1、AEROSPACE INFORMATION REPORTAIR5464Issued 2002-06Metal Clad Fibers for Electrical Shielding & Harness OverbraidFOREWORDIn August 1996 AE-8D received a request from Air Force and NavAir to study and issue a report on metal clad fibers for shielding electrical cables, harness overbraids and electrical
2、 wire conductors. At the October 1996 meeting an AE-8D Task Group was formed and meetings of this Task Group have been held twice a year since then with discussions and presentations on the properties, test results and applications of these fibers by McDonnell Douglas, Glenair, DuPont, and others. T
3、his report is a compilation of these items. It will be updated as more information becomes available.1. SCOPE:Over the past decade several metal clad fibers and fabrics have been developed to provide aerospace vehicle designers with a conductive, lighter weight alternative to coated copper or steel
4、for shielding and harness overbraids of electrical cables. Several of these candidates have been unable to provide the strength or thermal stability necessary for the aerospace environment. However, the aramid-based products have shown remarkable resistance to the rigorous environment of aerospace v
5、ehicles.Concurrent with these fiber developments, there have been changes in the structures of aerospace vehicles involving greater use of nonmetallic outer surfaces. This has resulted in a need for increased shielding of electrical cables which adds substantial weight to the vehicle. Thus, a lighte
6、r weight shielding material has become more critical to meet the performance requirements of the vehicle.This report covers the properties of metal clad aramid fibers (MCAF), test results when this product is used as a shield or harness overbraid and a listing of some of the known applications in th
7、e aerospace field. The use of these fibers as an electrical conductor is still being studied but has not yet resulted in a documented aerospace adoption.Reaffirmed 2008-03SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineer
8、ing sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be
9、reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2008 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, r
10、ecording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE AIR5464 - 2 -2. REFERENCES:Metal Clad Arami
11、d Fibers for Aircraft/Aerospace Cable Shielding by E.W. Tokarsky et al, AEISC - October 1993New Developments on Metal Clad Aramid Fibers for Aerospace Wire & Cable by E.W. Tokarsky et al, AEISC - October 1995Metal Clad Fiber for Specialty Cable Shielding and Conductor by E.W. Tokarsky et al, Wire &
12、Cable FOCUS - September 1996Case Histories of ARACON Metal Clad Aramid Fibers by E.W. Tokarsky, Wire & Cable FOCUS - September 1998Case Histories of Aerospace Wire and Cable Uses of Metal Clad Fibers in Harness Overbraids and Shielding by E.W. Tokarsky, AEISC - October 19993. TECHNICAL INFORMATION:3
13、.1 Properties:3.1.1 Thermal Stability: Metal clad aramid fibers can be rated at 200 C based upon thermal aging tests. Oven aging at 220 C for 7 days (168 hours) and 21 days (504 hours) for several samples shows an increase in DC resistance of 8% after 7 days and 14% after 21 days (see Figure 1). In
14、addition, MCAF are not cold brittle materials and have been tested to -195 C without embrittlement or change in resistance.SAE AIR5464 - 3 -FIGURE 13.1.2 Strength: Break strength of metal clad aramid fibers (MCAF) is 310,000 to 325,000 psi versus copper at 30 to 50,000 psi or steel and some high str
15、ength copper alloys up to 100,000 psi (see Figures 2 and 3).FIGURE 2SAE AIR5464 - 4 -FIGURE 33.1.3 Weight: The average specific gravity of MCAF is 3.1 but it can vary from 2.0 to 5.0, depending upon the metal thickness. The specific gravity of copper is 8.9 (see Figure 4). Cables made with MCAF shie
16、lds have demonstrated a weight savings of 20 to 60%.FIGURE 43.1.4 Flexibility: MCAF have the inherent limpness of textiles versus the stiffness of metals such as copper and steel.SAE AIR5464 - 5 -3.1.5 Flex Life: Insulated MCAF wires show an improvement of 10 to 1000 X in the Boeing flex fatigue tes
