3-D stress intensity factors for internal cracks in an overstrained cylindrical pressure vessel—Part I: The effect of autofrettage level

Three-dimensional, mode I, stress intensity factor (SIF) distributions for arrays of internal surface cracks emanating from the bore of an autofrettaged thick-walled cylinder are evaluated in Part I of this paper. The 3-D analysis is performed via the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. The autofrettage residual stress field is simulated using an equivalent temperature field. More than 200 different crack configurations were analyzed. SIFs for numerous crack arrays (n = 1-180 cracks), a wide range of crack-depth-to-wall-thickness ratios (a/t = 0.05-0.6), various ellipticities (a/c = 0.2-1.5), and different levels of autofrettage (e = 10-100 percent) were evaluated. The results clearly indicate the importance of autofrettage in reducing the effective stress intensity factor, and thus, slowing the crack growth rate. The sensitivity of this favorable effect to the number of cracks in the array as well as to the level of autofrettage are also discussed. The combined effect of pressure and autofrettage is discussed in detail in Part II of this paper.