Table 514.8C: -iii. Vehicles used for TWT composite

MIL-STD-810H

METHOD 514.8, ANNEX C

Method of Combination of Spectra: A statistical method as described in Annex F, Appendix C,

• was used to create the spectra for the individual trailers in Table 514.8C-III. This method makes use of the spectral variance from different measurement locations and test conditions and produces a spectrum that is a very conservative estimate of the actual measured environments. This procedure produced an ASD for each trailer in each of the orthogonal axes. The composite two-wheeled trailer spectrum was created by enveloping the individual trailers. Ideally a statistical method would have been used (as was done for the Composite Wheeled Vehicle below) but because the number of samples was so low an enveloping method was employed.
• Location of Control Accelerometer(s): 2 accelerometers at opposite corners, within 30 cm (12 in.) from test item

Recommended Control Scheme: Average (Extremal control may be appropriate for some

• applications). Based on the field data characteristics and the conservatism associated with the composite vehicle VSD process, drive limiting to 3 sigma is recommended.

For movement direction definitions, see paragraph 4.4 in the front part of this Method.

^1 Approximate values for a Gaussian random distribution which may vary based on the control system and spectral resolution. Peak velocity and displacement values are based on an acceleration maximum of three times the standard deviation (3σ) and a spectral resolution of 1 Hz.

² For shaker systems that are incapable of the displacement requirements of this schedule, minor adjustments may be made to the low frequency within the tolerances specified in 4.2.2.1a (main body) to accommodate the shaker limitations. If any schedule needs to be modified, make sure that all parties involved (tester, customer, etc.) are aware of the reason for the changes, and agree to the changes prior to test. Ensure an adequate test is performed and all deviations from the published schedules are properly documented.

³ For test items for which the test item orientation is unknown or variable the Envelope profile should be run for all three axes (Figure 514.8C-5 and Table 514.8C-V).

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MIL-STD-810H METHOD 514.8, ANNEX C

Figure description:

Vibration Schedule ASD

Vibration Schedule ASD vs. Frequency

Legend

• Vertical — color: red; symbol: Solid line
• Transverse — color: purple; symbol: Solid line
• Longitudinal — color: blue; symbol: Solid line

Figure 514.8C-4. - Category 4 - Composite two-wheeled trailer vibration exposure.

MIL-STD-810H METHOD 514.8, ANNEX C

Figure description:

Vibration Schedule Profile Vibration profile for test item orientation

Vibration Schedule ASD vs. Frequency

Annotations

• If the orientation of the test item is unknown or variable use this profile for all three orthogonal axes (text_label - position: Centered at approximately x=25 Hz, y=0.005 g²/Hz)

Figure 514.8C-5.- Category 4 – Composite two-wheeled trailer vibration exposure for unknown orientation.

(2) Composite wheeled vehicle (CWV). Exposures are shown in Figure 514.8C-6, and are followed by the respective data table (Table 514.8C-VII). If the orientation of the test item is unknown or variable, see exposure levels shown in Figure 514.8C-7 and Table 514.8C-VIII. (See paragraph 6.1, references pp to vv.)

Test Schedule: Secured Cargo - Composite Wheeled Vehicle

Vehicles Used for Composite: Measured vibration data from the following vehicles (Table 514.8C-VI) were used to develop the Composite Wheeled Vehicle test schedule:

Measured Locations: 9 locations on frame under cargo bed (3X3 matrix) except as noted in the table above

Type of Test Load: Sand filled ammo boxes (or other similar cargo) were secured to the cargo bed, and loaded to 3/4 of vehicle rated load.

Scenario to be Simulated: 805 km (500 mi) from the port staging area to the forward supply point described as follows: The typical mission/field transport scenario starts at the port staging area (PSA). The movement prior to this point would include transport by commercial common carrier, military long range aircraft, ship, and/or railroad. This movement would occur over improved road surfaces or in platforms that have been proven to impose significantly lower vibration levels than those vehicles used for transport from the port staging area to the using unit. The typical scenario has established that 805 km of transport are expected between the PSA and the forward supply point (FSP). This transport is in trucks and/or semitrailers. The road surfaces will be paved, secondary, and cross country.

MIL-STD-810H

METHOD 514.8, ANNEX C

Assumptions (Scenario, Load, Failure Mechanism, etc.):

Total Mission of 805 km (500 miles) is accounted for as follows:

• • 35 percent of total mission, 282 km (175 miles), is on-road and considered benign compared to the off-road environment.
• • 65 percent of total mission, 523 km (325 miles), is off-road:
• One-third of the off-road environment, 174 km (108 miles), is rough terrain consistent with the Belgian Block, Two-Inch Washboard, Radial Washboard, and Three-Inch Spaced Bump courses used to collect data. Average Speed over these courses was 26 km/hr (16 mph).
• Two-thirds of the off-road environment, 349 km (217 miles), is considered benign compared to the test conditions described above.

