A model for microcrack initiation and propagation beneath Hertzian contacts in polycrystalline ceramics
- National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Lab.
- Lehigh Univ., Bethlehem, PA (United States). Dept. of Materials Science and Engineering
- Univ. de Extremadura, Badajoz (Spain). Dept. de Fisica
A fracture mechanics model of damage evolution within Hertzian stress fields in heterogeneous brittle ceramics is developed. Discrete microcracks generate from shear faults associated with the heterogeneous ceramic microstructure; e.g. in polycrystalline alumina, they initiate at the ends of intragrain twin lamellae and extend along intergrain boundaries. Unlike the well-defined classical cone fracture that occurs in the weakly tensile region outside the surface contact in homogeneous brittle solids, the fault-microcrack damage in polycrystalline ceramics is distributed within a subsurface shear-compression zone below the contact. The shear faults are modeled as sliding interfaces with friction, in the manner of established rock mechanics descriptions but with provision for critical nucleation and matrix restraining stresses. This allows for constrained microcrack pop-in during the loading half-cycle. Ensuing stable microcrack extension is then analyzed in terms of a K-field formulation. For simplicity, only mode 1 extension is considered specifically here, although provision exists for including mode 2. The compressive stresses in the subsurface field constrain microcrack growth during the loading half-cycle, such that enhanced extension occurs during unloading. Data from damage observations in alumina ceramics are used to illustrate the theoretical predictions. Implications of the results in the practical context of wear and fatigue properties are discussed.
- OSTI ID:
- 5155103
- Journal Information:
- Acta Metallurgica et Materialia; (United States), Journal Name: Acta Metallurgica et Materialia; (United States) Vol. 42:5; ISSN 0956-7151; ISSN AMATEB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CERAMICS
CHALCOGENIDES
CRACK PROPAGATION
DATA
GRAIN SIZE
INFORMATION
MATHEMATICAL MODELS
MICROSTRUCTURE
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
SIZE
STRESS INTENSITY FACTORS
THEORETICAL DATA