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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 therefr
2、om, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. QUESTIONS REGARDING THIS DOCUMENT: (412) 772-8512 FAX: (412) 776-0243 TO PLACE A DOCU
3、MENT ORDER; (412) 776-4970 FAX: (412) 776-0790 SAE WEB ADDRESS http:/www.sae.org Copyright 1993 Society of Automotive Engineers, Inc. All rights reserved.Printed in U.S.A. SURFACE VEHICLE 400 Commonwealth Drive, Warrendale, PA 15096-0001 RECOMMENDED PRACTICE An American National Standard J1637 ISSUE
4、D FEB93 Issued1993-02-01 LABORATORY MEASUREMENT OF THE COMPOSITE VIBRATION DAMPING PROPERTIES OF MATERIALS ON A SUPPORTING STEEL BAR ForewordThis Document has not changed other than to put it into the new SAE Technical Standards Board Format. 1.ScopeThis SAE Recommended Practice describes a laborato
5、ry test procedure for measuring the vibration damping performance of a system consisting of a damping 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 fo
6、r damping treatments may include homogeneous materials, nonhomogeneous materials, or a combination of 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 aircra
7、ft to reduce vibration at resonance, and thus reduce the noise radiation from the vibrating surface. However, the test method described herein was developed to rank order materials used in PASSENGER VEHICLE APPLICATIONS with steel sheet metal and may not be fully applicable to other situations. Damp
8、ing performance for most materials and systems varies as a function of both frequency and temperature. Accordingly, this test procedure includes provisions for measuring damping over a range of frequencies and temperatures found applicable to many transportation systems. The measured damping perform
9、ance will be expressed in terms of composite loss factor, c, within the frequency range of approximately 100 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 test procedure described here is base
10、d 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, the bar size, and the mounting conditions of the test samples. This document provides a means of rank ordering damping materials according to th
11、eir composite loss factor values from test samples that represent typical passenger vehicle applications. The ASTM E 756 should be followed to determine the damping properties of materials alone, including loss factor , Youngs modulus E, and shear modulus G. SAE J1637 Issued FEB93 -2- 2.References 2
12、.1Applicable PublicationsThe following publications form a part of this specification to the extent specified herein. The latest issue of SAE publications shall apply. 2.1.1SAE PUBLICATIONAvailable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. SAE TSB 003Rules for SAE Use of SI (Metri
13、c) Units 2.1.2ANSI PUBLICATIONSAvailable from ANSI, 11 West 42nd Street, New York, NY 10036-8002. ANSI S1.1Acoustical Terminology ANSI S2.9Nomenclature for Specifying Damping Properties of Materials 2.1.3ASTM PUBLICATIONSAvailable from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. A
14、STM E 691Conducting an Interlaboratory Study to Determine the Precision of a Test Method ASTM E 756Measuring VibrationDamping Properties of Materials 2.1.4DIN PUBLICATIONSAvailable from DIN Deutsches Institute fur Normung, Burggrafengstrasse 6, Postfach 1107, D-1000 Berlin 30 Germany. DIN 53 440Test
15、ing of Plastics and Damped Laminated Systems; Bending Vibration Test Teil 1General Rudiments of Dynamic Elastic Properties of Bars and Strips Teil 2Determination of Complex Modulus of Elasticity Teil 3Determination of Dynamic-Elastic Values of Damped Laminated Systems 2.1.5JASO PUBLICATIONAvailable
16、from The Society of Automotive Engineers of Japan, Inc., 10-2, Goban-cho, Chiyoda-ku, Tokyo 102, Japan. JASO M 329Asphalt Sheet for Automobiles 3.Test MethodThe method is based on exciting the damped bar at various modes of vibration at a given temperature of interest, and obtaining the damping perf
17、ormance using the half-power bandwidth technique. In this technique, first the resonant frequency, f, at a given mode of the bar is measured. Next, the lower and upper frequencies (fl and fu, respectively) are measured on the response curve on either side of the resonant frequency where the levels a
18、re 3 dB lower than the level at resonance (3 dB down points or half-power points). The difference of fu and fl in this case, 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 Fig
19、ure 1: (Eq. 1) where: f = fu fl = frequency bandwidth, Hz f = resonant frequency, Hz c = composite loss factor at resonant frequency, f, dimensionless c f f -= SAE J1637 Issued FEB93 -3- 4.InstrumentationThe instrumentation to be used is as follows (see Figure 2 for a schematic of a typical set- up)
20、: 4.1A 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 boundary conditions (clamped-free). FIGURE 1COMPOSITE DAMPING PERFORMANCE COMPUTATION SAE J1637 Issued FEB93 -4- FIGURE 2SCHEMATIC OF A TYPICAL TES
21、T SET-UP FOR DAMPING PERFORMANCE EVALUATION 4.2A temperature chamber so that the sample can be maintained at the appropriate temperature. 4.3Two transducers with associated power supplies and signal conditionersone applies the excitation force (called the excitation transducer or the exciter) and th
22、e other measures the response of the bar (called the pick- up transducer). The purpose is to measure only the damping of the test sample, without any additional damping from any other effects. Therefore, it is preferable that the pick-up transducer be a noncontacting type transducer. If a contacting
23、 type transducer is used as a pick-up transducer, extreme care should be taken to ensure that the transducer does not contribute to the damping of the test sample (i.e., overdamp the test sample). Refer to 7.2.2. The excitation transducer is generally a noncontacting type electromagnetic vibration e
24、xciter. SAE J1637 Issued FEB93 -5- 4.4A signal generator that generates a sinusoidal or a random 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. 4.5An analyzer or an analysis system capab
25、le of determining the transfer function between the excitation signal and the response signal. 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
26、with separate excitation and response analysis systems can be used. However, efforts must be 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 resolu
