CWA 15627:2007

SLOVENSKI STANDARD
01-marec-2008
Preskusna metoda za kovinske materiale z uporabo majhnega bata (Small Punch
Test)
Small Punch Test Method for Metallic Materials
Ta slovenski standard je istoveten z: CWA 15627:2007
ICS:
77.040.10
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN
CWA 15627
WORKSHOP
December 2007
AGREEMENT
ICS 77.040.10     Supersedes CWA 15627:2006
English version
Small Punch Test Method for Metallic Materials
This CEN Workshop Agreement has been drafted and approved by a Workshop of representatives of interested parties, the constitution of
which is indicated in the foreword of this Workshop Agreement.

The formal process followed by the Workshop in the development of this Workshop Agreement has been endorsed by the National
Members of CEN but neither the National Members of CEN nor the CEN Management Centre can be held accountable for the technical
content of this CEN Workshop Agreement or possible conflicts with standards or legislation.

This CEN Workshop Agreement can in no way be held as being an official standard developed by CEN and its Members.

This CEN Workshop Agreement is publicly available as a reference document from the CEN Members National Standard Bodies.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2007 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No.:CWA 15627:2007 D/E/F
CONTENTS
FOREWORD 4
PART A: A Code of Practice for Small Punch Creep Testing

0. INTRODUCTION 7
1. SCOPE 8
2. DEFINITIONS 8
3. APPARATUS 10
3.1 Test Rig 10
3.2 Loading System 10
3.3 Strain Measurement System 10
3.4 Heating System 11
3.5 Test Environment 11
3.6 Additional Measurements 11
3.7 Data Recording 11
4. TEST PIECES 11
4.1 Design 11
4.2 Manufacture and Metrology 12
4.3 Identification and Documentation 12

5 TEST PROCEDURE 12
5.1 Test Piece Installation 12
5.2 Determination Of Test Load 12
5.3 Application Of Load And Temperature 14
5.4 Monitoring and maintaining test conditions 14
5.5 Test interruption and termination 14
5.6 Post test examination 14
5.7 Data records 14
6 REPORT 15
6.1 Minimum requirements 15
6.2 Additional information
7 REFERENCES 16
ANNEX A1: Relationship to uniaxial creep test properties 20

ANNEX A2: Guidance on relevant technological issues: specimen sampling from
components 25
Part B: A Code of Practice for Small Punch Testing for Tensile and Fracture
Behaviour
0. INTRODUCTION 39
1. SCOPE 40
2. DEFINITIONS 40
3. APPARATUS 42
3.1 Test Rig 42
3.2 Loading System 43
3.3 Displacement Measurement System 43
3.4 Deflection Measurement System 43
3.5 Heating or Cooling System 43
3.6 Test Environment 44
3.7 Additional Measurements 44
3.8 Data Recording 44
4. TEST SPECIMEN PREPARATION 44
4.1 Specimen for Small Punch Bulge Test 44
4.2 Specimen for Small Punch Drawing Test 45
4.3 Identification and Documentation 45

5 TEST TEMPERATURE CONSIDERATIONS 45

6 TEST PROCEDURE 45
6.1 Installation of the Test Specimen 45
6.2 Test Speed 46
6.3 Test Record 46
7 POST TEST EXAMINATION 47
7.1 Determination of the elastic plastic transition load 47
7.2 Determination of the SP Fracture Energy 48
7.3 Determination of the Effective Fracture Strain 48

8 TEST REPORT 49
8.1 Minimum Requirements 49
8.2 Additional Information 49
9 REFERENCES 50
ANNEX B1: Derivation of tensile and fracture material properties 52

