ASTM E471-96(2002)
(Test Method)Standard Test Method for Obtaining Char Density Profile of Ablative Materials by Machining and Weighing
Standard Test Method for Obtaining Char Density Profile of Ablative Materials by Machining and Weighing
ABSTRACT
This test method covers the determination of the char density profile of a charred ablator. The total thickness of the char and degradation zone must be larger than the machining thicknesses required. Density variation throughout a charred ablator material is determined by successively measuring, machining, and weighing a sample of known size to obtain the density of the material removed by machining. The apparatus required for this method includes a laboratory balance capable of measuring to the nearest ten thousandth gram, and a machining technique capable of removing material in increments as small as a thousandth mm.
SCOPE
1.1 This test method covers the determination of the char density profile of a charred ablator that can be used with the following limitations:
1.1.1 The local surface imperfections must be removed, and the char must be able to be machined off in a plane parallel to the char-virgin material interface before the density profiles can be determined.
1.1.2 The char must be strong enough to withstand the machining and handling techniques employed.
1.1.3 The material should have orderly density variations. The total thickness of the char and degradation zone must be larger than the machining thicknesses required.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E471 – 96 (Reapproved 2002)
Standard Test Method for
Obtaining Char Density Profile of Ablative Materials by
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Machining and Weighing
This standard is issued under the fixed designation E471; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Theablationcharacteristicsofcharringmaterialsmustbewellknowninordertodesignthematerial
for a specific set of environmental conditions. The char density profile and the environmental
conditions under which it was formed can provide useful information about the ablation performance.
Amethod of obtaining the char density profile from a charred sample of material is described in the
following sections. Some chars are very friable and are easily broken before they can be measured.
Other chars are relatively strong and can be handled with ease. The type of char density profile
measurement described in this method is applicable if the char is strong enough to be machined
without breaking.
1. Scope weighing a sample of known size to obtain the density of the
material removed by machining.
1.1 This test method covers the determination of the char
density profile of a charred ablator that can be used with the
3. Apparatus
following limitations:
3.1 The apparatus required for this method includes a
1.1.1 The local surface imperfections must be removed, and
laboratory balance capable of measuring to the nearest 0.0001
the char must be able to be machined off in a plane parallel to
g, and a machining technique capable of removing material in
the char-virgin material interface before the density profiles
increments as small as 0.025 mm (0.001 in.). For example, flat
can be determined.
specimens can be machined with a surface grinder using a
1.1.2 The char must be strong enough to withstand the
medium fine grit ceramic grinding wheel of a soft grade
machining and handling techniques employed.
dressed to the proper contour. Cylindrical specimens can be
1.1.3 The material should have orderly density variations.
mounted in a lathe and the char can be removed with a sharp
The total thickness of the char and degradation zone must be
carbide or diamond tip tool.
larger than the machining thicknesses required.
1.2 This standard does not purport to address all of the
4. Sampling
safety concerns, if any, associated with its use. It is the
4.1 The charred sample selected for machining and weigh-
responsibility of the user of this standard to establish appro-
ing should be taken from a representative section of the ablated
priate safety and health practices and determine the applica-
specimen where the environmental conditions are well known,
bility of regulatory limitations prior to use.
and where the surface is parallel to the char-virgin material
interface. Where large sections are available, this condition is
2. Summary of Test Method
usually met. For small samples which have been exposed to
2.1 Density variation throughout a charred ablator material
varying environmental conditions along the length of the
is determined by successively measuring, machining, and
sample, the sample size will be smaller.
5. Test Specimens
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This test method is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of Space Technology and is the direct responsibility of
5.1 A typical specimen size obtained from a channel, pipe
Subcommittee E21.08 on Thermal Protection.
flow, or rocket motor section may be 12.7 by 12.7 mm (0.5 by
Current edition approved April 10, 2002. Published April 2002. Originally
0.5 in.), or 12.7 mm (0.5 in.) in diameter.The sample thickness
approved in 1973. Last previous edition approved in 1996 as E471 – 96. DOI:
10.1520/E0471-96R02. is determined by the available thickness of material. Smaller or
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E471 – 96 (2002)
FIG. 1 Typical Specimen for Measuring Char Density Profile
larger samples can be used depending upon the accuracy, 6.3 Dimensional Measurements:
weighing apparatus, and specimen size. Larger samples reduce 6.3.1 The increment of material removed between weigh-
edge effects. Excess virgin material should be eliminated, if ings is usually 0.254 mm (0.010 in.) depending upon the total
possible. char thickness and the uniformity of the charred specimen. If
5.2 The specimen is rough-cut out of the ablated section, the char is relatively uniform in density down to the char-virgin
and then machined so as to make the sides perpendicular and material interface, inc
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