514.8-55 analysis of results

514.8-5 DATA REQUIRED

Care must be taken when recording data to ensure that it can be correlated with data taken during previous tests of the same type of vehicle. Parameters such as sampling rate and filtering will affect the ability to compare/combine environments during analysis. The analysis filter bandwidth is particularly important and must be recorded. Comparing/combining different data sets must be done using the same analysis filter bandwidth. Obtain the following:

• a. An accurate log of accelerometer locations and axis orientations.
• b. An accurate log of test courses and speeds.
• c. Recorded data in terms of acceleration amplitudes versus time for time intervals sufficient to ensure accurate analysis.
• d. Graphic representation of the cargo load/installed equipment mounting configuration.
• e. Filter type and cut-off frequency and data sampling rates.

After the data have been acquired it is necessary to insure that the data accurately represent the physical phenomenon that was measured. This can be accomplished by inspecting the data visually and by performing amplitude distributions and other time and frequency domain statistical analysis. There are certain anomalies that need to be identified and corrected before the data can be considered valid. These include but are not limited to outliers (wild points) and shifts in the bias level of a transducer (DC shifts).

Thorough documentation is absolutely critical in all phases of the LVTS development process. During the data acquisition phase, a general list of resources such as vehicle specific serial numbers, identification of all instrumented assets, transducers, data recorders, filters, and software employed shall be included as part of the final report in all

MIL-STD-810H METHOD 514.8, ANNEX F, APPENDIX A

VSD efforts. A detailed calibration list shall be included for all transducers and signal analysis equipment employed during the data acquisition phase. All user defined parameters such as sampling frequency and filter settings shall also be recorded.

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MIL-STD-810H

METHOD 514.8, ANNEX F, APPENDIX A

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MIL-STD-810H METHOD 514.8, ANNEX F, APPENDIX B METHOD 514.8, ANNEX F, APPENDIX B Combination of Spectra (Statistical)

514.8-5 ALTERNATE BROADBAND DEVELOPMENT BASED ON FATIGUE DAMAGE SPECTRUM

One method to develop a LVTS ASD(Final) and associated runtime was presented in paragraphs 2.6 to 2.8. An alternative approach could be derived from the Fatigue Damage Spectrum methods discussed in Appendix C.

MIL-STD-810H

METHOD 514.8, ANNEX F, APPENDIX D

514.8-5.1 Road Transport - Wheeled Vehicle

Equipment secured for transport in a wheeled vehicle will primarily be exposed to broadband random vibration, with the majority of the energy at low frequencies (relative to a tracked vehicle). It is often argued that items transported on both tracked and wheeled vehicle need only be tested to the tracked vehicle exposure under the assumption that tracked vehicle transport is more severe. However, this is not the case for items that may be sensitive to high-level low-frequency vibration, or the resultant high velocities and displacements characteristic of a wheeled vehicle.

Sinusoidal washboard courses are sometimes used to replicate real world exposure when road testing vehicles. Vibration data on these courses are often recorded and utilized for VSD. The vibration induced by these courses will include harmonically related spectral spikes superimposed over broadband random. Employing standard analysis techniques such as histograms, bandpass filters, and harmonic relationships between spectral spikes, one may deduce that the time histories yielding the dominant spectral spikes to be more nearly sinusoidal than narrowband in nature, with the frequencies being speed dependent. A swept SOR test is typically used to replicate washboard exposure. However, an assessment of the project specific data should be made to determine the nature of the vibration.

The terrain and severity of the vibration environment changes from relatively smooth asphalt/concrete roads through secondary roads to trails and virgin cross-country. Trails and cross-country terrains provide the most severe vibration environment for a given speed, and paved road produce the least severe. Many test tracks have been built to allow vehicle testing and data acquisition in a controlled test environment. Some of these tracks were designed specifically to replicate real world worst case environments and can be beneficial for VSD development. Other test tracks were developed to investigate aspects of vehicle handling and reliability and may not be appropriate for VSD. Courses often used for wheeled vehicle VSD include paved road, gravel road, Belgian block, radial washboard, embedded rock, two-inch washboard, and cross-country. Embedded rock and the washboard courses replicate the worst case exposure. Typically transport over asphalt/concrete roads produces vibration levels that are insignificant in comparison; therefore, that portion of a scenario is often ignored for VSD purposes. Additional wheeled vehicle transport vibration issues are discussed in AECTP 240, Leaflets 242/1, 242/5, and 245/2 (reference m).