ANNEX B2: Guidance on relevant technological issues: specimens sampling from
components      57
Foreword
This CEN Workshop 21 on “Small Punch Test Method for Metallic Materials” has been established
and a Business Plan approved by a Workshop of representatives of interested parties on 2004-09-24
[1], the constitution of which was supported by CEN following the public call for participation made on
2004-09-08.
Following a decision from the Workshop, it has been decided to re-publish CWA 15627:2006 in order
to correct a typing error in a formula. This version corrects and supersedes the CWA published in
December 2006.
The formal process followed by the Workshop in the development of the CEN Workshop Agreement
has been endorsed by the National Members of CEN but neither the National Members of CEN nor
the CEN Management Centre can be held accountable for the technical content of the CEN Workshop
Agreement or possible conflict with standards or legislation. This CEN Workshop Agreement can in no
way be held as being an official standard developed by CEN and it’s members. These organizations
were drawn from a number of economic sectors including academia, accreditation authorities,
aerospace, automotive, material producers, material testing laboratories, national standards
institutions and power generation.
The formal process followed by the Workshop in the development of the CEN Workshop Agreement
has been endorsed by the National Members of CEN but neither the National Members of CEN nor
the CEN Management Centre can be held accountable for the technical content of the CEN Workshop
Agreement or possible conflict with standards or legislation.
This CEN Workshop Agreement can in no way be held as being an official standard developed by
CEN and its members.
The final review/endorsement round for this CWA was successfully closed on (2007-10-29).

This CWA has been developed with the aim of providing guidance in the selection of the experimental
conditions in a special type of mechanical test, namely the Small Punch (SP) test, suitable to obtain
robust, reproducible and accurate results. In addition to recommending in the main body of this
document the experimental procedures (“code of practice”), in two separate annexes guidance is
given in the interpretation of the SP test results (namely the question of the comparability with /
derivation of fundamental material strength data, i.e. those from the standard tests), and guidance in
the use of SP tests to address relevant technological issues (e.g. specimen sampling from
components, characterization of heat affected zones in welds, SP test applicability for non isotropic
materials .).
Actually two main versions of this SP test were developed historically, covering the two distinct scopes
of measuring mechanical properties of materials in the high temperature (time dependent, creep
viscous) and low temperature (time independent) domains. Not only the experimental set up and test
procedures have to be different in order to match the distinct aims and conditions of time-dependent
and time-independent SP testing, but also the technological & market scenario (the demand of SP
tests by industry) is often different too; consequently, depending on their business position and
strategy, some labs had been developing (or newcomers may be willing to develop) the high
temperature version, while others developed (or would like to develop) the low temperature version
only.
Therefore, in view of the considerations above, the group of developers of this document felt
convenient to provide a document made of two main and fully self-consistent parts, having the
maximum flexibility of current use and of future development routes (modifications, standardizations):
Part A is for time dependent SP testing,
Part B is for time independent SP testing,
each part is equipped with its own Annexes, A1 and A2 for Part A and B1 and B2 for Part B,
it is noted only that A2 and B2 are identical.

This CEN Workshop Agreement is publicly available as a reference document from the National
Members of CEN: AENOR, AFNOR, ASRO, BDS, BSI, CSNI, CYS, DIN, DS, ELOT, EVS, IBN, IPQ,
IST, LVS, LST, MSA, MSZT, NEN, NSAI, ON, PKN, SEE, SIS, SIST, SFS, SN, SNV, SUTN and UNI

Comments or suggestions from the users of the CEN Workshop Agreement are welcome and should
be addressed to the CEN Management Centre.

Part A: A Code of Practice for Small Punch Creep Testing

0. INTRODUCTION
The life assessment and potential for possible failure of in service components is a critical
issue in the safety and reliability analysis of industrial plants. In the case of plant operating at
elevated temperature for long times, any of several degradation processes may potentially
impair the mechanical properties, in particular the creep resistance, of their structural
components. For most of the plant operating currently, the design life at the time of
construction was usually based on relatively simplistic codes endorsed by practical
experience, and finally corrected by an appropriate safety factor. Indeed, in light of the major
advances in metallurgical knowledge and currently available analytical methodologies, today
it would be possible to reduce the safety factor and to thus extend design lives. In addition,
the new policies for environmental protection and the safety regulations for industrial plants
make it more practical and economically convenient to extend the lifetime of existing
component beyond their original design life rather than to build new plants. However, major
investment to modernise and make existing plants more efficient is only profitable if the plant
under consideration has sufficient residual life. Hence, reducing the uncertainty in the
estimation and monitoring of remaining life of plant components is of fundamental importance
to industry.
The component integrity can be rarely evaluated with the traditional and well-standardised
mechanical test techniques, such as the uniaxial creep test, because there is insufficient
material to sample non-invasively from the component. Hence, the need for evaluating the
residual mechanical properties of structural components by direct testing methods has led to
innovative techniques based on miniaturised specimens. Among these, a technique called
the Small Punch Creep (SPC) test has emerged as a promising candidate as it can be
considered as effectively a non-destructive technique because of the very limited amount of
material to be sampled. It is an efficient and cost-effective technique and has the potential to
enable measurement of the realistic material properties for the specific component,
identifying the present state of damage and focusing on the more critical (more stressed,
more damaged) locations in the component. Before the promise of the technique can be
turned into reality, a standardized and acceptable test methodology must be made available
which is the fundamental purpose of this Code of Practice.

