519.8-33 information required

519.8-3 CONCLUSION

It is generally unusual to have an SRS estimate for a gunfire event without the accompanying measurement time history, however, if this is the case Procedure II must be applied. In all cases where measurement time history trace information is available Procedure I must be applied. When an ensemble of SRS estimates are available from multiple independent gunfiring events a certain degree of statistical processing may be introduced via enveloping of the set of SRS estimates or even in detail modeling each SRS with an SRS beat generation form of deterministic time history.

MIL-STD-810H METHOD 519.8 ANNEX C

3.1 Pretest

The following information is required to conduct a gunfire test for a significant gunfire shock environment. (In this section SESA is assumed, however obtain the same pretest information if MEMA testing is required, and Method 527.2 MEMA is substituted for Method 525.2 SESA. In addition, if the gunfire environment is benign non-transient vibration, see Method 514.8 for SESA or Method 527.2 for MEMA spectrum control.).

• a. General. Information listed in Part One, paragraphs 5.7, 5.8, and 5.9; and Annex A, Task 405 of this Standard.
• b. Specific to this Method.
• (1) Knowledge of the test fixture, test item, and combined test fixture/test item modal frequencies, and their relationship to the gunfire rate. Ideally, this would consist of an experimental modal survey for the test configuration including fixturing. If this is not practical, a supporting analytical assessment of the modal characteristics of the test configuration needs to be developed and interpreted by a trained analyst.
• (2) Gunfire environment according to the gunfire schedule defining the number of individual firing events. Either:
• (a) Measured time traces that are input directly as compensated waveforms into an exciter system under TWR control Method 525.2 (SESA) (Method 527.2 MEMA) for Procedure I.
• (b) Time traces generated based on SRS reference criteria as compensated waveforms into an exciter system under TWR control Method 525.2 (SESA) (Method 527.2 MEMA) for Procedure II.
• (c) Measured gun/materiel mechanical and geometrical parameters that have been specified, and predicted SOR spectrum derived. The predicted SOR form of spectrum is then used to generate a repetitive shock time trace input to the materiel at the gunfire rate.
• (3) Techniques used in the processing of the input, and the materiel response data including means of satisfying the prescribed tolerance limits.
• (4) An analog anti-alias filter configuration will be used that will:
• (a) Not alias more than a 5 percent measurement error into the frequency band of interest.
• (b) Have linear phase-shift characteristics in the data passband.
• (c) Have a passband uniform to within one dB across the frequency band of interest (see paragraph 4.3).
• (5) In subsequent processing of the data, use any additional filtering that is compatible with the anti-alias analog filtering. In particular, additional digital filtering must maintain phase linearity for processing gunfire time traces for Procedure I. In checking for test tolerance satisfaction, use the principles outlined in Method 525.2 - in particular, bandpass filter the control time trace to the bandwidth of the reference time trace or, alternatively, match the bandpass filter characteristics of the control time trace to the measured time trace.
• (6) Generally, there are three bandwidths of concern: (1) the field measured time trace bandwidth based upon the instrumentation signal conditioning configuration, (2) the reference time trace to be used in testing (5 Hz to 2kHz), and (3) the measured control time trace from the test that may have energy exceeding 2kHz. Test tolerance procedures must compare common bandwidth information. Common bandwidths may be established by digital filtering between either (1) the field measured time trace and the measured test control time trace, or (2) the test reference time trace and the bandlimited control time trace. The procedures for establishing common bandwidths are provided in Method 525.2.
• (7) For all Procedures, the measured or generated time history trace should be over-sampled by a factor of 10. Ideally, for 2 kHz data, a sample rate of 20,480 (with a linear phase anti-alias filter set at

3.2 During Test

Collect the following information during conduct of the gunfire test for a significant gunfire shock environment. (In this section SESA is assumed, however obtain the same test information if MEMA testing is required and Method 527.2 MEMA (TWR) is substituted for Method 525.2 SESA. In addition, if the gunfire environment is benign and non-transient vibration, see Method 514.8 for SESA, or Method 527.2 for MEMA spectrum control).

• a. General. Information in Part One, paragraph 5.10; and in Part One, Annex A, Task 405 and 406 of this Standard.
• b. Specific to this Method. Information related to failure criteria. Other environmental conditions at which testing is to be carried out if other than at standard laboratory conditions, and the specific features of the test assembly (exciter, fixture, interface connections, etc.). For test validation purposes, record achieved test parameters, deviations from pre-test procedures including parameter levels, any procedural anomalies, and any test failures. Save in digital form the reference, control, and monitoring acceleration time traces for post-test processing, including test tolerance verification, under the guidelines provided in Method 525.2.

3.3 Post-Test

The following post test data shall be included in the test report. (In this section SESA is assumed; however, obtain the same pretest information if MEMA testing is required, and Method 527.2 MEMA TWR is substituted for Method 525.2 SESA. In addition, if the gunfire environment is benign and non-transient vibration, see Method 514.8 for SESA or Method 527.2 for MEMA spectrum control).

• a. General. Information listed in Part One, paragraph. 5.13; and in Annex A, Task 406 of this Standard.
• b. Specific to this Method.
• (1) Duration of each exposure and number of exposures.
• (2) Functional and physical integrity of the test item after each test based upon operational testing and visual examination.
• (3) Reference, control, and monitor time traces along with the information processed from these time traces to ensure test tolerances were met in the course of testing (see Method 525.2).
• (4) Results of operational checks.
• (5) Test item and/or fixture modal analysis data.