ISO 10813-2:2019

Vibration-generating machines — Guidance for selection — Part 2: Equipment for dynamic structural testing

This document provides guidance to select a vibration generator that will be used to evaluate frequency responses of a test structure or to study how vibration grows/decreases along the structure. These structural dynamics tests can be carried out under field or laboratory conditions (see the ISO 7626 or ISO 10846[4][5][6][7] series). This document describes the selection procedure in terms of the force developed by a single vibration generator. Meanwhile, to move massive structures such as dams or bridges, an assembly of vibration generators is usually applied. Properly phased generators produce in total the same force as calculated for a single vibration generator (see 6.2.6). Guidance also can be applied for the selection of equipment to be used for modal testing to determine natural frequencies, modal shapes and damping in a structure; however, for such a test, more factors than covered by this document usually need to be considered. This document deals only with translational excitation. For equipment applied to generate angular vibration, see Reference [8].

Générateurs de vibrations — Lignes directrices pour la sélection — Partie 2: Moyens pour les essais dynamiques

General Information

• Status: Published
• Publication Date: 11-Jul-2019
• ICS: 17.160 - Vibrations, shock and vibration measurements
• Technical Committee: ISO/TC 108/SC 6 - Vibration and shock generating systems
• Drafting Committee: ISO/TC 108/SC 6/WG 3 - Guidance for selection of vibration generators
• Current Stage: 6060 - International Standard published
• Start Date: 01-Sep-2019
• Due Date: 15-Sep-2019
• Completion Date: 12-Jul-2019

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 10813-2
First edition
2019-07
Vibration-generating machines —
Guidance for selection —
Part 2:
Equipment for dynamic structural
testing
Générateurs de vibrations — Lignes directrices pour la sélection —
Partie 2: Moyens pour les essais dynamiques
Reference number
ISO 10813-2:2019(E)
©
ISO 2019

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ISO 10813-2:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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ISO 10813-2:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Dynamic structural testing . 2
4.1 General . 2
4.2 Excitation types . 2
5 Vibration generators . 2
5.1 Main types of equipment . 2
5.2 Principal characteristics of vibration generators. 3
5.3 Features of different vibration generators . 3
5.3.1 Electrodynamic generator . 3
5.3.2 Electromagnetic vibration generator . 3
5.3.3 Piezoelectric vibration generator . 4
5.3.4 Magnetostrictive vibration generator. 4
5.3.5 Hydraulic vibration generator. 4
5.3.6 Mechanical vibration generator. 4
5.3.7 Impactor . 5
6 Selection procedure . 5
6.1 General . 5
6.2 Procedure . 5
Annex A (informative) Prognosis of mechanical impedance for some types of structures .8
Annex B (informative) Examples of equipment selection .19
Bibliography .22
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ISO 10813-2:2019(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.
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 of the voluntary nature of standards, 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 www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and
condition monitoring, Subcommittee SC 6, Vibration and shock generating systems.
A list of all parts in the ISO 10813 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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ISO 10813-2:2019(E)

