Test for Open-Hole Tensile Strength of Advanced Ceramics ASTM C1869

Test for Open-Hole Tensile Strength of Advanced Ceramics ASTM C1869

ASTM C1869 is used to determine the open-hole (notched) tensile strength of continuous fiber-reinforced ceramic matrix composite (CMC) at ambient temperature. It determines the effect of a hole (notch) on the tensile strength and stress response of CMCs. ASTM C1869 produces tensile strength data for structural design allowables, material specifications, material development and comparison, material characterization, and quality assurance.


    In ASTM C1869, the open-hole tensile (OHT) test determines the effect of a single hole (notch) on the tensile strength of CMCs. This test is used for the material and design development of composite materials. It informs how a composite performs with a notch and how to design one for notches. 

    The tensile strength of the notched specimen is compared to that of an unnotched specimen to determine the effect of the notch on the tensile strength. If material is sensitive to a notch, then its open-hole tensile (OHT) strength varies with the notch size. Usually, larger holes reduce the OHT strength because a notch reduces the area available to carry an applied force, causes stress concentrations, and introduces new edges where delamination can occur. 

    The mechanical properties of a notched specimen, calculated from this test method, are the open-hole (notched) tensile strength, the net section tensile strength, the proportional limit stress, and the stress response of the specimen. 

    This test method is used for ceramic matrix composites with continuous fiber reinforcement in multiple directions. Usually, The CMC material tested is fiber reinforced, 2D, and laminated. The laminate is balanced and symmetrical. Composites with different reinforcements (1D, 3D, braided, unbalanced) are also tested with this method. Composites with different architecture are affected differently with a notch. Therefore, the composite architecture is kept into consideration. 

    Although the OHT test is not used for discontinuous fiber-reinforced, whisker-reinforced, or particulate-reinforced ceramics, it can equally apply to these composites. The CMCs are essentially matrices reinforced by fibers. The matrices and fibers of an OHT test specimen can be made of a wide range of materials (oxide-oxide composites, silicon carbide fibers in SiC matrices, carbon fibers in SiC matrices, and carbon-carbon composites).

    Test Procedure:

    ASTM C1869 defines two specimen geometries and a test procedure for producing reproducible and comparable results. Test specimens are flat, straight-sided ceramic composite with a defined laminate fiber architecture. Test specimens contain a single notch of either 6 mm or 3 mm at the center of the specimen.

    The tensile test is uniaxial and monotonic, performed along the defined test reinforcement axis at ambient temperature, measuring the applied force versus time/displacement. Measurement of the gage length extension/strain is optional, using extensometer/displacement transducers. Bonded strain gages are optional for measuring localized strains and assessing bending strains in the gage section.

     Specimen size:

    The test specimen has a defined single notch with a diameter of either 6 mm or 3 mm, centered by length and width in the defined gage section. Minimum ten test specimens are required.


    Tensile strength:

    TOHT = Pmax /A

    TOHT = the tensile strength
    Pmax = the maximum load

    A = Wh

    W = average specimen width, and
    h = average distance between the notches


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