ISO 20392:2007
(Main)Thermal-insulating materials — Determination of compressive creep
Thermal-insulating materials — Determination of compressive creep
ISO 20392:2007 specifies equipment and procedures for determining the compressive creep of test specimens under various conditions of stress. It is applicable to thermal-insulation products.
Matériaux d'isolation thermique — Détermination du fluage en compression
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 20392
First edition
2007-06-15
Thermal-insulating materials —
Determination of compressive creep
Matériaux d'isolation thermique — Détermination du fluage en
compression
Reference number
ISO 20392:2007(E)
©
ISO 2007
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ISO 20392:2007(E)
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ii © ISO 2007 – All rights reserved
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ISO 20392:2007(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle. 3
5 Apparatus . 3
6 Test specimens . 4
7 Procedure . 5
8 Calculation and expression of results. 8
9 Precision. 9
10 Test report . 9
Annex A (normative) Calculation of long-term compressive creep. 10
Annex B (informative) Example of a linear regression analysis . 13
Bibliography . 17
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ISO 20392:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 20392 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 10, Cellular plastics.
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INTERNATIONAL STANDARD ISO 20392:2007(E)
Thermal-insulating materials — Determination of compressive
creep
1 Scope
This International Standard specifies equipment and procedures for determining the compressive creep of test
specimens under various conditions of stress. It is applicable to thermal-insulation products.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 844, Rigid cellular plastics — Determination of compression properties
ISO 1923, Cellular plastics and rubbers — Determination of linear dimensions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
thickness
linear dimension measured perpendicular to the length and width plane
3.1.1
thickness d
original product thickness
3.1.2
thickness d
s
initial thickness of the test specimen
3.1.3
thickness d
L
thickness of the test specimen under the basic compressive stress of the loading device (“dead weight”)
3.1.4
thickness d
0
thickness of the test specimen 60 s after the beginning of loading
3.1.5
thickness d
t
thickness of the test specimen at a given time t
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ISO 20392:2007(E)
3.2
compressive stress
σ
c
ratio of the compressive force to the initial cross-sectional area of the test specimen
3.3
deformation
X
reduction in thickness of the test specimen
3.4
relative deformation
ε
ratio of the deformation X of the test specimen and its thickness d , measured in the direction of the load
s
3.5
compressive creep
X
ct
increase, with time, in the deformation of the test specimen under a constant stress under specified conditions
of temperature and humidity
NOTE X = X − X
ct t 0
where
X is the deformation at time t;
t
X is the initial deformation (60 s after the beginning of loading).
0
An illustration of the different thicknesses and deformations is given in Figure 1.
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ISO 20392:2007(E)
Key
X time, t
Y thickness
1 thickness under the “dead weight” of the loading device (< 10 % of the smallest chosen stress for the creep test)
2 point when load is applied for the compressive-creep test
3 deformation curve
a
In the illustration, d is used as the reference value for the measurements of deformation. If d is used as the
L s
reference value, the illustration can be used with the omission of the column for d (see 7.3).
L
Figure 1 — Illustration of the various thicknesses and deformations
4 Principle
The compressive creep is determined by measuring the increase in deformation of a test specimen under a
constant compressive stress and specified conditions of temperature, humidity and time.
5 Apparatus
5.1 Loading device, consisting of two flat plates, one of which shall be movable, so arranged that they
compress the test specimen in the vertical direction. The movable plate shall be mounted in such a manner as
to be self-aligning. The plates shall be capable of being loaded smoothly and without distortion so that, during
the test, the static stress does not change by more than ± 5 %.
5.2 Measuring device (e.g. dial gauge), capable of determining the distance between the two plates, i.e.
the deformation of the test specimen, to an accuracy of 0,01 mm.
5.3 Suitable damping facilities, to minimize the effects of external vibration, e.g. a substantial base
supporting the apparatus.
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ISO 20392:2007(E)
Examples of test apparatus are given in Figure 2.
Key
1 displacement transducer or dial gauge
2 loading bridge
3 load-distribution plate (movable, self-aligning)
4 test specimen
5 base supporting apparatus
6 weights providing the load
Figure 2 — Examples of test apparatus
6 Test specimens
6.1 Preparation
The test specimens for determining the compressive creep shall be taken from the same test sample, with the
same preparation, as the test specimens used for the determination of compression properties in accordance
with ISO 844.
