Scope:

The ASTM E458 test method is used to determine the heat of ablation of materials that have been exposed to thermal conditions. The heat of ablation is a measurement of a material’s capacity to act as a heat protection element in a high-temperature environment. The property is determined by the material as well as the environment in which it is used. As a result, laboratory heat of ablation measurements must as precisely as possible mimic the service environment. Even if all of the service environmental data are not accessible, screening testing of various materials under simulated use settings can be highly useful. These tests can be used in material selection research, material development activities, and a variety of other applications.

Test Procedure:

The heat source employed, test specimen arrangement and test objectives will all influence the ASTM E458 test method’s exact technique. Mass measurements are taken before and after the test for hygroscopic materials, chars, or both. The material specimen is introduced into the test environment and exposed for a predetermined test period or until the test objectives are met after the test condition has been verified. When working with fragile char, it’s occasionally preferable to end the test by turning off the heat rather than retracting the test specimen. After the test specimen is allowed to cool for handling, post-test mass and length measurements are taken.

Video 01: Ablation of Materials

Specimen Size: 

According to ASTM E458, the size and shape of the test specimen will be determined by the apparatus used, the desired results, service conditions, and the type of test.

Data:

According to ASTM E458, the mass loss is calculated in two ways, mass loss and length change:

The mass-transfer rate is equal to the initial mass minus the final mass divided by the test duration. The proper area, which the mass loss is measured, must be included.

m = (w_i – w_f)/tA_c

where:

w_i = initial mass of specimen or core

w_f = final mass of specimen or core

A_c = area of the specimen or cross-sectional area of core

The mass-transfer rate due to length change is computed as follows:

m = (L_i – L_f)/P₀A_c

where:

L_i = initial length

L_f = final length

These two mass-transfer rate values and accounts are compared for any variations, such as material swelling or handling damage. In the computation of heat of ablation, the value most indicative of the test conditions and objectives is chosen.

Conclusion:

ASTM E458 test method is used to determine the heat of ablation of materials that have been exposed to thermal conditions.