ASTM E458-08(2015)

Standard Test Method for Heat of Ablation

SIGNIFICANCE AND USE
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 T...
SCOPE
1.1 This test method covers determination of the heat of ablation of materials subjected to thermal environments requiring the use of ablation as an energy dissipation process. Three concepts of the parameter are described and defined: cold wall, effective, and thermochemical heat of ablation.  
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.

General Information

• Status: Historical
• Publication Date: 30-Apr-2015
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.08 - Thermal Protection

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E458 − 08 (Reapproved 2015)
Standard Test Method for
1
Heat of Ablation
This standard is issued under the fixed designation E458; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope tion of both the material and the environment to which it is
subjected. In general, it is defined as the incident heat dissi-
1.1 This test method covers determination of the heat of
pated by the ablative material per unit of mass removed, or
ablationofmaterialssubjectedtothermalenvironmentsrequir-
ing the use of ablation as an energy dissipation process. Three Q* 5 q/m (1)
conceptsoftheparameteraredescribedanddefined:coldwall,
where:
effective, and thermochemical heat of ablation.
Q* = heat of ablation, kJ/kg,
2
1.2 This standard does not purport to address all of the
q = incident heat transfer rate, kW/m , and
2
safety concerns, if any, associated with its use. It is the
m = total mass transfer rate, kg/m ·s.
responsibility of the user of this standard to establish appro-
3.1.2 The heat of ablation may be represented in three
priate safety and health practices and determine the applica-
different ways depending on the investigator’s requirements:
bility of regulatory limitations prior to use.
3.1.3 cold-wall heat of ablation—The most commonly and
easilydeterminedvalueisthecold-wallheatofablation,andis
2. Referenced Documents
defined as the incident cold-wall heat dissipated per unit mass
2
2.1 ASTM Standards:
of material ablated, as follows:
E285Test Method for Oxyacetylene Ablation Testing of
Q* 5 q /m (2)
cw cw
Thermal Insulation Materials
E422Test Method for Measuring Heat Flux Using a Water-
where:
Cooled Calorimeter
Q* = cold-wall heat of ablation, kJ/kg,
cw
E457Test Method for Measuring Heat-Transfer Rate Using
q = heattransferratefromthetestenvironmenttoacold
cw
2
a Thermal Capacitance (Slug) Calorimeter
wall, kW/m , and
2
E459Test Method for Measuring Heat Transfer Rate Using
m = total mass transfer rate, kg/m ·s.
a Thin-Skin Calorimeter
The temperature of the cold-wall reference for the cold-wall
E511TestMethodforMeasuringHeatFluxUsingaCopper-
heat transfer rate is usually considered to be room temperature
Constantan Circular Foil, Heat-Flux Transducer
or close enough such that the hot-wall correction given in Eq
E617Specification for Laboratory Weights and Precision
8 is less than 5% of the cold-wall heat transfer rate.
Mass Standards
3.1.4 effective heat of ablation—The effective heat of abla-
tion is defined as the incident hot-wall heat dissipated per unit
3. Terminology
mass ablated, as follows:
3.1 Descriptions of Terms Specific to This Standard:
Q* 5 q /m (3)
3.1.1 heatofablation—aparameterthatindicatestheability eff hw
of a material to provide heat protection when used as a
where:
sacrificial thermal protection device. The parameter is a func-
Q* = effective heat of ablation, kJ/kg,
eff
q = heat transfer rate from the test environment to a
hw
nonablating wall at the surface temperature of the
1
This test method is under the jurisdiction of ASTM Committee E21 on Space
2
material under test, kW/m , and
Simulation andApplications of SpaceTechnology and is the direct responsibility of
2
m = total mass transfer rate, kg/m ·s.
Subcommittee E21.08 on Thermal Protection.
Current edition approved May 1, 2015. Published June 2015. Originally
3.1.5 thermochemical heat of ablation—The derivation of
approved in 1972. Last previous edition approved in 2008 as E458–08. DOI:
the thermochemical heat of ablation originated with the
10.1520/E0458-08R15.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
