FINITE-ELEMENT ANALYSIS OF THE EFFECTS OF CORNERS ON RESIDUAL-STRESSES IN PROTECTIVE OXIDE SCALES

Finite element simulations are used to examine residual thermal stress es and strains in corner regions of protective Al2O3 scales on Fe3Al s pecimens, both during cooling from oxide formation temperatures and du ring subsequent thermal cycling. The effects of a corner's radius of c urvature and oxide thickness, as well as the impact of aluminide plast icity, are considered. Localized plasticity is found to have a major i nfluence on net deformation and on the magnitude and location of maxim um stress. As the ratio of corner curvature to oxide thickness (r(s)/f ) is reduced, stresses within the oxide corner shift from highly compr essive to tensile and the location of the maximum principal stress mov es from the substrate to the oxide scale. Based on these stress distri butions prior to the development of any flaws, key implications about the tendencies for damage are addressed. The stress evolution during c ooling and thermal cycling is presented; these results demonstrate the effects of temperature-dependent material properties. For the materia l behavior assumed in this study, thermal cycling does not cause signi ficant stress relaxation. (C) 1997 Elsevier Science S.A.