EN ISO 10846-1:1998
(Main)Acoustics and vibration - Laboratory measurement of vibro-acoustic transfer properties of resilient elements - Part 1: Principles and guidelines (ISO 10846-1:1997)
Acoustics and vibration - Laboratory measurement of vibro-acoustic transfer properties of resilient elements - Part 1: Principles and guidelines (ISO 10846-1:1997)
Migrated from Progress Sheet (TC Comment) (2000-07-10): UAP to be launched on ISO 10846-1, when available
Akustik und Schwingungstechnik - Laborverfahren zur Messung der vibro-akustischen Transfereigenschaften elastischer Elemente - Teil 1: Grundlagen und Übersicht (ISO 10846-1:1997)
Dieser Teil von ISO 10846 gibt Grundsätze an, die den Teilen 2 bis 5 von ISO 10846 für die Bestimmung der Transfereigenschaften von Schwingungsisolatoren auf der Grundlage von Labormessungen unterliegen und gibt Hilfestellung bei der Auswahl der jeweils geeigneten Norm. Schwingungsisolatoren, für die dieser Teil von ISO 10846 zutrifft, werden verwendet: a) um die Übertragung von Schwingungen im Hörbereich (Körperschall, 20 Hz - 20 kHz) auf Strukturen zu vermindern, welche dann z.B. Fluidschall (Luftschall, Wasserschall oder dergleichen) abstrahlen können.
Acoustique et vibrations - Mesurage en laboratoire des propriétés de transfert vibro-acoustique des éléments élastiques - Partie 1: Principes et lignes directrices (ISO 10846-1:1997)
Akustika in vibracije - Laboratorijsko merjenje vibro-akustičnih prenosnih lastnosti elastičnih elementov - 1. del: Načela in smernice (ISO 10846-1:1997)
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik und Schwingungstechnik - Laborverfahren zur Messung der vibro-akustischen Transfereigenschaften elastischer Elemente - Teil 1: Grundlagen und Übersicht (ISO 10846-1:1997)Acoustique et vibrations - Mesurage en laboratoire des propriétés de transfert vibro-acoustique des éléments élastiques - Partie 1: Principes et lignes directrices (ISO 10846-1:1997)Acoustics and vibration - Laboratory measurement of vibro-acoustic transfer properties of resilient elements - Part 1: Principles and guidelines (ISO 10846-1:1997)17.160Vibracije, meritve udarcev in vibracijVibrations, shock and vibration measurements17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:EN ISO 10846-1:1998SIST EN ISO 10846-1:1999en01-november-1999SIST EN ISO 10846-1:1999SLOVENSKI
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SIST EN ISO 10846-1:1999
SIST EN ISO 10846-1:1999
SIST EN ISO 10846-1:1999
AReference numberISO 10846-1:1997(E)INTERNATIONALSTANDARDISO10846-1First edition1997-10-15Acoustics and vibration — Laboratorymeasurement of vibro-acoustic transferproperties of resilient elements —Part 1:Principles and guidelinesAcoustique et vibrations — Mesurage en laboratoire des propriétésde transfert vibro-acoustique des éléments élastiques —Partie 1: Principes et lignes directricesSIST EN ISO 10846-1:1999
ISO 10846-1:1997(E)©
ISO 1997All rights reserved. Unless otherwise specified, no part of this publication may be reproducedor utilized in any form or by any means, electronic or mechanical, including photocopying andmicrofilm, without permission in writing from the publisher.International Organization for StandardizationCase postale 56 · CH-1211 Genève 20 · SwitzerlandInternetcentral@iso.chX.400c=ch; a=400net; p=iso; o=isocs; s=centralPrinted in SwitzerlandiiForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISOmember bodies). The work of preparing International Standards is normally carried out through ISO technicalcommittees. Each member body interested in a subject for which a technical committee has been established hasthe right to be represented on that committee. International organizations, governmental and non-governmental, inliaison with ISO, also take part in the work. ISO collaborates closely with the International ElectrotechnicalCommission (IEC) on all matters of electrotechnical standardization.Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.International Standard ISO 10846-1 was prepared jointly by Technical Committees ISO/TC 43, Acoustics,Subcommittee SC 1, Noise, and ISO/TC 108, Mechanical vibration and shock.Annexes A to E of this part of ISO 10846 are for information only.SIST EN ISO 10846-1:1999
