Downloaded from https://www.everyspec.com MIL-STD-81OC f. = 500 Hz for al1 other cross-sections t= local store average skin thickness where radius, R, is measured--inches R= (inches) of the elliptical-cross-section (for a cylindrical section use local average radius; for conical secti’onuse smallest f. calculated using geometry within 1 foot of accelerometermounting point) one-half the average of maior and minor external diameters I NOTE: If calculated f. s 1,200 Hz, use 2,000 Hz Acceptable range for t/R2 . .’001~ t/R2 .02 If calculated values fall outside these Timits, use these limit values. 4.6.3.2.4. Test setug.
The store shall be mounted and tested with its longitudinal axis horizontal and positioned so that its.mounting lugs are on top of the store using 4.6.3.2.4a or, as an alternate, 4.6.3.2.4b, depend- ing on the facilities available. a. Mounting method. The store shall be suspended from a structural frame I by means of its normal mounting lugs using hooks and sway braces which simulate the operational mounting apparatus. The test setup shal1 be such that th~ rigid body modes (translationand rotation) of vibration for the store/frame/suspensionsystem are between 5-20 Hz.
.Vibrationshall be t applied to the store by means of a rod or other suitable mounting device running from a vibration shaker to a relatively hard structurally supported point on the surface of the store. b. Alternate mounting method. The store shall be hard mounted directly to the shaker, using its normal mounting lugs and a suitable fixture. The stiffness of the mounting fixture shall be such that its induced resonant frequencies are as high as possible but none are below one-third of any f. frequency. 4.6.3.2.5 Determination of resonance response peaks. Vibration shall be applied at an input level sufficient to excite vibratory responses within the store.
The frequencies at which significant resonance ~esponse peaks occur shall be identified for each store mounted accelerometerusing no greater than a 10 percent constant percentage bandwidth analysis. A res- onance response peak shall have at least a 6 dB amplification of input level to be considered significant. This shall be done for both vertically and laterally applied vibration. METHOD 514.2 S14.2-12