NOTE Special methods of preparation, when needed, may be given in the relevant product standard.
6.2 Dimensions
The test specimens shall be right prisms with a square base. The thickness of the specimens shall be the
original product thickness. The length and width of the specimen base shall not be less than their thickness.
Products with facings or integrally moulded skins which are retained in use shall be tested with these faces or
skins intact.
Test specimens shall not be layered to produce a greater thickness for testing.
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ISO 20392:2007(E)
The length and width of the test specimen base are normally specified in the relevant product standard. If not,
they shall be agreed between the interested parties, in which case the recommended dimensions are:
50 mm × 50 mm or
100 mm × 100 mm or
150 mm × 150 mm or
200 mm × 200 mm or
300 mm × 300 mm.
The length and width of the test specimen base shall be measured in accordance with ISO 1923 to an
accuracy of 0,5 %.
The tolerance on parallelism between the upper and lower faces of the test specimens and the tolerance on
the flatness of the upper and lower faces shall not be greater than 0,5 % of the test specimen length or width,
with a maximum of 0,5 mm.
If a test specimen is not flat, it shall be ground flat or a suitable coating applied to prepare the surface for the
test. If it is coated, no significant creep shall occur in the coating or, if creep does occur in the coating, this
shall be taken into account by deducting it from the measurements.
6.3 Number
The number of test specimens shall be as specified in the relevant product standard. If the number is not
specified, then at least three test specimens shall be used for each of the compressive stresses selected
in 7.2.
In the absence of a product standard, the number of test specimens may be agreed between the interested
parties.
6.4 Conditioning
The test specimens shall be conditioned for at least 24 h under the test conditions. In cases of dispute, the
time for conditioning (equilibration of moisture content) shall be as specified in the relevant product standard.
7 Procedure
7.1 Test conditions
The test shall be carried out at
(23 ± 2) °C and (50 ± 10) % relative humidity
or
+20
(23 ± 5) °C and 50 % relative humidity
−10
or
+20
(27 ± 5) °C and 65 % relative humidity
−10
unless other conditions are given in the relevant product standard.
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ISO 20392:2007(E)
7.2 Stress selection
The test shall be carried out at three or more different stresses.
The alternative stresses, σ , for the creep investigation shall be based on either the compressive strength, σ ,
c m
or the compressive stress, σ , at 10 % deformation measured in accordance with ISO 844, and shall be
10
calculated as follows:
σ=×0,15 σ or σ=×0,15 σ
cm c10
σ=×0,20 σ or σ=×0,20 σ
cm c10
σ=×0,25 σ or σ=×0,25 σ
cm c10
σ=×0,30 σ or σ=×0,30 σ
cm c10
σ=×0,35 σ or σ=×0,35 σ
cm c10
If appropriate, other values of σ may be chosen.
c
7.3 Test procedure
If the thickness of a test specimen, d , is determined without using the loading device, it shall be measured to
s
the nearest 0,1 mm in accordance with ISO 1923.
Place the test specimen carefully in the loading device under the “dead weight” of the loading device. The
thickness under this load, d , is considered as the reference value for the measurements of deformation.
L
Determine d to the nearest 0,01 mm.
L
The stress imposed by the “dead weight” shall be less than 10 % of the lowest stress selected for the test.
If the thickness of the test specimen, d , is determined using the loading device, the specimen shall be
s
preloaded with a pressure of (250 ± 10) Pa and the thickness measured to the nearest 0,01 mm. This value
shall then be used as the reference value for measurements of deformation. If significant deformation occurs
under the pressure of 250 Pa, then a load corresponding to 50 Pa may be used assuming it is specified in the
relevant product standard. In this case, the thickness d shall be determined under the same load.
s
Apply the first of the selected stresses uniformly to the test specimen within (10 ± 5) s. Determine the initial
deformation, X , to the nearest 0,01 mm (60 ± 5) s after the beginning of loading.
0
Determine the deformation, X , to the nearest 0,01 mm at the following times after loading: 0,1 h, 1 h, 5 h and
t
then at 1 day, 2 days,
...
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