Study and analysis of the stress state in a ceramic, button-head, tensile specimen
The final results are reported for a study to identify and correct the causes of nongage-section failures (notably button-head failures) in ceramic tensile specimens observed in several laboratories. Numerical modeling of several candidate specimen gripping systems has shown inherent stress concentrations near the specimen button head at which the maximum stress may approach 75 to 100% of the gage-section stress for certain grip conditions. Empirical comparisons of both tapered- and straight-collet gripping systems revealed compromises in both systems. The straight-collet system, with deformable collets, is simpler to use but produces statistically significant greater average percent bending for all tests than those produced for the tapered-collet system, which is slightly more difficult to use. Empirical tensile tests of {approximately}50 aluminium oxide and {approximately}50 silicon nitride specimens were conducted to evaluate the loading capability of both gripping systems, the percent bending in each system, and the potential of consistently producing successful test results. These tests revealed that, due to variations in individuals specimens or the individual specimen/grip interfaces, neither of the gripping systems can consistently produce bending of less than 3 to 4% at failure although occasional values of {approximately}0.5% bending were attained. Refinements of grinding procedures and dimensional measurement techniques have shown critical details in both the practices and consistency of machining necessary for achieving the dimensional tolerances while minimizing subsurface damage. Numerical integration techniques indicate that up to a consistent 5.0% bending during fast- fracture tests can be tolerated before large influences are detected in the determination of the Weibull modulus and the Weibull characteristic strength.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5766576
- Report Number(s):
- ORNL/TM-11767; ON: DE92007794
- Country of Publication:
- United States
- Language:
- English
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Study and Analysis of the Stress State in a Ceramic, Button-Head, Tensile Specimen
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