prEN ISO 148-2

SLOVENSKI STANDARD
01-december-2025
Kovinski materiali - Udarni preskus po Charpyju - 2. del: Preverjanje preskusnih
naprav (ISO/DIS 148-2:2025)
Metallic materials - Charpy pendulum impact test - Part 2: Verification of testing
machines (ISO/DIS 148-2:2025)
Metallische Werkstoffe - Kerbschlagbiegeversuch nach Charpy - Teil 2: Überprüfung der
Prüfmaschinen (Pendelschlagwerke) (ISO/DIS 148-2:2025)
Matériaux métalliques - Essai de flexion par choc sur éprouvette Charpy - Partie 2:
Vérification des machines d'essai (mouton-pendule) (ISO/DIS 148-2:2025)
Ta slovenski standard je istoveten z: prEN ISO 148-2
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 148-2
ISO/TC 164/SC 4
Metallic materials — Charpy
Secretariat: ANSI
pendulum impact test —
Voting begins on:
Part 2: 2025-10-28
Verification of testing machines
Voting terminates on:
2026-01-20
Matériaux métalliques — Essai de flexion par choc sur éprouvette
Charpy —
Partie 2: Vérification des machines d'essai (mouton-pendule)
ICS: 77.040.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
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Reference number
ISO/DIS 148-2:2025(en)
DRAFT
ISO/DIS 148-2:2025(en)
International
Standard
ISO/DIS 148-2
ISO/TC 164/SC 4
Metallic materials — Charpy
Secretariat: ANSI
pendulum impact test —
Voting begins on:
Part 2:
Verification of testing machines
Voting terminates on:
Matériaux métalliques — Essai de flexion par choc sur éprouvette
Charpy —
Partie 2: Vérification des machines d'essai (mouton-pendule)
ICS: 77.040.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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Published in Switzerland Reference number
ISO/DIS 148-2:2025(en)
ii
ISO/DIS 148-2:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Definitions pertaining to the machine .2
3.2 Definitions pertaining to energy .3
3.3 Definitions pertaining to test pieces .4
4 Symbols and abbreviated terms. 4
5 Testing machine. 6
6 Full direct verification . 6
6.1 General .6
6.2 Foundation/installation .7
6.3 Machine framework .7
6.4 Machine .8
6.5 Anvils and supports .11
6.6 Indicating equipment . 12
7 Indirect verification by use of certified reference test pieces .13
7.1 Certified reference test pieces used . 13
7.2 Absorbed energy levels . 13
7.3 Requirements for certified reference test pieces . 13
7.4 Limited direct verification . 13
7.5 Bias and repeatability .14
7.5.1 Repeatability .14
7.5.2 Bias .14
8 Frequency of verification . 14
9 Verification report .15
9.1 General . 15
9.2 Direct verification . . 15
9.3 Indirect verification . 15
10 Uncertainty .15
Annex A (informative) Measurement uncertainty of the result of the indirect verification of a
Charpy pendulum impact machine .21
Annex B (informative) Measurement uncertainty of the results of the full direct verification of
a Charpy pendulum impact testing machine .25
Annex C (informative) Direct method of verifying the geometric properties of pendulum impact
testing machines using a jig .31
Bibliography .36

iii
ISO/DIS 148-2:2025(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 4, Fatigue, fracture and toughness testing.
This fourth edition cancels and replaces the third edition (ISO 148-2:2016), which has been technically
revised.
ISO 148 consists of the following parts, under the general title Metallic materials — Charpy pendulum impact test:
— Part 1: Test method
— Part 2: Verification of testing machines
— Part 3: Preparation and characterization of Charpy V-notch certified reference test pieces for indirect
verification of pendulum impact machines
— Part 4: Testing of miniature Charpy test pieces (in preparation).

