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Xuan Liang - One of the best experts on this subject based on the ideXlab platform.

  • on incorporating scanning strategy effects into the modified Inherent Strain modeling framework for laser powder bed fusion
    Additive manufacturing, 2021
    Co-Authors: Xuan Liang, Wen Dong, Qian Chen
    Abstract:

    Abstract Laser powder bed fusion ( L -PBF) has been the most popular metal additive manufacturing (AM) process thus far. However, residual deformation of the metal builds has been a significant issue. Laser scanning strategies adopted in the laser-assisted fabricating process have proved to have important influence on the residual stress and deformation. As the main contribution of this paper, the effects of different laser scanning strategies are incorporated into the modified Inherent Strain modeling (MISM) framework for the first time to enable accurate simulation for residual deformation of the L -PBF metal parts. Anisotropy in mechanical property of the fabricated components caused by the laser scanning strategies is also fully considered. For the rotational laser scanning strategies, only a small-scale representative volume element (RVE) is modeled by employing both the Inherent Strains and asymptotic homogenization. By employing the homogenized Inherent Strains, residual deformation can be predicted for the L -PBF manufactured components using different rotational scanning strategies accurately. Regarding the unidirectional parallel line scanning strategy, the directional Inherent Strain vector and orthotropic mechanical properties are used in the MISM-based layer-wise simulation. Good accuracy of the proposed framework is fully validated through comparing the simulated residual deformations with the experimental results for Inconel 718 parts produced by different laser scanning strategies. Thus, it is demonstrated that the effects of both parallel line and rotational laser scanning strategies have been successfully integrated into the MISM framework for predicting residual deformations of the L -PBF builds.

  • efficient prediction of cracking at solid lattice support interface during laser powder bed fusion via global local j integral analysis based on modified Inherent Strain method and lattice support homogenization
    Additive manufacturing, 2020
    Co-Authors: Hai T Tran, Xuan Liang
    Abstract:

    Abstract Residual stress induced cracking at the solid-lattice support interface is often observed in laser powder bed fusion (LPBF) additive manufactured metals. Therefore, it is crucial to predict possible cracking before printing a part especially when it is large and complex. Previously, a method has been proposed to predict interfacial cracking during LPBF processing based on performing Inherent Strain simulations and evaluating J-integral at the critical point in a single model. However, that method is limited to application to small parts due to the high computational cost of explicit modeling of the lattice structure. In the present work, a more robust method based on the global-local technique is proposed to perform homogenized Inherent Strain analysis for the entire part (global) first, followed by J-integral analysis at several suspected critical locations (local). The proposed local-global analysis technique is validated both numerically and experimentally that it is both efficient and accurate in predicting interfacial cracking in as-built LPBF processed parts.

  • sensitivity analysis and lattice density optimization for sequential Inherent Strain method used in additive manufacturing process
    Computer Methods in Applied Mechanics and Engineering, 2020
    Co-Authors: Akihiro Takezawa, Xuan Liang, Qian Chen, Florian Dugast, Xiaopeng Zhang, Mitsuru Kitamura
    Abstract:

    Abstract Compensation of the thermal distortion that occurs during the fabrication process is an important issue in the field of metal additive manufacturing. Considering the problem in forming a lattice structure inside an object to reduce the thermal distortion, we developed a lattice volume fraction distribution optimization method. Assuming that the linear elastic problem is solved using the finite element method (FEM), an Inherent Strain method applying a layer-by-layer process utilizing the element activation during the FEM is formed as a recurrence relation, and the sensitivity of an objective function is derived based on the adjoint method. The unit lattice shape is a simple cube with a cube or a sphere-shaped air hole, and its distribution is optimized by considering the minimum thickness of the wall surrounding it as a design variable. The effective stiffness tensor of the lattice is derived using a homogenization method. The functions of the effective properties with respect to the design variables are approximated through polynomial functions. The optimization problem is formulated as an unconStrained minimization problem. The design variables are optimized using the method of moving asymptotes. Herein, the validity of the proposed method is discussed based on quasi two-dimensional and three-dimensional numerical studies including a re-analysis through full-scale thermo-mechanical analysis.

