Chen Dai-Heng

A crack normal to and terminating at a bimaterial interface

Abstract This paper investigates the plane problem of a crack normal to and terminating at a bimaterial interface. The general expression for the singular stress field at the crack tip that touches the interface is given in an explicit closed form. The singular stress fields are expressed as a sum of two independent terms, which correspond to the symmetric and skew-symmetric stress fields, respectively. The intensities of the symmetric and skew-symmetric singular stress fields are defined in terms of two factors K I and K II , respectively. The body force method is used to determine the values of K I and K II . The numerical results are given for a broad range of material combinations.

Analysis of singular stress field around the inclusion corner tip

Abstract The plane problem of an infinite plate containing an inclusion is considered. The singular stress field around the inclusion corner tip is expressed as a sum of two independent types: a symmetric type with a stress singularity 1 r 1−λ1 and a skew-symmetric type with a stress singularity 1 r 1−λ2 . The intensities of the symmetric and skew-symmetric singular stress fields are defined in terms of constants KIλ 1 and KII,λ2, respectively. The body force method is used to calculate the values of KI,λ1 and KII,λ2. In numerical analysis, basic density functions of the body forces are introduced to characterize the stress singularity at the inclusion corner. The advantages of this technique are the high accuracy of results, due to the smoothness of the unknown weight functions, and the presence of the direct relation between the values of KI,λ1, KII,λ2 and the values of unknown weight functions at the corner tip.

Analysis of the delaying effects of overloads on fatigue crack propagation

Abstract In this paper a simulation analysis of fatigue crack propagation was carried out in order to investigate the delaying effects of overload on fatigue crack propagation. The analysis was based on the Dugdale hypothesis, but the method of analysis used here is the extended body force method, which has been developed recently by the authors and is applicable to a wide range of problems. Based on the results analysed the retardation of crack propagation due to overloads was discussed quantitatively. The results of simulation analysis were compared with the experimental data obtained by other researchers.

Detection of a crack by body force method

Abstract A new practical method is proposed to determine the location and the size of a crack and the loading stresses based on the data of measured strains in the structure. The unknown parameters are determined by the condition which minimizes an objective function. The objective function is denned as the square sum of the residuals between the computed and measured values. The method of gradient search is employed to find out the optimal set of parameters. The body force method is used to calculate the strain field around the crack. In order to avoid problems due to the local minimum in the gradient searching process, the starting point of the gradient search is efficiently selected based on the basic concept of the body force method. In order to shorten the calculation time, the strain field around the crack is represented by several concentrated force doublets. Numerical experiments are carried out, which show that the unknown parameters are determined efficiently with good accuracy and in a short time.

Effect of elastic constants on stress in multi-phases under plane deformation

Abstract The reduction of the elastic parameters necessary to describe the stress field in a composite under plane deformation is discussed based on the body force method and the eigenstrain theory. When the composite body subjected to prescribed surface tractions consists of N different elastic phases and each phase is characterized by M γ ( γ = 0,1,…, N − 1) independent elastic constants, the stress fields generally depend on (∑ γ =0 N −1 M γ ) − 1 parameters involving the elastic constants. If the vector sums of the tractions on holes vanish for every individual hole, however, the stress depends on the elastic constants through only (∑ γ =0 N −1 M γ )− 2 parameters formed from ∑ γ =0 N −1 M γ elastic constants.

Combination of BFM and FEM for Analysis of the Stress Intensity Factor of Cracks

In this paper a combination of BFM and FEM for problems with cracks has been developed. It is found that there is always a local incompatibility of displacements or stresses on the interface of two domains in which BFM and FEM are used, respectively. The accuracy of this analysis is usually in fluenced by the incompatibility. Three types of equivalent nodal forces were compared. It is demonstrated that the equivalent nodal force defined as a resultant force between two middle points of adjacent boundary elements is useful.