Three-dimensional analysis of thermal shock effect on inner semi-elliptical surface cracks in a cylindrical pressure vessel

摘要

Transient mode I stress intensity factors (K_(IT))distributions along semi-elliptical crack fronts resulting fromthermal shock typical to a firing gun are investigated, K_(IT)distributions for various crack arrays of n=2 to 48 cracks, bearingcracks of relative depths of a/W=0.1 to 0.4 and with ellipticitiesof a/c=0.5, 1.0 and 1.5 are evaluated for a cylindrical pressurevessel of radii ratio of R_0/R_i=2. As decoupling between thethermal and the elastic problems is assumed, the solution isperformed in two steps via the finite element (FE) method usingthe standard ANSYS 5.0 code. In the first step temperaturedistributions brought he vessel's wall are evaluated for varioustime steps in the interval 2 to 10 msec assuming convectiveboundary conditions. The temperature fields evaluated in the firststep serve as input to the second step, the elastic analysis, inwhich K_(IT) is evaluated. The results show that K_(IT) isusually negative, as could have been anticipated, and reaches itslargest negative value at the intersection of the crack plane withthe inner surface of the cylinder. In general, the negativemagnitude of K_(IT) increases as the number of cracks in thearray decreases, as the crack elliptically increases, and as timeelapses from firing.