Thermal Mechanical Fatigue Cracks Growth from Laser Drilled Holes in Single Crystal Material (Preprint).

摘要

The crack growth test results undergoing thermomechanical fatigue showed that the life of TMF specimens with notched laser drilled holes exhibit a debit by as much as 4 times that of smooth gage section specimens under the same loading conditions. Such a significant change in number of cycles to failure must be accounted in any damage tolerant design system. The detailed fractographic analysis demonstrated that the all cracks start crystallographically along the octahedral crystallographic planes and later change to mixed mode fracture. Major crack propagation takes place at the low temperature portion of the cycle in the OP test; however there is noticeable damage accumulation during the high temperature compressive load portion of the cycle. Crack propagation under TMF loading conditions is considerably faster than corresponding isothermal LCF crack growth tested at the temperature and similar loading conditions of the tensile part of the TMF cycle. As results show, the applicability of the LEFM methods for single crystal TMF crack growth prediction is limited and at least should consist of mixed mode crack analysis.