1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2013 SAE International All rights reserved. No part of this p
3、ublication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/J1637_201306 SURFACE VEHICLE RECOMMENDED PRACTICE J1637 JUN2013 Issued 1993-02 Re
5、affirmed 2013-06 Superseding J1637 AUG2007 Laboratory Measurement of the Composite Vibration Damping Properties of Materials on a Supporting Steel Bar RATIONALE This recommended practice was last updated in 2007 and is in active use. Round robin testing scheduled to begin in 2013 but a revision, if
6、necessary, will not be ready for several more years. Reaffirmation recognizes that the procedures in the practice are still in active use. 1. SCOPE This SAE Recommended Practice describes a laboratory test procedure for measuring the vibration damping performance of a system consisting of a damping
7、material bonded to a vibrating cantilevered steel bar. The bar is often called the Oberst bar (named after Dr. H. Oberst) and the test method is often called the Oberst Bar Test Method. Materials for damping treatments may include homogeneous materials, nonhomogeneous materials, or a combination of
8、homogeneous, nonhomogeneous, and/or inelastic (such as aluminum foil) materials. These materials are commonly installed in transportation systems such as ground vehicles, marine products, and aircraft to reduce vibration at resonance, and thus reduce the noise radiation from the vibrating surface. T
9、he test method described herein was developed to rank order materials for application on panels using general automotive steel but also may be applicable to other situations or conditions. Damping performance for most materials and systems varies as a function of both frequency and temperature. Acco
10、rdingly, this test procedure includes provisions for measuring damping over a range of frequencies and temperatures found applicable to many transportation systems. The measured damping performance will be expressed in terms of composite loss factor, c, within the frequency range of approximately 10
11、0 to 1000 Hz, and over the useful temperature range for the given application. The term composite refers to the steel and damping material combination. The composite loss factor is, therefore, dependent upon the thickness, damping and modulus of both the steel and damping material layer. The test pr
12、ocedure described here is based on the method described in ASTM E 756. However, this SAE document differs from the ASTM E 756 method in that the SAE practice specifies the bar material, three bar sizes, and the mounting conditions of the test samples. This document provides a means of rank ordering
13、damping materials according to their composite loss factor values from test samples that represent typical sheet metal applications. The material properties of the damping material alone, including Youngs modulus E, and the material loss factor , may be computed from the test samples specified in th
14、is document if additional conditions are met. ASTM E 756 defines these additional conditions as well as the equations to be used to compute the damping material properties for the single layer (Oberst beam) configuration. 2. REFERENCES 2.1 Applicable Publications The following publications form a pa
15、rt of this specification to the extent specified herein. The latest issue of SAE publications shall apply. 2.1.1 SAE Publication Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. SAE TSB 003 Ru
16、les for SAE Use of SI (Metric) Units 2.1.2 ANSI Publications Available from ANSI, 25 West 43rd Street, New York, NY 10036-8002, Tel: 212-642-4900, www.ansi.org. ANSI S1.1 Acoustical Terminology ANSI S2.9 Nomenclature for Specifying Damping Properties of Materials 2.1.3 ASTM Publications Available fr
17、om ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, Tel: 610-832-9585, www.astm.org. ASTM E 691 Conducting an Interlaboratory Study to Determine the Precision of a Test Method ASTM E 756 Measuring VibrationDamping Properties of Materials 2.1.4 DIN Publications Available from Deutsches