iv
ISO/DIS 148-2:2025(en)
Introduction
The suitability of a pendulum impact testing machine for acceptance testing of metallic materials has
usually been based on a calibration of its scale and verification of compliance with specified dimensions,
such as the shape and spacing of the anvils supporting the test piece. The scale calibration is commonly
verified by measuring the mass of the pendulum and its elevation at various scale readings. This procedure
for evaluation of machines had the distinct advantage of requiring only measurements of quantities that
could be traced to national standards. The objective nature of these traceable measurements minimized the
necessity for arbitration regarding the suitability of the machines for material acceptance tests.
However, sometimes two machines that had been evaluated by the direct-verification procedures described
above, and which met all dimensional requirements, were found to give significantly different impact values
when testing test pieces of the same material.
This difference was commercially important when values obtained using one machine met the material
specification, while the values obtained using the other machine did not. To avoid such disagreements,
some purchasers of materials added the requirement that all pendulum impact testing machines used for
acceptance testing of material sold to them are to be indirectly verified by testing certified reference test
pieces supplied by them. A machine was considered acceptable only if the values obtained using the machine
agreed, within specified limits, with the value furnished with the certified reference test pieces.
This part of ISO 148 describes both the direct verification and the indirect verification procedures.

v
DRAFT International Standard ISO/DIS 148-2:2025(en)
Metallic materials — Charpy pendulum impact test —
Part 2:
Verification of testing machines
1 Scope
This part of ISO 148 covers the verification of pendulum-type impact testing machines, in terms of their
constructional elements, their overall performance and the accuracy of the results they produce. It is
applicable to machines with 2 mm or 8 mm strikers used for pendulum impact tests performed in accordance
with ISO 148-1.
It can be applied to pendulum impact testing machines of various capacities and of different design.
Impact machines used for industrial, general or research laboratory testing of metallic materials in
accordance with this part of ISO 148 are referred to as industrial machines. Those with more stringent
requirements are referred to as reference machines. Specifications for the verification of reference machines
are found in ISO 148-3.
This part of ISO 148 describes two methods of verification.
a) The direct method, which is static in nature, involves measurement of the critical parts of the machine
to ensure that it meets the requirements of this part of ISO 148. Instruments used for the verification
and calibration are traceable to national or international standards.
b) The indirect method, which is dynamic in nature, uses certified reference test pieces to verify points on
the measuring scale for absorbed energy. The requirements for the certified reference test pieces are
found in ISO 148-3.
A pendulum impact testing machine is not in compliance with this part of ISO 148 until it has been verified
by both the direct and indirect methods and meets the requirements of Clause 6 and Clause 7.
This part of ISO 148 describes how to assess the different components of the total energy absorbed in
fracturing a test piece. This total absorbed energy consists of
— the energy needed to fracture the test piece itself, and
— the internal energy losses of the pendulum impact testing machine performing the first half-cycle swing
from the initial position.
NOTE Internal energy losses are due to the following:
— air resistance, friction of the bearings of the rotation axis and of the indicating pointer of the machine which can
be determined by the direct method (see 6.4.5);
— shock of the foundation, vibration of the frame and pendulum for which no suitable measuring methods and
apparatus have been developed.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.

ISO/DIS 148-2:2025(en)
ISO 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 148-3, Metallic materials — Charpy pendulum impact test — Part 3: Preparation and characterization of
Charpy V-notch certified reference test pieces for indirect verification of pendulum impact machines
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Definitions pertaining to the machine
3.1.1
anvil
portion of the machine that serves to properly position the test piece for impact with respect to the striker
and the test piece supports, and supports the test piece under the force of the strike
3.1.2
base
part of the framework of the machine located below the horizontal plane of the supports
3.1.3
centre of percussion
point in a body at which, on striking a blow, the percussive action is the same as if the whole mass of the
body were concentrated at the point
Note 1 to entry: When a simple pendulum delivers a blow along a horizontal line passing through the centre of
percussion, there is no resulting horizontal reaction at the axis of rotation.
Note 2 to entry: See Figure 4.
3.1.4
centre of strike
point on the striking edge of the pendulum at which, in the free hanging position of the pendulum, the
vertical edge of the striker meets the upper horizontal plane of a test piece of half standard thickness (i.e.
5 mm) or equivalent gauge bar resting on the test piece supports
Note 1 to entry: See Figure 4.
3.1.5
industrial machine
pendulum impact testing machine used for industrial, general or most research-laboratory testing of
metallic materials
Note 1 to entry: Industrial machines are not used to establish reference absorbed energy values for batches of certified
reference test pieces, unless they also meet the requirements of a reference machine (see ISO 148-3) .
Note 2 to entry: Industrial machines are verified using the procedures described in this part of ISO 148.
3.1.6
pendulum impact testing machine
testing machine equipped with a swinging hammer (pendulum) that is used to perform impact tests on
Charpy test pieces
Note 1 to entry: For the sake of simplicity, the term “machine” is often used in this document to generically indicate a
pendulum impact testing machine.
3.1.7
reference machine
pendulum impact testing machine used to determine reference absorbed energy values for batches of
certifiedtest pieces (3.3.4)
Note 1 to entry: Reference machines are verified using the procedures described in ISO 148-3.