  • Inherent Strain homogenization for fast residual deformation simulation of thin walled lattice support structures built by laser powder bed fusion additive manufacturing
    Additive manufacturing, 2020
    Co-Authors: Xuan Liang, Lin Cheng, Qian Chen, Wen Dong, Shawn Hinnebusch, Hai T Tran, John Lemon, Zekai Zhou, Devlin Hayduke
    Abstract:

    Abstract Numerical simulation of residual deformation in metallic components with dense lattice support structures by the laser powder bed fusion (L-PBF) additive manufacturing process has been a significant challenge due to the very high computational expense in performing both finite element meshing and analysis. In this work, the modified Inherent Strain method is extended to enable efficient residual deformation simulation of l -PBF components with lattice support structures. The asymptotic homogenization method is employed to obtain the equivalent mechanical properties including the anisotropic elastic modulus and Inherent Strains given the topological configuration and laser scanning strategy of the thin-walled lattice support structures. A key finding is that the in-plane homogenized Inherent Strain values decrease with increasing volume density, which can be attributed to the directional dependence of Inherent Strains for the AM-processed material. Based on the homogenized mechanical properties and Inherent Strains, the thin-walled lattice support structures can be considered to be an effective solid continuum so that the simulation can be accelerated significantly to obtain residual deformation. Good accuracy of the homogenized mechanical property and Inherent Strains is validated by comparing the simulated residual deformation with experimental deformation measurement of several lattice structured beams of different volume densities. Efficiency of the proposed method is also demonstrated through numerical examples to have 80 % reduction in number of elements and nearly 10x speedup in computing time. In addition, the scalability of the proposed method is also verified through application to a complex L-PBF component fabricated with thin-walled support structures.

  • an Inherent Strain based multiscale modeling framework for simulating part scale residual deformation for direct metal laser sintering
    Additive manufacturing, 2019
    Co-Authors: Qian Chen, Devlin Hayduke, Xuan Liang, Lin Cheng, Jikai Liu, Jason Oskin, Ryan Whitmore
    Abstract:

    Abstract Residual distortion is a major technical challenge for laser powder bed fusion (LPBF) additive manufacturing (AM), since excessive distortion can cause build failure, cracks and loss in structural integrity. However, residual distortion can hardly be avoided due to the rapid heating and cooling Inherent in this AM process. Thus, fast and accurate distortion prediction is an effective way to ensure manufacturability and build quality. This paper proposes a multiscale process modeling framework for efficiently and accurately simulating residual distortion and stress at the part-scale for the direct metal laser sintering (DMLS) process. In this framework, Inherent Strains are extracted from detailed process simulation of micro-scale model based on the recently proposed modified Inherent Strain model. The micro-scale detailed process simulation employs the actual parameters of the DMLS process such as laser power, velocity, and scanning path. Uniform but anisotropic Strains are then applied to the part in a layer-by-layer fashion in a quasi-static equilibrium finite element analysis, in order to predict residual distortion/stress for the entire AM build. Using this approach, the total computational time can be significantly reduced from potentially days or weeks to a few hours for part-scale prediction. Effectiveness of this proposed framework is demonstrated by simulating a double cantilever beam and a canonical part with varying wall thicknesses and comparing with experimental measurements which show very good agreement.

Masahito Mochizuki - One of the best experts on this subject based on the ideXlab platform.

Hidekazu Murakawa - One of the best experts on this subject based on the ideXlab platform.

  • Inherent Strain Method for Residual Stress Measurement and Welding Distortion Prediction
    Volume 9: Prof. Norman Jones Honoring Symposium on Impact Engineering; Prof. Yukio Ueda Honoring Symposium on Idealized Nonlinear Mechanics for Weldin, 2016
    Co-Authors: Keiji Nakacho, Hui Huang, Akira Maekawa, Naoki Ogawa, Takahiko Ohta, Hidekazu Murakawa
    Abstract:

    Inherent Strain method was employed to measure the distribution of three dimensional welding residual stresses in several multi-pass welded joints of thick pipes and thick cladded plates. Since a function expression approach to the distribution of Inherent Strains was developed, the measuring efficiency for three dimensional internal welding residual stresses in complicated welded joints was improved a lot. The residual stresses measured by Inherent Strain method were compared with the high cost stress release method and neutron diffraction method. Furthermore, Inherent deformation parameters, which are defined by integrated values of Inherent Strains on transverse sections, were used for the fast prediction of welding distortion in assembling structures. Based the predicted welding distortion, its mitigation methods such as tack welding and jig conStraint were discussed.

