Zhang Kangda

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.

Comparison of the fracture and fatigue properties of 16MnR steel weld metal, the HAZ and the base metal

Abstract The fracture toughness and fatigue crack growth rate of 16MnR steel weld metal, the HAZ and the base metal were measured. The fracture toughness J tc of the HAZ is lowest among the weld and base metals and the HAZ, the J tc of the base metal being a little higher than that of the HAZ and that of the weld metal being the highest. The crack growth in the HAZ is faster than those in the weld and the base metal, which are nearly the same. Thus both the fracture and fatigue properties in the HAZ are worse than those in both the weld and the base metals.

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%.

Interactions of two coplanar elliptical cracks embedded in finite thickness plates under uniform tension

Abstract This paper includes the analysis of the interactions of two coplanar elliptical cracks, with equal or different crack sizes, embedded in finite thickness plates under uniform tension. 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, interactions 1 and 2, with a total of 42 crack configurations, are studied and the stress intensity factors along the crack front are presented. The numerical results show that interaction 2 has a stronger interaction than interaction 1. The numerical analyses are carried out by the hybrid boundary element method.

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.

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.

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.