1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-14a71 Center Point of Contact: JPLa71 Submitted by: Wil HarkinsSubject: Pyrotechnic Shock Testing Practice: Subject potentially sensitive flight assemblies that contain electronic equipment or mechanical devices, as well a
2、s entire flight systems, to pyrotechnic shock (pyroshock) as part of a development, acceptance, protoflight, or qualification test program. Perform visual inspection and functional verification testing before and after each pyroshock exposure. Where feasible, perform assembly-level and system-level
3、pyroshock tests with the test article powered and operational to better detect intermittent failures.Abstract: Preferred Practice for Design & Test. Non-practice poses a higher risk of flight failure, particularly for small components near the explosive source. Subject potentially sensitive flight a
4、ssemblies that contain electronic equipment or mechanical devices, as well as entire flight systems, to pyrotechnic shock (pyroshock) as part of a development, acceptance, protoflight, or qualification test program. Perform visual inspection and functional verification testing before and after each
5、pyroshock exposure. Where feasible, perform assembly-level and system-level pyroshock tests with the test article powered and operational to better detect intermittent failures.Programs that Certify Usage: This practice has been used on the Mariner series, Viking, Voyager, Galileo and Magellan space
6、craft.Center to Contact for Information: JPLImplementation Method: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-This Lesson Learned is based on Reliability Practice number PT-TE-1408A, from NASA Technical Memorandum 4322A, Reliability Preferred Pr
7、actices for Design and Test.Benefit:Early assembly-level pyroshock testing can often reduce the impacts of design and manufacturing/assembly deficiencies upon program cost and schedule prior to system-level test. Such testing can provide a test margin over flight pyroshock conditions which cannot be
8、 achieved in system testing. Conversely, system-level shock testing can be used to verify system performance under pyroshock exposure, thus providing increased confidence in mission success and verifying the adequacy of the assembly-level tests.Implementation Method:Pyroshock testing of assemblies m
9、ay be achieved by using one of the following types of sources:a71 An explosive device Ref. 1,2,a71 Impact of one structural member (e.g., a hammer) upon another (e.g., a beam, plate, shell, or combinations thereof) Ref. 2-5, ora71 A vibration exciter or shaker programmed to generate short duration t
10、ransient motion Ref. 2,3,6,7.JPL has historically used a shaker, or a beam or plate excited by an explosive device or by hammer-type impact. The test magnitude should include a margin over maximum predicted flight conditions, which at JPL is commonly selected to be equal to 1.5 times the maximum exp
11、ected flight environment over a frequency range anticipated to encompass the critical resonant frequencies of the test article. This test condition is monitored by accelerometers located at the facility/test article interface. Usually three shocks are specified for qualification testing, or one shoc
12、k for protoflight, in each of three orthogonal directions. In most cases, the test article is electrically powered and operational, even when no power is to be applied to the hardware during the flight event.For system-level acceptance testing, the actual pyrotechnic or explosive device(s) are commo
13、nly used, with multiple firings (three at JPL) of the devices that generate the dominant shock environment(s) applied to account for firing-to-firing variations. Power-on testing is normally utilized, with the operational mode applicable to the flight pyro event monitored.Pyroshock tests nearly alwa
14、ys utilize instrumentation for the purpose of environmental evaluation or test control. Pyroshock measurements are normally made with accelerometers despite some potentially serious deficiencies. Often in the near-field (within 6 in. or 15 cm) and sometimes in the mid-field (within 2 ft or 60 cm) of
15、 the source, improperly selected accelerometers may break, hard-bottom, or saturate under pyroshock loading, or incorrectly-set signal conditioners may saturate if Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-accelerometer resonances are sufficien
16、tly excited Ref. 8-10. Such nonlinear responses will usually make the resulting data invalid over the entire spectrum.Once valid signals are acquired, routine data analysis is performed to provide the desired acceleration time histories and shock response spectrum (SRS) Ref. 11. The SRS is utilized
17、with natural frequencies usually selected to correspond to either 1/3 or 1/6 octave band center frequencies and a constant quality factor selected as Q=10. Assembly-level test control is usually specified to match the desired SRS, with additional limits placed on total shock duration. With impacting
18、 and explosive shock simulation, this SRS matching is usually performed iteratively with a dynamically similar model. With shaker shock simulation, the SRS matching is performed automatically at low levels, checked at intermediate levels, and then applied at full level.Pyrotechnic shock or pyroshock
19、 is the transient motion of structural elements, assemblies, subsystems, or systems due to explosive loading induced by the detonation of ordnance devices incorporated into or attached to the structure. Pyroshock is often characterized by its high peak acceleration (300 g- to 300 kg), high frequency