  • Prediction of Distortion Produced in Welded Structures During Straightening Process Using the Inherent Strain Method
    Volume 9: Prof. Norman Jones Honoring Symposium on Impact Engineering; Prof. Yukio Ueda Honoring Symposium on Idealized Nonlinear Mechanics for Weldin, 2016
    Co-Authors: Hector Olmedo Ruiz Valdes, Hidekazu Murakawa, Naoki Osawa, Sherif Rashed
    Abstract:

    In order to optimize the straightening process, it is necessary to predict the deformation due to local heating. Numerical simulation is an advantageous way to do this. In this study, Osaka University’s Inherent Strain based welding simulation code JWRIAN is modified so that Inherent Strain’s equivalent nodal forces are calculated in cases where the Inherent Strain confines within narrow region whose size is smaller than element size. In the developed code, the initial Strain force vector and element stiffness matrix’s non-linear term which includes stress components are integrated using higher order (e.g. 20 × 20 × 6 for 4-nodes shell elements) Gauss-Legendre quadrature while other quantities are evaluated by using ordinary order (2 × 2 × 2) quadrature. The validity of the developed software is examined by comparing rectangular plate’s angular distortion due to gas line heating calculated by three-dimensional thermal-elastic-plastic analysis and that calculated by the developed system.

  • iterative substructure method employing concept of Inherent Strain for large scale welding problems
    Welding in The World, 2015
    Co-Authors: Hidekazu Murakawa, Hui Huang
    Abstract:

    When structures such as ships, automobiles, and bridges are assembled by welding, distortion and residual stress are produced as unavoidable consequence of local shrinkage due to welding. The dimensional error deteriorates the performance of the structures and becomes an obstacle to achieve smooth manufacturing if the error exceeds the tolerable limit. On the other hand, residual stress plays an important role in crack initiation and fatigue life. Thus, it is necessary to predict the welding distortion and stress beforehand, so that effective measure and control can be taken. Since the welding is a highly nonlinear problem, it is difficult to predict the distortion quantitatively. For accurate prediction, finite element analysis (FEA) can be a powerful tool. In this research, an enhanced FEA scheme namely i-ISM is developed based on the Inherent Strain concept and iterative substructure method (ISM). Its capability of solving large-scale practical problems is demonstrated through typical models.

  • numerical analysis of the straightening process of thin plate structures by elastic fem based on the Inherent Strain method
    Transactions of JWRI, 2012
    Co-Authors: Adan Vega, Alexandra Camano, Juan Blandon, Hisashi Serizawa, Hidekazu Murakawa
    Abstract:

    Welding distortion is practically an expected feature in shipbuilding, with a few exceptions; when thick plates are used, for example. Nowadays, the trend is to use thinner plates in order to reduce weight, aiming to reduce waste of fuel. However, thin plates are drastically affected by welding distortion, this finally represents a significant - unnecessary expenditure of money and time on straightening the structure. Here it is necessary to realize that even with the most effective welding process, welding distortion in thin plates appears, so it is unrealistic to think about free of distortion lightweight welded structures. Although there have been gradual movements to optimize the straightening process, still many question remain to be answered. In this paper, an Elastic Finite Element Model based on Inherent Strain Method is developed in order to study the process of straightening deformed plates. Some techniques, usually used in the practice, are numerically evaluated and their effectiveness compared. Finally, useful recommendations that aim to the optimization of the process are drawn.

