Elastic-Plastic Analysis of Small Cracks in Tubes

Abstract

Analytical methods for predicting the elastic or elastic-plastic behavior of large circumferential through-wall cracks in tubes subjected to bending, tension, or combined bending and tension are well developed. Gilles and Brust (1991) and Gilles et al. (1991) summarize five such methods and provide a number of comparisons between analytically predicted results and experimental data. These techniques consist of developing a method for estimating the value of the J-integral. Classical J-tearing theory is utilized for the analyses. A method has also been recently developed to estimate J for a through-wall crack in a pipe weld (Rahman et al., 1991; Rahman and Brust, 1992). Unfortunately, the ability of these J-estimation techniques to predict the crack growth behavior for small cracks ({<=} 12 percent of the circumference) has not been established, even though such small cracks are often the concern in practical structures. Indeed, the finite element solutions compiled in the GE/EPRI handbook (Kumar et al., 1984) appear quite inadequate for small-size cracks (Gilles and Brust, 1991; Gilles et al., 1991). This paper presents the results of a series of finite element solutions for small cracks tabulated in the spirit of the handbook (Kumar et al., 1984). The theoretical background for the developmentmore » and use of simplified elastic-plastic fracture methods is fully discussed in Gilles and Brust (1991). Here, the authors provide the solutions for J-integral and the crack opening displacements for small crack problems under pure bending. Ongoing work will complete these solutions for tension and for combined tension-bending loads.« less