© ISOISO 10846-1:1997(E)iiiIntroductionPassive vibration isolators of various kinds are used to reduce the transmission of vibrations. Examples are automobileengine mounts, elastic supports for buildings, elastic mounts and flexible shaft couplings for shipboard machinery andsmall isolators in household appliances.This part of ISO 10846 serves as an introduction and a guide to parts 2 to 5 of ISO 10846, which describelaboratory measurement methods for the determination of the most important quantities which govern thetransmission of vibrations through linear isolators, i.e. frequency-dependent dynamic stiffnesses.This part of ISO 10846 provides the theoretical background, the principles of the methods, the limitations of themethods and guidance for the selection of the most appropriate standard of the series.The laboratory conditions described in all parts of ISO 10846 include the application of static preload.The results of the methods are useful for isolators which are used to prevent low-frequency vibration problems and toattenuate structure-borne sound. The methods are not sufficiently appropriate to characterize completely isolatorswhich are used to attenuate shock excursions.SIST EN ISO 10846-1:1999
SIST EN ISO 10846-1:1999
INTERNATIONAL STANDARD
© ISOISO 10846-1:1997(E)1Acoustics and vibration — Laboratory measurement ofvibro-acoustic transfer properties of resilient elements —Part 1:Principles and guidelines1 ScopeThis part of ISO 10846 explains the principles underlying parts 2 to 5 of ISO 10846 for determining the transferproperties of vibration isolators from laboratory measurements, and provides assistance in the selection of theappropriate part of this series.This part of ISO 10846 is applicable to vibration isolators which are used to reduce:a) the transmission of audiofrequency vibrations (structure-borne sound, 20 Hz to 20 kHz) to a structure whichmay, for example, radiate fluid-borne sound (airborne, waterborne, or other);b) the transmission of low frequency vibrations (typically 1 Hz to 80 Hz) which may, for example, act upon humans orcause damage to structures when vibration is too severe.The data obtained with the measurement methods which are outlined in this part of ISO 10846 and further detailed inparts 2 to 5 of ISO 10846 can be used for:¾ product information provided by manufacturers and suppliers;¾ information during product development;¾ quality control;¾ computation of the transfer of vibrations through isolators.The conditions for the validity of the measurement methods area) linearity of the vibrational behaviour of the isolator (this includes elastic elements with non-linear static load-deflection characteristics as long as the elements show approximate linearity for vibrational behaviour for agiven static preload);b) the contact interfaces of the vibration isolator with the adjacent source and receiver structures can be consideredas point contacts.2 Normative referenceThe following standard contains provisions which, through reference in this text, constitute provisions of this part ofISO 10846. At the time of publication, the edition indicated was valid. All standards are subject to revision, and partiesto agreements based on this part of ISO 10846 are encouraged to investigate the possibility of applying the mostrecent edition of the standard indicated below. Members of ISO and IEC maintain registers of currently validInternational Standards.ISO 2041:1990, Vibration and shock — Vocabulary.SIST EN ISO 10846-1:1999
ISO 10846-1:1997(E)© ISO23 DefinitionsFor purposes of this part of ISO 10846, the definitions given in ISO 2041 and the following apply.3.1resilient element(see vibration isolator)3.2vibration isolatorisolator designed to attenuate the transmission of vibration in a frequency range [ISO 2041:1990, 2.110]3.3elastic supportvibration isolator suitable for supporting a part of the mass of a machine, a building or another type of structure3.4blocking forceFbdynamic force at the output side of a vibration isolator which results in zero displacement output3.5dynamic driving point stiffnessk1,1frequency-dependent complex ratio of the force on the input side of a vibration isolator with the output side blockedto the complex displacement on the input side during simple harmonic vibrationNOTE 1 k1,1 may depend on the static preload, temperature and other conditions.NOTE 2At low frequencies k1,1, is solely determined by elastic and dissipative forces. At higher frequencies inertial forces in theresilient element play a role as well.3.6dynamic transfer stiffnessk2,1frequency-dependent complex ratio of the force on the blocked output side of a vibration isolator to the