ISO/DIS 148-2:2025(en)
3.1.8
striker
portion of the pendulum that contacts the test piece
Note 1 to entry: The edge that actually contacts the test piece has a radius of 2 mm (the 2 mm striker) or a radius of
8 mm (the 8 mm striker).
Note 2 to entry: See Figure 2.
3.1.9
supports
portion of the machine that serves to properly position the test piece for impact with respect to the centre of
percussion (3.1.3) of the pendulum, the striker (3.1.7) and the anvils (3.1.1)
Note 1 to entry: See Figure 2 and Figure 3.
3.2 Definitions pertaining to energy
3.2.1
total energy
K
T
total absorbed energy spent to break a test piece with a pendulum impact testing machine, which is not
corrected for any losses of energy
Note 1 to entry: It is equal to the difference in the potential energy from the starting position of the pendulum to the
end of the first half swing during which the test piece is broken.
3.2.2
initial potential energy
potential energy
K
P
potential energy of the pendulum hammer prior to its release for the impact test, as determined by direct
verification
Note 1 to entry: See 6.4.2.
3.2.3
absorbed energy
K
energy necessary to break a test piece with a pendulum impact testing machine, after correction for friction
as described in 6.4.5
Note 1 to entry: The letter V or U is used to indicate the notch geometry, which is KV or KU. The number 2 or 8 is used
as a subscript to indicate striker radius, for example KV .
3.2.4
calculated energy
K
calc
energy calculated from values of angle, length and force measured during direct verification
3.2.5
nominal initial potential energy
nominal energy
K
N
energy assigned by the manufacturer of the pendulum impact testing machine
3.2.6
indicated absorbed energy
K
S
energy indicated by the display/dial of the testing machine, which may or may not need to be corrected for
friction and air resistance to determine the absorbed energy, K (3.2.3)

