Early growth behavior of crack originated from cooling holes during thermo-mechanical fatigue loadings

It is important to get basic understandings on early stage crack propagation behavior around the cooling holes machined in high temperature hot section components in advanced gas turbine system. For the purpose a new testing system has been developed in this work. By means of the test system the thermo-mechanical fatigue (TMF) crack propagation tests were carried out specifying a directionally solidified Ni-base superalloy specimen in which some cooling holes were introduced in the gauge section part of specimen. Fracture mechanics discussions were made on the specific crack propagation behavior from two roles of cooling hole: one was a source of stress concentration and the other is a source of thermal stress which is induced by inhomogeneous temperature distribution. (author)