EFFECTS OF GRAIN-BOUNDARY DIFFUSION AND POWER-LAW CREEP ON CYLINDRICAL CAVITY DEFORMATION

Volume growth rate, rupture time and the phenomenological creep damage parameter are investigated using both grain boundary diffusion and po wer law creep. Voids are assumed to be cylindrically shaped with a dih edral angle of pi/2, and are arrayed in the grain boundary at constant spacing and radius. The grain boundary separation velocity is obtaine d from a modification of the stress analysis result obtained from a pr evious analysis. The (L/a) coupling term is included in the modified r esult, where L is the effective diffusion length (D(g)OMEGA(a)delta(b) sigma infinity/KTepsilon(infinity))1/3 and a is the void radius. The r esults obtained in the analysis are compared with the results obtained using the spherical cap (dihedral angle, phi = 70-degrees) of Needlem an and Rice. The results show that if L/a is large, cavity deformation is controlled by the grain boundary diffusion mechanism while power l aw creep controls the deformation in the range of small L/a. These res ults are consistent with the results obtained by Needleman and Rice. T he coupling effects in terms of the L/a parameter on the cylindrical v oid deformation is less pronounced than that of the spherical cap sinc e the present analysis is an approximate solution. The coupling effect in the present analysis begins at approximately L/a = 5.0 while the s pherical cap model begins at approximately L/a = 10. The Monkman-Grant constant obtained from the analysis is larger than that obtained by N eedleman and Rice in the region where coupling effect is prominent (10 less-than-or-equal-to L/a less-than-or-equal-to 1.0). The Monkman-Gra nt constant of the cylindrical cavity in the region controlled by powe r law creep is smaller than that of the spherical cap. Finally the dam age parameter of creeping material is significantly affected by the co upling parameter (L/a).