simplisticsurfaceenergyequationemployedintheearly60sto
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
describe the effects of surface ablation, that is:
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. q 2 q 5 q 1q 1q (4)
hw rr cond abl block
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
E458 − 08 (2015)
where: pressure, gas composition, heat transfer rate, mode of heat
2
transfer, and gas enthalpy. As laboratory duplication of all
q = energy re-radiated from the heated surface, kW/m ,
rr
parameters is usually difficult, the user of the data should
q = net energy conducted into the solid during steady-
cond
2
consider the differences between the service and the test
state ablation = mc (T −T ), kW/m ,
p
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E458 − 08 E458 − 08 (Reapproved 2015)
Standard Test Method for
1
Heat of Ablation
This standard is issued under the fixed designation E458; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers determination of the heat of ablation of materials subjected to thermal environments requiring the
use of ablation as an energy dissipation process. Three concepts of the parameter are described and defined: cold wall, effective,
and thermochemical heat of ablation.
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.
2. Referenced Documents
2
2.1 ASTM Standards:
E285 Test Method for Oxyacetylene Ablation Testing of Thermal Insulation Materials
E422 Test Method for Measuring Heat Flux Using a Water-Cooled Calorimeter
E457 Test Method for Measuring Heat-Transfer Rate Using a Thermal Capacitance (Slug) Calorimeter
E459 Test Method for Measuring Heat Transfer Rate Using a Thin-Skin Calorimeter
E511 Test Method for Measuring Heat Flux Using a Copper-Constantan Circular Foil, Heat-Flux Transducer
E617 Specification for Laboratory Weights and Precision Mass Standards
3. Terminology
3.1 Descriptions of Terms Specific to This Standard:
3.1.1 heat of ablation—a parameter that indicates the ability of a material to provide heat protection when used as a sacrificial
thermal protection device. The parameter is a function of both the material and the environment to which it is subjected. In general,
it is defined as the incident heat dissipated by the ablative material per unit of mass removed, or
Q*5 q/m (1)
where:
Q* = heat of ablation, kJ/kg,
2
q = incident heat transfer rate, kW/m , and
2
m = total mass transfer rate, kg/m ·s.
3.1.2 The heat of ablation may be represented in three different ways depending on the investigator’s requirements:
3.1.3 cold-wall heat of ablation—The most commonly and easily determined value is the cold-wall heat of ablation, and is
defined as the incident cold-wall heat dissipated per unit mass of material ablated, as follows:
Q* 5 q /m (2)
cw cw
where:
Q* = cold-wall heat of ablation, kJ/kg,
cw
2
q = heat transfer rate from the test environment to a cold wall, kW/m , and
cw
1
This test method is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.08 on Thermal Protection.
Current edition approved May 1, 2008May 1, 2015. Published July 2008June 2015. Originally approved in 1972. Last previous edition approved in 20022008 as
E458–72(2002)E458–08. DOI: 10.1520/E0458-08.10.1520/E0458-08R15.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
E458 − 08 (2015)
2
m = total mass transfer rate, kg/m ·s.
The temperature of the cold-wall reference for the cold-wall heat transfer rate is usually considered to be room temperature or
close enough such that the hot-wall correction given in Eq 8 is less than 5 % of the cold-wall heat transfer rate.
3.1.4 effective heat of ablation—The effective heat of ablation is defined as the incident hot-wall heat dissipated per unit mass
ablated, as follows:
Q* 5 q /m (3)
eff hw
where:
Q* = effective heat of ablation, kJ/kg,
eff
q = heat transfer rate from the test environment to a nonablating wall at the surface temperature of the material under test,
hw
2
kW/m , and
2
m = total mass transfer rate, kg/m ·s.
3.1.5 thermochemical heat of ablation—The derivation of the thermochemical heat of ablation originated with the simplistic
surface energy equation employed in the early 60s to describe the effects of surface ablation, that is:
q 2 q 5 q 1q 1q (4)
hw rr cond abl block
where:
...