Test for Compressive Strength of Advanced Ceramics ASTM C1358

Scope:

The ASTM C1358 test method applies to advanced ceramic matrix composites with continuous fiber reinforcement. It could be unidirectional (1D), bidirectional (2D), and tri-directional (3D), or other multi-directional reinforcements. This test is also applicable to glass (amorphous) matrix composites with 1D, 2D, 3D, and other multi-directional continuous fiber reinforcements. Although ASTM C1358 does not directly address discontinuous, fiber-reinforced, whisker-reinforced, or particulate-reinforced ceramics, it can be equally applicable to these composites.

Compressive strength refers to the compressive strength obtained under monotonic uniaxial loading, where monotonic refers to a continuous nonstop test rate with no reversals during the tests.

Test Procedure:

The specimen is mounted in the load train. Specimens with different grip interfaces and specimen geometry are mounted differently. The dimensions of the specimens are determined. The test modes and rates to be used for specific specimens are determined.

The test mode and test rate is 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 material tensile test specimen geometry. The data acquisition and test mode are initiated. Specimen is compressed till fracture. After that, the action of the test machine and the data collection of the data acquisition system is disabled.

The breaking load is measured and reported within 61.0% of the load range. The specimen is carefully removed from the grip interfaces. The specimen halves are placed along with other fragments from the gage section into a suitable, non metallic container for later analysis.

 Specimen size:

The test specimens should have solid rectangular cross sections. The minimum gage length should be 25 mm. The length of the gripped sections at each end of the specimen should be at least 50 mm. The minimum width should be 10 mm and the minimum thickness should be 3 mm.

Data:

1. Engineering Stress: 

σ=P/A

σ = the engineering stress, 

P = the applied, uniaxial tensile load. 

A = the original cross-sectional area.

2. Engineering Strain

€= (I – I₀) I₀

ε = the engineering strain, 

I = the extensometer gage length at any time, and I₀ = the original gage length of the extensometer. 

3. Tensile strength:

S_u = P_max  /A

S_u  = the tensile strength

P_max = the maximum load

4. Modulus of Elasticity:

E=Δσ_h/ Δσ_h

where 

E = modulus of elasticity, 

Δσ_h/ Δσ_h = the slope of the (σ_h– ε_h) curve within the linear region.