complexdisplacement on the input side during simple harmonic vibrationNOTE 1k2,1 may depend on the static preload, temperature and other conditions.NOTE 2At low frequencies k2,1 is solely determined by elastic and dissipative forces and k2,1 = k1,1 At higher frequencies inertialforces in the resilient element play a role as well and k2,1 ¹ k1,13.7loss factor of resilient elementhfrequency-dependent ratio of the imaginary part of k2,1 to the real part of k2,1 (i.e. tangent of the phase angle of k2,1) inthe low-frequency range where inertial forces in the element are negligible3.8point contactcontact area which vibrates as the surface of a rigid body3.9linearityproperty of the dynamic behaviour of a vibration isolator if it satisfies the principle of superpositionNOTE 1The principle of superposition can be stated as follows: if an input x1(t) produces an output y1(t) and in a separate test aninput x2(t) produces an output y2(t), superposition holds if the input a x1(t) + b x2(t) produces the output a y1(t) + b y2(t). This must holdfor all values of a, b and x1(t), x2 (t); a and b are arbitrary constants.SIST EN ISO 10846-1:1999
© ISOISO 10846-1:1997(E)3NOTE 2In practice the above test for linearity is impractical and a limited check of linearity is done by measuring the dynamictransfer stiffness for a range of input levels. For a specific preload, if the dynamic transfer stiffness is nominally invariant the systemcan be considered linear. In effect this procedure checks for a proportional relationship between the response and the excitation.3.10direct methodmethod in which either the input displacement, velocity or acceleration and the blocking output force are measured3.11indirect methodmethod in which the transmissibility (for displacement, velocity or acceleration) of an isolator is measured, with theoutput loaded by a mass/effective mass3.12driving point methodmethod in which either the input displacement, velocity or acceleration and the input force are measured, with theoutput side of the vibration isolator blocked4 Selection of appropriate International StandardTable 1 provides guidance for the selection of the appropriate part of ISO 10846.Table 1 — Guidance for selectionInternational Standard and method typeISO 10846-2Direct methodISO 10846-3Indirect methodISO 10846-4Indirect methodISO 10846-5Driving pointmethodType of vibrationisolatorsupportsupportother than supportsupportExamplesresilient mountings for instruments, equipment,machinery and buildingsbellows, hoses, elasticshaft couplings, powersupply cablessee under ISO 10846-2and ISO 10846-3Frequency range1 Hz to f1f1 dependent on test rig;typically (but not limitedto) 300 Hz < f1 < 500 Hzf2 to f3f2 typically (but notlimited to) 20 Hz to50 Hz. For very stiffmountings f2 > 100 Hz.f3 typically 2 kHz to5 kHz, but dependenton the test rigf2 to f3f2 typically (but notlimited to) 20 Hz to50 Hz. For very stiffelements f2 > 100 Hz.f3 typically 2 kHz to5 kHz, but dependenton the test rig1 Hz to f4f4typically (but notlimited to) < 100 HzTranslationalcomponents1, 2 or 31, 2 or 31, 2 or 31, 2 or 3Rotationalcomponentsnoneinformative annexinformative annexnoneClassification ofmethodengineeringengineeringengineering/surveyengineering/surveyNOTE
At the low-frequency end, the direct method and the driving point method yield the same result.Further guidance is given in clauses 5 and 6.SIST EN ISO 10846-1:1999
ISO 10846-1:1997(E)© ISO45 Theoretical background5.1 Dynamic transfer stiffnessThis clause explains why the dynamic transfer stiffness is most appropriate to characterize the vibro-acoustictransfer properties of isolators for many practical applications. It also indicates briefly for which special situationsother vibro-acoustic isolator properties, of which the measurement is not covered in ISO 10846, would be needed inaddition.The dynamic transfer stiffness, as defined in 3.6, is determined by the elastic, inertia and damping properties of theisolator. The reason for choosing a presentation of test results in terms of a stiffness is the practical considerationthat it complies with data of static and/or low-frequency dynamic stiffness which are commonly used. The additionalimportance of inertial forces (i.e. elastic wave effects in the isolators) makes the dynamic transfer stiffness at highfrequencies more complex than at low frequencies. Because at low frequencies only elastic and damping forces areimportant, the low-frequency dynamic stiffness is only weakly dependent on frequency due to material properties.NOTE —
