Yongqiang Chen

Peking University | PKU · Department of Mechanics & Engineering Science

The analytical stress-strain relation with heterogeneous parameters is derived for the heterogeneous brittle materials under a uniaxial extensional load, in which the distributions of the elastic modulus and the failure strength are assumed to be statistically independent. This theoretical solution gives an approximate estimate of the equivalent st...

This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion tensor, and specific heats of the multi-phase composites are derived by means of the volume average of free-energies of these phases....

In recent years, the research and development of composites have received more attention due to rapid increase in demand for composites in various applications. The particulate composites have been used in many fields, for example, to produce functionally graded materials which are potential solutions to biomedical and other modern engineering appl...

The surface/interface energy theory based on three configurations proposed by Huang et al. is used to study the effective properties of thermoelastic nanocomposites. The particular emphasis is placed on the discussion of the influence of the residual interface stress on the thermal expansion coefficient of a thermoelastic composite filled with nano...

A new micromechanics method is proposed to investigate the effective properties of saturated porous media with connected pores. This topic is seldom discussed in the literature because it is difficult to describe the connected pores and skeleton using conventional micromechanics methods. A new micromechanics model (i.e., Model I) is suggested to ch...

The boundary element method (BEM) employing the partial pivot adaptive cross approximation (PACA) algorithm has been observed to experience convergence failures and reduced solution accuracy when solving elasticity problems, especially at large scales. To address this issue, this paper proposes an improved algorithm for both 2D and 3D elasticity pr...

In this paper, a novel mixed cell compressed sparse row (mCCSR) scheme is proposed to address the sparsity, block structure, and partial sub-matrix symmetry inherent in the coefficient matrix of the time domain boundary element method (TDBEM) in elastodynamics. The impulse function used in the fundamental solution of TDBEM introduces a time-lag phe...

A novel scheme, termed mixed cell compressed sparse row (mCCSR) is proposed to address the sparsity, block structure, and partial sub-matrix symmetry in the matrix. Time domain boundary element method (TDBEM) in elastodynamics. The compression performance of mCCSR scheme is much better than other compression methods in TDBEM, such as adaptive cro...

The fast multipole boundary element method (FMBEM) is a powerful technique for solving large-scale problems. Its effectiveness heavily relies on the iterative solver, which in turn depends crucially on the performance of the preconditioner. Although a leaf-based preconditioner has proven effective in the single domain FMBEM (SFB), it encounters cha...

In the boundary element method (BEM), the sinh transformation method is an effective method for evaluating nearly singular integrals, but a relationship between the integration accuracy and the number of Gaussian points is needed to achieve adaptive computation. Based on deep learning, we propose a novel integration scheme, adaptive sinh transforma...

The time domain boundary element method (TDBEM) is suitable for dealing with dynamic problems in the semi infinite domain (such as the propagation of seismic waves). The fundamental solution in the TDBEM is an impulse function with time terms, and the formed coefficient matrix is sparse. In this paper, a TDBEM using the compressed storage algorithm...

The paper presents a novel numerical scheme to effectively solve the weak, strong, and hyper-singular time-space integrals in the 3D time domain boundary element method (BEM). To deal with the singularities of P- or S-wavefront elements, the element subdivision method is used to identify non-zero valued sub-elements on the wavefronts, and the non-z...

In recent years, enhanced thermal conductive properties of polymer composites filled with reduced graphene oxide (rGO) have been studied for diverse applications. However, rGO fillers tend to form aggregates, making it difficult to reach the maximum enhancement through the use of rGO. Experiments have shown that the hydrogen bond between rGO and mo...

a r t i c l e i n f o Keywords: Nonlinear interface model Boundary element method (BEM) Particulate composites Interface debonding process Fast multipole expansion a b s t r a c t A fast multipole boundary element method (BEM) is used herein to simulate the two-dimensional interfacial debonding of particulate composites. The behavior of the interfa...

Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical, automobile, aerospace including defence technology. Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites. Due to their favourable properties, particle-based met...

This paper proposes a new error upper bound formula for the Gaussian integration of the near-singular integral using the Boundary Element Method. First, this study found through numerical tests that the maximum relative error of the Gaussian integration has a downward concave shape but an approximately linear relationship with the relative distance...

A new particular solution method is proposed to indirectly calculate the strong singular integrals and free terms in conventional Helmholtz boundary integral equation (CBIE) and hyper-strong singular integrals in Burton-Miller boundary integral equation (BMBIE).For the acoustic problem of interior field,the particular solution satisfying Helmholtz...

This paper proposes a new constitutive model for geotechnical materials that consists two basic constitutive functions, the free energy function and the dissipation rate function, within the framework of hyperplastic theory. This free energy function is capable of describing the pressure-dependent elastic behavior of soils. The new constructed diss...

The increasing development of big data technology has brought great opportunities and challenges to innovation of complex system such as Intelligent Transportation System (ITS), especially in the method of big data driven modelling. This paper focused on analyzing the feasibility of model study based on noisy trajectory data collected by cell phone...

In order to apply classical micromechanics in predicting the effective prop- erties of nanocomposites incorporating interface energy, a concept of equivalent inclusion (EI) is usually adopted. The properties of EI are obtained by embedding a single inclusion with the interface into an infinite matrix. However, whether such an EI is universal for di...

Surface/interface effect plays a significant role in the study of the mechanical properties of nanocomposites. Most previous papers in the literature only considered the surface/interface elasticity, whereas some papers only considered the residual surface/interface stress (surface/interface tension). In this paper, an energy-based surface/interfac...

In multiphase particulate composites, the deviation and mismatch of the elastic moduli of different particles may significantly affect the overall mechanical performance of the composites. This study investigates the effects of such deviations on the macroscopic properties of multiphase compositesvia an iterative micromechanics-based method. The el...

The effective thermoelastic properties of spherical particulate composites with inhomogeneous interphases are studied. Particular emphasis is put on discussing the influence of the radial distribution of the interphase properties on the effective specific heats. Firstly, the inhomogeneous interphase is modeled by multiple concentric layers and the...

The interface energy theory developed by Huang et al. is further extended to incorporate the effect of the residual interface stresses on the effective specific heats of multiphase thermoelastic nanocomposites. First, a micromechanics-based method is employed to derive the expressions of the effective specific heats at constant-strain and constant-...

A micromechanics-based elastoplastic constitutive model for porous materials is proposed. With an assumption of modified three-dimensional Ramberg–Osgood equation for the compressible matrix material, the variational principle based on a linear comparison composite is applied to study the effective mechanical properties of the porous materials. Ana...

In this paper, the surface/interface energy theory to investigate the mechanical behavior of nano-sized structures and nanocomposites developed by the present authors is further extended to incorporate the thermal effect. Specifically, the discussion will focus on the influence of the “residual interface stress” on the effective thermal expansion c...

To enforce accurate displacement constraints, essential boundary conditions and interface continuity conditions in mesh-less method are treated as Multi-Point Constraints (MPC) of displacement, which are illustrated by using SPH(Smoothed Particle Hydrodynamics) method incorporated with algebraic master-slave relations. An example of linear elastic...

In this paper, a new method of topological cleanup for quadrilateral mesh is presented. The method first selects a patch of mesh around an irregular node. It then seeks the best connection of the selected patch according to its irregular valence using a new topological operation: small polygon reconnection (SPR). By replacing the original patch wit...

In subspace iteration method (SIM), the relative difference of approximated eigenvalues between two consecutive iterations is usually employed as the convergence criterion. However, though it controls the convergence of eigenvalues well, it cannot guarantee the convergence of eigenvectors in all cases. In the case when there is no shifting, the bes...

