Criteria evaluation for the transition of cracking modes in a single-crystal nickel-base superalloy

Crack growth in single crystal gas turbine blade alloys under service-like conditions

“…To make this modelling strategy possible, reliable predictions of the transition from Mode I crack propagation to crystallographic crack propagation is of key importance. This transition has been studied previously by Kagawa 91 , Reed 88 and Busse 12 and is further studied and modelled in Paper 4 of this thesis. A cracking mode transition criterion is proposed, which is inspired by the work of Kagawa 91 et al and based on the anticipated crystallographic crack growth rate relative to the mode I crack growth rate, evaluated locally along the crack front.…”

“…The same single crystal nickel-base superalloy studied in the present work was previously studied by Busse et al [9][10][11][12] . The work by Busse was mainly focused on modelling of the crystallographic crack growth behaviour and finding a suitable crack driving force parameter for crystallographic crack growth.…”

“…Both models were successfully used to predict which of the {111} planes the first crystallographic crack would initiate on. In subsequent publications by Busse 10,12 and in Paper 4 of this thesis, Model 1 is used. Model 1 was chosen due to its lower computation time compared Model 2.…”

“…This definition of crystallographic crack driving force parameter was adopted in Busse's 10,12 further work regarding the crystallographic crack growth rates and prediction of the transition from Mode I to crystallographic crack growth. The work presented in Paper 4 of this thesis also relies on the same definition of the crack driving force parameter, according to Eq.…”

“…Several researchers propose crack driving force parameters based on shear stress intensity factors resolved onto the {111} planes [4][5][6][7][8][9] , but there is no general consensus regarding the precise definition. Within the present PhD thesis work, testing was done to investigate the crystallographic crack growth behaviour under different testing conditions and the results were used in the development of the crystallographic crack driving force parameter recently proposed by Busse et al [9][10][11][12] . While the complexity of localized inelastic deformation and crystallographic crack growth is mainly associated with lower temperatures, there are other challenges associated with fatigue crack growth in single crystal superalloys at higher temperatures.…”