For many vibration isolators, static stiffness and low-frequency dynamic transfer stiffness are different.In principle the dynamic transfer stiffness of vibro-acoustic isolators is dependent on static preload and temperature.In the following theory linearity, as defined in 3.9, is assumed. See annex D for further information.Relationships between the dynamic transfer stiffness and other quantities are listed in annex A. These relationshipsimply that, for the actual performance of the tests, only practical considerations will determine whetherdisplacements, velocities or accelerations are measured. However, for presentation of the results in agreement withthe other parts of ISO 10846, appropriate conversions may be needed.5.2 Dynamic stiffness matrix of vibration isolators5.2.1 General conceptA familiar approach to the analysis of complex vibratory systems is the use of stiffness — compliance — ortransmission matrix concepts. The matrix elements are basically special forms of frequency-response functions;they describe linear properties of mechanical and acoustical systems. On the basis of the knowledge of theindividual subsystem properties, corresponding properties of assemblies of subsystems can be calculated. Thethree matrix forms mentioned above are interrelated and can be readily transformed amongst themselves [5].However, only stiffness-type quantities are specified in ISO 10846 for the experimental characterization of isolatorsunder static preload.The general conceptual framework for the proposed isolator characterization is shown in figure 1.Figure 1 — Block diagram of source/isolators/receiver systemThe system consists of three blocks, which respectively represent the vibration source, a number n of isolators andthe receiving structures. A point contact is assumed at each connection between source and isolator and betweenisolator and receiver. To each connection point a force vector F containing three orthogonal forces and threeorthogonal moments and a displacement vector u containing three orthogonal translational and three orthogonalrotational components are assigned. In figure 1 just one component of each of the vectors F1, u1, F2 and u2 is shown.These vectors contain 6n elements, where n denotes the number of isolators.To show that the blocked transfer stiffness, defined in 3.6 as dynamic transfer stiffness, is suitable for isolatorcharacterization in many practical cases, the discussion will proceed from the simplest case of unidirectionalvibration to the multidirectional case for a single isolator.SIST EN ISO 10846-1:1999
© ISOISO 10846-1:1997(E)55.2.2 Single isolator, single vibration directionFor unidirectional vibration of a single vibration isolator, the isolator equilibrium may be expressed by the followingstiffness equations:F1 = k1,1 u1 + k1,2 u2(1)F2 = k2,1 u1 + k2,2 u2(2)wherek1,1 and k2,2 are driving point stiffnesses when the isolator is blocked at the opposite side (i.e. u2 = 0, u1 = 0,respectively);k1,2 and k2,1 are blocked transfer stiffnesses, i.e. they denote the ratio between the force on the blocked side andthe displacement on the driven side. k1,2 = k2,1 for passive isolators, because passive linear isolators arereciprocal.Due to additional inertial forces, k1,1 and k2,2 become different at higher frequencies. At low frequencies onlyelastic and damping forces play a role, making all ki,j equal.NOTE —
These equations are for single frequencies. Fi and ui are phasors and ki,j are complex quantities.The matrix form of equations (1) and (2) isF = [k] u(3)with the dynamic stiffness matrix[]k=kkkk1,11,22,12,2éëêùûú(4)For excitation of the receiving structure via the isolatorr22k=Fu-(5)where kr denotes the dynamic driving point stiffness of the receiver. The minus sign is a consequence of theconvention adopted in figure 1.From equations (2) and (5) it follows that22,12,2r11F = k + kk u(6)Therefore, for a given source displacement u1, the force F2 depends both on the isolator driving point dynamicstiffness and on the receiver driving point dynamic stiffness. However, if |k2,2| < 0,1|kr|, then F2 approximates the so-called blocking force to within 10 %, i.e.22,blocking2,11
