ASTM C1499 Test for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature

Scope:

ASTM C1499 method provides information on the strength and deformation of ceramics under multiple tensile stresses. In many applications, ceramics are subjected to biaxial stresses, stresses in two axes. The resistance to biaxial stresses is measured in terms of flexural strength. The equibiaxial flexural strength distributions of ceramics are probabilistic. Therefore, an adequate number of test specimens is required at each testing condition for statistical estimation of the equibiaxial strength.

This ASTM C1499 test is used for material development, material comparison, quality assurance, characterization, and design code or model verification of advanced ceramics. 

This method applies to advanced ceramics that show isotropic, homogeneous, continuous behavior. Certain whisker or particle-reinforced composite ceramics, and certain discontinuous fiber-reinforced composite ceramics, can also be tested.

Test Procedure:

In ASTM C1499, the test specimen’s dimensions and support ring diameter are measured. The test rate is determined. Test modes such as load rate and displacement rate are determined. Displacement rate is the rate of movement of the test machine actuator, a motor that moves the machine. Different test specimen sizes require different displacement rates for a specified stress rate. Cellophane tape is stuck to the surface of the specimen to retain fracture fragments. The tape should be wide enough to cover the test specimen’s face but not more than that. The compliant layer and friction reduction layer are large enough to cover the outer diameter of the respective ring, but not more than that.

Equibiaxial flexural strength is the maximum stress that a material can sustain when subjected to flexure between two concentric rings. The specimen and the rings are cleaned and lubricated. The specimen is aligned with the fixture. The autograph and data acquisition systems are initiated. The test mode and test rate are selected and initiated on the test machine. After the test specimen’s fracture, the test machine and the data acquisition system are disabled. The measured breaking load is recorded. Test specimen fragments are collected from the fixturing and stored in a suitable, non-metallic container for later analysis. 

Specimen size:

Test specimen dimensions for ASTM C1499: Choose the dimension such that the test specimen thickness is:

D_S = the support ring diameter,

σ_f = the expected equibiaxial fracture strength, and 

E = the modulus of elasticity.

Choose the test specimen and support ring diameters such that the difference in diameters (D–DS) is: 

D = the test specimen diameter in units of mm for circular test specimens.

As per ASTM C1499, it is recommended that the test specimens be circular, however, sometimes it is better to fabricate rectangular test specimens. For a rectangular test specimen, the value of D is:

l_I and l₂ = the lengths of the edges. The edge lengths should be within 0.98 ≤ l₁/l₂ ≤ 1.02.

The number of test specimens: Because this test is probabilistic, the higher the number of test specimens tested, the more accurate the results. Minimum 10 specimens validly tested are required for estimating a mean biaxial flexural strength. Minimum 30 test specimens validly tested are recommended for estimating the Weibull parameters. If specimen availability or material cost limits the number of tests to be conducted, fewer tests can be conducted.

Data: 

Equibiaxial Strength calculating for ASTM C1499: Equibiaxial strength, σƒ, of a circular plate is calculated by:

F = breaking load.

Conclusion:

ASTM C1499 method provides information on the strength and deformation of ceramics under multiple tensile stresses.