Ct Wu

Ct Wu
ANSYS · Mechanical Engineering

PhD

About

98
Publications
23,989
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4,027
Citations
Introduction
I lead the Computational and Multiscale Mechanics group for LS-DYNA development at Livermore Software Technology, Livermore, CA https://www.lstc-cmmg.org
Additional affiliations
March 2001 - present
Independent Researcher
Independent Researcher
Position
  • Group Leader

Publications

Publications (98)
Article
This paper presents a new approach in the construction of meshfree approximations as well as the weak Kronecker-delta property at the boundary, referred to as a generalized meshfree (GMF) approximation. The GMF approximation introduces an enriched basis function in the original Shepard's method. This enriched basis function is introduced to meet th...
Article
This paper presents a meshfree-enriched finite element formulation for triangular and tetrahedral elements in the analysis of two and three-dimensional compressible and nearly incompressible solids. The new formulation is first established in two-dimensional case by introducing a meshfree approximation into a linear triangular finite element with a...
Article
In this work, an enhanced cell-based smoothed finite element method (FEM) is presented for the Reissner–Mindlin plate bending analysis. The smoothed curvature computed by a boundary integral along the boundaries of smoothing cells in original smoothed FEM is reformulated, and the relationship between the original approach and the present method in...
Article
Full-text available
A novel meshfree approach for the elastic analysis of composite solids is proposed. This approach introduces a new meshfree discretization technique that can be applied to the composite solids with overlapping sub-domains. Since each sub-domain is discretized individually by the finite element model, substantial user interaction for generating the...
Article
This paper presents a bubble-enhanced smoothed finite element formulation for the analysis of volume-constrained problems in two-dimensional linear elasticity. The new formulation is derived based on the variational multi-scale approach in which unequal order displacement-pressure pairs are used for the mixed finite element approximation and hierar...
Article
Modeling nonlinear materials with arbitrary microstructures and loading paths is crucial in structural analyses with heterogeneous materials with uncertainty. However, it is computationally prohibitive because (1) fine meshes are required to resolve the microstructures for nonlinear simulations, (2) enormous model evaluations are expected to simula...
Article
In this work, a variational Bayesian learning-based computation algorithm is developed to “inversely” identify the deformation field of a crashed car and hence their residual strain fields based on its final damaged structural configuration (wreckage), which is important in three-dimensional traffic collision reconstruction and its forensic analysi...
Article
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In this work, we developed a Generalized Bayesian Regularization Network (GBRN) approach that can quantitatively identify the defect shapes and locations by mapping the distorted lattice structure to its original designed configuration, making registration between manufactured parts with defects and the perfect design models in the preliminary desi...
Article
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To predict the mixed damage modes of unidirectional fiber-reinforced polymer (FRP) laminates under dynamic loading, an FEM-based peridynamic model is introduced in this paper. Based on its geometric structure and material composition, a long fiber lamina is considered a transversely isotropic medium as a result of homogenization at the meso-scale....
Conference Paper
Full-text available
Injection-molded short-fiber-reinforced composites (SFRC) have been widely used for structural applications in automotive and electronics industries. Due to the heterogeneous microstructures across different length scales, the nonlinear anisotropic behaviors of SFRC are very challenging to model. Therefore, an effective multiscale approach that lin...
Article
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The Representative Volume Element (RVE) analysis method provides a rigorous means to obtain homogenized macroscopic material properties at the upper length scale from the properties of the material constituents and structures at a lower length scale. Recently, we have developed an RVE module (keyword: *RVE_ANALYSIS_FEM) in the multiphysics simulati...
Article
Residual deformation and failure are two critical issues in powder bed fusion (PBF) additive manufacturing (AM) of metal products. Residual deformation caused by the non-uniform residual stress distribution dramatically affects the quality of AM product and can result in catastrophic failure in operation. Therefore, the development of an effective...