ISO/DIS 148-2:2025(en)
3.2.7
reference absorbed energy
K
R
reference value of absorbed energy (3.2.3) assigned to the certifiedreference test pieces (3.3.4) used to verify
the performance of pendulum impact machines
3.3 Definitions pertaining to test pieces
3.3.1
width
W
distance between the notched face and the opposite face
Note 1 to entry: Prior to 2016, the distance between the notched face and the opposite face was specified as “height”.
Changing this dimension to “width” makes ISO 148-2 consistent with the terminology used in other ISO fracture
standards.
3.3.2
thickness
B
dimension perpendicular to the width (3.3.1) and parallel to the notch
Note 1 to entry: Prior to 2016, the dimension perpendicular to the width that is parallel to the notch was specified as
“width”. Changing this dimension to “thickness” makes ISO 148-2 consistent with the terminology used in other ISO
fracture standards.
3.3.3
length
L
largest dimension perpendicular to the notch
3.3.4
certified reference test piece
impact test piece used to verify the suitability of a pendulum impact testing machine by comparing the
indicated absorbed energy (3.2.3) measured by that machine with the reference absorbed energy (3.2.7)
associated with the test pieces
Note 1 to entry: Certified test pieces are prepared in accordance with ISO 148-3.
4 Symbols and abbreviated terms
Table 1 — Symbols/abbreviated terms and their designations and units
Symbol/
abbreviated Unit Designation
a
term
B J Bias of the pendulum impact machine as determined through indirect verification
V
b J Repeatability
CRM — Certified reference material
F N Force exerted by the pendulum when measured at a distance l
F N Force exerted by the pendulum due to gravity
g
g m/s Acceleration due to gravity
[1]
GUM — Guide to the expression of uncertainty in measurement
h m Height of fall of pendulum
h m Height of rise of pendulum
a
See Figure 4.
ISO/DIS 148-2:2025(en)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol/
abbreviated Unit Designation
a
term
Absorbed energy (expressed as K , K , K , K , to identify specific notch geome-
V2 V8 U2 U8
K J
tries and the radius of the striking edge)
K J Total absorbed energy
T
K J Indicated absorbed energy
S
K J Calculated energy
calc
Certified K value of the certified reference material used in the indirect verifica-
V
K J
VR
tion
J Mean K value of the certified reference test pieces tested for indirect verification
K
V
VV
K J Nominal initial potential energy (nominal energy)
N
K J Initial potential energy (potential energy)
P
K J Reference absorbed energy of a set of Charpy certified reference test pieces
R
Indicated absorbed energy when the machine is operated in the normal manner
K J
without a test piece in position
Indicated absorbed energy when the machine is operated in the normal manner
K J
without a test piece in position and without resetting the indication mechanism
Indicated absorbed energy after 11 half swings when the machine is operated
K J in the normal manner without a test piece in position and without resetting the
indication mechanism
Distance to centre of test piece (centre of strike) from the axis of rotation (length
l m
of pendulum)
l m Distance to the centre of percussion from the axis of rotation
l m Distance to the point of application of the force F from the axis of rotation
M N·m Moment equal to the product F·l
Number of certified reference samples tested for the indirect verification of a
n —
V
pendulum impact testing machine
p J Absorbed energy loss caused by pointer friction
p' J Absorbed energy loss caused by bearing friction and air resistance
p J Correction of absorbed energy losses for an angle of rise β
β
r J Resolution of the machine scale
s J Standard deviation of the KV values obtained on n certified reference test pieces
V V
S J Bias in the scale mechanism
t s Period of the pendulum
T s Total time for 100 swings of the pendulum
T s Maximum value of T
max
T s Minimum value of T
min
u — Standard uncertainty
uK J
Standard uncertainty of K
()
VV
VV
u(B ) J Standard uncertainty contribution from bias
V
u(F) J Standard uncertainty of the measured force, F
u(F ) J Standard uncertainty of the force transducer
ftd
u(r) J Standard uncertainty contribution from resolution
Standard uncertainty of the reference value for the certified reference material
u J
CRM
used for the indirect verification
a
See Figure 4.
ISO/DIS 148-2:2025(en)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol/
abbreviated Unit Designation
a
term
Expanded uncertainty of the reference value for the certified reference material
U J
CRM
used for the indirect verification
u J Standard uncertainty of the indirect verification result
V
α ° Angle of fall of the pendulum
β ° Angle of rise of the pendulum
Angle of rise when the machine is operated in the normal manner without a test
β °
piece in position
Angle of rise when the machine is operated in the normal manner without a test
β °
piece in position and without resetting the indication mechanism
Angle of rise after 11 half swings when the machine is operated in the normal
β ° manner without a test piece in position and without resetting the indication
mechanism
υ — Degrees of freedom corresponding to u(B )
B V
υ — Degrees of freedom corresponding to u
V V
υ — Degrees of freedom corresponding to u
CRM RM
a
See Figure 4.
5 Testing machine
A pendulum impact testing machine consists of the following parts (see Figure 1 to Figure 3):
a) foundation/installation;
b) machine framework: the structure supporting the pendulum, excluding the foundation;
c) pendulum, including the hammer;
d) anvils and supports (see Figure 2 and Figure 3);
e) indicating equipment for the absorbed energy (e.g. scale and friction pointer or electronic readout
device).
6 Full direct verification
6.1 General
Full direct verification of the machine involves the inspection of the items a) to e) listed in Clause 5.
Uncertainty estimates are required under Clause 6 for direct verification measurements to harmonize the
accuracy of the applied verification procedures. Uncertainty estimates required in Clause 6 are not related
to product standards or material property databases in any way.
The uncertainty of dial gauges, micrometres, callipers, and other commercial instrumentation used for the
direct verification measurements shall be estimated once, by the producer.
Uncertainty of a method to measure a direct verification parameter is assessed as part of the method
validation. Once method validation is completed, the uncertainty can be routinely used (provided the same
method is followed, the same instrumentation is used, and the operators are trained).