17、t (similar to test method 704 of AS7373) (see Figure 5).FIGURE 53.1.6 Conductivity: MCAF have a DC conductivity of 60 to 65% of copper, depending upon outer metal coating (silver or nickel) (see Figure 6).FIGURE 6SAE AIR5464 - 6 -3.1.7 Shielding: The shielding effectiveness of cables with MCAF is be
18、tter than copper based shields above 5 to 25 megahertz frequencies and has been used in cables up to 40 gigahertz. Due to lower conductivity, MCAF has lower shielding effectiveness at or near DC (see Figures 7 and 8).FIGURE 7SAE AIR5464 - 7 -FIGURE 83.1.8 Other Properties:1. MCAF are braidable on st
19、andard braiding machines used for either textiles or metals and can be mixed with metals when braiding.2. MCAF have been successfully tested in both crimp and soldered terminations (see Figures 9 and 10). Care should be taken when terminating with MCAF to prevent fraying of the fibers. Proper cuttin
20、g tools such as those used with aramid fibers will prevent fraying. (Reference: DuPont bulletin “Cutting of Kevlar“ - H.62647-3.)SAE AIR5464 - 8 -FIGURE 9FIGURE 10SAE AIR5464 - 9 -3.1.8 (Continued):3. Cables shielded with MCAF have passed lightning strike tests with little change in resistance (see
21、Figure 11). It should be noted that the induced voltage from lightning strike is higher with MCAF than with metal shields. This increase is proportional to the DC resistance of the cables. The increase can be partially offset by blending copper with MCAF in the shields.FIGURE 114. MCAF have passed f
22、luid resistance tests per AS4373, Method 601 with a maximum of 10% change in resistance.5. MCAF have been tested for salt fog stability per ASTM B 117 for 500 hours and show a maximum change in resistance of 10%.6. MCAF are being used in blends with copper wire for shielding to provide a balance in
23、weight savings with acceptable resistance (see Figure 12).SAE AIR5464 - 10 -FIGURE 123.1.8 (Continued):7. MCAF are being used for EMI shielding and sox where they provide high coverage but still excellent flexibility and push-back characteristics. Users have noted that MCAF shielded cables even when
24、 bent do not “window“ (braids dont open) as do some braided metal shields.8. MCAF are available in several sizes with either a silver or nickel coating and with different coating thicknesses dependent upon the intended use.9. MCAF have been tested in cables for vacuum outgassing and have passed the
25、most stringent requirements (details proprietary to user).4. TEST RESULTS:Figures 1 through 13 show data on the MCAF properties listed above.5. APPLICATIONS:Metal clad aramid fibers are being used in satellites, pilot helmet signal/power cables, military and commercial aircraft, a variety of coaxial
26、 cables and EMI sox and sleeving. Figure 13 has a listing of some of these uses.SAE AIR5464 - 11 -FIGURE 136. SUMMARY AND CONCLUSIONS:6.1 Metal clad aramid fibers have demonstrated advantages as an electrical shield in a variety of aerospace uses.6.2 MCAF can save weight in a cable or harness versus
27、 a copper wire and have demonstrated greater strength and flexibility.6.3 MCAF are also being used in blends with copper wires as an electrical shield.6.4 MCAF shields or conductors can be terminated by conventional methods.6.5 The major reasons MCAF have been selected for aerospace usage are weight
28、 savings, flexibility, flex life, ease of installation and shielding effectiveness.6.6 MCAF are more costly (20 to 200%) on a material basis when compared with commodity priced materials such as copper or steel. However, users have considered this increase to be small when compared with the total co
29、st of a final assembly or vehicle and it is offset by the property advantages of MCAF.6.7 As more data are obtained on MCAF or other metal clad fibers, this report will be updated.PREPARED UNDER THE JURISDICTION OFSAE SUBCOMMITTEE AE-8D, WIRE AND CABLE OFCOMMITTEE AE-8, AEROSPACE ELECTRICAL/ELECTRONIC DISTRIBUTION SYSTEMS
