Reliability analysis of structural ceramics subjected to biaxial flexure

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7071865

Chao, Luen-Yuan

Two weakest-link fracture statistics formulations for multiaxial loading, Batdorf's flaw density and orientation distribution approach and Evans' elemental strength approach, were compared for identical fracture criteria and flaw-size distribution function. Despite some fundamental differences in the methodology used in calculating fracture probabilities for multiaxial loading, the two approaches gave identical predictions. A recent contradictory conclusion reported in the literature is shown to be incorrect. Fracture stresses of a sintered alumina and silicon nitride were assessed in qualified uniaxial (three-point and four-point) and biaxial (uniform-pressure-on-disk) flexure tests in inert conditions. The size and stress-state effects on the inert fracture stress of alumina were explained by a reliability analysis based on randomly oriented surface flaws and a mixed-mode fracture criterion. Fracture stresses of silicon nitride were in accord with a reliability analysis based on volume flaws with preferred orientation (crack plane normal to the maximum principal stress) and a normal stress fracture criterion. The preferred orientation of the flaws in silicon nitride resulted from stress-induced nucleation of cracks around pores. Alumina ceramic was also tested in deionized water at a low stressing rate (1 MPa/s). The decreased fracture stresses measured in both uniaxial and biaxial flexure tests in water as compared to the inert fracture stresses were consistent with subcritical crack growth behavior inferred from dynamic fatigue tests in water. The analysis of the size and stress-state effects on and time-dependent degradation of fracture stresses included consideration of the statistical uncertainties (90 percent confidence intervals) of the estimated Weibull (Weibull modulus, m, and characteristic strength, sigma[sub theta]) and slow-crack-growth (stress-intensity exponent, N, and critical crack growth rate, V[sub C]) parameters.

• Research Organization: Utah Univ., Salt Lake City, UT (United States)
• OSTI ID: 7071865
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CERAMICS
CHALCOGENIDES
FRACTURE PROPERTIES
MECHANICAL PROPERTIES
NITRIDES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
SILICON COMPOUNDS
SILICON NITRIDES
STRESS INTENSITY FACTORS