ISO/DIS 148-2:2025(en)
6.2 Foundation/installation
6.2.1 The foundation to which the machine is fixed and the method(s) of fixing the machine to the
foundation are of the utmost importance.
6.2.2 Inspection of the machine foundation can usually not be made once the machine has been installed;
thus, documentation made at the time of installation shall be produced to provide assurance that the mass
of the foundation is not less than 40 times that of the pendulum.
6.2.3 Inspection of the installed machine shall consist of the following.
a) Ensuring that the bolts are torqued to the value specified by the machine manufacturer. The torque
value shall be noted in the document provided by the manufacturer of the machine (see 6.2.1). If other
mounting arrangements are used or selected by an end user, equivalency shall be demonstrated.
b) Ensuring that the machine is not subject to external vibrations transmitted through the foundation at
the time of the impact test.
NOTE This can be accomplished, for example, by placing a small container of water on any convenient location
on the machine framework. The absence of ripples on the water surface during an impact test indicates that this
requirement has been met.
6.3 Machine framework
6.3.1 Inspection of the machine framework (see Figure 1) shall consist of determining the following items:
a) free position of the pendulum;
b) location of the pendulum in relation to the supports;
c) transverse and radial play of the pendulum bearings;
d) clearance between the hammer and the framework.
Machines manufactured after 1998 shall have a reference plane from which measurements can be made.
NOTE Annex C is provided for information.
6.3.2 The axis of rotation of the pendulum shall be parallel to the reference plane to within 2/1 000. This
shall be certified by the manufacturer.
6.3.3 The machine shall be installed so that the reference plane is horizontal to within 2/1 000.
For pendulum impact testing machines without a reference plane, the axis of rotation shall be established
to be horizontal to within 4/1 000 directly or a reference plane shall be established from which the
horizontality of the axis of rotation can be verified as described above.
6.3.4 When hanging free, the pendulum shall hang so that the striking edge is within 0,5 mm of the
position where it would just touch the test piece.
NOTE This condition can be determined using a gauge in the form of a bar that is approximately 55 mm in length
and of rectangular section 7,5 mm by 12,5 mm (see Figure 3).
6.3.5 The plane of swing of the pendulum shall be 90,0° ± 0,1° to the axis of rotation (u < 0,05°).
6.3.6 The striker shall make contact over the full thickness of the test piece.
One method of verifying this is to use a test piece having dimensions of 55 mm × 10 mm × 10 mm that is
tightly wrapped in thin paper (e.g. by means of adhesive tape) and a striking edge that is tightly wrapped in