This document guides the user through several steps necessary to carry out a SP Creep
test. The available methods for analysing the test records and, when needed and feasible, to
infer basic, fundamental material characteristics (i.e. test method independent, specimen
size independent) are described in Annex A1. Moreover in the Annex A2 informative
guidance is given on industrial and technological issue: e.g. sampling guidance such as for
example from components, from coated elements in gas turbines, from weldments.

1. SCOPE
This Code of Practice gives guidance on the procedure to be followed when carrying out
Small Punch Creep tests. The objectives of such tests are to evaluate the creep behaviour of
materials exposed in operating plant components in order to provide data needed for plant
life and integrity assessment. The Code of Practice primarily addresses metallic materials
tested under creep loading but can also be used for other materials. Determination of tensile
test data at elevated temperature can also be realised using the proposed methodology. But
the methodology applied in Part B of this document should be applied.

The scope of the Code of Practice covers the following:

Test Piece
Test pieces are discs of specified dimensions procured from components or any other
source. They may be homogeneous or contain manufacturing features such as for example
joints, weldments, defects or coatings

Load
The load may be applied to the disc from a pneumatic, hydraulic or any other mechanical
source. The Code of Practice particularly addresses the usual situation where the load is
maintained constant throughout the test, but the general principles apply also to tests where
the load is cycled, with dwell periods.

Temperature
The test temperature will usually be within the creep range for the materials under test. The
Code of Practice specifically addresses the usual situation where the temperature is
maintained constant throughout the test, but the general principles also apply to thermal
cycling with or without dwell periods.

Environment
The test pieces will usually be tested in an inert gas environment. However, the general
principles should also apply when other environments are used. Although special
precautions will be necessary where hazardous or corrosive environments are used, these
are not detailed in this document.

2. DEFINITIONS
For the purpose of this Code of Practice, the symbols and designations are as given in Table
1 and the following definitions apply.

2.1 Small Punch test
A mechanical test carried out on a small disc shaped test piece by means of the application
of a mechanical load applied to one surface of the test piece by means of a shaped punch in
order to investigate its response to the load.

2.1.1 Small Punch Bulge test
As 2.1 above, but under the condition that the perimeter of the disc is clamped and does not
displace during the test.
2.1.2 Small Punch Drawing test

As 2.1 above but under the condition that the perimeter of the disc is not fully clamped and
may displace during the test.
2.2 Small Punch Creep Test
Small Punch Test carried out under creep conditions

2.2.1 Test Piece
The disc under investigation, independent of its material of composition, its structure and its
manufacturing route.
2.2.2 Test Piece Environment
The environment which is in contact with all surfaces of the test-piece.

2.3 Small Punch Creep Test Stress

The calculated stress induced in the test piece by the load, considered equivalent to the
initial stress in a uniaxial test piece or component under creep conditions.

Table 1 - Symbols and Designations
Symbol Unit Designation
h mm SP disc initial thickness
r mm Radius of punch indenter
d mm Diameter of disc
D,R mm Diameter, radius of receiving aperture

L mm Length of receiving die edge chamfer
u u mm Punch Displacement, Disc Deflection respectively
1 , 2
V m/s Punch velocity
F N Punch load
σ Pa SP disc initial stress (calculated)
k - SP creep test correlation factor
SP
t s Test time
T K Test Temperature
3. APPARATUS
The apparatus should comprise some or all of the following:

