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.
其他摘要：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.
