Qing-Sheng Yang

Modelling the effective elasto-plastic properties of unidirectional composites reinforced by fibre bundles under transverse tension and shear loading

Abstract The effect of fibre bundling on the effective transverse properties of unidirectional fibre composites has been investigated by way of finite element method and micromechanics models of fibre bundles. Based on the micromechanical model of single-fibre composites, plane strain models for composites reinforced by fibre bundles are presented. The effective elasto-plastic stress–strain behaviour was obtained numerically by analysing a boron/aluminium composite reinforced by three-fibre and four-fibre bundles. The results are compared with the modelled behaviour for the composites reinforced by single fibres. The study shows that there is a remarkable influence of fibre bundling on plastic deformation, transverse tension and shear tangent stiffness of composites, while the influence on effective elastic properties can be ignored, fibre bundling enhances the transverse tangent stiffness of plastic deformation of composite materials, and the transverse normal stress–strain relations are more sensitive to fibre bundling than the transverse shear stress–strain relations.

Size effects in the fiber pullout test

In this paper, a numerical simulation method is used to study the effect of specimen size on interfacial behavior of the specimen in fiber pullout tests. Interfacial shear stress and normal stress are analyzed for different sizes of the test specimen. The interface between fiber and matrix is assumed to be bonded perfectly. For simplicity, all materials are assumed to be linear and elastic solids, and the effects of thermal residual stress and friction between crack faces are ignored. The effects on interfacial behavior of both length of the fiber embedded in the matrix and thickness of the matrix around the fiber are studied using the finite element approach. Furthermore, the effect of the specimen size on the interfacial crack growth is also studied by way of energy release rate. The study shows that the size of the test specimen can influence interfacial stresses and fracture characteristics dramatically.

Macro-micro theory on multifield coupling behavior of heterogeneous materials

Introduction.- Homogenization theory of heterogeneous media.- Thermo-electro-elastic problems.- Thermo-magneto-electro-elastic problems.- Thermo-chemo-electro-elastic problems.- Thermoelectroelastic bone remodelling.- Effective coupling properties of heterogeneous media.- Effective properties of thermopiezoelectricity.- Effective properties of magneto-electro-elastic solids.

Micro-mechanical analysis of composite materials by BEM

Applications to composites of a unit-cell model in conjunction with boundary element method (BEM) for determining their effective mechanical properties are discussed in this paper. The composite considered here consists of inclusion and matrix phases. A unit-cell model for composites with periodically distributed inhomogeneities is developed and introduced into a boundary element formulation to provide an effective means for estimating overall material constants of two-phase composites. In this model, the volume average stress and strain is calculated by the boundary tractions and displacements of the unit-cell and the periodic conditions of the composite are expressed by the periodic boundary conditions of the unit-cell. Thus BEM is suitable for performing calculations on average stress and strain fields of such composites. Numerical results for a two-phase composite with circular rigid inclusions are presented to illustrate the application of the proposed unit-cell boundary element formulation.

Analytical and numerical investigation of interfacial stresses of FRP–concrete hybrid structure

Abstract This paper presents a study on interfacial stresses of a concrete column confined by fiber-reinforced plastic (FRP) plate, which has been widely applied in the civil engineering for rehabilitation and retrofitting of conventional structures. It is assumed that both the FRP plate and concrete structures are elastic and the interface between them is perfectly bonded. An analytical model for analysis of the interfacial stresses is developed and the finite element modeling is carried out for an axisymmetric FRP–concrete hybrid column. Components of the FRP plate with different geometric and material properties are considered to study their effects on the interfacial stresses. The study shows that the interfacial stresses are influenced by several factors, such as modulus ratio of FRP and concrete and thickness of FRP. This work provides a comprehensive investigation on the mechanical behavior of the interface in hybrid structures.