3.1 Test Rig
Fig. 1 illustrates schematically a cross-sectional view of the specimen holder with a spherical
punch and the test specimen. It is recommended that, prior to the test, the holder is forced to
clamp the specimen rigidly to limit specimen deformation in the region at the hole of the
lower fixture. It is accepted that the test can be carried out without the disc being fully
clamped but rather guided, known as clamp without load. For such a case this aspect must
be recorded in the test report as this is known to influence the stress to which the disc is
subjected. The receiving aperture of radius R is recommended to be 2mm with a 45 chamfer
at R + 0.2mm. The materials of construction of the upper and lower die should be the same
and of a similar coefficient of thermal expansion to the disc under test so as to minimise
thermal stresses. The surface of the upper part of specimen holder in contact with the test

specimen shall be plane and parallel to the surface of the lower part of specimen holder.
Both surfaces shall be clean and free from oxide build-up, corrosion and dirt. The working
surfaces of the upper and lower part of the specimen holder shall have a hardness of 55
HRC or higher. The test rig shall have a spherical (hemispherical)-ended punch capable of
forcing the central portion of the test specimen through the aperture in the receiving die until
the end point of the test occurs. Alternatively a spherical ball indenter may be used but is not
recommended due to the difficulty to avoid ovality, the possibility of its’ lateral displacement
and the risk of it embedding within the disc at the end of the test. The hemispherical portion
of the punch or alternatively the sphere shall have hardness not less than 55 HRC to be
sufficiently rigid so as not to be deformed during the test. The punch radius r is
recommended to be between 1.0 and 1.25mm.

3.2 Loading System
The method of application of the load shall be such that the load can be controlled to ±1%
agreeing with the latest recommendations for creep testing provided by the European Creep
Collaborative Committee (ECCC) and the draft EN/ISO standard for uniaxial creep testing of
metallic materials. The loading system should be calibrated for accuracy using a proving ring
or similar certified device and the results recorded at least once per annum.

3.3 Strain Measurement System
Extensometry, strain gauging or other methods of determining the deformation of the test-
piece in a continuous fashion may be used providing that they are suitably calibrated and
applied in accordance with good testing practice and the manufacturer’s instructions. The
accuracy and frequency of disc deflection measurements will be determined by the nature of
the actual test being done. Alternatively, or additionally, the displacement of the punch
should be continuously recorded. The difference between punch displacement and disc
deflection represents eventual thinning of the disc and should be recorded if possible.
Furthermore, a discontinuous method may be employed to take dimensional measurements.
The technique is analogous to the taking of interrupted strain measurements during a
uniaxial creep test and should conform to the appropriate standard. The method also permits
the dimensions at a large number of locations within the disc to be monitored during the test
but has serious drawbacks associated with re-insertion of the disc specimen after
measurements.
3.4 Heating System
The heating system should provide a uniform temperature distribution throughout the test
section of the disc. In the case of a clamped perimeter in the Small Punch Bulge test, the
section beneath the clamp is not considered as part of the test section.
A temperature measuring system is to be supplied comprising thermometers, usually
thermocouples, appropriately located to determine that the full test section remains within the
temperature limits prescribed for the test. The thermocouples should be of a type and
composition suitable for the test temperature regime selected for the test and calibrated in
accordance with the appropriate ISO or EN standard.
The temperature control system should be capable of maintaining the temperature constant
to within ± 0.25% of the set temperature in degrees absolute, K, by automatic means
throughout the test. See Table 2 for conversion to degrees C and comparison with the draft
EN/ISO standard for uniaxial creep testing of metallic materials.

3.5 Test Environment
Due to the small dimensions of the Small Punch Creep test-pieces, it is recommended that
the tests are carried out in an inert environment to prevent oxidation or corrosion of the
exposed surfaces of the test-piece. For studies where the effect of the environment on creep
behaviour is of specific interest, other environments may be employed but this purpose must
be clearly stated in the test report and the publication of the test results. For all
environments, including inert environments, the composition should be known and, if
necessary, strictly controlled within specified limits.

3.6 Additional Measurements
Other test parameters may be monitored such as crack initiation or growth either by
continuous (potential drop, acoustic emission) or by discontinuous methods. These additional
measurements may not be allowed to affect the results of the Small Punch Creep test itself.
Any additional measurement made should be reported with the test results.