Introduction
A proper selection of vibration generating system, when purchasing new test equipment or updating
existing equipment for the purposes of a specific test or when choosing between the equipment
proposed by a test laboratory or even selecting a laboratory which offers its service to carry out such
a test, is very important. When making this type of selection, several factors should be considered
simultaneously, as follows:
— the type of the test to be carried out (e.g. environmental testing, normal and/or accelerated, dynamic
structural testing, diagnosis, calibration, etc.);
— the motions to be generated during the test;
— the test conditions (e.g. single or multiple excitations, one mode of vibration or combined vibration,
single or combined test, for example, dynamic plus climatic, etc.);
— the objects to be tested and their mounting.
This document deals only with equipment intended to be used for dynamic structural testing, and
selection procedures are predominantly designed to meet the requirements of this testing. However,
specific test conditions and the specific object to be tested can significantly influence the selection.
If the equipment is expected to be used for different types of tests, all possible applications should
be accounted for when selecting. Thus, if the vibration generator is acquired to be applied during
both environmental and dynamic structural testing, ISO 10813-1 and this document should be used
simultaneously. In this document, it is presumed that a system can be selected if it enables to swing
the test object up to a specified level. To generate an excitation without undesired motions, a suitable
control system should be used. The selection of a control system is not considered in this document.
Vibration generating systems are complex machines, so the correct selection always demands a certain
degree of engineering judgement. Consequently, the purchaser, when selecting the vibration test
equipment, can resort to the help of a third party. In such a case, this document can help the purchaser to
ascertain if the solution proposed by the third party is acceptable or not. Designers and manufacturers
can also use this document to assess the market environment.
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INTERNATIONAL STANDARD ISO 10813-2:2019(E)
Vibration-generating machines — Guidance for
selection —
Part 2:
Equipment for dynamic structural testing
1 Scope
This document provides guidance to select a vibration generator that will be used to evaluate frequency
responses of a test structure or to study how vibration grows/decreases along the structure. These
structural dynamics tests can be carried out under field or laboratory conditions (see the ISO 7626 or
[4][5][6][7]
ISO 10846 series).
This document describes the selection procedure in terms of the force developed by a single vibration
generator. Meanwhile, to move massive structures such as dams or bridges, an assembly of vibration
generators is usually applied. Properly phased generators produce in total the same force as calculated
for a single vibration generator (see 6.2.6).
Guidance also can be applied for the selection of equipment to be used for modal testing to determine
natural frequencies, modal shapes and damping in a structure; however, for such a test, more factors
than covered by this document usually need to be considered.
This document deals only with translational excitation. For equipment applied to generate angular
vibration, see Reference [8].
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 2041, Mechanical vibration, shock and condition monitoring — Vocabulary
ISO 7626-1, Mechanical vibration and shock — Experimental determination of mechanical mobility —
Part 1: Basic terms and definitions, and transducer specifications
ISO 10846-1, Acoustics and vibration — Laboratory measurement of vibro-acoustic transfer properties of
resilient elements — Part 1: Principles and guidelines
ISO 15261, Vibration and shock generating systems — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2041, ISO 7626-1, ISO 10846-1
and ISO 15261 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
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ISO 10813-2:2019(E)

