1、MIL-HDBK-78b ND 7779770 0037875 7 1 OLiUUtit 1- MILITARY STANDARDIZATION HANDBOOK FIELD ASSURANCE OF ACOUSTIC EMISSION SYSTEM OPERATION USING SIMULATED ACOUSTIC EMISSION EVENTS rdo DELIVERABLE DATA REQUIRED BY THIS DOCUMENT I AMSC NtA DISTRlBUTI9N STATEMENT A Approved for public redease; distributio
2、n urdirnited. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-786 ND 7979970 0037876 O m DEPAHTMENT OF DEPENCE WASHINGTON, D.C. 20301 MIL.-HDBK -786 F,-”LD ASSURANCE OF ACOUSTIC EMISSION SYSTEM OPERATION U3ING SIMULATED ACOUSTIC EMISSION EVE
3、NTS 1. This standardization handbook was developed by the Department of Defense with the assistance of the U.S Army Materials Technology Laboratory and under a contract with Physical Acoustics Corporation. It is approved for use by cil1 departments and agencies of the Department of Defense. 2. Benef
4、icial comments (recommendations, addiicns, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Director, US Army LaboTatory Commnnd, Materials Technology Laboratory, ATTN: SLCMT-MSE, Watertown, MA 02172-0001 by using the Standardization Document I
5、mprovement Proposal (DD Form 1426) appearing at the end of this document or by letter. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-7b ND m 7777770 0037877 2 m The use of acoustic emission testing and monitoring is growing rapidly. Bemuse
6、 acoustic emission testing is carried out with complex, often L.praputerized, electronic equipment it is important to verify the proper functioning and setup of the equipment during a field teat. This handbook has been developed to assist Department cf 3efenae Personnel in determLning that the acous
7、tic emission equipment functions properly upon arrival at the field test site, that the sensors are coupled efficiently to the test structure, that neither the acoustic emission system or the sensors underwent a performance degradation during the test, and that similar sensitivity levels exist betwe
8、en channels prior to the start of the test. iii Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-786 ND m 9999970 0039878 4 m I klLu-,LsA.JI- . ve CONTENTS Paragraph 1 . SCOPE 1.1 Purpose 1.2 Method. 1.3 Terminology 2.0 REFERENCED DOCUMENTS .
9、 2.1 Government documents 2.1.1 Specifications. standards and handbooks 2.2 Other publications . 3.0 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.3 393.1 3.5.2 3.3.3 4 . 4.1 Figure 1 VERIFICATION PROCZDURE. . Mounting of sensors Mounting method Structure preparation . Couplant/bon
10、ding agent selection Couplant/bonding agent application . Sensor spacing consideration Generating acoustic emission Pencil requirement8 Lead length Breaking of pencil lead Technique verification . System operation verification . Detecting performance degradation . Verifying sensor coupling . Adjusti
11、ng channel sensitivity . NOTES Subject term (key word) listing FIGURES (a) Neilson-shoe on Hsu Pencil Source. (b) Neilsen Shoe. . Page 1 1 1 1 3 3 3 3 3 3 3 3 4 4 4 4 4 4 5 5 7 7 8 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-78b ND 99999
12、70 0039879 b = 1. SCOPE 1.1 Purpose. This handbook provides R procedure for assuring the proper operatlon of an acoustic emission system installed on a field test article. This f-.mdbook allows the user: 1. to insure that no degradation of performance has occurred from the laboratory sensor/system c
13、alibration upon arrival at the test site; 2. to check for proper sensor installation and coupling to the test article before the test; 3. to provide a method for adjusting all system channels to similar sensitivity levels prior to testing; and 4. to detect any performance changes during the test due
14、 to electronic malfunctions or sensor coupling problems. 1.2 Method. This handbook relies on the Hsu Pencil Source to provide repeatable simulated acoustic emission events. Full details on the procedure to be followed for the proper use of the Hsu Pencil Source are embodied in 3.2 of this handbook.