Modeling the Mechanical Properties of Functionalized Carbon Nanotubes and Their Composites: Design at the Atomic Level

This investigation focuses on the design of functionalization configuration at the atomic level to determine the influence of atomic structure on the mechanical properties of functionalized carbon nanotubes (F-CNTs) and their composites. Tension and compressive buckling behaviors of different configurations of CNTs functionalized by H atoms are studied by a molecular dynamics (MD) method. It is shown that H-atom functionalization reduces Young’s modulus of CNTs, but Young’s modulus is not sensitive to the functionalization configuration. The configuration does, however, affect the tensile strength and critical buckling stress of CNTs. Further, the stress-strain relations of composites reinforced by nonfunctionalized and various functionalized CNTs are analyzed.

Analysis of intelligent hinged shell structures: deployable deformation and shape memory effect

Shape memory polymers (SMPs) are a class of intelligent materials with the ability to recover their initial shape from a temporarily fixable state when subjected to external stimuli. In this work, the thermo-mechanical behavior of a deployable SMP-based hinged structure is modeled by the finite element method using a 3D constitutive model with shape memory effect. The influences of hinge structure parameters on the nonlinear loading process are investigated. The total shape memory of the processes the hinged structure goes through, including loading at high temperature, decreasing temperature with load carrying, unloading at low temperature and recovering the initial shape with increasing temperature, are illustrated. Numerical results show that the present constitutive theory and the finite element method can effectively predict the complicated thermo-mechanical deformation behavior and shape memory effect of SMP-based hinged shell structures.

Parametric analysis and temperature effect of deployable hinged shells using shape memory polymers

Shape memory polymers (SMPs) are a class of intelligent materials, which are defined by their capacity to store a temporary shape and recover an original shape. In this work, the shape memory effect of SMP deployable hinged shell is simulated by using compiled user defined material subroutine (UMAT) subroutine of ABAQUS. Variations of bending moment and strain energy of the hinged shells with different temperatures and structural parameters in the loading process are given. The effects of the parameters and temperature on the nonlinear deformation process are emphasized. The entire thermodynamic cycle of SMP deployable hinged shell includes loading at high temperature, load carrying with cooling, unloading at low temperature and recovering the original shape with heating. The results show that the complicated thermo-mechanical deformation and shape memory effect of SMP deployable hinge are influenced by the structural parameters and temperature. The design ability of SMP smart hinged structures in practical application is prospected.

Numerical simulation of cracking processes in dissimilar media

This paper presents a novel numerical technique to simulate the crack propagation process for inhomogeneous solids. The criteria of crack growth and path selection are expressed in terms of some simple functions of fracture energy and loading phase angle. The energy release rate and loading phase angle for mixed mode cracks are evaluated by the finite element method with a mesh-adaptive technique. Examples are considered to show that the method is effective for simulating and predicting crack paths in inhomogeneous solids. They include crack growth or kinking in bi-materials and damage processes of fiber-reinforced composites.

New Coarse-Grained Model and Its Implementation in Simulations of Graphene Assemblies

Graphene is a one-atom thick layer of carbon atoms arranged in a hexagonal pattern, which makes it the strongest material in the world. The Tersoff potential is a suitable potential for simulating the mechanical behavior of the complex covalently bonded system of graphene. In this paper, we describe a new coarse-grained (CG) potential, TersoffCG, which is based on the function form of the Tersoff potential. The TersoffCG applies to a CG model of graphene that uses the same hexagonal pattern as the atomistic model. The parameters of the TersoffCG potential are determined using structural feature and potential-energy fitting between the CG model and the atomic model. The modeling process of graphene is highly simplified using the present CG model as it avoids the necessity to define bonds/angles/dihedrals connectivity. What is more, the present CG model provides a new perspective of coarse-graining scheme for crystal structures of nanomaterials. The structural changes and mechanical properties of multilayer graphene were calculated using the new potential. Furthermore, a CG model of a graphene aerogel was built in a specific form of assembly. The chemical bonding in the joints of graphene-aerogel forms automatically during the energy relaxation process. The compressive and recover test of the graphene aerogel was reproduced to study its high elasticity. Our computational examples show that the TersoffCG potential can be used for simulations of graphene and its assemblies, which have many applications in areas of environmental protection, aerospace engineering, and others.