3.7 Data recording
Equipment should be provided which will record the test parameters automatically with a
resolution which matches that of the measuring instruments and should be accurate to within
±1% of full scale deflection at least and preferably within, ±1% of the measured signal, when
all sources of error are taken into account.
4. TEST PIECES
4.1 Design
A single test piece design is recommended in this Code, which is a disc of diameter, d, 8mm
and initial thickness, h , 0.5mm.  Exceptions to these dimensions can be accepted provided
that they are fully reported with the test results as follows:

i) a larger diameter is allowed for the case of a Small Punch Bulge Test
where the disc is clamped with load around its periphery. The clamped area
should be greater than one third of the total area.
ii) a different disc thickness is allowed if there is a good justification made for
micro-structural reasons such as grain size, coating thickness, inclusion of a
weldment etc.
4.2 Manufacture and metrology
The test piece is to be procured from standard test material, e.g. bar or sheet or from
engineering components prior to or during operation. Methods for extracting material from
components are detailed in Annex A2. In order to minimise work hardening in the surface of
the test piece, the disc should be machined to a thickness of approximately 0.55mm and
then ground to at least 200 grit on both sides (one side for coated specimens) to achieve the
final dimension of 0.5mm with a tolerance of no more than ±0.5%. With the exception of the
case mentioned in 4.1 i) above for a specimen clamped with load, the disc diameter should
be 8mm ±1%. The thickness of the test piece should be measured at four positions around
the perimeter at 90° intervals and at the central position. The diameter should be measured
in two positions at 90°
4.3 Identification and documentation

Test-pieces should be permanently marked on the curved edge with a unique identifier. The
position of the identifier should also enable the position of the four thickness measurements
to be traced.
A written record of each test piece should be kept, listing:

Identification
Material composition and cast
Material condition and original location
Test piece manufacturing route
Test piece original dimensions

This information should be transferred to the test documentation to form a complete test
record.
5. TEST PROCEDURE
5.1 Test piece installation
a) Insert the test piece and clamp it centrally into its position
b) If preparing for an SP Drawing test, clamp the test-piece without load.
c) Locate the extensometer against the test-piece at its centre opposite to the punch tip
d) Close the system and evacuate and flush twice with high purity argon or other
appropriate inert gas. In some cases an active gas may be used if required for the
purpose of the test.
5.2 Determination of test load

The applied load in any test has to be determined from geometrical factors and material
properties in order that creep failure in the Small Punch test will occur at the same time as
that in a conventional uniaxial creep test at the same temperature. For the case where there
is no prior information on expected behaviour, the ratio of SP test load (F) to the uniaxial
creep stress (σ) should be given by:

-0.2 1.2
F/σ = 3.33k R r h
SP 0
where
r is the radius of the punch indenter,
h is the test-piece thickness,
R is the radius of the receiving hole.

This equation is derived from stretching membrane theory (Annex A1) and applies for an
unclamped test providing the disc deflection exceeds 0.8 mm. For the case of the disc
clamped with load it is estimated that this ratio should be reduced by approximately 20%.
The SP creep test correlation factor, k , has first to be determined empirically for the
SP
particular material under test. Where k is not known, the first tests should be set up
SP
assuming k =1 and a series of a minimum of 5 tests at one particular temperature carried
SP
out in order to evaluate k through comparison with the stress rupture behaviour defined
SP
from conventional uniaxial testing.
h
Key
1. SP disc test-piece
2. Hemispherical ended punch
3. Lower die
4. Upper die
5. Dilatometer push rod
Figure 1 - Geometry of the SP Creep test installation
5.3 Application of load and temperature

The application of load and temperature should be as applied in a conventional uniaxial
creep test as given by the European Creep Collaborative Committee (ECCC) and the draft
EN/ISO standard for uniaxial creep testing of metallic materials. The temperature should be
raised as quickly as possible after filling the chamber with inert gas however, for the Small
Punch test, once the planned test temperature has been achieved and stabilised, the load
should be applied immediately. Depending upon the material and test conditions, the effects
of loading rate may be significant. In all cases the load should be increased smoothly to the
test load and as rapidly as possible consistent with the load application system incorporated
in the test machine. Should there be a marked difference between the thermal expansion
coefficient of the punch and disc material, any effect of thermal loading on the test due to
expansion coefficients should be carefully evaluated.

