Scope:

ASTM C1465 test evaluates the slow crack growth susceptibility of ceramic materials under specified environments. ASTM C1465 determines slow crack growth using flexural testing. Flexural testing measures the weight a beam can handle before bending or cracking. Slow crack growth parameters are used for the development of new and improved ceramics. This test is used for material development, quality control, characterization, and limited design data generation purposes. It is not intended to determine crack growth velocity. 

This test applies to advanced ceramics that are macroscopically homogeneous and isotropic. It can also be applied to certain whisker- or particle-reinforced ceramics that show macroscopically homogeneous behavior. This test is conducted under various test environments such as air, vacuum, inert, and any other gaseous environments.

Test Procedure:

ASTM C1465 employs a flexural test to determine slow crack growth parameters. The two most common types of flexure tests are three-point and four-point flexural bending tests. The three-point bend test consists of the sample placed horizontally upon two points and the force applied to the top of the sample through a single point so that the sample is bent in the shape of a “V”. A four-point bend test is roughly the same except that instead of the force applied through a single point on top it is applied through two points so that the sample experiences contact at four different points and is bent more in the shape of a “U”. The three-point flexure test is ideal for the testing of a specific location of the sample, whereas, the four-point flexure test is more suited towards the testing of a large section of the sample, which highlights the defects of the sample better than a 3-point bending test. Therefore, this test employs four-point flexural bending tests. The specimen is heated during the test, and the ASTM C1465 test is carried out in predetermined environmental conditions, for instance, a vacuum. 

Video 01: Flexural test (3-point bend test)

Specimen size:

Usually, the test specimens are rectangular beams. The specimens should be 2.0 by 1.5 by 25 mm (minimum), respectively, in width (b), depth (d), and length for Size A test specimens. For Size B, the test specimens should be 4.0 by 3.0 by 45 mm (minimum). And for Size C, the test specimen should be 8.0 by 6.0 by 90 mm (minimum). 

A minimum of 10 specimens per test rate is recommended in this ASTM C1465 test method. The total number of test specimens should be at least 40, with at least four different test rates. 

Data:

The following data is calculated in ASTM C1465:

The strength of a beam in four-point 1⁄4-point flexure is calculated by:

σ_f = flexural strength,

 P = break load, 

L = outer (support) span of the test fixture,  

b = test specimen width, and 

d = test specimen depth. 

Stress Rate: The stress rate of each test specimen subjected to either displacement-control or load-control mode is calculated using the actual load rate determined as follows:

where: 

σ˙ = stress rate, and 

P˙ = load rate.

Slow Crack Growth Parameters, n and D:

Conclusion:

ASTM C1465 test evaluates the slow crack growth susceptibility of ceramic materials under specified environments.