BS 7439-1991 Method for exchange of information for the analytical assessment of shock resistance of mechanical systems《机械系统冲击阻抗的分析评估信息交换方法》.pdf

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1、BRITISH STANDARD BS7439:1991 ISO9688:1990 Method for Exchange of information for the analytical assessment of shock resistance of mechanical systemsBS7439:1991 This BritishStandard, having been prepared under the directionof the General Mechanical Engineering Standards Policy Committee, waspublished

2、 underthe authorityof the Standards Boardand comes into effect on 30April1991 BSI01-2000 The following BSI references relate to the work on this standard: Committee reference GME/21 Draft for comment89/74834 DC ISBN 0 580 19627 5 Committees responsible for this BritishStandard The preparation of thi

3、s BritishStandard was entrusted by the General Mechanical Engineering Standards Policy Committee (GME/-) to Technical Committee GME/21, upon which the following bodies were represented: Department of Trade and Industry (National Engineering Laboratory) Electricity Supply Industry in England and Wale

4、s Engineering Equipment and Materials Users Association Institute of Sound and Vibration Research Institution of Mechanical Engineers Lloyds Register of Shipping Ministry of Defence Power Generation Contractors Association (BEAMA Ltd.) Society of British Aerospace Companies Ltd. Society of Environme

5、ntal Engineers Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date CommentsBS7439:1991 BSI 01-2000 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 Scope 2 2 Normative reference 2 3 Definitions 2 4 Inform

6、ation to be supplied by the user of the analysis 4 5 Information to be furnished in a report by the person carrying out the analysis 5 6 Responsibility for design changes resulting from interpretation of an assessment 6 Publication(s) referred to Inside back coverBS7439:1991 ii BSI 01-2000 National

7、foreword This BritishStandard has been prepared under the direction of the General Mechanical Engineering Standards Policy Committee. It is identical with ISO9688:1990 “Mechanical vibration and shock Analytical methods of assessing shock resistance of mechanical systems Information exchange between

8、suppliers and users of analyses”, which was prepared by Technical Committee ISO/TC108, Mechanical vibration and shock, of the International Organization for Standardization (ISO) and in the development of which theUnited Kingdom played an active part. The Technical Committee has reviewed the provisi

9、ons of ISO2041:1990, to which reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A related BritishStandard to ISO2041 is BS3015:1976 “Glossary of terms relating to mechanical vibration and shock”. A British Standard does not purport to

10、include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding BritishStandard IEC68-2-27

11、:1987 BS2011 Environmental testing Part2.1 Ea:1988 Test Ea. Shock (Identical) ISO8568:1989 BS7347:1990 Guide for characteristics and performance of mechanical shock testing machines (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, a

12、n inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7439:1991 BSI 01-2000 1 Introduction This International Standard specifies the elements of the

13、 essential technical dialogue that must be established between a customer (who needs an analytical assessment of shock resistance) and the supplier (the person carrying out the analysis). It is intended to be a guide on what information should be exchanged between a customer and a supplier of an ass

14、essment of the shock resistance of a mechanical system (a product or human subject) where the assessment is based on computational analysis. Normally, and where practicable, the shock resistance of the equipment or structural components should be verified by shock tests. Test procedures and test per

15、formance are already covered in some fields by International Standards, such as IEC68-2-27:1987, Environmental testing Part2:Tests Test Ea and Guidance: Shock. ISO8568:1989, Mechanical shock Testing machines Characteristics and performance. Through hands-on experience, a shock test can provide engin

16、eers with insight into the mechanical response of a machine, vehicle, structure or human subject to which an impact load has been applied. Such tests enable an engineer to determine the mechanical and functional reliability of a product and of a human subject more accurately than by computation. A p

17、roduct subjected to a physical test to assess its resistance to shock usually shows greater resistance than is indicated by an assessment of its resistance based on a mathematical analysis. However, there is an increasing reliance on assessments based on numerical results obtained using computationa

18、l methods, primarily because of improvements in the methods by which computational analyses are accomplished and because their relationship with the real world is now understood better than before. Analytical methods are preferred over shock tests when shock tests are not considered possible or prac

19、tical, for example in cases where the structure or equipment for which an assessment is required is excessively large or expensive; an assessment of shock resistance is required as part of the design process and/or for the purpose of testing and improving the model used by the designer; the designer

20、 needs analytical support in deciding whether and how to test the product for which an assessment is required; the designer is seeking a basis for generalizing the results of shock tests performed on a product or class of products; or the shock resistance can be assessed adequately by using simple m

21、athematical models (for example, in shock isolation design or the layout of fastenings for shock-resistant installations). Depending upon the mechanical behaviour and complexity of the product, its functional importance relative to other parts of the system in which it will be used, and the safety r

22、equirements imposed on the product or the system of which it is a part, the analytical approach selected to assess appropriately the products shock resistance may be relatively simple or sophisticated. It may be as simple as an equivalent-static-load (g-load) analysis, or an analysis of simple model

23、s using the elastic and/or plastic deformation-energy capability of the model as a measure of the models capability to accept without failure the energy associated with a shock-pulse input. It may be as sophisticated as computational methods that make use of time history, finite elements, and analyt

24、ical modal analysis. In order to avoid misunderstandings between the customer and the supplier of an analytical assessment, many details need to be discussed and established concerning a) the mechanical properties of the product and its environment (i.e.size, weight, material, method of construction

25、 or manufacture, operating conditions, safety, shock-sensitive components, pipe connections, fasteners, etc.); b) the specification of the shock-input parameters, tolerance-limit requirements or other acceptance criteria; c) the appropriate mathematical model, the adequacy of which can be measured b

26、y the models capability for characterizing the mechanical properties of the product in terms of the least number of parameters required to yield useful results. These include the kind of force-deflection constraints (linear or non-linear, elastic or plastic, singly or in combination), the type of sy