MIL-STD-810H

METHOD 514.8

• a. Failure definition. "Materiel is deemed to have failed if it suffers permanent deformation or fracture; if any fixed part or assembly loosens; if any moving or movable part of an assembly becomes free or sluggish in operation; if any movable part or control shifts in setting, position or adjustment, and if test item performance does not meet specification requirements while exposed to functional levels and following endurance tests." Ensure this statement is accompanied by references to appropriate specifications, drawings, and inspection methods.
• b. Test completion. "A vibration qualification test is complete when all elements of the test item have successfully passed a complete test. When a failure occurs, stop the test, analyze the failure, and either repair the test item or replace with a modified test item. Continue or repeat the test until all fixes have been exposed to a complete test. Each individual element is considered qualified when it has successfully passed a complete test (see paragraph 4.3). Qualified elements that fail during extended tests are not considered failures, and can be repaired to allow test completion."

514.8-5.2 Road Transport - Tracked Vehicle

The vibration induced into secured equipment by tracked vehicles will include harmonically related spectral spikes superimposed over broadband random. The frequency of these narrowbands created by the interaction between the

tracks and hard road surface and is proportional to vehicle speed. This proportion can be described as follows:

f=.28" р

in which: $f=$ frequency (Hz), $p=$ track pitch (m), and $v=$ velocity (km/h)

Employing standard analysis techniques such as histograms, bandpass filters, and harmonic relationships between spectral spikes, one may deduce that the time histories yielding the dominant spectral spikes to be more nearly narrowband random in nature than sinusoidal, with the frequencies being speed dependent. A swept NBROR test is typically used to replicate tracked vehicle exposure. However, an assessment of the project specific data should be made to determine the nature of the vibration.

Road courses typically used for tracked vehicle VSD include paved road, gravel road, and cross-country. Asphalt/concrete roads provide the most severe vibration levels in a tracked vehicle because of the relatively constant impact of the track blocks on the hard surface. Hard packed gravel or dirt secondary roads will produce levels nearly equivalent to asphalt/concrete roads and should be considered in the development of vibration schedules as well. Additional tracked vehicle transport vibration issues are discussed in TOP 01-2-601 (reference c) and AECTP 240, Leaflet 245/1 (reference m).

514.8-5.3 Air Transport - Rotor Wing

The vibration induced into equipment transported by rotor wing platforms (whether captive carry, mounted internally, or secured in the cargo area) will include harmonically related spectral spikes superimposed over broadband random Employing standard analysis techniques such as histograms, bandpass filters, and harmonic relationships between spectral spikes, one may deduce that the time histories yielding the dominant spectral spikes to be more nearly sinusoidal in nature than narrowband random, with the frequencies being dependent upon the number of rotor blades and the main rotor rate. Predominate frequencies are determined by the normally constant blade passing frequency and are independent of vehicle speed. Vibration of equipment mounted near the tail rotor may be dominated by the tail rotor blade passing frequency. A SOR test is typically used to replicate rotor wing platform exposure, with the sine tone frequencies held constant. However, an assessment of the project specific data should be made to determine the nature of the vibration.

Vibration severity is related to flight conditions. The vibration environment at a given location in or on a helicopter is affected by the power output of the engine, the aerodynamic buffeting of the rotor(s), and atmospheric conditions. VSD should include analysis of all aircraft maneuvers that constitute a significant portion of the expected flight time and that produce significant vibration amplitudes. Additional rotor wing transport vibration issues are discussed in TOP 01-2-603 (reference q) and AECP 240, Leaflet 242/3 (reference m).

MIL-STD-810H

input than materiel mounted on the hull or deck. The overall ship's structure, materiel mounting structure, and materiel transmissibility (amplifications) greatly affect materiel vibration. VSD for shipboard materiel should address both the levels of environmental inputs and the coincidence of materiel/mounting resonances and input frequencies although in the transport by sea case, the vibration amplitudes are relatively benign and can often be considered as if they were wideband in nature. It is often not necessary to test for sea transport if an item is tested to other more severe transport, such as ground or jet aircraft transport. Additional sea transport vibration issues are discussed in AECTP 240, Leaflet 242/4 (reference m). For US Navy vessels refer to Method 528.1.