  • Introduction to Welding Mechanics
    Welding Deformation and Residual Stress Prevention, 2012
    Co-Authors: Yukio Ueda, Hidekazu Murakawa
    Abstract:

    The welding phenomenon is complicated and interdisciplinary among three categories: metallurgy, welding process, and mechanics. The main purpose of this book is to provide methods for how to analyze the mechanical behavior during welding by the finite element method using a computer. The method is referred to as computational welding mechanics. In this first chapter, basic knowledge on welding and welding mechanics is introduced. Before discussing details of computational welding mechanics, using a simple three-bar model, transient welding stress and distortion under thermal processes are analyzed with the aid of the basic theory of thermal elastic-plastic analysis. The production mechanism of residual stress is explained by the concept of Inherent Strain (plastic Strain). Then, reproduction of residual stress by Inherent Strain and inverse analysis for Inherent Strain from residual stress are illustrated. Numerical examples of residual stress, Inherent Strain, and Inherent displacement are presented.

Changdoo Jang - One of the best experts on this subject based on the ideXlab platform.

  • welding distortion analysis of hull blocks using equivalent load method based on Inherent Strain
    Journal of Ship Research, 2012
    Co-Authors: Tae Yoon Park, Changdoo Jang
    Abstract:

    Welding deformation reduces the dimensional accuracy of ship hull blocks and decreases productivity due to the correction work. Prediction and minimizing of welding distortion at the design stage will lead to higher quality as well as higher productivity. Therefore, it is strongly required to develop an effective method to accurately predict the weld distortion of hull blocks considering the fabrication sequences. In the case of hull block welding work in shipyard, the welding process of curved stiffened plate has large amounts of workload. This paper suggests an efficient method for predicting the welding deformation of stiffened curved plates based on the Inherent Strain theory combined with the finite element method. The equivalent load was determined by integrating Inherent Strain components which are calculated in the vicinity of heat affected zone using the highest temperature and the degree of reStraint. The welding distortion of curved stiffened panels under equivalent load are calculated by elastic analysis and compared with that by intensive elasto-plastic finite element analysis. It is verified that the proposed method has a high efficiency and accuracy.

  • Welding Distortion Analysis of Hull Blocks using Equivalent Load Method Based on Inherent Strain
    Journal of Ship Research, 2012
    Co-Authors: Yong Tai Kim, Tae Yoon Park, Tae Jun Kim, Changdoo Jang
    Abstract:

    Welding deformation reduces the dimensional accuracy of ship hull blocks and decreases productivity due to the correction work. Prediction and minimizing of welding distortion at the design stage will lead to higher quality as well as higher productivity. Therefore, the development of an effective method to predict accurately the weld distortion of hull blocks considering the fabrication sequences is required. In the case of hull block welding work in shipyards, the welding process of curved stiffened plates has large amounts of workload. This paper suggests an efficient method for predicting the welding deformation of stiffened curved plates based on the Inherent Strain theory combined with the finite element method. The equivalent load was determined by integrating Inherent Strain components which are calculated in the vicinity of heat affected zone using the highest temperature and the degree of reStraint. The welding distortion of curved stiffened panels under equivalent load are calculated by elastic analysis and compared with that by intensive elasto-plastic finite element analysis. It is verified that the proposed method has a high efficiency and accuracy.

  • prediction of welding deformation of hull panel blocks using an advanced Inherent Strain analysis method considering the heat equivalent layer effect
    Metals and Materials International, 2011
    Co-Authors: Changdoo Jang
    Abstract:

    When a large-scale structure is fabricated via a complex welding process, deformation and residual stress are challenges that must be resolved. In a thermo-elasto-plastic analysis, calculations are carried out from room temperature through the heating and cooling of the welded joint section where the base metal is melted by the welding heat. It is difficult to apply this type of analysis to large, complex structures due to the prolonged computational time and huge processing volume required. Inherent Strain analysis is a more effective approach to analyzing welding Strain, and enables the use of an elastic analysis instead of a thermo-elastoplastic analysis to predict the Strain residual stress that occurs in the welded part. This study compares an existing method that analyzes the Strain in the welded part by using the correlation between the zone affected by the heat and the adjacent zone conStraining the heat-affected zone, and an advanced analysis method that is intended to enhance the accuracy of the results by considering the heat equilibrium zone that exists between the adjacent regions conStraining the heat-affected zone. The advanced Inherent Strain analysis method is applied to obtain more accurate results for a hull panel block model, which is one of the most complex welding structures, by considering a reStraint diagram organized according to the welding and fabrication sequence of the members.

