ASTM C1576 Test for Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing at Ambient Temperature

Scope:

The life of many ceramic components is limited by the subcritical growth of cracks. ASTM C1576 method is used to determine the relative slow crack growth susceptibility of ceramic materials under specified environments at ambient temperature. In addition, this method is used to determine the effects of processing variables and composition on slow crack growth as well as on strength of materials. The information obtained from this ASTM C1576 test method is used for material development, quality control, characterization, design code, or model verification, and limited design data generation purposes. This method is primarily used to test monolithic advanced ceramics that are macroscopically homogeneous and isotropic. It is also applicable to whisker- or particle-reinforced ceramics and discontinuous fiber-reinforced composite ceramics that exhibit macroscopically homogeneous behavior. 

Test Procedure:

ASTM C1576 method is conducted under a predetermined test environment. A four-point flexure test is used in this standard. In this method, a sample is placed on two supporting structures and the force is applied on the specimen from above through two loading pins. These two loading pins are lowered from above at a constant rate until sample failure. Each test specimen is carefully placed into the test fixture to avoid damage and contamination and to ensure alignment of the specimen with the fixture. 

The test fixture/specimen assembly is then mounted into the ASTM C1576 test machine. The data acquisition is initiated. The force is applied to the test specimen. Time-measuring devices record the time to failure. If failure does not occur within the specific time agreed upon in the test program, it is recorded as a run-out. A force versus time curve is recorded for each test to check the requirement of force variation of testing machines. Fragments are collected. They are cleaned and stored in a protective container for further analysis, including fractography. Fractographic analysis of fractured test specimens is employed to ensure that all the fracture origins are from the same population and to characterize the types, locations, and sizes of fracture origins as well as the flaw extensions due to slow crack growth. 

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

Specimen size:

The types and dimensions of rectangular beam specimens as described in test method C1161 should be used in this ASTM C1576 test method. 

Data:

The flexural strength is calculated in the ASTM C1576 test according to the formula for the strength of a beam in four-point 1⁄4 point flexure. 

Time to failure of flexure test specimens is determined as a function of constant applied stress in a given environment at ambient temperature. 

The fatigue curve and the slow crack growth parameters n and D are determined. 

Conclusion:

ASTM C1576 method is used to determine the relative slow crack growth susceptibility of ceramic materials under specified environments at ambient temperature.