ASTM E458-08(2015)
烧蚀的热试验方法

Standard Test Method for Heat of Ablation

被代替

标准号

ASTM E458-08(2015)

发布

2008年

发布单位

美国材料与试验协会

替代标准

ASTM E458-08(2020)

当前最新

ASTM E458-08(2020)

 

 

引用标准

ASTM E285 ASTM E422 ASTM E457 ASTM E459 ASTM E511 ASTM E617

适用范围

4.1 General—The heat of ablation provides a measure of the ability of a material to serve as a heat protection element in a severe thermal environment. The parameter is a function of both the material and the environment to which it is subjected. It is therefore required that laboratory measurements of heat of ablation simulate the service environment as closely as possible. Some of the parameters affecting the heat of ablation are pressure, gas composition, heat transfer rate, mode of heat transfer, and gas enthalpy. As laboratory duplication of all parameters is usually difficult, the user of the data should consider the differences between the service and the test environments. Screening tests of various materials under simulated use conditions may be quite valuable even if all the service environmental parameters are not available. These tests are useful in material selection studies, materials development work, and many other areas.

4.2 Steady-State Conditions—The nature of the definition of heat of ablation requires steady-state conditions. Variances from steady-state may be required in certain circumstances; however, it must be realized that transient phenomena make the values obtained functions of the test duration and therefore make material comparisons difficult.

4.2.1 Temperature Requirements—In a steady-state condition, the temperature propagation into the material will move at the same velocity as the gas-ablation surface interface. A constant distance is maintained between the ablation surface and the isotherm representing the temperature front. Under steady-state ablation the mass loss and length change are linearly related.

where:
t	=	test time, s,
ρo	=	virgin material density, kg/m3,
δL	=	change in length or ablation depth, m,
ρc	=	char density, kg/m3, and
δc	=	char depth, m.

This relationship may be used to verify the existence of steady-state ablation in the tests of charring ablators.

4.2.2 Exposure Time Requirements—The exposure time required to achieve steady-state may be determined experimentally by the use of multiple models by plotting the total mass loss as a function of the exposure time. The point at which the curve departs significantly fro......

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