FF = k u»(7)Because vibration isolators are only effective between structures of relatively large dynamic stiffness on both sides ofthe isolator, equation (7) represents the intended situation at the receiver side. This forms the background for themeasuring methods of ISO 10846. Measurement of the blocked transfer stiffness (or a directly related function) for anisolator under static preload is easier than measurement of the complete stiffness matrix (or the complete transfermatrix). Moreover it forms the representative isolator characteristic under the intended circumstances.NOTE —
In cases that the condition |k2,2| << |kr| is not fulfilled, equation (6) also shows that k2,2 and kr need to be known topredict F2 for a given source displacement u1.SIST EN ISO 10846-1:1999
ISO 10846-1:1997(E)© ISO65.2.3 Single isolator, six vibration directionsIf forces and motions at each interface can be characterized by six orthogonal components (three translations, threerotations), the isolator may be described as a 12-port [11]. The matrix form of the 12 dynamic stiffness equations isequal to equation (3), where nowuF=uu, =FF1212ìíîüýþìíîüýþ(8)are the vectors of the six displacements, six angles of rotations, six forces and six moments. The 12 ´ 12 dynamicstiffness matrix may be decomposed into four 6 ´ 6 submatrices[][][][][]k=kkkk1,11,22,12,2éëêùûú(9)where[k1,1] and [k2,2] are (symmetric) matrices of the driving point stiffnesses;[k1,2] and [k2,1] are the blocked transfer stiffness matrices.Reciprocity implies that these transfer matrices equal their transpose.Again, if the receiver has relatively large driving point dynamic stiffnesses compared to the isolator, the forcesexerted on the receiver approximate the blocking forces:2,blocking2,11F = k u[]×(10)Therefore, the blocked transfer stiffnesses are appropriate quantities to characterize vibro-acoustic transfer propertiesof isolators, and also in the case of multidirectional vibration transmission.5.3 Number of relevant blocked transfer stiffnessesFor the general case the blocked transfer stiffness matrix [k2,1] of a single isolator contains 36 elements. However,structural symmetry causes most elements to be zero. The most symmetrical shapes (a circular cylinder or asquare block) have 10 non-zero elements, i.e. five different pairs (see annex B and reference [11]).In practical situations the number of elements relevant for characterization of the vibro-acoustic transfer is usuallyeven smaller than the number of non-zero elements. In many cases it will be sufficient to take into account only one,two or three diagonal elements for translation vibration, i.e. for only one vibration direction (often vertical) or for twoor three perpendicular directions (see annex C for further discussion). For these translational directions,measurement methods will be defined in parts 2 to 5 of ISO 10846.For some special technical cases, rotational degrees of freedom also play a significant role (see annex C). Althoughit is not considered as a subject for standardization in ISO 10846, reference is made in 6.3.5 to literature thatdescribes how rotational elements may be handled in the same way as the translational elements. ISO 10846-3 andISO 10846-4 have informative annexes relevant to this subject.5.4 Flanking transmissionThe model shown in figure 1 and of equations (1) to (10) is correct under the assumption that the isolators form theonly transfer path between the vibration source and the receiving structure. In practice there may be mechanical oracoustical parallel transmission paths which cause flanking transmission. For any measurement method of isolatorproperties, the possible interference of such flanking with proper measurements has to be minimized.SIST EN ISO 10846-1:1999
© ISOISO 10846-1:1997(E)75.5 Loss factorThe objective of ISO 10846 is to standardize measurements of the frequency-dependent dynamic transferstiffnesses k2,1 of resilient elements. Certain users of ISO 10846 also will be interested in the damping properties ofisolators. However, ISO 10846 does not standardize the measurement of damping properties of isolators becausethis would become overly complex. Nevertheless, in parts 2 to 5 of ISO 10846, descriptions are given of how phasedata of the complex dynamic transfer stiffness k2,1 can be optionally used to give information about the dampingproperties. The discussion in this subclause is given as background information for the procedures.For the purposes of the discussion it is sufficient to consider the case of 5.2.2, i.e. a single isolator and a singlevibration direction. Because only measurements with a blocked output side are considered