ASTM WK46849

    New Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing (Stress Rupture) at Elevated Temperatures

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    WK46849

    1. Scope

    1.1 This standard test method covers the determination of slow crack growth (SCG) parameters of advanced ceramics in a given test environment at elevated temperatures in which the time-to-failure of four-point-1/4 point flexural test specimens (See Figure 1) is determined as a function of different levels of constant applied stress. This SCG constant stress test procedure is also called a slow crack growth (SCG) stress rupture test. The test method addresses the test equipment, test specimen fabrication methods, test stress levels and experimental procedures, data collection and analysis, and reporting requirements. 1.2 In this test method the decrease in time-to-failure with increasing levels of applied stress in specified test conditions and temperatures is measured and used to analyze the slow crack growth parameters of the ceramic. The preferred analysis method is based on a power law relationship between crack velocity and applied stress intensity; alternative analysis approaches are also discussed for situations where the power law relationship is not applicable. NOTE 1The test method in this standard is historically referred to in earlier technical literature as static fatigue testing [Refs (1-3)] in which the term fatigue is used interchangeably with the term slow crack growth. To avoid possible confusion with the fatigue phenomenon of a material that occurs exclusively under cyclic stress loading, as defined in E1823, this test method uses the term constant stress testing rather than static fatigue testing. 1.3 This test method uses a 4-point flexural test mode and applies primarily to monolithic advanced ceramics that are macroscopically homogeneous and isotropic. This test method may also be applied to certain whisker- or particle-reinforced ceramics as well as certain discontinuous fiber-reinforced composite ceramics that exhibit macroscopically homogeneous behavior. Generally, continuous fiber ceramic composites do not exhibit macroscopically isotropic, homogeneous, elastic continuous behavior, and the application of this test method to these materials is not recommended. 1.4 This test method is intended for use at elevated temperature with various test environments such as air, vacuum, inert gas, and steam. This test method is similar to Test Method C1576 with the addition of provisions for testing at elevated temperatures to establish the effects of those temperatures on slow crack growth. The elevated temperature testing provisions are derived from Test Methods C1211 and C1465. 1.5 Creep deformation at elevated temperatures in ceramics is a competitive mechanism with slow crack growth and those creep effects may interact and interfere with the slow crack growth effects (Sec. 5.2). This test method is intended to be used primarily for test specimens with negligible creep, This test method imposes specific upper-bound limits on measured creep strain (no more than 0.05%, per Sec. 5.2). 1.6. The values stated in SI units are to be regarded as the standard and in accordance with IEEE/ASTM SI 10 Standard.

    This draft test standard is a high temperature version of C1576 Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing (Stress Rupture) at Ambient Temperature. This new standard is needed because slow crack growth (SCG) testing is also being done at elevated temperatures. The two constant stress SCG tests (this high temperature draft and the ambient temperature C1576 test are parallel to the two constant stress-rate test standards C1368 Ambient Temperature SCG at Constant Stress Rate and C1465 Elevated Temperature SCG at Constant Stress Rate. 4.3This test method may be used for material development, quality control, characterization, design code or model verification, time-to-failure, and limited design data generation purposes.


    Keywords

    Advanced ceramics; slow crack growth; slow crack growth parameters; time-to-failure; four-point flexure; flexural testing; stress rupture; constant stress testing; elevated temperature.

    The title and scope are in draft form and are under development within this ASTM Committee.

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    Work Item Status

    Date Initiated:
    07-28-2014

    Technical Contact:
    Stephen Gonczy

    Item:
    001

    Ballot:
    C28.01 (14-03)

    Status:
    In Balloting