15、I 1.3 Terminology. Definitions for many terms u8ed in this handbook are contained in MIL-STD-1945. 1 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-786 ND = 9997770 0039880 2 W 2. REFERENCED DOCUMENTS 2.1 Government documents. 2.1.1 Specifi
16、cations, standards, and handbooks. The following specifications, standards, and handbooks form a part of this handbook to the extent specified herein. Unless otherwise specified, the issues of these documents shall be those listed in the issue of the Department of Defense Index of Specifications and
17、 Standards (DODISS) and supplement thereto, cited in the solicitation. ST ANDARDS MILITARY MIL-STD-1945 - Glossary of Terms and Definitions for Acoustic Emission Testing Procedures (Copies of specifications, standards, handbooks, drawings, publications, and other Government documents required by con
18、tractors in connection with specific acquisition functions should be obtained from the contracting activity or as directed by the contracting activity.) 2.2 Other publications. The following document(s) form a part of this handbook to the extent specified herein. Unless otherwise specified, the issu
19、es of the documents which are DOD adopted shall be those listed in the issue of the DODISS specified in the solicitation. Unless otherwise specified, the issues of documents not listed in the DODISS shall be the issue of the non-government documents which is current on the date of the solicitation.
20、AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) ASTM E650 - Mounting Piezoelectric Acoustic Emission Contact Sensors ASTM J3”50 - Standard Practice for Measuring the Operating characteristics ASTM E975 ASTM E1106 - Primary Calibration of Acoustic Emission Sensors of Acoustic Emission Instrumentati
21、on - Guide for Determining the Reproducibility of Acoustic Emission Sensor Reaponse (Application for copies should be addressed to the American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103.) 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without
22、 license from IHS-,-,-I MIL-HDBK-786 ND m 9977970 0039L 4 3. VHRIFICATION PROCEDURE 3.1 Mounting of sensors. Sensors should be mounted as prescribed in the testing procedure. In the absence of specific mounting instructions, the guidelines described in ASTM N650 should be followed. The following are
23、 important considerations in the mounting of acoustic emission sensors. 3.1.1 Mounting method. The mounting method has the purpose of holding the sensor on the structure in a fixed position and ensuring that the acoustic coupling between the sensor and the structure is adequate and constant. Compres
24、sional methods (using springs, torqued-screw threads, magnets, tape, or elastic bands) in conjunction with an acoustic couplant are one means of mounting sensors. couplant) forms another means. Bonding (using a suitable adhesive which acts as a 3.1.2 Structure preparation. Contacting surfaces should
25、 be cleaned and mechanically prepared in a manner compatible with the materials of the structure and the sensor. Possible losses in acoustic energy transmission caused by paint, encapsulants, loose mill scale, weld spatter, oxides, and surface curvature at the sensor/structure contact area must be c
26、onsidered. 3.1.3 Couplant/bonding agent selection. The couplant/bonding agent selection has both environmental and acoustic aspects. From the environmental standpoint the couplant should be chemically compatible with the sensor and structure, should not cause corrosion, should be removable from the
27、surface after testing, and should be stable with respect to the temperatures, pressures, gases or liquids, and surface deformations present during the acoustic emission test. From an acoustic standpoint the couplant must wet the surfaces of both the sensor and the structure, and should have suitable
28、 viscosity for transmitting the type of wave motion of interest. Ideally, the acoustic impedance (defined as the density of the material times the wave speed in the material) of the couplant should be halfway between the acoustic impedance of the structure and the acoustic impedance of the wearplate
29、 of the sensor. epoxy glue. Typical couplant/bonding agents include silicon vacuum grease and Double-sided adhesive tape is not recommended. 3.1.4 Couplant/bonding agent application. The effective sensitivity of the sensor can be adversely changed if too thick a couplant layer ia used, if voids exis
30、t in the couplant, or if the couplant layer is tapered. method for applying couplant is to place a small amount in the center of the sensor face, then carefully press the sensor onto the structure surface, spreading the cou7lant uniformly from the center to the outside of the sensor face. A useful 3
31、.1.5 Sensor spacing consideration. Materials attenuate acoustic waves. If sensors are too far apart it is possible that acoustic erission events of significince will not be detected. 3.2 Generating acoustic emission. Many different methods of generating simulated acoustic emission events exist. Repe
32、atable acoustic emis8ion event8 will be generated for the purpose of this handbook using the Hsu pencil source. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-_ MIL-HDBK-78b ND W 9999970 0039882 b = 3.2.1 Pencil requirements. The Hsu penc!l source c
33、onsists of a mechanical pencil using 0.5 mm or 0.3 mm diameter 2H hardness lead. (Pencils and lead manufactured by Pente1 or its equivalent have been found satisfactory for this purpose). Figure 1, to ensure consistent lend breakage. The use of 0.5 mm diameter lead is recommended but 0.3 mm diameter
34、 lead may be used instead if an oscilloscope record shows saturation of the system electronics has occurred when the lead is broken on the face of the sensor. Whichever diameter lead is chosen, it must be used consistently during both the laboratory and field procedures described in 3.3.1 through 3.
