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

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Publication Date
05-Jun-2007
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9060 - Close of review
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05-Jun-2021
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ISO 20392:2007 - Thermal-insulating materials -- Determination of compressive creep
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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
---------------------- Page: 1 ----------------------
ISO 20392:2007(E)
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© ISO 2007

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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

© ISO 2007 – All rights reserved iii
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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.

iv © ISO 2007 – All rights reserved
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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
initial thickness of the test specimen
3.1.3
thickness d

thickness of the test specimen under the basic compressive stress of the loading device (“dead weight”)

3.1.4
thickness d
thickness of the test specimen 60 s after the beginning of loading
3.1.5
thickness d
thickness of the test specimen at a given time t
© ISO 2007 – All rights reserved 1
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ISO 20392:2007(E)
3.2
compressive stress

ratio of the compressive force to the initial cross-sectional area of the test specimen

3.3
deformation
reduction in thickness of the test specimen
3.4
relative deformation

ratio of the deformation X of the test specimen and its thickness d , measured in the direction of the load

3.5
compressive creep

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;
X is the initial deformation (60 s after the beginning of loading).

An illustration of the different thicknesses and deformations is given in Figure 1.

2 © ISO 2007 – All rights reserved
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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

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).

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.
© ISO 2007 – All rights reserved 3
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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.
4 © ISO 2007 – All rights reserved
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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
+20
(23 ± 5) °C and 50 % relative humidity
−10
+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

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.
7.3 Test procedure

If the thickness of a test specimen, d , is determined without using the loading device, it shall be measured to

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.

Determine d to the nearest 0,01 mm.

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

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.

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.

Determine the deformation, X , to the nearest 0,01 mm at the following times after loading: 0,1 h, 1 h, 5 h and

then at 1 day, 2 days,
...

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