in ISO 10846, thephasor equations (1) and (2) are reduced toF1 = k1,1u1(11)F2 = k2,1u1(12)At low frequencies, where inertial forces (e.g. wave effects) play no role, there is a simple relationship between thephase angle of the dynamic transfer stiffness and the damping properties of the resilient element. At these lowfrequencies, the frequency-dependent stiffness can be approximated byk » k1,1 » k2,1(13)This complex low-frequency dynamic stiffness can be written ask = k0(1+jh)(14)where k0 denotes the real part. The frequency-dependent loss factor h in equation (14) characterizes the damping ofthe resilient element at low frequencies (see 3.7).The relationship between the loss factor and the phase angle f of k is given byh = tan f(15)Therefore, the loss factor of a resilient element can be estimated according toh » tan f2,1(16)where f2,1 is the phase angle of the dynamic transfer stiffness k2,1.The following points should be kept in mind.a) The measurement of small loss factors using equation (16), is extremely sensitive to phase measurementerrors [12]. However, for rubber-type resilient elements this problem is not critical except at frequencies below afew hertz.b) For higher frequencies, where the approximations of equation (13) are no longer valid, it is no longer correct touse equation (16) as a characterization of the damping properties of the resilient element. Although there areno simple and strict criteria for when this occurs, a rather sudden change of the slope of h with increasingfrequency is usually a good indication that equation (16) can no longer be used.6 Measurement principles6.1 Dynamic transfer stiffnessThe dynamic transfer stiffness is dependent on frequency. In addition it is also dependent on static preload and, inmany cases, on temperature. Three methods are in use to obtain the appropriate test data. Because they arecomplementary with respect to their strong and weak points, they are all described in ISO 10846.SIST EN ISO 10846-1:1999
ISO 10846-1:1997(E)© ISO8The direct method requires the measurement of input displacement (velocity, acceleration) and blocking outputforce. At low frequencies, where the driving point stiffness and the transfer stiffness are equal, both force anddisplacement may be measured on the driven side of the isolator. This method is called the driving point method.The indirect method uses a measurement of vibration transmissibility (for displacement, velocity or acceleration). Toobtain the blocking output force, the isolator is terminated with a mass which provides a large dynamic stiffness. In aspecified frequency range, the product of the measured displacement and the known point dynamic stiffness of thetermination should provide a good approximation of the blocking force.The basic features of these methods and the general requirements for their proper use are described in this part ofISO 10846. Detailed requirements are specified in parts 2 to 5 of ISO 10846.6.2 Direct method6.2.1 Basic test set-upThe basic principle for the measurement of the dynamic transfer stiffness is shown in figure 2.The isolator under test is placed between a vibration exciter on the input side and a rigid termination on the outputside. A dynamic force transducer is placed between the isolator and the rigid termination. Often it will be necessaryto insert force-distribution plates. These serve to approximate point contact conditions and unidirectional motion. Forexample, in the case of a large isolator flange supported by a small force transducer only, the flange vibration andtherefore the dynamic transfer stiffness may deviate significantly from that in practice. For large isolators with a highstatic preload, stability requirements may make it necessary to measure the force with a number of forcetransducers.6.2.2 Measurement quantitiesThe dynamic quantities to be measured are the force and either the displacement, velocity or acceleration.Key1Hydraulic actuator (static preload and dynamic excitation)4Rigid foundation2Moveable traverse5Force measurement system3Columns6Test objectFigure 2 — Example of a typical test set-up for the direct methodSIST EN ISO 10846-1:1999