In this paper, we revisit the point-in-polyhedron problem. After reviewing previous work, we develop further insight into the problem. We then claim that, for a given testing point and a three-dimensional polyhedron, a single determining triangle can be found which suffices to determine whether the point is inside or outside the polyhedron.This wor...

In this paper, a modified projection method is combined with a self-adaptive time step procedure to develop numerical scheme for large eddy simulation (LES) of low Ma number turbulent reactive flows. The projection method introduced by Chorin is modified in this study to satisfy the simulation requirement of low Ma number reactive flow. The time st...

Local transformation, or topological reconnection, is one of the effective procedures for mesh improvement method, especially for three-dimensional tetrahedral mesh. The most frequently used local transformations for tetrahedral mesh are so-called elementary flips, such as 2-3 flip, 3-2 flip, 2-2 flip, and 4-4 flip. Owing to the reason that these b...

In this paper we report two advances in the classical subspace iteration method for eigenvalue problems arising in finite element analysis. One extends the computable error bound proposed by Matthies to the case with nonzero shift and the other is an aggressive shift for the subspace iteration. Numerical tests show that the propose method can effec...

There are two important problems in the context of Delaunay based mesh generation namely boundary recovery after Delaunay tetrahedralization and sliver removal. Both of them can be solved to a large extent using a new method, the so called small polyhedron reconnection or SPR for abbreviation. For sliver remove, an operation is developed according...

Numerical simulations of fire disaster in a specific gymnasium were performed and the temperature distribution and the structure failure process induced by fire were investigated. The results showed that the elastic modulus of steel material dropped quickly with the increasing of temperature caused by fire. This would lead to the weakening of the s...

Sphere packing is an attractive way to generate high quality mesh. Several algorithms have been proposed in this topic, however these algorithms are not sufficiently fast for large scale problems. The paper presents an efficient sphere packing algorithm which is much faster and appears to be the most practical among all sphere packing methods prese...

Owing to the growing size of the eigenvalue problem and the growing number of eigenvalues desired, solution methods of iterative nature are becoming more popular than ever, which however suffer from low efficiency and lack of proper convergence criteria. In this paper, three efficient iterative eigenvalue algorithms are considered, i.e., subspace i...

In this paper, we investigate boundary recovery, the problem that has troubled researchers ever since Delaunay-based methods were applied to generate mesh. There are a number of algorithms for boundary recovery already and most of them depend heavily on adding extra nodes. In this paper, we make an effort to seek a method to recover boundaries with...

A general numerical approach was developed to simulate the mechanical properties and the failure of heterogeneous elasto-plastic materials using statistical distributions of the material properties. An appropriate elastic-plastic constitutive relation is used to describe the material behavior and failure in each element, with a two-parameter Weibul...

A general numerical approach is developed to simulate the failure process of structure or heterogeneous material, in which different local failure models are defined for different structures and materials to describe the failure of structure joint or material element. A two-parameter Weibull distribution is employed to produce the initial heterogen...

The wide range of temporal scales involved in the turbulent reactive flow brings great requirements to the numerical simulation processes. The modeling of reactive flows with multi-step detailed chemical kinetics calls for the small enough time step size, which will result directly in a huge computational cost. Different from the fixed time step me...

The lattice model and statistical distributions are used to represent the initial heterogeneous distribution of material properties. Equations of the reduplicate multi-sub-region (RMSR) boundary element method are established for the lattice model of 2-D heterogeneous materials. Each row of sub-regions in the lattice are integrated into a super-sub...

By using the lattice model combined with finite element methods and statistical techniques, a numerical approach is developed to establish mechanical models of three-dimensional heterogeneous brittle materials. A special numerical code is introduced, in which a lattice model and statistical approaches are used to simulate the initial heterogeneity...

The analytical stress-strain relations with heterogeneity parameters are derived for a one-dimensional heterogeneous brittle material, assuming that the elastic modulus and failure strength distributions are random and mutually independent. The analytical solutions, which agree well with numerical results, describe the essential relations between m...