ISO/DIS 148-2:2025(en)
carbon paper with the carbon side outermost (i.e. not facing the striker). From its position of equilibrium, the
pendulum is raised a few degrees, released so that it contacts the test piece, and prevented from contacting
the test piece a second time. The mark made by the carbon paper on the paper covering the test piece should
extend completely across the paper. This verification can be performed concurrently with that of checking
the angle of contact between the striker and the test piece (see 6.4.8).
As an alternative to the use of carbon paper, the striking edge may also be dyed with a colourant, such as red
or blue pigment, before contacting the test piece.
6.3.7 The pendulum shall be located so that the centre of the striker and the centre of the gap between the
anvils are coincident to within 0,5 mm (u < 0,1 mm).
6.3.8 Axial play in the pendulum bearings shall not exceed 0,25 mm (u < 0,05 mm) measured at the centre-
of-rotation under a transverse force of approximately 4 % of the effective weight of the pendulum, F [see
g
Figure 4 b)], applied at the centre of strike.
6.3.9 Radial play of the shaft in the pendulum bearings shall not exceed 0,08 mm (u < 0,02 mm) when a
force of 150 N ± 10 N is applied at a distance l perpendicular to the plane of swing of the pendulum.
NOTE The radial play can be measured, for example, by a dial gauge mounted on the machine frame at the bearing
housing in order to indicate movement at the end of the shaft (in the bearings) when a force of about 150 N is applied to
the pendulum perpendicularly to the plane of the swing.
6.3.10 It is recommended that the mass of the base of the machine framework be at least 12 times that of
the pendulum.
6.4 Machine
6.4.1 The verification of the machine (including striker) shall consist of determining the following
quantities:
a) potential energy, K ;
P
b) error in the indicated absorbed energy, K ;
S
c) velocity of the pendulum at the instant of impact;
d) energy absorbed by friction;
e) position of the centre of percussion (i.e. distance from the centre of percussion to the axis of rotation);
f) radius of the striking edge of the striker;
g) angle between the line of contact of the striker and the horizontal axis of the test piece.
6.4.2 The potential energy, K , shall not differ from the nominal energy, K , by more than ±1 %. The
P N
potential energy, K , shall be determined as follows.
P
The moment of the pendulum is determined by supporting the pendulum at a chosen distance, l , from
the axis of rotation by means of a knife edge on a balance or dynamometer in such a manner that the line
through the axis of rotation that joins the centre of gravity of the pendulum is horizontal within 15/1 000
[see Figure 4 a)] (u < 5/1 000).
The force, F, and the length, l , shall each be determined to an accuracy of ±0,2 %. The moment, M, is the
product of F · l .
NOTE Length l can be equal to length l.
The angle of fall, α, shall be measured to an accuracy of ±0,2°; this angle can be greater than 90°.

ISO/DIS 148-2:2025(en)
The potential energy, K , is then calculated by Formula (1):
P
KM=−()1cosα (1)
P
6.4.3 The graduation marks on the scale corresponding approximately to values of absorbed energy of
0 %, 10 %, 20 %, 30 %, 50 % and 80 % of the nominal energy shall be verified.
For each of these graduation marks, the pendulum shall be supported so that the graduation mark is
indicated by the pointer, and the angle of rise, β, then determined to ±0,2°. The calculated energy is given by
Formula (2):
KM=−()coscβαos (2)
calc
NOTE 1 The measurement uncertainty of l , F and β, as specified, yields a mean total measurement uncertainty of
K of approximately ±0,3 % of the full-scale value.
calc
The difference between the indicated absorbed energy, K , and the calculated energy from the measured
S
values, K , shall not be greater than ±1 % of the energy reading or ±0,5 % of the nominal energy, K . In
calc N
each case, the greater value is permitted, i.e.
KK−
calc S
·100 ≤ 1 % at between 50 % and 80 % of the nominal energy, K (3)
N
K
S
KK−
calc S
·100 ≤ 0,5 % at less than 50 % of the nominal energy, K (4)
N
K
S
NOTE 2 Attention is drawn to the fact that the accuracy of the absorbed energy reading is inversely proportional to
its value, and this is important when K is small in comparison with K .
N
NOTE 3 For machines with scales and readout devices that are corrected for energy losses, K should be corrected
calc
in order to compare the results properly.
6.4.4 The velocity at impact can be determined from Formula (5):
vg=−21l cosα (5)
()
where g is the local acceleration of gravity known to 1 part in 1 000 or better, in m/s . For the purposes of
[2]
this document, g can be calculated using Formula (6) :
−−3 2 6 2 −6
 
g=+9,,780318 15 30241×∅05sin,−×8102sin,∅ −×3 086 110 h (6)
() ()
 
where
∅ is the latitude, and
h is the elevation above sea level, in metres.
The velocity at impact shall be 5 m/s to 5,5 m/s (u < 0,1 m/s); however, for machines manufactured prior to
1998, any value within the range of 4,3 m/s to 7 m/s is permissible and the value shall be stated in the report.
6.4.5 The energy absorbed by friction includes, but is not limited to, air resistance, bearing friction and
the friction of the indicating pointer. These losses shall be estimated as follows.
6.4.5.1 To determine the loss caused by pointer friction, the machine is operated in the normal manner,
but without a test piece in position, and the angle of rise, β , or energy reading, K , is noted as indicated by
1 1
the pointer. A second test is then carried out without resetting the indication pointer and the new angle of

