The stress dependence of the crack growth rate during creep

✍ Scribed by R. J. Dimelfi; W. D. Nix

• Publisher: Springer Netherlands
• Year: 1977
• Tongue: English
• Weight: 437 KB
• Volume: 13
• Category: Article
• ISSN: 1573-2673
• DOI: 10.1007/bf00040148

✦ Synopsis

An equation is derived for the crack growth rate under creep conditions. In the model, the propagation of a grain boundary crack is controlled by the plastic growth of cavities located in the grain boundaries ahead of the crack. It is assumed that the cavities grow by power law creep in the elastic crack tip stress field. Hence, the stress dependence of the crack velocity is provided through the elastic stress intensity factor, i.e., dC/dt = BK~.

The cavity spacing, A, appears as an important factor in the coefficient, B g a -~p-2)/2. At large values of A, corresponding to less severe creep damage in the grain boundaries, the above equation would predict very low values for the crack velocity. Under such conditions, we suggest that another mechanism, whose stress dependence is provided through the net section stress, becomes active, i.e., dCldt = B'o-~,'~. Since A increases with decreasing applied stress, one should observe the ~rnc, correlation at low stresses. The results of recent creep crack growth experiments which tend to support this hypothesis are presented.