Article
A new particle Galerkin method is introduced to solve the Naiver‐Stokes equations in a Lagrangian fashion. The present method aims to suppress key numerical instabilities observed in the strong form Lagrangian particle methods such as SPH, ISPH and MPS for incompressible free surface flow simulations. It is well‐known that strong form Lagrangian pa...
Preprint
Full-text available
In the paper, we present an integrated data-driven modeling framework based on process modeling, material homogenization, mechanistic machine learning, and concurrent multiscale simulation. We are interested in the injection-molded short fiber reinforced composites, which have been identified as key material systems in automotive, aerospace, and el...
Article
A new numerical approach for modeling the three-dimensional ductile crack propagation problem is presented. The approach is obtained by the introduction of an h-adaptive finite element refinement scheme using the element-wise meshfree enrichments and meshfree visibility criteria to achieve the desired accuracy due to the material nonlinearity and t...
Article
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This paper introduces a new stabilization algorithm to Lagrangian particle methods for the coupled thermal mechanical analysis in the friction drilling simulation. Different from the conventional penalty method which utilizes a direct smoothing of velocity fields in the weak formulation, the proposed algorithm introduces the smoothed velocity field...
Article
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Modern materials design requires reliable and consistent structure–property relationships. The paper addresses the need through transfer learning of deep material network (DMN). In the proposed learning strategy, we store the knowledge of a pre-trained network and reuse it to generate the initial structure for a new material via a naive approach. S...
Chapter
This paper presents an up-to-date Lagrangian particle method for the analysis of a coupled thermo-mechanical problem in the friction drilling simulation. The method is obtained by a modification of variational equations using the penalized approach to avoid onerous stability problems in conventional Lagrangian particle methods and to obtain semi-di...
Article
Flow drill screw (FDS) joining is a modern mechanical fastening technique for connecting metal parts in lightweight car structures. Finite element simulation of FDS joining probably is one of the biggest challenges for CAE engineers in automotive applications. This is mainly because finite element methods inevitably encounter utmost numerical diffi...
Article
This paper extends the deep material network (DMN) proposed by Liu et al. (2019) to tackle general 3-dimensional (3D) problems with arbitrary material and geometric nonlinearities. It discovers a new way of describing multiscale heterogeneous materials by a multi-layer network structure and mechanistic building blocks. The data-driven framework of...
Article
Full-text available
Purpose Although high-order smooth reproducing kernel mesh-free approximation enables the analysis of structural vibrations in an efficient collocation formulation, there is still a lack of systematic theoretical accuracy assessment for such approach. The purpose of this paper is to present a detailed accuracy analysis for the reproducing kernel m...
Preprint
Full-text available
This paper extends the deep material network (DMN) proposed by Liu et al. (2019) to tackle general 3-dimensional (3D) problems with arbitrary material and geometric nonlinearities. It discovers a new way of describing multiscale heterogeneous materials by a multi-layer network structure and mechanistic building blocks. The data-driven framework of...
Article
Full-text available
This paper presents a discontinuous Galerkin weak form for bond-based peridynamic models to predict the damage of fiber-reinforced composite laminates. To represent the anisotropy of a laminate in a peridynamic model, a lamina is simplified as a transversely isotropic medium under a plane stress condition. The laminated structure is modeled by stac...
Article
In this paper, a new data-driven multiscale material modeling method, which we refer to as deep material network, is developed based on mechanistic homogenization theory of representative volume element (RVE) and advanced machine learning techniques. We propose to use a collection of connected mechanistic building blocks with analytical homogenizat...
Article
This paper applies the smoothed particle Galerkin (SPG) method to the analysis of penetration and perforation of metal targets. The SPG weak form is integrated using the direct nodal integration (DNI) technique with a nonresidual penalty-type stabilization term derived from strain smoothing. An adaptive anisotropic Lagrangian kernel is used to mode...
Preprint
Full-text available
In this paper, a new data-driven multiscale material modeling method, which we refer to as deep material network, is developed based on mechanistic homogenization theory of representative volume element (RVE) and advanced machine learning techniques. We propose to use a collection of connected mechanistic building blocks with analytical homogenizat...
