Recrystallization

A new recrystallization phase-field model is proposed, in which the three stages of static recrystallization phenomena, i.e., recovery, nucleation and nucleus growth are sequentially taken into account in a computation. From the information of subgrain patterns and crystal orientations in a polycrystal that are obtained by a dislocation-crystal plasticity FE analysis based on a reaction-diffusion model, subgrain groups surrounded by high angle boundary are found out. Next, subgrains in the group are coalesced into a nucleus by rotation of crystal orientation and migration of subgrain boundaries through a phase-field simulation. Then a computation of nucleus growth is performed also using the phase-field model on account of an autonomic incubation period of nucleation, in which stored dislocation energy assumes a role of driving force. It is shown that the present method can numerically reproduce the three stages of static recrystallization as a sequence of computational procedure. (author)