35、3.3. The pencil must be equipped with a Nielsen guide ring, shown in 3.2.2 Lead length. The lead is extended between 2 and 3 mm from the end of the Hsu pencil source, as shown in Figure 1. After some experimentation, it will be found that a specific number of llclickst of the pencil will produce a c
36、onsistent and proper lead length. 3.2.3 Breaking of pencil lead. The Hsu pencil source must be placed on the surface of the structure, resting on the end of the lead and the flange of the Nielsen guide ring, as shown in Figure 1 and in ASTM E976. The Hsu pencil source must be held such that the lead
37、 touches an imaginary line drawn between the sensor under test and the Nielsen guide ring surface contact point, with the lead lying between the sensor and the Nielsen guide ring. Gently tilt the Hsu pencil source upwards, pivoting on the Nielsen guide ring, until the lead breaks. Care should be tak
38、en so that the ti? of Nielsen guide ring does not hit the structure surface, nor that the contact point of the Nielsen guide ring scrapes along the structure surface. 3.2.4 Technique verificatiou means that the average test procedure specified threshold will be used. To perform channel sensitivity a
39、djustment, repeat the procedure outlined in 3.3.2 several times, but use only the count parameter (even if the system - can perform amplitude measurements). individual cliannel thresholds as needed to make Dave - 3x = O. Note - Under - no circumstances should individual channel thresholds be changed
40、 more than 3 dB (a factor of 1.41 upwards and 0.71 downwards if thresholds are measured in volts) from their original settings of Tx - return all thresholds to Tx and nbandon the procedures of this paragraph if more change is necessary. Channel sensitivities are truly identical when all channels hav
41、e Dx count At the end of each repetition of the procedure, adjust Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-78b ND U 7999970 0039884 T = Fl L-HObk-/WJ values equal to Dave, but it will usually be necessary to compromise somewhat and co
42、nsider channels identical when a Dx count value is within 1% of Dave. Remember to return each channels threshold to its original value of Tx following the conclusion of the acoustic emission test, so as to obtain valid measurements for the post-test sensor coupling check as described in 3.3.2. Provi
43、ded by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I 1 MIL-HDBK-78b ND 7779770 0037885 I m 4. NOTES 3 4.1 Subject term (key word) listing. Acoustic Emission Field Calibration of Acoustic Emission Systems Custodians Army - MR Navy - AS Air Force - 20 Review a
44、ctivities: Army - AT, AV (WP# I.D.O194B/Disk 0520A. (FOR MTL USE ONLY) Preparing activity: Army - MR Project NDTI-0150 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-7b ND 9999970 0039b 3 MIL-HDUK-786 OUIOE RIMO LEA0 GUIO A Tun LEHJTH 3-n D
45、IA. .Lmm HARO. 2H (ti) Niclson-Shw on Iisu lcncil Sourcc GUiCE RING TEFLON OItAEHJIOf43 OIVEW IM mm TOLEnAHCES 2 O. lmm PTGUPF 1. (a) (b) Conatruction detailR for the Neleon Shoe. (After ASTU E97d. Contact points 01: eitructure surface prior to Ereeking lee$. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