Failure mode: fatigue

Test Time Compression: Test time was computed from:

$\frac{t_{2}}{t_{1}} = \left[\frac{W(f)_{1}}{W(f)_{2}}\right]^{m/2}$ Where: $t_{1}$ = equivalent test time $t_{2}$ = in-service time for specified condition $W(f)_{1}$ = ASD at test condition, $\text{g}^{2}/\text{Hz}$ $W(f)_{2}$ = ASD at in-service condition, $\text{g}^{2}/\text{Hz}$ $m$ = 7.5 (see paragraph 2.2 of Annex A for further explanation)

Test Time: 40 minutes per axis

Exaggeration Factor: $\left[\frac{W(f)_1}{W(f)_2}\right] = 1.85$

Method of Combination of Spectra: A statistical method, as described in Annex F, Appendix C, was used to create the spectra for the individual vehicles in Table 514.8C-VI. This method makes use of the spectral variance from different measurement locations and test conditions and produces a spectrum that is a very conservative estimate of the actual measured environments. This procedure produced an ASD for each vehicle in each of the orthogonal axes. The composite wheeled vehicle spectrum was created by applying the upper normal one-sided tolerance limit to the spectrum data. The upper normal one-sided tolerance limit is based on two values, $\beta$ and $\gamma$. For these data $\beta$ was set to 0.90 and $\gamma$ was set to 0.50. This means that one is 50 percent confident that 90 percent of the vibration profiles of all wheeled cargo vehicles will fall below the composite wheeled vehicle vibration schedules presented below. The upper normal one- sided tolerance limit is described more fully in Annex F, Appendix B, paragraph 2.3.

• Location of Control Accelerometer(s): 2 accelerometers at opposite corners, within 30 cm (12 in.) from test item
• Recommended Control Scheme: Average (Extremal control may be appropriate for some applications). Based on the field data characteristics and the conservatism associated with the composite vehicle VSD process, drive limiting to 3 sigma is recommended.

For movement direction definitions, see paragraph 4.4 in the front part of this Method.

MIL-STD-810H METHOD 514.8, ANNEX C

RMS Acceleration:1,3 (G-rms): Vertical – 2.24; Transverse – 1.45; Longitudinal – 1.32; Envelope – 2.24.

Velocity (in/sec) (peak single amplitude): 1,3

Vertical 28.76; Transverse 17.83; Longitudinal 12.75; Envelope - 28.76.

Displacement (in) (peak double amplitude): 1,2,3 Vertical – 1.22; Transverse – 0.73; Longitudinal – 0.51; Envelope – 1.22.

^1 Approximate values for a Gaussian random distribution which may vary based on the control system and spectral resolution. Peak velocity and displacement values are based on an acceleration maximum of three times the standard deviation (3σ) and a spectral resolution of 1 Hz.

2 For shaker systems that are incapable of the displacement requirements of this schedule, minor adjustments may be made to the low frequency ASD values within the tolerances specified in 4.2.2.1a (main body) to accommodate the shaker limitations. If any schedule needs to be modified, make sure that all parties involved (tester, customer, etc.) are aware of the reason for the changes, and agree to the changes prior to test. Ensure an adequate test is performed and all deviations from the published schedules are properly documented.

3 For test items for which the test item orientation is unknown or variable the Envelope profile should

³For test items for which the test item orientation is unknown or variable the Envelope profile should be run for all three axes (Figure 514.8C-7 and Table 514.8C-VIII).

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MIL-STD-810H METHOD 514.8, ANNEX C

Figure description:

Vibration Schedule ASD vs Frequency (Log-Log Plot Analysis

Vibration Schedule ASD vs Frequency

Legend

• Vertical — color: red; symbol: Thick solid line
• Transverse — color: purple; symbol: Medium solid line with triangle marker
• Longitudinal — color: blue; symbol: Thin solid line with diamond marker

Figure 514.8C-6. - Category 4 - Composite wheeled vehicle vibration exposure.

MIL-STD-810H METHOD 514.8, ANNEX C

Figure description:

Vibration Schedule ASD vs Frequency

Annotations

• If the orientation of the test item is unknown or variable use this profile for all three orthogonal axes (text_label - position: Center-left in the bottom half of the chart, roughly x=5 to 20, y=0.003 to 0.007)

Figure 514.8C-7. - Category 4 - Composite wheeled vehicle vibration exposure for unknown orientation.