ASTM E471-96(2011)
(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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.2.1 Exception—Certain inch-pound equivalent units are included in parentheses for information only.
1.3 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 2011)
Standard Test Method for
Obtaining Char Density Profile of Ablative Materials by
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 2. Summary of Test Method
2.1 Density variation throughout a charred ablator material
1.1 This test method covers the determination of the char
is determined by successively measuring, machining, and
density profile of a charred ablator that can be used with the
weighing a sample of known size to obtain the density of the
following limitations:
material removed by machining.
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
3. Apparatus
the char-virgin material interface before the density profiles
can be determined. 3.1 The apparatus required for this method includes a
laboratory balance capable of measuring to the nearest 0.0001
1.1.2 The char must be strong enough to withstand the
g, and a machining technique capable of removing material in
machining and handling techniques employed.
increments as small as 0.025 mm (0.001 in.). For example, flat
1.1.3 The material should have orderly density variations.
specimens can be machined with a surface grinder using a
The total thickness of the char and degradation zone must be
medium fine grit ceramic grinding wheel of a soft grade
larger than the machining thicknesses required.
dressed to the proper contour. Cylindrical specimens can be
1.2 The values stated in SI units are to be regarded as
mounted in a lathe and the char can be removed with a sharp
standard. No other units of measurement are included in this
carbide or diamond tip tool.
standard.
1.2.1 Exception—Certain inch-pound equivalent units are
4. Sampling
included in parentheses for information only.
4.1 The charred sample selected for machining and weigh-
1.3 This standard does not purport to address all of the ing should be taken from a representative section of the ablated
safety concerns, if any, associated with its use. It is the
specimen where the environmental conditions are well known,
responsibility of the user of this standard to establish appro-
and where the surface is parallel to the char-virgin material
priate safety and health practices and determine the applica-
interface. Where large sections are available, this condition is
bility of regulatory limitations prior to use.
usually met. For small samples which have been exposed to
varying environmental conditions along the length of the
sample, the sample size will be smaller.
This test method is under the jurisdiction of ASTM Committee E21 on Space
5. Test Specimens
Simulation andApplications of Space Technology and is the direct responsibility of
Subcommittee E21.08 on Thermal Protection.
5.1 A typical specimen size obtained from a channel, pipe
Current edition approved Jan. 1, 2011. Published April 2011. Originally
flow, or rocket motor section may be 12.7 by 12.7 mm (0.5 by
approved in 1973. Last previous edition approved in 2002 as E471 – 96 (2002).
DOI: 10.1520/E0471-96R11. 0.5 in.), or 12.7 mm (0.5 in.) in diameter.The sample thickness
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E471−96 (2011)
FIG. 1Typical Specimen for Measuring Char Density Profile
is determined by the available thickness of material. Smaller or dust after each machining operation with about 34 kPa (5 psi)
larger samples can be used depending upon the accuracy, air through a nozzle held about 25 mm (1 in.) from the
weighing apparatus, and specimen size. Larger samples reduce machined surface.
edge effects. Excess virgin material should be eliminated, if
6.3 Dimensional Measurements:
possible.
6.3.1 The increment of material removed between weigh-
5.2 The specimen is rough-cut out of the ablated section, ings is usually 0.254 mm (0.010 in.) depending upon the total
and then machined so as to make the sides perpendicular and char thickness and the uniformity of the charred specimen. If
the front surface parallel to the char-virgin interface as shown the char is relatively uniform in density down to the char-virgin
in Fig. 1. material interface, increase the machining increments. If the
char-virgin material interface is sharply defined, take smaller
5.3 For simplicity and ease of handling, the base of the
machining increments. Exercise extreme care when making the
sample (the backface or side opposite the charred surface) may
dimensional measurements with a micrometer to avoid crush-
be cemented to a thin piece of steel. This permits the sample to
ing the char.
be handled with tweezers and facilitates the mounting of the
sample on a magnetic chuck or other mounting jig for 6.4 Weight Measurements:
machining the surface from a fixed reference plane. 6.4.1 Maintain t
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