摘要：Prediction of life in fatigue is still based on purely phenomenological or
empiric relations, in most cases in Engineering practice. The Paris’ law is
one of the few consolidated tools to calculate propagation velocity of
fatigue cracks based on Fracture Mechanics, although being also a
phenomenological relation. The cohesive interface method has been used
intensively lately as a tool to simulate cracking process in metals with
great success. More recently, few attempts to use this method to predict life
in fatigue have been done. Such works follow the general idea that during
the loading-unloading, cohesive law should present some hysteresis, function
of parameters that measure damage during cycling process. In this work,
the cohesive surface method will be used as an attempt to model the
rupture in fatigue. However, dissipation during cyclic loading in the present
work will not introduce new damage parameters, being a residual opening after
unloading the only source of irreversibility. Such hypothesis is based on the
fact that oxidation films develop after opening. The unloading path may have
also an important effect on monotonic crack propagation, since local
unloading, near the crack tip, are expected. To simulate propagation, the
cohesive surface was implemented in a Element code. Preliminary results for a
7075-T6 aluminum show good data fitting, indicating that the hypothesis is
feasible. In the examples analyzed, only Mode I of propagation was
considered. Plastic strains on the crack tip were small, indicating the
validity of the Linear Elastic Fracture Mechanics. Dynamic and monotonic
crack propagation are also considered here, showing that the local unloading
near crack tip may have an important effect on the kinematics of
the propagation.