27、stem or modal damping, the manner in which energy is propagated through the system, and the form and number of degrees of freedom of the model (lumped-parameter and finite, or continuous and infinite);BS7439:1991 2 BSI 01-2000 d) an appropriate method of analysis, frequency range of interest, and th

28、e purpose and limits of the investigation; e) the method and style of presenting the results. Sometimes the supplier is handicapped in applying his background knowledge properly because sufficient technical information is not or cannot be furnished by the customer; however, the customer should be aw

29、are of what he can expect from an analytical assessment. 1 Scope This International Standard establishes the procedures for specifying the analytical methods which can be used to assess the shock resistance of mechanical systems (products or human subjects). It provides a protocol for conducting and

30、 documenting a shock analysis and identifies the requirements of the protocol. It applies to any product or human subject for which an analytical assessment of its shock resistance is required. NOTE 1In this International Standard, unless noted otherwise, the term “product” is used to designate an e

31、ngineering artifact (for example, equipment, component, machine, vehicle or structure). NOTE 2Neither the parameters characterizing the shock environments of concern nor acceptable levels of performance are associated with specific numerical values in this International Standard. When evaluating the

32、 shock resistance of a specific product to specific shock environments and/or levels of performance, it is necessary that appropriate numerical values be assigned to these parameters; this International Standard only establishes how such an evaluation can be carried out and does not specify the nume

33、rical values that could or should be assigned in any specific instance. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All stand

34、ards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO204

35、1:1990, Vibration and shock Vocabulary. 3 Definitions For the purposes of this International Standard, the following definitions apply. Definitions taken from ISO2041 are cited as quotations. 3.1 mechanical system 1) In the field of mechanical shock, the mechanical configuration of a product, includ

36、ing all constraints and interactive parts of its environment which must be present or accounted for in order to describe adequately the mechanical behaviour of the mounted product and its components. 2) “An aggregate of matter comprising a defined configuration of mass, stiffness and damping.” ISO20

37、41:1990,1.22 3.2 shock resistance the ability of a system to withstand shock excitation, given in terms of a specified shock pulse, where the system responses do not exceed specified acceptable limits NOTE 3In quantitative terms, the shock resistance of a system is stated as the shock input values t

38、he system can accept without the responses of the system exceeding defined (quantified) acceptable limits. 3.3 (shock) performance criteria the set of system response values or other functional criteria which define the acceptable performance of a product or human subject when it is subjected to imp

39、act loading NOTE 4These response values may include stress, strain, strain rate and/or human tolerance. 3.4 modal analysis an analytical procedure by which the response characteristics of a product or human subject are established (for example stress and strain in the elements of a structure or the

40、shock resistance of a human subject) using quantitative measures of the parameters of mass, stiffness and damping assigned to each mode of a group of the lowest modes into which the model of a product or human subject is partitionedBS7439:1991 BSI 01-2000 3 3.5 spectrum “a description of a quantity

41、as a function of frequency or wavelength NOTEThe term “spectrum” may be used to signify a continuous range of components, usually wide in extent, which have some common characteristics, for example audio-frequency spectrum.” ISO2041:1990,1.56 NOTE 5In the field of mechanical shock, spectra are not g

42、iven as a function of wavelength. 3.6 mechanical shock; shock “a sudden change of force, position, velocity or acceleration that excites transient disturbance in a system NOTEThe change is normally considered sudden if it takes place in a time that is short compared with the fundamental periods of c

43、oncern.” ISO2041:1990,3.1 3.7 shock pulse “a form of shock excitation characterized by a sudden rise and/or sudden decay of a time-dependent parameter (such as motion, force, orvelocity) NOTEA descriptive mechanical term should be used, for example acceleration shock pulse.” ISO2041:1990,3.2 3.8 app

44、lied shock; shock excitation “an excitation, applied to a system, that produces a mechanical shock” ISO2041:1990,3.3 3.9 shock motion “a transient motion causing, or resulting from, a shock excitation” ISO2041:1990,3.4 3.10 impact “a single collision of one mass with a second mass” ISO2041:1990,3.5

45、3.11 impulse 1) “The integral with respect to time of a force taken over the time during which the force is applied. 2) For a constant force, the product of the force and the time during which the force is applied. NOTEIn shock usage, the time-interval is short.” ISO2041:1990,3.6 3.12 bump “a form o

46、f shock which is repeated many times for test purposes” ISO2041:1990,3.7 3.13 ideal shock pulse “a shock pulse that is described by a simple time function” ISO2041:1990,3.8 3.14 nominal shock pulse; nominal pulse “a specified shock pulse that is given with specified tolerances NOTE 1“Nominal shock p

47、ulse” is a generic term. It requires an additional modifier to make its meaning specific, for example nominal half-sine shock pulse, or nominal sawtooth shock pulse. NOTE 2The tolerances of the nominal pulse from the ideal may be expressed in terms of pulse shapes (including area), or corresponding

48、spectra.” ISO2041:1990,3.16 3.15 nominal value of a shock pulse “a specified value (for example peak value or duration) given with specified tolerances” ISO2041:1990,3.17 3.16 duration of shock pulse “the time-interval between the instant the motion rises above some stated fraction of the maximum va

49、lue and the instant it decays to this fraction NOTE 1This definition is limited to pulses of simple shape. NOTE 2For measured pulses, the “stated fraction” is usually taken as1/10. For ideal pulses, it is taken as zero.” ISO2041:1990,3.18 3.17 rise time; pulse rise time “the interval of time required for the value of the pulse to rise from some specified small fraction of the maximum value to some specified large fraction of the maximum value NOTEFor measured pulses, the “specified small fraction” is usually t