Isoparametric Singular Elements Research Articles

Stress Intensity Factors of Slanted Cracks in Bi-Material Plates

In this study, the stress intensity factors (SIF) of slanted cracks in bi-material plates subjected to mode I loading is numerically solved. Based on the literature survey, tremendous amount of research works are available studying the normal cracks in both similar and dissimilar plates. However, lack of SIF behavior for slanted cracks especially when it is embedded in bi-material plates. The slanted cracks are then modelled numerically using ANSYS finite element program. Two plates of different in mechanical properties are firmly bonded obliquely and then slanted edge cracks are introduced at the lower inclined edge. Isoparametric singular element is used to model the crack tip and the SIF is determined which is based on the domain integral method. Three mechanical mismatched and four slanted angles are used to model the cracks. According to the present results, the effects of mechanical mismatch on the SIF for normal cracks are not significant. However, it is played an important role when slanted angles are introduced. It is suggested that higher SIF can be obtained when the cracks are inclined comparing with the normal cracks. Consequently, accelerating the crack growth at the interface between two distinct materials.

Stress intensity factors under mode III loadings

This study presents a numerical investigation on the stress intensity factors (SIF) obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node ¼-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed that this proposed model was validated for analyzing mode III problems. It was found that, the FII and FIII were dependent on the crack geometries and the behavior of crack growth were also dependent on a/b and a/D.

Mode III Stress Intensity Factors of Surface Crack in Round Bars

This study presents a numerical investigation on the stress intensity factors (SIF), K of surface cracks in round bars that were obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node ¼-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed this proposed model validated for analyzing mode III problems. It was found that, the mode II SIF, FII and mode III SIF, FIII were dependent on the crack geometries and the sites of crack growth were also dependent on a/b and a/D.

631 アイソパラメトリック特異要素を用いた楕円環状き裂の応力拡大係数の有限要素解析

631 アイソパラメトリック特異要素を用いた楕円環状き裂の応力拡大係数の有限要素解析

The Analysis of Dynamic Stress Intensity Factor for Semi-Circular Surface Crack Using Time-Domain BEM Formulation

The time-domain BEM was developed to analyze the dynamic stress intensity factor (DSIF) of 3-D elastodynamic crack problems. To simulate the stress singularity along the front of a crack, eight-node isoparametric singular elements were used, and the DSIF for a semi-circular surface crack was firstly calculated based on displacement equation using the time-domain BEM formulation. The new scheme to determine the time step was brought forward. By the dynamic analysis program of time-domain BEM compiled by us, several numerical examples are presented, which demonstrate the unconditional stability and high accuracy of time-domain BEM applied to 3-D elastodynamic crack problems.

Evaluation of stress intensity factor for a crack normal to bimaterial interface using cubic isoparametric finite elements

When a crack meets bimaterial interface stress singularity depends on the elastic constants of the adjacent materials. In the present study we are going to describe the finite element formulation for problems with a crack to be embedded in the stiffer material. The cubic isoparametric singular element, represented by adequately shifting the mid-side nodes adjacent to the crack tip is constructed to enclose the crack tip. An alternative method to obtain the optimal position of the mid-side nodes of cubic isoparametric elements is presented. In addition, a proper definition for the stress intensity factors of a crack normal to bimaterial interface is provided. It is based upon near a tip displacement solutions. Models for numerical analysis are two dimensional elastic bodies with a through crack under plain strain. The results obtained are compared with the previous solutions.

Computation of SIF (stress intensity factor) of corner crack in interior wall of nozzle of nuclear vessel

The computation of the stress intensity factor (SIF) of a corner crack in the interior wall of a nozzle for a steel nuclear vessel is a complicated 3-D case. The finite element method is a powerful tool for this case. An improved 3-D collapsed isoparametric singular element with quarter-points is presented in this paper and the required inverse square root singularity in these vertical planes of a crack is derived. The method of construction for the corresponding transitional element that was extensively used in the 3-D case is also presented. The Williams formula as well as the least-squares linear fitting method was used to compute K I according to the displacements near the crack front. The SIF of a corner crack in the interior wall of a nozzle of a Reactor Pressure Vessel (RPV) of a typical 300-MW nuclear power plant was computed and verified by the 3-D photo-elastic test and the diffusion of light test. To analyse the effect of various factors on the SIF, the computations were carried out on 12 models.

Investigation in weighted function and optimization of isoparametric singular boundary elements' size in 3-d crack problem

In this paper, there are several measures being used to simplify the analytic method and improve the computational accuracy. We have emphatically studied: (1) An explicit weighted function expression in isoparametric singular BEM. (2) A reasonable collocation of 8-nodes isoparametric boundary elements and application of transition elements. (3) Optimization of the sizes of isoparametric singular elements. The study shows: (i) the deduced explicit weighted function expression of 8-nodes isoparametric BEM is good at setting up a general method of computing the SIF of 3-D crack problem under complex load, (ii) The reasonable collocation of isoparametric boundary elements and the optimization of the size of the singular boundary elements obviously improved the accuracy of numerical computation.