Effect of elastic anisotropy on fatigue band in polycrystalline solids

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:175179

Teng, N J; Lin, T H ^[1]

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1. Univ. of California, Los Angeles, CA (United States)

Extrusions and intrusions in fatigued specimens are favorable sites for fatigue cracks. These extrusions or intrusions have been considered to be composed of the thin slices P, Q and R in the surface crystal of a polycrystal. These thin slices are taken to be in the most favorably-oriented crystal at the free surface. Previous study, concerns mainly the bands in aluminum and its alloys. The anisotropy of the elastic constants of these alloys is small and neglected. Then the polycrystal was considered as an elastically homogeneous and isotropic medium. A tensile or compressive load {tau}{sub 22} causes a maximum shear stress in the surface crystal with a slip direction and slip plane making 45{degrees} with the loading axis. However, the anisotropy of the elastic constants of some other metal crystals such as titanium and some intermetallic alloys is large. Significant errors will be introduced in the calculated fatigue band if this anisotropy is neglected. In the present paper, the effect of anisotropy is analyzed. The elastic anisotropy of the surface crystal and its surrounding crystals is considered. Since the metal exterior to the aggregate is composed of crystals with random orientations, this aggregate of anisotropic crystals is taken as being embedded in an elastic isotropic semi-infinite medium. This heterogeneous solid is transformed into a homogeneous one using Eshelby`s Equivalent Inclusion Method. In this method, an extra set of eigenstrains (which are the same as the inelastic strains) is introduced. The eigenstrains and plastic strains developed to relieve the resolved shear stress cause a stress field in the body. In the following numerical calculation, the anisotropic elastic constants of Ni{sub 3}Al monocrystalline intermetallic compound are used. The isotropic elastic constants of the surrounding metal are taken from experimental data.

• OSTI ID: 175179
• Report Number(s): CONF-950686--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
99 GENERAL AND MISCELLANEOUS
ALUMINIUM ALLOYS
ANISOTROPY
CRACKS
ELASTICITY
FATIGUE
INTERMETALLIC COMPOUNDS
NICKEL ALLOYS
SLIP
STRAINS
TITANIUM