© ISOISO 10846-1:1997(E)96.2.3 Measurement under static preloadBecause the dynamic transfer stiffness may be heavily dependent on static load, tests should be provided undernominal static load conditions. Often special test rigs are needed to apply such loads. Combined static pre-loading andvibration is typically applied using a hydraulic actuator on top. However, test rigs with separated components for pre-loading and for vibration excitation are also considered in ISO 10846.6.2.4 Frequency limitations of the direct methodThe frequency range of validity of the direct method is mainly determined by the test rig properties. One limitation isgiven by the actuator bandwidth. Another limitation is often determined by the occurrence of flanking transmission athigh frequencies through the frame which is used to apply the static preload. The fundamental frame mode, whichusually causes serious problems, is determined by the mass of the traverse and the longitudinal stiffness of thevertical beams. A typical upper frequency of 300 Hz < f < 500 Hz is mentioned in table 1. These values are reportedby owners of test rigs with a static load capacity up to 100 kN (see reference [10]). Of course for smaller and morecompact rigs this upper limit would move to higher frequencies. For example, for small size elements with smallpreloads, very simple test set-ups may suffice, having a frequency range for valid measurements up to severalkilohertz.However, generally speaking, the indirect method (see below) gives better possibilities with respect to highfrequency measurements. The indirect method gives less flanking transmission because the test isolator isdynamically uncoupled from the load frame.6.2.5 Directions of vibrationThe direct method can be applied for translational and rotational vibration both in the normal load direction and in thetransverse directions. However, use of the direct method for rotational vibration is not considered in this part ofISO 10846.6.3 Indirect method6.3.1 Basic test arrangementThe basic principle for the measurement of blocked transfer stiffness is illustrated by the examples given in figure 3.Figure 3 — Examples of typical test set-ups for the indirect methodSIST EN ISO 10846-1:1999
ISO 10846-1:1997(E)© ISO10The isolator under test is fitted between two rigid masses.The mass on the input side of the isolator has a dual function:¾ its rigidity is used to provide point contact conditions;¾ it may also be used to obtain unidirectional excitation in different directions (see ISO 10846-3 and ISO 10846-4).The mass on the output side also has a dual function:¾ its rigidity is used for point contact conditions on the receiver side of the isolator;¾ its mass and rotational inertias should be large enough to form a high dynamic stiffness termination for allexcitation components of the isolator. Therefore, the six natural frequencies of the mass/spring system formed bycombination of the test isolator and mass m2, should be well below the frequency range of interest (see discussionbelow). The forces exerted by the isolator on the mass are then approximately equal to the blocking forces. Thesecan be derived from the accelerations of the mass on the output side.The displacements of the masses are denoted by u1 and u2. The ratio u2/u1 is usually called (displacement)transmissibility. It is equal to the corresponding velocity and acceleration ratio.The relationship between the dynamic transfer stiffness and the displacement transmissibility is found by usingNewton's law. Therefore,2,12122210(2)
for >>kFuuu ff»»-pfm(17)where f0 is the eigenfrequency of the mass/spring system formed by m2 and the test isolator [and, as in figure 3 b),by the auxiliary isolators].Equation (17) uses the assumption of equation (7), i.e. that F2 is approximately equal to the blocking force.6.3.2 Measurement quantitiesThe dynamic quantity to be measured is either the displacement, velocity or acceleration.6.3.3 Measurement under static preload6.3.3.1 Principle of applying preloadFigure 3 shows basic principles for test rigs in which a static preload can be applied.In figure 3 a) the gravity force on the mass on the output side is used for static preloading. This test set-up requireseither a vibration exciter which can withstand the static load or an auxiliary structure (e.g. vibration isolators) whichtakes the static load. This test rig principle has the danger of instability, especially for large isolators with highpreloads.In figure 3 b) a frame and an actuator (e.g. hydraulic) are used to apply the static preload. The mass m2 on theoutput side of the isolator is dynamically decoupled from the frame using auxiliary isolators. Such auxiliary iso
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