18、Institut fr Normung e.V., Burggrafenstrasse 6, 10787 Berlin, Germany, www.din.de. DIN 53 440 Testing of Plastics and Damped Laminated Systems; Bending Vibration Test Teil 1 General Rudiments of Dynamic Elastic Properties of Bars and Strips Teil 2 Determination of Complex Modulus of Elasticity Teil 3
19、 Determination of Dynamic-Elastic Values of Damped Laminated Systems 2.1.5 JASO Publication Available from Society of Automotive Engineers of Japan, 10-2, Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan, Tel: +81-3-3262-8211, www.jsae.or.jp. JASO M 329 Asphalt Sheet for Automobiles _ SAE J1637 Reaffirme
20、d JUN2013 Page 2 of 163. TEST METHOD The method is based on exciting the damped bar at various modes of vibration at a given temperature of interest, and obtaining the damping performance using the half-power bandwidth technique. In this technique, first the resonant frequency, f, at a given mode of
21、 the bar is measured. Next, the lower and upper frequencies (fland fu, respectively) are measured on the response curve on either side of the resonant frequency where the levels are 3 dB lower than the level at resonance (3 dB down points or half-power points). The difference of fuand flin this case
22、, is called the half-power bandwidth. This procedure is repeated for other modes of vibration and temperatures. The composite damping performance is given by Equation 1 (see Figure 1): cff-=(Eq. 1) where: f = fu fl= frequency bandwidth, Hz f = resonant frequency, Hz c= composite loss factor at reson
23、ant frequency, f, dimensionless 4. INSTRUMENTATION The instrumentation to be used is as follows (see Figure 2 for a schematic of a typical set-up): 4.1 A bar mounting fixture (test fixture) that is heavy, rigid, and can provide adequate force at the clamped end of the bar to simulate the cantilever
24、boundary conditions (clamped-free). ff=c FIGURE 1 - COMPOSITE DAMPING PERFORMANCE COMPUTATION _ SAE J1637 Reaffirmed JUN2013 Page 3 of 16FIGURE 2 - SCHEMATIC OF A TYPICAL TEST SET-UP FOR DAMPING PERFORMANCE EVALUATION 4.2 A temperature chamber so that the sample can be maintained at the appropriate
25、temperature. 4.3 Two transducers with associated power supplies and signal conditionersone applies the excitation force (called the excitation transducer or the exciter) and the other measures the response of the bar (called the pick-up transducer). The purpose is to measure only the damping of the
26、test sample, without any additional damping from any other effects. Therefore, the pick-up transducer used is often a non-contacting type transducer. If a contacting type transducer is used as a pick-up transducer, extreme care should be taken to ensure that the transducer does not contribute to the
27、 damping of the test sample (i.e., overdamp the test sample). The mass of the contacting type transducer shall not exceed 0.5 g. Refer to 7.2.2. The excitation transducer is generally a non-contacting type electromagnetic vibration exciter. 4.4 A signal generator that generates a sinusoidal or a ran
28、dom signal. The signal is applied to the excitation transducer by means of a power amplifier. The response of the bar will be measured using the pick-up transducer. 4.5 An analyzer or an analysis system capable of determining the transfer function between the excitation signal and the response signa
29、l. Examples include: a two-channel spectrum analyzer (e.g., based on Fast Fourier Transform algorithm) that is suitable for the signal, such as the random noise signal. Alternatively, a single channel system with separate excitation and response analysis systems can be used. However, efforts must be
30、 made to make the excitation force constant with frequency so that the response can be measured directly. The minimum amplitude precision of the measuring system should be 0.1 dB. The minimum frequency resolution of the measuring system should be 0.1 Hz. _ SAE J1637 Reaffirmed JUN2013 Page 4 of 165.
