| The three-dimensional boundary element method has been determined to be an efficient computational method for solving elastostatic problems, particularly those for cracked geometries. For this reason, it is employed for the analysis of thick-walled internally pressurized curved tubing. The stress distribution in a pipe bend is investigated with respect to bend radius ratio, radius ratio of the cross-section, and angle of curvature. Upon verifying the intrados as the most likely site for crack nucleation, independent of the geometric parameters, a semi-elliptical crack of semi-minor to semi-major axis ratio b/a=0.8 is introduced. Stress intensity factors are determined along the crack periphery, &phis;, for the internal pressure case, with pressure acting on the crack faces.;The stress factor in an uncracked internally pressurized pipe bend is observed to increase for smaller bend radii, lower radius ratios and larger angles of curvature. The effect of the longitudinal angle is minimal and becomes negligible at the larger bend radius. Once a semi-elliptical crack is introduced, with pressure acting on the crack faces, the normalized stress intensity factor results obtained are consistent with these observations. Furthermore, it is found that the normalized stress intensity factor is approximately constant up to &phis;=60°, after which it increases rapidly as the free surface is approached.;Polynomial influence coefficients are computed for all instances and used to verify the stress intensity factors for the previous load case; they are shown to agree to within 2.5% difference. Influence coefficients may be combined through superposition to determine the stress intensity factor for any load case with the same cracked geometry. This is demonstrated using a representative set of models for various levels of overstrain due to partial autofrettage. |