20、 content (100 Hz to 1 MHZ) and short duration (10 sec to 20 msec), which is largely dependent on the source type and strength, structural type and configuration, and especially the distance from the source to the response point of interest. For aerospace applications, explosive devices are generally
21、 used to separate structural subsystems (e.g., payloads from launch vehicles), deploy appendages (e.g., solar panels), or activate on-board operational subsystems (e.g., propellant valves) Ref. 1,2. In certain cases, the explosive loading may be accompanied by the release of stored energy due to str
22、uctural preload. Current spacecraft design often utilizes numerous explosive devices over the course of a mission.JPL has historically utilized most of the available pyrotechnic or explosive devices, which can be divided into two general categories: point sources and line sources. Point sources incl
23、ude explosive bolts, separation nuts, pin pullers and pushers, bolt and cable cutters, and certain combinations of point sources and operational hardware (e.g., pyrovalves). Line sources include flexible linear shaped charges (FLSCs), mild detonating fuses (MDFs), primer cords, and certain commercia
24、lly-available products intended to capture explosive and structural debris after separation (e.g., Super-ZipTM). Point and line sources have also been combined: V-band (Marmon) clamps use point explosive sources which may then allow the rapid release of stored strain energy from a structural preload
25、 acting along a line of contact between the two structures being separated.Because of the high frequency content, many small elements resistant to random vibration are susceptible to pyroshock induced failure. Numerous flight equipment failures have been attributed to pyroshock exposure, some result
26、ing in catastrophic mission loss Ref. 12-13. Particular examples of pyroshock induced failures include cracks and fracture in crystals, ceramics, epoxies, glass envelopes, solder joints and wire leads, seal failure, migration of contaminating particles, relay and switch chatter and transfer, and def
27、ormation of very small lightweight structural elements. On the other hand, deformation or failure of major structural elements is rare except in those regions close to the source where structural failure is intended.Provided by IHSNot for ResaleNo reproduction or networking permitted without license
28、 from IHS-,-,-If feasible, assembly-level pyroshock testing should be performed with the test article powered and operational, even when no power is to be applied to the hardware during the flight event, to improve the detection of intermittent failures which might not otherwise be detected until mu
29、ch later in the test program or in flight. Certain hardware can be expected to malfunction during pyroshock exposure but will resume operation within tolerance after the event.Analytical methods and computational procedures have historically been inapplicable to pyroshock prediction. Thus, pyroshock
30、 is considered to be an experimental art Ref. 4,5,7.References:1. Kalbfleisch, K.C., “Review of Pyro-Shock Generating Devices and Source Levels“, IES Pyrotechnic Shock Tutorial Program, 31st ATM, Institute of Environmental Sciences, Apr.-May 1985.2. Powers, D.R., “Pyro Shock Test Simulation Methods“
31、, IES Pyrotechnic Shock Tutorial Program, 31st ATM, Institute of Environmental Sciences, April-May 1985.3. Powers, D.R., “Summary of Testing Techniques“, Shock and Vibration Bulletin, No. 56, Pt. 3, pp 135-142, August 1986.4. Davie, N.T., and Bateman, V.I., “Pyroshock Testing“, Shock and Vibration H
32、andbook (C.M. Harris, Ed.), 4th ed., Ch. 26, Pt II, McGraw-Hill, NY, 19965. Bateman, V.I., and Davie, N.T., “Recommended Practice for Pyroschock“, Proceedings of the 41st ATM, Institute of Environmental Sciences, pp 208-216, April-May 1995.6. Luhrs, H.N., “Equipment Sensitivity to Pyrotechnic Shock“
33、, Proceedings of the 22nd ATM, Institute of Environmental Sciences, pp 3-4, April 1976.7. Zimmerman, R.M., “Pyroshock Bibliography“, Proc. 39th ATM, Institute of Environmental Sciences, Vol.2, pp 471-479, May 1993.8. Himelblau, H., Piersol, A.G., Wise, J.H., and Grundvig, M.R., “Handbook for Dynamic
34、 Data Acquisition and Analysis“, IES-RP-DTE012.1, App. A, Institute of Environmental Sciences, Mt. Prospect, IL, March 1994.9. Piersol, A.G., “Recommendations for the Acquisition and Analysis of Pryoshock Data“, Sound and Vibration, Vol. 26, No.4, pp 18-21, April 199210. Piersol, A.G., “Pyroshock Re
35、commendations in Proposed MIL-HDBK on Guidelines for Dynamic Data Acquisition and Analysis“, Journal of the Institute of Environmental Sciences, Vol. XXXV, No. 5, pp21-26, Sept-Oct. 1992.11. Ref. 8, Sec. 5.12. Moening, C.J., “Pryotechnic Shock Flight Failures“, IES Pryotechnic Shock Tutorial Program
36、, 31st ATM, Institute of Environmental Sciences, April-May 1985.13. Moening, C.J., “Views of the World of Pyrotechnic Shock“, Shock and Vibration Bulletin, No. 56, Pt. 3, pp 3-28, August 1986.14. “Powered-On Vibration,“ Reliability Preferred Practice No. PT-TE-1405.Impact of Non-Practice: Provided b
37、y IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Nonpractice poses a higher risk of flight failure, particularly for small components near the explosive source.Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-04-14a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