Article
This paper presents a finite element continuous-discontinuous approach for the dynamic ductile failure analysis of shell structures. The continuum damage model based on continuous displacements is used in the continuous stage to describe the diffuse micro-cracking in ductile failure of high-strength steel before a macro-crack is formed. In the cont...
Article
This paper presents a new Lagrangian particle method for the simulation of manufacturing processes involving large strain and material failure. The starting point is to introduce some stabilization terms as a means of circumventing the onerous zero-energy deformation in the Lagrangian particle method. The stabilization terms are derived from the ap...
Article
Full-text available
In this paper, a numerical approach with an experimental validation is introduced for modelling high-speed metal grinding processes in 6061-T6 aluminum alloys. The derivation of the present numerical method starts with an establishment of a stabilized particle Galerkin approximation. A non-residual penalty term from strain smoothing is introduced a...
Article
This paper proposes an adaptive meshfree method to calculate the image stresses of the dislocations at the free boundaries and bicrystal interfaces. Based on the superposition method (van der and Needleman, 1995) originally proposed for single crystal material with free boundaries, a weak formulation is developed for the bicrystal materials contain...
Article
In this paper, we model the three-dimensional concrete impact and penetration problems using a stabilized meshfree method. The present method is established using a non-residual penalty term from strain smoothing as a means of stabilizing the meshfree nodal integration method under the Galerkin framework. As a result, the meshfree discretization le...
Article
Full-text available
A consistent multiscale formulation is presented for the bending analysis of heterogeneous thin plate structures containing three dimensional reinforcements with in-plane periodicity. A multiscale asymptotic expansion of the displacement field is proposed to represent the in-plane periodicity, in which the microscopic and macroscopic thickness coor...
Article
Full-text available
This paper presents a combined continuous–discontinuous modeling technique for the dynamic ductile fracture analysis using an interactive particle enrichment algorithm and a strain-morphed nonlocal meshfree method. The strain-morphed nonlocal meshfree method is a nodel-integrated meshfree method which was recently proposed for the analysis of elast...
Article
Peridynamics is a new nonlocal theory that provides the ability to represent displacement discontinuities in a continuum body without explicitly modeling the crack surface. In this paper, an explicit dynamics implementation of the bond-based peridynamics formulation is presented to simulate the dynamic fracture process in 3D elastic solid. Based on...
Article
A dynamic extended isogeometric analysis (XIGA) is developed for transient fracture of cracked magnetoelectroelastic (MEE) solids under coupled electro-magneto-mechanical loading, taking the advantages of high order NURBS basis functions and enrichment methods. The extended dynamic fracture parameters are estimated through the electro-magneto-mecha...
Article
This paper presents a new particle formulation for extreme material flow analyses in the bulk forming applications. The new formulation is first established by an introduction of a smoothed displacement field to the standard Galerkin formulation to eliminate zero-energy modes in conventional particle methods. The discretized system of linear equati...
Article
We present a selective edge-based smoothed finite element method (sES-FEM) of kinematic theorem for predicting the plastic limit loads in structures. The basic idea in this method is to use two levels of mesh repartitioning for the finite element limit analysis. The master level begins with an adaptive primal-mesh strategy guided by a dissipation-b...
Article
Full-text available
In this work, a strain-morphed nonlocal meshfree method is developed to overcome the computational challenges for the simulation of elastic-damage induced strain localization problem when the spatial domain integration is performed based on the background cells and Gaussian quadrature rule. The new method is established by introducing the decompose...
Article
This paper introduces an immersed meshfree approach within a Galerkin framework for the elastic analysis of particle-reinforced composites. A new meshfree discretization is developed and applied to the composite solids with overlapping sub-domains. Since each sub-domain is discretized independently, the generation of a conforming mesh in the finite...
Article
We investigate new numerical results of thermal buckling for functionally graded plates (FGPs) with internal defects (e.g., crack or cutout) using an effective numerical method. The new formulation employs the first-order shear deformation plate theory associated with extended isogeometric analysis (XIGA) and level sets. The material properties of...
