ON MODE-I AND MODE-II ENERGY-RELEASE RATES OF AN INTERFACE CRACK

The opening (mode I) and sliding (mode II) components of the energy that is released during an incremental extension of an interface crack between two different elastic materials are evaluated by the Irwin's crack closure method. Each component of the energies (G(I)DELTA and G(II)DELTA) is expressed in terms of the functions of the length of the incremental crack extension (DELTA-a) and the real and imaginary part of the complex stress intensity factor defined by Malyshev and Salganik. It is found that values of G(I)DELTA/DELTA-a and G(II)DELTA/DELTA-a oscillate violently when DELTA-a approaches zero and that, hence, in contrast with the case for homogeneous materials, each energy release rate should be defined as G(I)DELTA/DELTA-a and G(II)DELTA/DELTA-a for an actual crack growth step size.