This is not just another book on fracture mechanics. In recent years,
there have been many books published on this subject in an attempt to
assess the state of the art and its applications. The majority of the
work dealt with energy release rate or critical stress intensity factor
and is applicable only to fracture toughness testing. The main reason
for this restriction is that the energy release concept cannot easily be
extended to mixed mode fracture that occurs in practice as the rule
rather than the exception. Cracks will normally curve or turn because
the direction of loading can change as a function of time. Their
directions of growth cannot be assumed as an a priori and must be
determined from a pre-assumed criterion. Analysts are still perplexed
with selecting an appropriate fracture criterion because it requires
much discernment and judgement. Criteria which often appeared valid for
idealized situations are quickly dis- credited when encountering more
complex physical phenomena. Moreover, the claim of generality cannot be
justified on the basis of agreement between theory and experiment for a
few simple examples.