4 Dynamic structural testing
4.1 General
Dynamic structural testing is performed to evaluate such characteristics of a structure as
— frequency responses over a wide range of frequencies,
— modal characteristics (mode shapes, natural frequencies, damping ratios, etc.),
— amplification/attenuation of vibration along the structure.
Knowledge of the dynamic behaviour of structures allows for the, for example:
— design of low-vibration mechanical systems (buildings, machinery, transport and their elements), and
— calculation of isolation systems and means used to reduce vibration.
Level of excitation during the structural testing is not so important as compared with environmental
testing (see ISO 10813-1) provided that linear behaviour of the test structure is maintained. However,
this level should be sufficient to produce the response of the test structure far above the noise floor
at frequencies where the mechanical impedance of the structure reaches its maximum values. For a
non-linear structure, vibration should be excited at the same level as observed under actual operating
conditions.
In a laboratory environment, the test structure can be freely suspended or rigidly supported, whichever
is defined in a relevant specification (see, for example, ISO 7626-2). Single-point or multi-point force
excitation may be used.
Under field conditions, the vibration generator may be used either coupled or uncoupled to the test
structure. Generally, the coupling should be rigid in the direction of excitation but flexible (to allow
rotational motions) in a transverse direction.
4.2 Excitation types
ISO 7626-2 and ISO 7626-5 define various possible types of vibration and shock excitation applicable for
dynamic structural testing.
In case of linear behaviour of the test structure, any type of excitation specified by ISO 7626-2 and
ISO 7626-5 can be used. In the contrary case, only sine vibration should be generated during the test.
5 Vibration generators
5.1 Main types of equipment
A vibration generator is an executive device of a vibration generating system designed to produce some
force or kinematic excitation of a test structure. Excitation parameters depend on the purposes and
conditions of the test.
Electrodynamic, electromagnetic, piezoelectric and magnetostrictive vibration generators are the
most common types of equipment used for dynamic structural testing. To resolve some problems in
generating vibration at low frequencies, pneumatic, hydraulic and mechanical vibration generators may
be preferred.
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5.2 Principal characteristics of vibration generators
Among other measurable parameters of vibration generators used in dynamic structural testing, the
following ones are of principal interest when selecting the test equipment:
— rated force;
— permissible static load;
— frequency range;
— limit values for displacement, velocity and acceleration;
— harmonic distortions;
— spurious motions;
— resonance frequencies.
Another key characteristic of the vibration generator is the manner in which it can be fastened to the
test structure, whether it requires external mechanical constraints or not. In addition, to provide a
specified force excitation, the driving-point impedance of the vibration generator should be far less
than the ones of the test structure.
5.3 Features of different vibration generators
5.3.1 Electrodynamic generator
An electrodynamic vibration generator is a device that transforms electric energy of interaction
between a static magnetic field and an alternating current conductor into mechanical motion. The
current conductor is usually designed as a coil connected to a test table and placed in a circular gap of
an iron circuit with a magnetic bias induced by a direct current coil or by a permanent magnet.
The electrodynamic generator produces a force proportional to the excitation current. This property
makes this type of equipment rather convenient for use in the broadest range of tests.
Another advantage of the electrodynamic generator is that it enables excitation in a broad range of
frequencies (up to 15 000 Hz) and that its input electrical impedance can be easily matched to the
output impedance of the power amplifier over the operating band.
In most of electrodynamic generator designs, the iron circuit is rigidly secured in the case and the coil
with the rigidly connected table is mounted in the case by means of flexible membranes of non-uniform
stiffness, for example, elastic in the axial direction and rigid in a transverse direction.
The principle characteristics of typical electrodynamic generators are given in ISO 10813-1.
Installation and fastening of electrodynamic vibration generators depend on the test purpose and
conditions. The electrodynamic vibration generator cannot withstand a considerable static load.
Therefore, if the test structure needs to experience a static deformation during the testing, such a
deformation should be provided by means of a separate device.
5.3.2 Electromagnetic vibration generator
An electromagnetic vibration generator is a device designed to drive a test structure through the
interaction between an electromagnetic field and a ferromagnetic body. The vibratory force grows in a
quadratic correlation with the exciting current. To linearize the process, polarization of magnetic flow
in the vibration generator iron circuit is applied by means of, for example, a permanent magnet field.
The electromagnetic vibration generator can be designed as either a one-gap or two-gap (differential)
device. The two-gap generator allows harmonic distortions much less than the one-gap device.
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While preparing the test, the constant force of the electromagnetic interaction as well as the mass
of generator’s armature should be considered, particularly when testing light-weight and/or flexible
structures. In these cases, it is recommended to use some unloading device and compensation of a
negative stiffness caused by the constant electromagnetic force.
The main advantage of the electromagnetic generator lies in its efficiency and reliability. However, high
distortions and a limited operation range confine the scope of its use.
5.3.3 Piezoelectric vibration generator
A piezoelectric vibration generator is a device in which the principle of piezoelectric element straining
as affected by electrical field is applied to produce a mechanical excitation of the test object. The
magnitude of the strain in the direction of the forcing electric field can achieve up to thousandths of the
piezoelectric element dimension in the same direction.
A specific feature of the piezoelectric vibration generator is its capacity to produce broadband
kinematic excitation (up to 15 kHz) of heavy and complex mechanical structures. Other advantages are
2
that it can work under very high static loads (up to 2 000 kg/cm ) and is capable of producing well-
directed excitations. The disadvantages are associated with some technological problems in designing
an amplifier that can effectively transmit a broadband signal to the piezoelectric generator.
5.3.4 Magnetostrictive vibration generator
The operation of a magnetostrictive vibration generator is based on the magnetostrictive effect —
deformation of a ferromagnetic body when it is magnetized.
Like the piezoelectric generator, the magnetostrictive generator is capable to produce broadband
kinematic excitation (up to 1 kHz) of heavy and complex mechanical structures. Also, it can be driven
with a relatively cheap power amplifier. Significant power consumption is its disadvantage.
5.3.5 Hydraulic vibration generator
A hydraulic vibration generator is a device that produces excitation of the test object by pulsing the
pressure of fluid in the hydraulic system controlled by one (or several) servovalve(s).
The basic advantages of the hydraulic vibration generator are the following:
— high magnitudes of displacements (up to 200 mm) and forces (up to 10 MN);
— low transverse vibration of the actuator (vibration table);
— large permissible static loading (up to several tons);
— simple and reliable design.
The basic disadvantages are the following:
— high level of non-linear distortions at low frequencies (up to 15 %);
— rather narrow frequency range not exceeding, as a rule, 200 Hz.
The principle characteristics of typical hydraulic vibration generators are given in ISO 10813-1.
5.3.6 Mechanical vibration generator
A mechanical vibration generator transforms energy of a mechanical driving device. According to their
operation, mechanical vibration generators are divided into direct-drive and reaction-type generators.
The basic advantages of mechanical vibration generators are as follows:
— high efficiency;
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ISO 10813-2:2019(E)