Article
A nonlinear nodal-integrated meshfree Galerkin formulation based on recently proposed strain gradient stabilization (SGS) method is developed for large deformation analysis of elastoplastic solids. The SGS is derived from a decomposed smoothed displacement field and is introduced to the standard variational formulation through the penalty method fo...
Article
The standard numerical integration of the immersed meshfree Galerkin weak form based on mismatching overlapping integration cells and high-order quadrature rules is very time consuming and requires a large memory in the three-dimensional case. The method even becomes numerically infeasible for the large-scale nonlinear problems in general industria...
Article
Full-text available
A meshfree modeling technique of material flow in the three-dimensional multiphysics thermomechanical friction stir welding process is presented. In this numerical model, the discretization in space is derived by the Element-Free Galerkin method using a Lagrangian meshfree convex approximation. The discrete thermal and mechanical equations are weak...
Article
This paper presents a non-ordinary state-based peridynamic formulation that can be applied to the metal machining analysis. The new formulation is first derived by utilizing the technique of mixed local/nonlocal gradient approximations to enforce the contact and essential boundary conditions associated in modeling the machining process. A stabilize...
Article
In this paper, we present a gradient-type stabilization formulation for the meshfree Galerkin nodal integration method in liner elastic analysis. The stabilization is introduced to the standard variational formulation through an enhanced strain induced by a decomposed smoothed displacement field using the first-order meshfree convex approximations....
Article
A direct displacement smoothing meshfree particle formulation is introduced to the material failure modeling of concrete and steel materials due to blast and high velocity impact loadings. A Lagrangian smoothing form of the shape function is developed for the direct displacement smoothing meshfree particle formulation, which is subsequently employe...
Article
Full-text available
In this work, we have developed nonlinear peridynamics models of drained and saturated geomaterials, and applied them to simulations of dynamic fragmentation and ejecta formation due to impulse loads. First, we have re-phrased and re-interpreted the non-local state-based peridynamics formulation to connect the non-local integral operator with the l...
Article
In contrast to the partial differential equation in the classical continuum mechanics, the equation of motion in standard state-based peridynamics utilizes an integral form and follows an anti-symmetric relationship for the pairwise particle forces. As a consequence, the kinematic constraints such as the boundary displacements and the coupling with...
Conference Paper
Full-text available
The various particle (mesh-free) methods available in LS-DYNA are presented such as: Discrete Element Method (DEM), Smoothed Particle Hydrodynamics (SPH), Element Free Galerkin (EFG) and others.
Article
A three dimensional large deformation meshfree simulation of concrete fragmentation is presented by using a nodally regularized Galerkin meshfree method. This nodally regularized meshfree method is established with the two-level Lagrangian nodal gradient smoothing technique to relieve the material instability in failure modeling. The rate formulati...
Article
This paper presents a meshfree smooth contact formulation for application to metal forming problems. The continuum-based contact formulation requires C2 continuity in the approximation of contact surface geometry and displacement variables, which is difficult for the conventional C0 finite elements. In this work, we introduce a reproducing kernel a...
Article
An averaged shear strain method, based on a nodal integration approach, is presented for the finite element analysis of Reissner–Mindlin plates. In this work, we combine the shear interpolation method from the MITC4 plate element with an area-weighted averaging technique for the nodal integration of shear energy to relieve shear locking in the thin...
Article
The state-based peridynamics is considered a nonlocal method in which the equations of motion utilize integral form as opposed to the partial differential equations in the classical continuum mechanics. As a result, the enforcement of boundary conditions in solid mechanics analyses cannot follow the standard way as in a classical continuum theory....
Article
Full-text available
The use of lightweight materials has been steadily increasing in the automotive industry, and presents new challenges to material joining. Among many joining processes, self-piercing riveting (SPR) is particularly promising for joining lightweight materials (such as aluminum alloys) and dissimilar materials (such as steel to Al, and metal to polyme...
