STP745

    Application of Single Edge Notched Beam and Indentation Techniques to Determine Fracture Toughness of Alpha Silicon Carbide

    Published: Jan 1981


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    Abstract

    This paper is concerned with procedural developments for the application of single edge notched beam (SENB) and indentation techniques to determine the fracture toughness of sintered alpha silicon carbide. For the SENB method, the following experimental variables were examined: relative notch depth, deformation speed, temperature, and atmosphere. Based on the results, a notch depth ratio of 0.4 and a deformation speed of 8.46 × 10−6 m/s (0.02 in./min) are recommended for this material. The effect of temperature in air on KIc determination is such that crack blunting occurs due to oxidation, yielding erroneous results. By using Vicker's indentation with varying loads, fracture toughness values were calculated from careful measurements of dimensions of median cracks and the indentations. In addition, Knoop indentations with loads ranging from 1 to 5 kg were made. The results of this controlled surface flaw technique showed that the fracture toughness was independent of the indentation load used. Residual stresses caused by indentation were removed by surface grinding as well as by annealing in argon at 1000 to 1200°C. These procedures increased KIc-values by approximately 20 to 40 percent. The greatest experimental difficulty in the controlled flaw method for alpha silicon carbide arises in the flaw profile estimation from SEM fractographs. In the majority of cases, there are no clear mirror-like surface flaws beneath the indent causing errors in measurement of flaw sizes.

    Keywords:

    composite materials, crack propagation, toughness test methods, silicon carbide, fracture properties


    Author Information:

    Srinivasan, M
    Senior research associate and senior development associate, The Carborundum Company, Niagara Falls, N. Y.

    Seshadri, SG
    Senior research associate and senior development associate, The Carborundum Company, Niagara Falls, N. Y.


    Paper ID: STP28297S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP28297S


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