Chai Guozhong

Stress intensity factors for semi-elliptical surface cracks in plates and cylindrical pressure vessels using the hybrid boundary element method

At first, a hybrid boundary element method used for three-dimensional linear elastic fracture analysis is established on the basis of the first and the second kind of boundary integral equations. Then the concerned basic theories and numerical approaches including the discretization of boundary integral equations, the divisions of different boundary elements, and the procedures for the calculations of singular and hypersingular integrals are presented in detail. Finally, the stress intensity factors of surface cracks in finite thickness plates and cylindrical pressure vessels are computed by the proposed method. The numerical results show that the hybrid boundary element method has very high accuracy for the analysis of surface crack.

Stress intensity factors for internal semi-elliptical surface cracks in pressurized thick-walled cylinders using the hybrid boundary element method

Abstract The purpose of this paper is to present a comprehensive range of results of mode I SIFs of three-dimensional surface cracks in internally pressurized thick-walled cylinders. The hybrid boundary element method is summarily reviewed and used to calculate the SIFs of surface cracks in pressurized thick-walled cylinders. The analyzed ratio of crack depth to wall thickness ranges from 0.2 to 0.8; the ratio of crack depth to crack length ranges from 0.25 to 1.0; and the ratio of wall thickness to cylinder radius is 0.5, 1.0 and 2.0. The present normalized SIFs are also compared with other solutions from the literature. The recent results of the body force method and the finite element method agree well ( ca 3%), and the early ones of the boundary integral equation and the finite element method agree fairly well ( ca 10%) with the present results.

Analyses of embedded elliptical cracks in finite thickness plates under uniform tension

Abstract This paper presents a comprehensive range of results of mode I stress intensity factors for the embedded elliptical cracks in finite thickness plates under uniform tension. The hybrid boundary element method developed by the author is used to calculate the stress intensity factors. The analyzed ratio of crack depth to crack length ( b a ) is 0.25, 0.5 and 1.0; the ratio of crack depth to plate thickness ( b t 1 , and b t 2 ) ranges from 0.0 to 0.8. The present normalized stress intensity factors are also compared with Isidas results obtained by the body force method. The two results agree excellently with each other, with a maximum difference of 2%.

Analyses on interactions of two identical semi-elliptical surface cracks in the internal surface of a cylindrical pressure vessel

Abstract This paper analyzes the interactions of two coplanar identical semi-elliptical surface cracks in the internal surface of a cylindrical pressure vessel. Few numerical solutions appear to be available in the literature so far for this kind of interaction. The analyzed ratios of the wall thickness to the radius of the cylinder ( t R i ) are 0·1 and 0·25; the ratios of crack deph to crack length ( b a ) are 0·25, 0·5 and 1·0; the relative distances between the centers of two cracks ( a d ) are 0·5, 0·7 and 0·9. In total 36 crack configurations are analyzed. The mode I stress intensity factors along the crack front are presented. The numerical analyses are carried out by the hybrid boundary element method.

Analysis of embedded elliptical cracks in cylindrical pressure vessels

Abstract This paper presents a comprehensive range of results of Mode I stress intensity factors for the embedded elliptical cracks in cylindrical pressure vessels. The hybrid boundary element method developed by the author is used to calculate the stress intensity factors. For practical uses an approximate method is proposed which is used to estimate the stress intensity factors of embedded elliptical cracks in cylindrical pressure vessels from the results of embedded cracks in finite thickness plates.

Approximate stress-intensity factor solutions for nozzle corner cracks

Abstract In this paper first the iso-stress lines at a nozzle corner are simplified into slanted straight lines at an angle of 45° with the walls of cylinder and nozzle and the natural nozzle corner cracks as quarter-circular ones. On the basis of this, a stress-intensity factor solution for an arbitrary point on the crack front is derived by means of approximate analysis. Following from this, approximate expressions of the maximum and average stress-intensity factors K i max and K im are proposed, which are very important to the analysis of fatigue and fracture of practical pressure vessel nozzle corner cracks. These expressions show good consistency with the results of FEM, Kobayashis approximate analysis and Besuners IFM for about 40 cracks from nine nozzle sections. The expressions of K i max and K im are not only very simple but also have excellent accuracy; for most cracks the error is less than 10%.

A hybrid boundary element method for three-dimensional fracture analysis

At first, a hybrid boundary element method used for three-dimensional linear elastic fracture analysis is established by introducing the relative displacement fundamental function into the first and the second kind of boundary integral equations. Then the numerical approaches are presented in detail. Finally, several numerical examples are given out to check the proposed method. The numerical results show that the hybrid boundary element method has a very high accuracy for analysis of a three-dimensional stress intensity factor.

Creep analysis of surface-cracked plates by a creep line-spring method

The creep line-spring method proposed in this paper is based on the solutions for the following two problems: a creep crack under non-steady creep condition; an elastic-plastic surface-cracked plate. For the problem of a non-steady creep crack, an engineering approach for estimating the load-line displacement, crack-tip J and C integrals is presented by extending the engineering approach for elastic-plastic fracture analysis to creep analysis. For solving the elastic-plastic surface crack, a simplified elastic-plastic line-spring method is applied. These two approximate solutions are checked by the finite element method. On the basis of the above two approximate methods, a creep line-spring method is proposed and the corresponding fundamental equations are established. The creep line-spring method is used to estimate creep fracture parameters for three-dimensional cracks. In order to check its accuracy, several surface-cracked plates under uniform tension are analyzed by the creep line-spring method and by the three-dimensional finite-element method. The numerical results show that the creep line-spring method is in good agreement with the finite-element method and has the same accuracy as the common elastic-plastic line-spring method.

Interactions of coplanar surface semi-elliptical cracks and embedded elliptical cracks in finite thickness plates under uniform tension

Abstract This paper analyzes the interactions of coplanar surface semi-elliptical cracks and embedded elliptical cracks in a finite thickness plate under uniform tension, for which no numerical solutions appear to be available in the literature. The ratios of crack depth to crack length ( b 1 a 1 and b 2 a 2 ) are 0·25 and 1·0; the relative distances between two cracks ( s 1 b min and s 2 b min ) range from 0·5 to 2·0. Two kinds of interactions, interaction 1 for which neither the long principal axes nor the short principal axes of two cracks are collinear and interaction 2 for which the short principal axes of two cracks are collinear within a total of 48 crack configurations, are studied. The mode I stress intensity factors along the crack front and the interacting coefficient of two cracks are presented. The numerical results show that interaction 2 has a stronger interacting effect from interaction 1. The numerical analyses are carried out by the hybrid boundary elements method.

Stress intensity analyses on tension of a finite thickness plate with two coplanar semi-elliptical surface cracks

Abstract This paper analyzes the interactions of two coplanar semi-elliptical surface cracks located, respectively, at the front and back surfaces in a finite thickness plate under uniform tension. Few numerical solutions appear to be available in the literature so far for this kind of interaction. The analyzed ratios of crack depth to crack length (b1/a2, b2/a2) are 0.25, 0.5 and 1.0; the minimum relative distances between two cracks (s2/bmin) range from 0.5 to 2.0. In total, 18 crack configurations are analyzed. The mode I stress intensity factors along the crack front and the interacting coefficient of two cracks are presented. The numerical analyses are carried out by the hybrid boundary element method.