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Title: STRENGTH OF A C-SPHERE FLEXURE SPECIMEN

Abstract

A 'C-Sphere' flexure strength specimen geometry was conceived and developed to measure a relevant strength of bearing-grade Si{sub 3}N{sub 4} balls and to relate that to surface-located strength-limiting flaws and to ultimately link those flaw populations to rolling contact fatigue performance. A slot was machined into the balls to a set depth to produce the C-sphere geometry. C-sphere specimens were then diametrally compressed to produce a monotonically increasing flexure or hoop tensile stress at their surface that caused their fracture. The strength was determined using the combination of failure load, C-sphere geometry, and FEA, and the stress field was used to determine C-sphere effective areas and effective volumes as a function of Weibull modulus. A description of the specimen and the aforementioned analysis are provided and a comparison of C-sphere flexure strength distributions of two bearing grade Si{sub 3}N{sub 4} materials (NBD200 and SN101C) is given.

Authors:
 [1];  [1];  [2];  [1];  [1]
  1. ORNL
  2. University of Wisconsin, Platteville
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); High Temperature Materials Laboratory
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
931246
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 30th International Conference and Exposition on Advanced Ceramics and Composites, Cocoa Beach, FL, USA, 20060122, 20060127
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; SILICON NITRIDES; BALL BEARINGS; FLEXURAL STRENGTH; DESTRUCTIVE TESTING; DEFECTS; PERFORMANCE; FINITE ELEMENT METHOD

Citation Formats

Wereszczak, Andrew A, Wang, Wei, Jadaan, Osama M., Lance, Michael J, and Lin, Hua-Tay. STRENGTH OF A C-SPHERE FLEXURE SPECIMEN. United States: N. p., 2007. Web.
Wereszczak, Andrew A, Wang, Wei, Jadaan, Osama M., Lance, Michael J, & Lin, Hua-Tay. STRENGTH OF A C-SPHERE FLEXURE SPECIMEN. United States.
Wereszczak, Andrew A, Wang, Wei, Jadaan, Osama M., Lance, Michael J, and Lin, Hua-Tay. Mon . "STRENGTH OF A C-SPHERE FLEXURE SPECIMEN". United States. doi:.
@article{osti_931246,
title = {STRENGTH OF A C-SPHERE FLEXURE SPECIMEN},
author = {Wereszczak, Andrew A and Wang, Wei and Jadaan, Osama M. and Lance, Michael J and Lin, Hua-Tay},
abstractNote = {A 'C-Sphere' flexure strength specimen geometry was conceived and developed to measure a relevant strength of bearing-grade Si{sub 3}N{sub 4} balls and to relate that to surface-located strength-limiting flaws and to ultimately link those flaw populations to rolling contact fatigue performance. A slot was machined into the balls to a set depth to produce the C-sphere geometry. C-sphere specimens were then diametrally compressed to produce a monotonically increasing flexure or hoop tensile stress at their surface that caused their fracture. The strength was determined using the combination of failure load, C-sphere geometry, and FEA, and the stress field was used to determine C-sphere effective areas and effective volumes as a function of Weibull modulus. A description of the specimen and the aforementioned analysis are provided and a comparison of C-sphere flexure strength distributions of two bearing grade Si{sub 3}N{sub 4} materials (NBD200 and SN101C) is given.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • A "C-sphere" flexure strength specimen geometry was conceived and developed to measure the hoop tensile strength of bearing-grade silicon nitride (Si3N4) balls. Because such a strength can be measured, the important study of surface-located strength-limiting flaws in ceramic sphere is also enabled with this specimen. A slot is machined into the balls to a set depth to produce the C-sphere geometry. A simple, monotonically increasing uniaxial compressive force produces a hoop tensile stress at the C-sphere's outer surface that ultimately initiates fracture. The strength is determined using the combination of failure load, C-sphere geometry, and finite element analysis. Additionally, themore » stress field was used to determine C-sphere effective areas and effective volumes as a function of Weibull modulus. To demonstrate this new specimen, C-sphere flexure strength distributions were determined for three commercially available bearing-grade Si3N4 materials (NBD200, SN101C, and TSN-03NH), and differences among their characteristic strengths and Weibull moduli were found.« less
  • A new test specimen, defined here as the "sectored flexure strength specimen", was developed to measure the strength of ceramic tubes specifically for circumstances when flaws located at the tube's outer diameter are the strength-limiter and subjected to axial tension. The understanding of such strength-limitation is relevant for when ceramic tubes are subjected to bending or when the internal temperature is hotter than the tube's exterior (e.g., heat exchangers). The specimen is both economically and statistically attractive because eight specimens (eight in the case of this project - but the user is not necessarily limited to eight) were extracted outmore » of each length of tube. An analytic expression for maximum or failure stress, and relationships portraying effective area and effective volume as a function of Weibull modulus were developed. Lastly, it was proven from the testing of two ceramics that the sectored flexure specimen was very effective at producing failures caused by strength-limiting flaws located on the tube's original outer diameter. Keywords: ceramics, strength, sectored flexure specimen, effective area, effective volume, finite-element analysis, Weibull distribution, and fractography.« less
  • A C-sphere specimen geometry was used to determine the failure strength distributions of a commercially available bearing-grade silicon nitride (Si3N4) having ball diameters of 12.7 and 25.4 mm. Strengths for both diameters were determined using the combination of failure load, C sphere geometry, and finite element analysis and fitted using two-parameter Weibull distributions. Effective areas of both diameters were estimated as a function of Weibull modulus and used to explore whether the strength distributions predictably strength-scaled between each size. They did not. That statistical observation suggested that the same flaw type did not limit the strength of both ball diametersmore » indicating a lack of material homogeneity between the two sizes. Optical fractography confirmed that. It showed there were two distinct strength-limiting flaw types in both ball diameters, that one flaw type was always associated with lower strength specimens, and that significantly higher fraction of the 24.5-mm-diameter c-sphere specimens failed from it. Predictable strength-size-scaling would therefore not result as a consequence of this because these flaw types were not homogenously distributed and sampled in both c-sphere geometries.« less
  • An elastic-plastic analysis of the end notched flexure (ENF) specimen with tough interlayer is conducted by two-dimensional finite element modeling. Interlayer refers to a mixture of thermoplastic particles and thermoset base resin, selectively localized between laminae as a thin resin film. It is observed experimentally that plastic deformation in the interlayer has direct effect upon the interlaminar delamination growth and the toughness. The purpose of study is to evaluate Mode II interlaminar fracture toughness of interlayer-toughened composites with fracture mechanics parameter, J-integral, which is applicable to elastic-plastic regime. Effect of the material nonlinearity on the load versus crack shear displacementmore » (CSD) diagram and J-integral is examined and limitation of linear elastic fracture mechanics approach to the tough composites is discussed.« less
  • A J-Integral analysis of the ENF specimen used to characterize mode 2 delamination fracture toughness of fiber reinforced composites has been developed. The analysis uses a two-dimensional form of the J-Integral and beam theory, accounts for geometric and material nonlinearities, crack tip deformations, and transverse shear. A linear elastic finite element assessment of the J-Integral has been made, and the feasibility of the analysis to incorporate it into an experimental procedure has been demonstrated. A major advantage of the proposed J for the ENF is that only loads and slopes at four locations along the beam are need to measuredmore » it. Material properties and crack lengths are not explicitly needed.« less