— simple and reliable design.
The basic disadvantages are the following:
— limited frequency range (usually 5 Hz to 100 Hz);
— high non-linear distortions;
— capability to excite sine vibration only.
The principle characteristics of mechanical vibration generators are given in ISO 10813-1.
5.3.7 Impactor
A typical hammer-type impactor consists of a rigid mass with a force sensor on one side of the impactor
mass and a flexible tip on the other side. The force sensor may be replaced with an accelerometer. If the
impactor mass oscillates as a rigid body then the output signal of accelerometer is proportional to the
force applied to the test subject.
5
The hammer provides forces up to 10 N over the frequency range from 2 Hz to 10 000 Hz. The frequency
range of excitation can be adjusted by means of tips (see ISO 7626-5).
To excite large massive objects, a large mass either suspended on cables or free-falling downwards is used.
6 Selection procedure
6.1 General
The selection of test equipment depends first on its functionality, reasonable practicality for specific
measurement tasks to be carried out, including requirements related to size, mounting, access to points
of excitation, etc. The test equipment should also guarantee the response to be measured to a specified
accuracy. This means that the equipment should be capable of generating sufficiently high vibration
over the whole frequency range of interest within specified tolerances (on direction, distortions, etc.).
In its turn, the minimum level of excitation depends on background vibration of the test structure
and electrical noise in the measurement circuit. Vibration generated by the test equipment should
be significantly higher than the background vibration at every point of measurement and at every
frequency of interest. The output signal of the vibration transducer should be significantly higher than
the electrical noise.
If a vibration generator enables the production of a constant force over the whole frequency range of
interest, then the force depends on the mechanical impedance Z( f ) of the test structure and a minimum
vibration velocity v( f ) [see Formula (1) below].
6.2 Procedure
6.2.1 The measurement task, including the test structure, characteristics to be evaluated and frequency
range of interest, is specified.
6.2.2 Data concerning the test structure is collected, including:
— the type of the structure (framed structure, machine, isolator, foundation, etc.);
— the size and mass;
— the test conditions (field or laboratory measurement, part of the structure to be tested, access to
excitation and measurement points, vibration generator mounting, compatibility of the vibration
generator and the test structure interfaces, etc.);
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ISO 10813-2:2019(E)

