ASTM C1425 Test for Interlaminar Shear Strength of Advanced Ceramics at Elevated Temperatures

Scope:

ASTM C1425 is used for calculating the Interlaminar shear strength of advanced ceramic with continuous fiber reinforcement having a laminated structure such as in unidirectional (1D) or bidirectional (2D) fiber architecture. This test method is not used for composites with non-laminated structures, such as (3D) fiber architecture or discontinuous fiber-reinforced, whisker reinforced, or particulate-reinforced ceramics. This test is used for material development, material comparison, quality assurance, characterization, and design data generation of advanced ceramics.

Test Procedure:

The test procedure for ASTM C1425 begins with measuring the dimensions of the specimen. The specimen is mounted. Specimens with different grip interfaces and specimen geometry are mounted differently in the load train. Thermocouples are positioned to measure and control the temperature during the test. 

The test mode and test rate are selected on the test machine. The specimen is preloaded to remove the “slack” from the load train, and the amount of preload used is reported. The amount of preload for each situation is specific to each specimen geometry. The data acquisition and test mode are initiated. The furnace heating is initiated. The specimen is heated until it reaches thermal equilibrium. In the load train, a constant minimal force is maintained for the thermal expansion of the specimen and the load train. 

The Specimen is compressed till fracture. After that, the test machine and the data acquisition system are disabled. As per ASTM C1425, the breaking load should be measured with an accuracy of 61% of the load range. The actuator is retracted and the furnace is allowed to cool down. The specimen is carefully removed from the fixture. 

 Specimen size:

In ASTM C1425 testing, the specimens are rectangular plates with notches created on both sides. The depth of the notches should be at least half of the specimen’s thickness. The distance between the notches is determined by the requirements of shear failure. 

Because the interlaminar shear strength depends on the notch separation, tests are conducted with different values of notch separation to determine this dependence. The edges of the specimens should be smooth, not rounded or beveled. 

Unless valid results can be obtained through fewer specimens, at least 10 test specimens per test condition are tested.  

Data:

Shear strength (S_u) calculation for ASTM C1425 testing:

S_u = P_max /A

Where,

P_max = the maximum load
A = average shear stressed area, which is calculated as:

A = Wh

Where,

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

Conclusion:

In ASTM C1425, a double notched specimen is compressed at elevated temperatures to determine the interlaminar shear strength of continuous fiber-reinforced ceramic composites (CFCCs).