5.4 Monitoring and maintaining test conditions

The test conditions should be monitored continuously and maintained at the required levels
as stated in Sections 3.1 and 3.3. This can be achieved by manual adjustment or fully
automatic means. The monitoring and control systems should be checked and calibrated
prior to each test and at regular intervals throughout the test period to ensure that the
required test conditions are accurately maintained.

5.5 Test interruption and termination

Should the test be interrupted, it is recommended to restart the test in exactly the same way
as the original starting procedure. It is not recommended to remove the test-piece for
evaluation and then to re-introduce the same test piece to continue the test. The termination
of the test equivalent to creep rupture failure of the test-piece can only be clearly defined
through the observation of a sudden rise in the deflection rate. Unless there is a major
fracture area developed, in most cases this rise in deflection rate will not be distinguishable
from the rise due to advanced tertiary creep. Consequently it is proposed that the deflection
at which the test should be terminated should be estimated before the test, based on
experience with the material at the test load and temperature. This termination can be
triggered automatically or manually and should be accompanied by switching off the furnace,
allowing the test piece to return to ambient temperature.

5.6 Post test examination
After the test the test-piece should be photographed on both faces and also from the side to
record a visual image of the total deflection. Measurements should be made of this total
deflection and also of the diameter of the disc in order to assess the effectiveness of the
clamping. Sectioning of the disc is recommended to analyse the variation in strain evidenced
by thinning.
5.7 Data records
Accurate records should be kept of temperature, load, deflection and test duration. In
addition, a record should be kept of all adjustments made to control or alter the test
conditions and of any events that lead to interruptions in the test periods.

6. REPORT
6.1 Minimum Requirements
It is obligatory to cover the following items of information:

a) Specific objective of the test,
b) Reference to procedures including stress calculation methods adopted being in
accordance with this Code of Practice,
c) Test piece description, including (i) manufacturing procedures and finishing, (ii) initial
measured dimensions and (iii) special features, if any,
d) Test conditions, including (i) test temperature, (ii) test load, (iii) test environment,
e) Description and relevant dimensions of testing equipment, including methods for
controlling test conditions,
f) Test results, including (i) total duration of the test, (ii) time to reach temperature and
the soaking time prior to each loading, (iii) deflection measurements, if any, and (iv)
final measured dimensions,
g) The position of failure, cracking or major deformation,
h) Report of any deviations from test conditions or from recommended procedures e.g.
unscheduled interruptions or excursions in temperature or load.