  • analysis of post weld deformation at the heat affected zone using external forces based on the Inherent Strain
    International Journal of Precision Engineering and Manufacturing, 2007
    Co-Authors: Yunsok Ha, Changdoo Jang
    Abstract:

    An analytical method to predict the post-weld deformation at the heat-affected zone (HAZ.) is presented in this paper. The method was based on the assumption that the post-weld deformation is caused by external forces resulting from the Inherent Strain, which is defined as the irrecoverable Strain after removing structural reStraints and loadings. In general, the equivalent loading method can be used to analyze distortions in welding areas because it is efficient and effective. However, if additional loads are applied after welding, it is difficult to determine the final Strain on a welded structure. To determine the final Strain of a welded structure at the HAZ. more accurately, we developed a modified equivalent loading method based on the Inherent Strain that incorporated hardening effects. The proposed method was applied to calculate the residual stress at the HAZ. Experiments were also conducted on welded plates to evaluate the validity of the proposed method.

  • an improved Inherent Strain analysis for plate bending by line heating considering phase transformation of steel
    International Journal of Offshore and Polar Engineering, 2007
    Co-Authors: Changdoo Jang
    Abstract:

    The Inherent Strain method is known to be very efficient in predicting plate deformation due to line heating. However, in the actual line heating process in a shipyard, the rapid quenching changes the phase of steel. In this study, when calculating Inherent Strain, material properties of steel are applied differently in heating and in cooling, considering phase transformation. In this process, a new method which can reflect the thermal volume expansion of martensite is suggested. By this method, the plate deformations by line heating could be predicted more precisely.

D Deng - One of the best experts on this subject based on the ideXlab platform.

  • predicting welding deformation in thin plate panel structure by means of Inherent Strain and interface element
    Science and Technology of Welding and Joining, 2012
    Co-Authors: D Deng
    Abstract:

    In this study, welding distortion in a large thin plate panel structure was predicted by means of elastic finite element method based on Inherent Strain theory and interface element formulation. The welding distortions in the thin plate model computed by large deformation theory and small deformation theory were compared. The comparison suggests that the geometrical non-linearity should be carefully considered when welding distortion in a thin plate structure is predicted. In addition, the influences of welding procedure and assembly sequence on the final distortion were examined numerically. Simulation results indicate that both welding procedure and assembly sequence significantly affect the final deformation.

  • applications of Inherent Strain and interface element to simulation of welding deformation in thin plate structures
    Computational Materials Science, 2012
    Co-Authors: D Deng, Jiangchao Wang
    Abstract:

    Welding-induced distortion not only reduces largely manufacturing accuracy but also decreases significantly productivity due to correction works. If welding distortion can be predicted through a simple and practical method beforehand, the predictions will be helpful for taking active as well as appropriate measures to control the dimension accuracy. Based on Inherent Strain theory and interface element formulation, we developed a practical prediction system to compute the accumulated distortion during the welding assembly process in the current study. Using the developed prediction method, we calculated the welding distortion in a thin plate structure with considering both the shrinkage due to heat input and the gap/misalignment generated during assembly process. Meanwhile, we investigated the influences of assembly sequence and gap correction on the final distortion.

  • prediction of deformation for large welded structures based on Inherent Strain
    Transactions of J W R I, 2004
    Co-Authors: Yu Luo, D Deng, Hidekazu Murakawa, Lei Xie, 村川 英一
    Abstract:

    Welding is one of the main joining techniques used in industry. Assembly in ships, cars, trains or civil engineering structures use this process more and more intensively. In this paper, the characteristics of the weldingInherent deformation, namely longitudinal shrinkage, transverse shrinkage and angular distortion, of the Aluminum Alloy butt weld were investigated using the thermal elastic plastic finite element method. Through a series of FEM analyses, a database of Inherent deformation was established. Based on the Inherent deformation database, an elastic FEM was developed to predict the welding deformation for larger welded structures. The usefulness of the proposed method was demonstrated by the prediction of welding deformation for a large aluminum alloy coping.

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