Papers by Author: Yu Zhou Sun

Abstract: The structural performance of the PMCRGF subjected to the static loading is actively investigated in this study. The structural properties and of the PMCRGF is briefly introduced at first and the construction process of the PMCRGF is discussed. The field measurement on the structural performance of the PMCRGF is carried out. The arrangement and process of the field measurement is illustrated in detail. The structural deformation and stress distribution are also computed based on finite element approach. The structural fine finite element model is constructed with the aiding of the commercial package ANSYS. The stresses at different section are computed and compared with those obtained from the field testing. The made conclusions from field testing and theoretical analysis can provide beneficial instruction for the real application the plastic mortar culvert reinforced by glass fiber (PMCRGF)

Abstract: This paper presents a study for the square crack in a three-dimensional infinite transversely isotropic medium, which can model the fracture damage of rock that displays transversely isotropic behavior. The study is based on a newly derived boundary integral equation. To carry out the numerical simulation, the crack opening displacement is first expressed as the product of the weight functions and the characteristic terms, and the unknown weight is approximated with the moving least-square approximation. A boundary type numerical scheme is established, and the effect of the orientation of the principle axis on the stress intensity factor is studied. The interaction between two coplanar square cracks are also modeled and discussed.

Abstract: In this study, effective dispersion of different amount of multiwall carbon nanotubes was achieved using a surfactant and in combination with the use of ultrasonic energy. The effects of surfactant and surfactant concentration on the plain cement mortar were investigated. Moreover, the mechanical behaviors of the carbon-nanotube reinforced composites were also analyzed. Experimental results indicate that the application of ultrasonic energy is absolutely necessary to produce a satisfactory dispersion of MWCNTs, and there exists an optimum weight ratio of surfactant to MWCNTs. It is found that the proper dispersion of MWCNTs can remarkably improve the flexural strength, compressive strength, and the toughness of the cement mortar composites.

Abstract: This paper presents a three-dimensional viscoelastic model to study the interactions of a penny-shaped interfacial crack and a center of dilatation in the infinite viscoelastic bimaterial, which can model the rock fracture subjected to stress and thermal dilatation during some engineering process. A distinct issue associated with the present work is the incorporation of viscoelastic behavior of bimaterial. The proposed problem is first transformed into the Laplace space, and the solution in the transform space is obtained by decomposing the original problem into two auxiliary problems: (I) a center of dilatation near a bimaterial interface (no crack); and (II) a penny-shaped interfacial crack subject to internal tractions that cancel out those induced in auxiliary problem (I). The mode I, II and III stress intensity factors (SIFs) in the time domain are obtained with the inverse Laplace transform.

Abstract: An atomic scale modeling method is provided to study the buckling behavior of the single-walled carbon nanotubes. The Brenner potential is employed to describe the C-C atomic interaction,and the stable state is determined using the Norton’s method with the first- and second-order derivatives of the total energy with respect to the atomic coordinates. The reponse of single-walled carbon nanotubes under the axial compressive, twisting and buckling loads is modeled using the developed Fortran codes, and the buckling patterns are obtained. The proposed method can be used to study the mechanical property of cabon nanotubes and explore its application in the cement composite in future.

Abstract: The carrying capacity and energy absorption characteristic of foamed aluminum (or aluminum foam), fabricated by melt foaming technique, are limited due to the lower strength of aluminum. The typical anti-vibration energy absorbing structures are designed as foamed aluminum-filled or sandwich structures. The deformation and absorption characteristics of foamed aluminum-filled structures subjected to impact loadings are analyzed using experimental and numerical methods in this work. The analysis shows that the steel shell of the combinative structure subjected to dynamic loadings dominates during energy absorption. The energy absorption capacity and initial instability loading increase as impact velocity increase and as increasing shell thickness duo to the interaction between steel shell and aluminum foam. The impact mass within the range of 100kg influences weakly on peak instability loading. Since the steel shell is the dominating part of load capacity and energy absorption, the reasonable design, taking into account of foam density and shell thickness and taking full advantage of interaction between steel shell and aluminum foam, should be adopted to increase the energy absorption characteristic of foam-filled structures.

Abstract: This paper presents a boundary element-free computational method for the fracture analysis of 2-D anisotropic bodies. The study starts from a derived traction boundary integral equation (BIE) in which the boundary conditions of both upper and lower crack surfaces are incorporated into and only the Cauchy singular kernal is involved. The boundary element-free method is achieved by combining this new BIE and the moving least-squares (MLS) approximation. The new BIE introduces two new variables: the displace density and The dislocation density. For each crack, the dislocation density is first expressed as the product of the characteristic term and unknown weight function, and the unknown weight function is approximated with the MLS approximation. The stress intensity factors (SIFs) can be calculated from the the weight function. The examples of the straight and circular-arc cracks are computed, and the convergence and efficiency are discussed.

Abstract: This paper presents a mesh-free numerical modeling approach for carbon nanotubes (CNTs) subjected to bending loads. The higher-order Cauchy-Born rule was employed to construct the higher-order continuum constitutive model. An initial equilibrium single-walled CNT (SWCNT) was viewed as been formed by rolling up a graphite sheet into a cylindrical shape. The deformation from an original SWCNT to the current configuration was approximated with the moving least-square (MLS) approximation, and the mesh-free computational framework was established in the theoretical scheme of higher-order gradient continuum. Mesh-free numerical simulations were carried out for SWCNTs, and the accuracy and convergence were discussed in comparison with the results of atomistic simulation. The buckling behavior was studied for various types of SWCNTs upon bending, and the buckling mechanism was investigated in virtue of the continuum variables, which showed that the maximum axial compressive strain played a vital role in the development of kinking.

Abstract: This paper introduces a multiscale modeling approach for carbon nanotubes (CNTs), in which a fine continuum model that has been developed by the present authors is employed to implement the continuum modleing. The entire domain is decomposed into a continuum modeling region and an atomic region with an overlapping region. For the atomic region, the atomic finite element method (AFEM) is used to trace the individual atomic motion. Whereas, the continuum region is viewed as the higher-order continuum media, and the mesh-free method is adopted to implement the continuum numerical discrization. For the overlapping region, the bridging domain method is used to efficiently couple two scales. Numerical computation is carried out and several examples are discussed.