27、tion of the measuring system should be 0.1 Hz. 5.Test Sample 5.1Test BarThe test bar to be used is as follows: 5.1.1The 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
28、Ground Gage Stock bars are commercially available. Alternatively, the bare bar may be manufactured by machining a mild steel bar stock. A new bar should be used for each application. 5.1.2The dimensions of the bar should be as follows (refer to Figure 3): a.Mounted free length: 200 mm 0.5 mm b.Total
29、 length: 225 mm c.Thickness: 0.8 mm 0.03 mm d.Width: 12.7 mm 0.03 mm (Precision ground gage stock steel bars are commercially available at various lengths with 0.8 mm thickness and 12.7 mm width. Should the bars be manufactured by machining a mild steel bar stock, precautions should be taken to ensu
30、re that the two faces of the bar are parallel to each other and that the edges and the ends are square with the face of the bar.) The modes of vibration of this size cantilevered steel bar (i.e., with free length of 200 mm) at 25 C are generally calculated as follows: SAE J1637 Issued FEB93 -6- FIGU
31、RE 3TEST SAMPLE FOR OBERST BAR SAE J1637 Issued FEB93 -7- 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 of a bare Oberst bar. Mode 1 is usually not used for this m
32、easurement, primarily for the following reasons: a.The bar and the fixture both tend to vibrate as a rigid body, thereby introducing error in measuring 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 th
33、e vibration of the free end of the bar. 5.1.3Some 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 simulated at the clamped end of the bar
34、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 f
35、ree length is precise, the clamped edge is perpendicular to the face of the bar, and that the bar mounting fixture is rigid and massive. 5.2Sample PreparationThe damping material should be attached to one side of the bar simulating the damping treatment in its intended application (refer to Figure 3
36、). The test sample should have material of uniform thickness and be flush with the edges and the free end of the bar, and of the same length as that of the free length of the bar. Other mounting conditions are explained in 6.1. The material should be applied using the manufacturers recommended bondi
37、ng method to simulate intended applications. Note that the bonding method (i.e., the adhesive layer or other bonding elements) will affect the damping performance in the laboratory tests as well as in the actual application. The preparation of the heat bondable test samples are specially critical, a
38、s some materials may shrink and some materials may expand during the heat bonding process. 6.Procedure 6.1Securely clamp the test sample in the test fixture to provide a sufficiently rigid mounting to simulate a cantilever bar condition. The test sample shall be mounted in the fixture with a free le
39、ngth of 200 mm and ensuring that the clamped edge is perpendicular to the face of the bar. The damping material should not touch the clamping mechanism or anything else associated with the test fixture. The gap between the clamping device and the edge of the damping material should be less than or e
40、qual to 1 mm, and yet maintain the tolerance of the mounted free length as mentioned in 5.1.2. TABLE 1(USING DENSITY OF STEEL: 7840 KG/M3 MODULUS OF STEEL: 2.0 X 1011 PA) ModeResonant Frequency (Hz) 2102 3286 4561 5927 SAE J1637 Issued FEB93 -8- FIGURE 4TYPICAL FREQUENCY RESPONSE OF A BARE BAR It is
41、 important to position the transducers at appropriate locations to obtain the best dynamic response and the optimal signal to noise ratio of the vibrating test sample. Generally, the transducers are located close to the clamped end of the bar and close to the free end of the bar. (The exciter and th
42、e pick-up transducers should be at least sufficient distance apart to reduce “cross-talk“ effects between the two transducers. Cross-talk can be verified by removing the sample bar.) This will permit correct measurement of the damping performance. For noncontacting type transducers, the transducers
43、may require positioning within 1 mm of the test sample. 6.2Place the test fixture inside a temperature chamber so the damping performance can be evaluated at different temperatures. The temperature in the chamber may vary considerably depending on where the temperature is measured. Therefore, the te
44、mperature shall be monitored close to the test sample. This requirement is best fulfilled by monitoring the temperature on a separate bare steel bar located very close to, but not touching the test sample. Once the separate bare bar has reached the test temperature, allow the sample to soak at that
45、temperature for at least 20 min to ensure that the test sample temperature has stabilized and is uniform everywhere in the sample. It is recommended that the damping performance be measured at 20 C, 5 C, 10 C, 25 C, 40 C, and 55C for materials that are formulated to be used in this temperature range
46、. Measurements shall be conducted at other temperature ranges should that be dictated by the usage. Measurements needed at a room temperature should be conducted at 25 C. All measurements should be conducted within 1 C of the nominal test temperature. SAE J1637 Issued FEB93 -9- 6.3Excite the test sa
47、mple at each mode of vibration using the excitation transducer. Measure the response of the bar using the pick-up transducer. Measurements can be made using either random or sinusoidal signals. The input signal should be adjusted such that the peak at each resonance frequency is distinct, and that t
48、he output signal is at least 10 dB higher than the “background noise.“ 6.4Measure the resonant frequency, the half-power bandwidth (3 dB down points) and then compute the composite loss factor as described in Section 3. Damping measurements should be made starting from the second mode of vibration f
49、or reasons explained in 5.1.2. 6.5If the 3 dB down points on either side of the resonant frequency are not measurable for various reasons (such as high damping performance), an “n dB“ down point technique can be implemented using Equation 2: (Eq. 2) where: x = 10n/20 n = “n dB“ down point fn = frequency bandwidth for “n dB“ down point, Hz 6.6The “n dB down point“ technique should not be used if n is less than or equal to 0.5 dB. In such cases, or if the composite loss factor could not be computed for other reasons (such as double