ISO/DIS 148-2:2025(en)
rise, β , or energy reading, K , is noted. Thus, the loss due to friction in the indicating pointer during the rise
2 2
is equal to as given by Formula (7):
pM=−coscββos (7)
()
when the scale is graduated in degrees, or as given by Formula (8):
pK=−K (8)
when the scale is graduated in energy units.
6.4.5.2 Determination of the losses caused by bearing friction and air resistance for one half swing is
performed as follows.
After determining β or K in accordance with 6.4.5.1, the pendulum is put into its initial position. Without
2 2
resetting the indicating mechanism, release the pendulum without shock and vibration and permit it to
swing 10 half swings. After the pendulum starts its eleventh half swing, move the indicating mechanism to
about 5 % of the scale-range capacity and record the value as β or K . The losses by bearing friction and air
3 3
resistance for one half swing are equal to as given by Formula (9):
M()coscββ− os
′
p = (9)
when the scale is graduated in degrees, or as given by Formula (10):
KK−
′
p = (10)
when the scale is graduated in energy units.
NOTE If it is required to take into account these losses in an actual test giving an angle of rise, β, the quantity as
given by Formula (11) can be subtracted from the value of the absorbed energy.
β αβ+
pp=+ p′ (11)
β
β αβ+
Because β and β are nearly equal to α, Formula (11) can be reduced to Formula (12):
1 2
β αβ+
pp=+ p′ (12)
β
α 2α
For machines graduated in energy units, the value of β can be calculated as given in Formula (13):
KK−
 
PT
β =−arccos 1 (13)
 
M
 
6.4.5.3 The values of β , β , and β , and the values of K , K , and K shall be the mean values from at least
1 2 3 1 2 3
two determinations. The total friction loss p + p′, so measured, shall not exceed 0,5 % of the nominal energy,
K . If it does, and it is not possible to bring the friction loss within the tolerance by reducing the pointer
N
friction, the bearings shall be cleaned or replaced.
6.4.6 The distance from the centre of percussion to the axis of rotation, l , is derived from the period (time
of swing) of the pendulum, and it shall be 0,995 l ± 0,005 l. The measurement uncertainty of the calculated
value of l shall be <0,5 mm.
The distance can be determined by swinging the pendulum through an angle not exceeding 5° and measuring
the time, t, of a complete swing in seconds.

ISO/DIS 148-2:2025(en)
l is derived from Formula (14):
gt
l = (14)
4π
where g is the local acceleration of gravity known to 1 part in 1 000 or better, in m/s .
The value of t shall be determined to within 0,1 %.
With a pendulum having a period of approximately 2 s, this accuracy may be achieved as follows. Determine
the time, T, of 100 complete swings, three times. An accurate measure of t is the average of the three values of T
divided by 100, provided the quantity (T − T ), which represents the repeatability, is not more than 0,2 s.
max min
6.4.7 The dimensions of the striker shall be checked. Either of two types of striker may be used, the 2 mm
striker or the 8 mm striker. The values for the radius of curvature and the angle of the tip for both types are
shown in Table 3.
The maximum width of that portion of the striker passing between the anvils shall be at least 10 mm but not
greater than 18 mm (u < 0,2 mm).
NOTE An example of a method of verifying the geometry of the striker is to make a replica for examination.
6.4.8 The angle between the line of contact of the striker and the horizontal axis of the test piece shall be
90° ± 2° (see 6.3.6) (u < 0,2°).
6.4.9 The mechanism for releasing the pendulum from its initial position shall operate freely and permit
release of the pendulum without initial impulse, retardation or side vibration.
6.4.10 If the machine has a brake mechanism, means shall be provided to prevent the brake from being
accidentally engaged. In addition, there shall be provision to disengage the brake mechanism, for example
during the measurement of period and friction losses.
6.4.11 Machines with automated lifting devices shall be constructed so that full direct verification can be
performed.
6.5 Anvils and supports
6.5.1 Inspection of the anvils and supports should consist of determining the following items (see Figure 2
and Figure 3 and Table 3):
a) configuration of the supports;
b) configuration of the anvils;
c) distance between the anvils;
d) taper of the anvils;
e) radius of the anvils;
f) clearance for the broken test piece to
...