31、 TEST SAMPLE 5.1 Test Bar The test bar to be used is as follows: 5.1.1 The metal for the bare bar should be steel. Precision Ground Gage Stock (or also called Precision Ground Flat Stock) bars should be used as the Oberst bar for damping tests. Precision Ground Gage Stock bars are commercially avail
32、able (see Appendix A). Alternatively, the bare bar may be manufactured by machining a mild steel bar stock. A new bar should be used for each application. Selection of which of the three bar sizes to use should be based on the steel thickness of the intended application. Multiple Oberst beam sizes m
33、ay be tested to determine the composite loss factor variation with steel thickness. For the purpose of rank ordering damping materials in extensional layer constructions, any one of the three bar sizes is sufficient. Overdamping can occur when an excessively high damping material thickness is used o
34、n the bar. Overdamping can cause the response of the bar vibration to be reduced to a level, which cannot be used to measure the composite loss factor. The damping material thickness at which overdamping occurs is based on the given materials damping properties. If overdamping occurs, the transfer f
35、unction of the bar will be very flat and the modes will be nearly eliminated. To prevent this from occurring, a thicker bar size may be used. 5.1.2 The dimensions of the bars shall be as shown in Table 1 (also refer to Figure 3). The modes of vibration for each beam size (uncoated) can be computed t
36、heoretically. Calculated values for modes two through five for the three SAE J1637 bar types are provided in Table 2. Experience has been that measured values of mode-frequencies within 2% of the calculated values at 25 C produce repeatable test results. Figure 4 shows the typical frequency response
37、 of a bare Oberst bar. TABLE 1 - TEST BAR DIMENSIONS Bar Free Length, LT(mm) Minimum Clamping Length (mm)(1)Minimum Total Length, L (mm) Minimum Width, W (mm)(2)Thickness, H2(mm) A 200 25 225 12.7 0.8 B 216 25 241 12.7 1.0 C 254 25 279 12.7 1.6 1. The Free Length of the bar is a critical factor in d
38、etermining the frequencies of the modes of vibration. The Clamping Length of the bar is important for ensuring that the prerequisite cantilever boundary condition is present for the test. The Total Length is the sum of the Free Length and the Clamping Length. The Clamping Length value given in the t
39、able is the minimum that can be used. It has been found that longer Clamping Lengths of the bar (with corresponding longer clamps on the fixture) tend to better match the desired cantilever condition. It is recommended that a Clamping Length longer than the minimum be used if possible. A Clamping Le
40、ngth of 50 mm has been found to perform especially well. 2. Since the width of the bar is not a critical factor in determining the frequencies of the modes of vibration, the width given in the table was chosen as a minimum practical width for preparing a sample bar and obtaining good clamping condit
41、ions. Wider bars may be used if they are more convenient to obtain. However, because the bar is intended to be excited in its bending modes only, there is a limit on the width of the bar. If the bar is too wide for a given thickness, torsional modes may be excited that will complicate the damping me
42、asurement. To avoid these torsional modes, the bar width should not exceed 50 mm. Dimension Tolerances: a. Mounted free length: 0.5 mm b. Total length: 1.0 mm c. Thickness: 0.03 mm _ SAE J1637 Reaffirmed JUN2013 Page 5 of 16TABLE 2 - BARE BAR MODE FREQUENCIES (USING DENSITY OF STEEL: 7840 kg/m3, MOD
43、ULUS OF STEEL: 2.0X1011Pa) Bar f2(Hz) f3(Hz) f4(Hz) f5(Hz) A 102 286 561 927 B 110 307 601 994 C 127 355 696 1150 Mode 1 is usually not used for this measurement, primarily for the following reasons: a. The bar and the fixture both tend to vibrate as a rigid body, thereby introducing error in measur
44、ing the composite loss factor. b. The first mode is most sensitive to any error due to the static magnetic field of the transducers that may influence the vibration of the free end of the bar. FIGURE 3 - TEST SAMPLE FOR OBERST BAR NOTE 1: The damping material should not touch the clamping mechanism
45、or the test fixture. The gap (G) between the clamping device and the material should be less than or equal to 1mm. NOTE 2: If a gap is present in the test fixture clamp (Clamp Gap), it should be filled with a spacer made of the same steel thickness as used in the Oberst beam. This is done to ensure
46、a rigid clamping force on the bar. _ SAE J1637 Reaffirmed JUN2013 Page 6 of 165.1.3 Some laboratories employ a stepped increase in bar thickness (also called roots) at the clamped end of the test bars to mount the bar in a fixture. These are not required, provided proper boundary conditions can be s
47、imulated at the clamped end of the bar to represent a fixed support cantilever condition. However, note that interlaboratory and intralaboratory studies suggest that the range of the results obtained from test bars without roots is likely to vary more than that of the test bars with roots, unless proper care is taken to ensure that the free length is precise, the clamped edge is perpendicular to the face of the bar, and that the bar mounting fixture is rigid and massive. 5.2 Sample Preparation The damping material should be attached t