Article
In this paper, a meshfree-enriched finite element method (ME-FEM) is introduced for the large deformation analysis of nonlinear path-dependent problems involving contact. In linear ME-FEM, the element formulation is established by introducing a meshfree convex approximation into the linear triangular element in 2D and linear tetrahedron element in...
Article
In this paper, a multi-scale meshfree-enriched finite element formulation is presented for the analysis of acoustic wave propagation problem. The scale splitting in this formulation is based on the Variational Multi-scale (VMS) method. While the standard finite element polynomials are used to represent the coarse scales, the approximation of fine-s...
Article
In this paper, a meshfree shell adaptive procedure is developed for the applications in the sheet metal forming simulation. The meshfree shell formulation is based on the first-order shear deformable shell theory and utilizes the degenerated continuum and updated Lagrangian approach for the nonlinear analysis. For the sheet metal forming simulation...
Article
This chapter presents a large deformation analysis of nonlinear path-independent and path-dependent problems based on Meshfree-enriched Finite element Method (ME-FEM). In ME-FEM, the problem domain in two-dimension is first discretized by a regular triangulation using linear triangular elements. The element formulation is then established by introd...
Article
SUMMARYA three‐dimensional microstructure‐based finite element framework is presented for modeling the mechanical response of rubber composites in the microscopic level. This framework introduces a novel finite element formulation, the meshfree‐enriched FEM, to overcome the volumetric locking and pressure oscillation problems that normally arise in...
Article
In this paper, a two‐dimensional displacement‐based meshfree‐enriched FEM (ME‐FEM) is presented for the linear analysis of compressible and near‐incompressible planar elasticity. The ME‐FEM element is established by injecting a first‐order convex meshfree approximation into a low‐order finite element with an additional node. The convex meshfree app...
Article
In this paper a displacement-based meshfree-enriched finite element method, which was proposed for the linear modeling of near-incompressible elasticity, is generalized for the nonlinear analysis of elastomers. A four-noded triangular element based on the convex meshfree approximation is utilized to discretize the domain. An area-weighted smoothing...
Article
We present an approach for repartitioning existing lower-order finite element mesh based on quadrilateral or triangular elements for the linear and nonlinear volumetric locking-free analysis. This approach contains two levels of mesh repartitioning. The first-level mesh re-partitioning is an h-adaptive mesh refinement for the generation of a refine...
Article
Macroscopic characteristics of tires are affected not only by the construction and shape of the tires but also the microscopic mechanical characteristics of rubber compounds and fiber reinforcements. Therefore, it is important to investigate both micro- and macro-scale structural behaviors in the tire concurrently. Rubber compounds are made of soft...
Article
This paper studies the dispersion characteristic and stable time step of the meshfree method in explicit dynamic problems using the generalized meshfree (GMF) approximation. In the dispersion analysis, the von Neumann method is applied to analyze the numerical dispersion errors for the spatial semi-discretization of a partial differential equation...
Article
Mesh distortion induced numerical instability is a major roadblock in automotive crashworthiness finite element simulations. Remedies such as wrapping elements with null shells and deletion of distorted meshes have been adopted but none of them seems robust enough to survive various scenarios. Meshfree methods have been developed over the past almo...
Article
This paper presents a meshfree procedure using a convex generalized meshfree (GMF) approximation for the large deformation analysis of particle-reinforced rubber compounds on microscopic level. The convex GMF approximation possesses the weak-Kronecker-delta property that guarantees the continuity of displacement across the material interface in the...
Article
Full-text available
Macroscopic characteristics of tires, such as rolling resistance, wear and braking performance, are affected not only by the construction and shape of the tire but also the microscopic mechanical characteristics of the rubber compound. It is important to investigate the micro-and macro-scale structural behaviors in the tire simultaneously. To work...
Article
Full-text available
Procedures to adaptively refine meshes are emerging as an important tool for improving accuracy and efficiency in large deformation and fracture analysis. Comparing to the mesh- based adaptive method, the grid-based adaptive mesh-free method has several built-in advantages including naturally conforming in shape functions, smoothed interpolations i...