PSI - Issue 61

Mehmet N. Balci et al. / Procedia Structural Integrity 61 (2024) 331–339 Balci and Yalcin / Structural Integrity Procedia 00 (2019) 000 – 000

338

8

modulus of the substrate ( s ) material is kept constant and elastic modulus of the surface coating ( sc ) is changed parametrically from 0.2 sc s E E = to 5.0. sc s E E = As the elastic modulus of the coating is increased, mode I and mode II SIFs are decreased in both hot and cold shocks. Change in SIFs in hot shock is greater than that observed in cold shock. Hence, phase angle implies that crack-tip stress field is shear dominant for larger values of , sc s E E such as 5.0. In the hot shock case, stress field starts to be normal and opening mode tend to be influential. In both shock cases, greater values of sc s E E leads to increase in energy release rate. Fig. 7 depicts the fracture parameters for the crack located between the substrate and the bond coating (Case-B). Mode I SIF is negative and increase in the crack length induces an increase first and then decrease in * . I K Increase in the crack length leads to an increase in * . II K For all length of cracks, the phase angle  is less than 45 degrees, which implies opening mode dominant crack-tip stress field. It is observed that phase angle  reaches a stable level after some time. Increase in the crack length leads to considerable increase in energy release rate, which may be critical for delamination failure. Fig. 8 illustrates temperature contours in the coating system at t=1.0s for different values of crack length in Case-B configuration. Obtained temperatures in Case-B are greater than those obtained in Case-A at the same shock time such as t=1.0s.

Fig. 7. The influence of crack length on (a) Normalized mode-I SIF vs time, (b) Normalized mode-II SIF vs time, (c) Total energy release rate vs time, (d) Phase angle vs time in a cold thermal shock Case-B configuration.

Fig. 8. Temperature contours in the coating system for cold shock at time t=1.0s for Case-B configuration (a) = 0.5 , (b) = 1.0 , (c) = 1.5 , (d) = 2.0 .