6.2 Additional Information
Although not obligatory the following items should be reported whenever possible:

a) Test piece details including processing route, metallurgical composition and
characteristics, known creep properties for this class of material at this stress and
temperature and service history, if applicable,
b) Results of any post-test examination including fracture characteristics,
c) Use of the test results in further analysis e.g. comparison with other data,
incorporation in life time assessment methods etc.
Table 2 - Allowable Test Temperature Tolerances
o
Test Temperature Tolerances ± C
o
C K SP test Draft EN/ISO
recommended standard
± 0.25%K
20 293 0.7
100 373 0.9
200 473 1.2
300 573 1.4
400 673 1.7
500 773 1.9
600 873 2.2
700 973 2.4
800 1073 2.7
900 1173 2.9
1000 1273 3.2
1100 1373 3.4
7. REFERENCES
Normative references:
(1) Manual of Codes of Practice for the determination of uncertainties in mechanical
tests on metallic materials. Project UNCERT, EU Contract SMT4-CT97-2165,
Standards Measurement & Testing Programme, ISBN 0 946754 41 1, Issue 1,
September 2000.
(2) UNCERT CoP n° 10, The Determination of Uncertainties in Creep Testing.
Project UNCERT, EU Contract SMT4-CT97-2165, Standards Measurement &
Testing Programme, ISBN 0 946754 41 1, Issue 1, September 2000.
(3) BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML: Guide to the Expression of
Uncertainty in Measurement. (ISO 1993) (Known as the “TAG4 Guide”).
(4) EN 10291: Metallic Materials - Uniaxial Creep Testing In Tension - Method of
Test.
(5) American Society for Testing and Materials: Designation E139 - 00: Standard
Test Method for Conducting Creep, Creep Rupture and Stress Rupture Tests of
Metallic Materials.
(6) American Society for Metals: Atlas of Creep and Stress-Rupture Curves (ASM
International1988).
(7) Loveday M.S., (1986), High Temperature Axial Extensometers: Standards,
Calibration and Usage, in High Temperature Strain Measurement, pp 31-47. Ed. R
C Hurst et al. Elsevier Applied Science.
(8) EN ISO 7500-2:1999, Metallic materials – Verification of static uniaxial testing
machines- Part 2: Tension creep testing machines- Verification of the applied load
(ISO 7500-2:1996).
(9) EN ISO 7500-1:2004, Metallic materials – Verification of static uniaxial testing
machines- Part 1: Tension/compression testing machines - Verification and
calibration of the force-measuring system (ISO 7500-1:2004).
(10) EN ISO 376:2004, Metallic materials – Calibration of force-proving instruments
used for the verification of uniaxial testing machines (ISO 376:2004).
(11) prEN ISO 204, Metallic materials – Uniaxial creep testing in tension – Method of
test (ISO/DIS 204:2005).
Small Punch creep test literature references:
[1] Baik, Jai-Man, Buck, O., and Kameda, J., Development of Small Punch Tests for
ductile-brittle transition temperature measurement of temper embrittled Ni-Cr steel,
ASTM STP888, Corwin W.R. and Lucas G.E. eds., ASTM Philadelphia USA, 1986,
92-111.
[2] Bicego, V., Lucon, E., and Crudeli, R., Integrated technologies for life assessment
of primary power plant components, Proc. of Int. Symp. on Materials ageing and
component life extension, Eds. Bicego, Nitta and Viswanathan, 1995, EMAS, Vol. I,
295-305.
[3] Bicego V., COPERNICUS – SP Test Method Assessment for the Determination of
the Residual Creep Life of Service Exposed Components, EC Contract ERB CIPA
CT94 0103, communication to partners, 28 Jan 1997.
[4] Bicego, V., Lucon, E., and Crudeli, R., Integrated Technologies for Life Assessment
of Primary Power Plant Components, J. of Nuclear Sci. and Engng, 1998.
[5] Bicego,V. and Lohr, R.D., Mechanical Testing On Miniature Specimens By The
Small Punch Method, Proc. Int. Symposium on Materials Ageing and Life
Management, Oct. 3-6 2000, Kalpakkam India, Eds. Baldev Raj et al, Vol. 3,
1445-1454.
[6] Bicego, V., Di Persio, F., Rantala, J. H., Small Punch Creep Test Method: Results
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ANNEX A1
Relationship to uniaxial creep test properties

The basic idea for determination of the load which should be applied in a Small Punch creep
test is to answer the question: “What is the load value to obtain the same time to rupture as
in a uniaxial creep test?” However, this question is not so easy to answer as stresses are not
maintained constant during the progression of creep deformation. Upon loading, deflections
are very small, and the load balance is through shear stresses induced by bending moments.
With further deflection, increasing the load balance is mainly through membrane stresses,
which vary with deflection and current thickness. A practical way is to determine the
membrane stresses at the steady state or stationary stage, which might be used to estimate
the rupture time of the test.
As reported by Li and Sturm (2005) and others, several relations between load and stress
are available and reviewed in the following paragraph. All of them are derived from
equilibrium between load and membrane stresses with bending stresses neglected. In the
Small Punch creep tests deflection at failure is usually about 3-4 times the specimen
thickness or about 40%-60% of the disc support distance. When the test specimen
undergoes such a large deformation, neglecting bending stresses is not unreasonable.

In total, four equations (a-d below) have been found in the literature, which are listed in the
round robin report ( Bicego et al, 2003) and quoted here. The argument which follows
explains the reasons for choosing the equation (based on Chakrabarty 1970) governing load
and stress given in the Code of Practice in Section 5.2. Chakrabarty’s stretch membrane
mod
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