— the background vibration.
6.2.3 Factors such as directivity of excitation, transverse motions, distortions, etc. which can affect the
measurement result are evaluated and limited.
NOTE The influence of some factors can be reduced by means of repetitive tests and averaging. For example,
if the test specification assumes the structure is to be impacted by a hammer several times, then the excitation
directivity can be improved to be within ±5° from a specified axis. Such a limit on the directivity provides an
error of the measured mechanical impedance magnitude to be less than 1 %.
6.2.4 Using knowledge of background vibration, the minimum motion to be developed by the
vibration generator is calculated in terms of root mean square (RMS) values of acceleration a (f),
RMS,min
velocity v (f) or displacement s (f).
RMS,min RMS,min
Generally, vibration developed by the vibration generator should be three to ten times higher than the
background vibration at every frequency of interest.
NOTE 1 If acceleration of the background vibration is uniformly spaced over the frequency range of interest
then velocity v ( f ) and displacement s ( f ) reach their maximums at the lower limit of the range.
RMS,min RMS,min
NOTE 2 High level of uniformly distributed background acceleration impedes application of vibration
generators unable to develop significant displacements at low frequencies such as piezoelectric ones.
6.2.5 The mechanical impedance Z(f) of the test structure over the frequency range of interest is
roughly estimated on the basis of physical modelling, prototype testing, handbook data, and so on. Some
recommendations on the rough estimation of Z(f) are given in Annex A for some types of structures.
NOTE Annex A establishes a simple way to evaluate impedances from mass-spring-damper models. There
are more complicated methods of a rough estimation of Z( f ) for specific structures, for example, using FEM-
[9][10]
models .
6.2.6 The vibratory force F (f) is given by Formula (1):
RMS,min
Ff =vf Zf (1)
() () ()
RMSR,min MS,min
where
v ( f ) is the minimum velocity to be developed by the vibration generator during the testing;
RMS,min
Z( f ) is the mechanical impedance of the test structure, driving point or transfer depending
on the testing purpose;
f is the frequency.
The frequency f at which F ( f ) reaches its maximum F , i.e. F = F ( f ) is fixed.
max RMS,min max max RMS,min max
If several vibration generators are applied to excite the test structure then they are to develop the same
vibratory force F ( f ) as calculated according to Formula (1), i.e.
RMS,min
N
2
Ff = Ff (2)
() ()
RMSR,min ∑ n;,MS min
n=1
where
th
F ( f ) is the force developed by the n vibration generator;
n;RMS,min
N is the number of vibration generators applied during the testing.
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6.2.7 The vibration generator is selected according to criteria related to:
a) test conditions and generator’s performance (see 6.2.1 to 6.2.3);
b) vibration parameters in terms of:
— vibratory force F at the frequency f and forces F ( f ) over the whole frequency range
max max RMS,min
of interest;
— minimum acceleration a ( f ), velocity v ( f ) and displacement s ( f ).
RMS,min RMS,min RMS,min
Examples of the selection of a vibration generator depending on the measurement task are given in
Annex B.
6.2.8 The vibration transducer is selected.
Vibration transducer and conditioning devices of the measurement circuit should be selected on the
assumption that the transducer output U for the minimum velocity v ( f) is at least three to
g min RMS,min
ten times higher than the internal circuit noise U . Given U , the transducer’s sensitivity S( f ) can be
n g min
calculated from Formula (3):
Sf =Uf vf (3)
() () ()
gmin,RMS min
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Annex A
(informative)

Prognosis of mechanical impedance for some types of structures
A.1 General
This annex provides envelopes of magnitude of mechanical impedances for some types of structures.
These envelopes lie above real curves of mechanical impedances, obtained as a result of extensive
studies (see, for example, Reference [8]), so as to involve some margin of safety. Thus, the envelope
curve associated with some structure can be dissimilar to an actual mechanical impedance curve for
that structure. Nevertheless, such an envelope allows to obtain a somewhat overestimated val
...