Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 c. lest se tUQ. The teet item shall be attached to the vibration generator directly or with a fixture, and securely held by its normal means of attachment. The fixture ehall incorporate actual service structures as much as poseible to minimize unrealistic response characteristics during test exposure. Any connection to the test item, such aa cables pipes, wires, and the like, shall be arranged eo that it imposes restraints and mase similar to those present when the equipment is installed in the operational configuration. Excitation shall be applied through the three orthogonal axes of the teet item. 1 - 3 . 2 .
11 9 v Equipment installed in shipe will receive vibration stresses resulting from natural environmental inputs to the shiprs superstructure and local unit transmiasibilitiee (amplifications) within the equipment and its mounting structure. Vibration testing of shipboard equipment should address both the levels of environmental inputs and the susceptibility y of equipment/mounting resonances to input frequencies. Shipboard vibration spectra have a random component induced by the variability of cruieing needa, sea statea, maneuvers, etc. and a periodic component imposed by propeller shaft rotation and hull resonance.
Equipment mounted on masts (such as antennas) can be expected to receive higher input than equipment mounted on the hull or deck. a. ~e. Whenever possible, measurements should be used to develop the test criteria. Appendix 1 provides guidance for’the development of.criteria from measured data. In the absence of shipboard measurements, levels fround in figure 514.3-3Q should be used.
The random vibration test of shipboard equipment should follow either the Baeic Transportation Teet (1.3.2.1) or the Bench Handling Shook Test (method 516.3, Procedure VI), In order to verify structural integrity and the compatibility of equipment/ mounting resonance frequencies with shipboard input frequencies, a sinusoidal vibration test ehould be conducted in accordance with MIL-STD-167 for Type I (Environment Vibration).
In the event that actual shipboard vibration data recorded on candidate vessels show levels or frequency ranges different from those for MIL-STD-167, Type 1, the test levels should be tailored to envelope the highest valuee for each frequency, with appropriate consideration given to the fatigue life of the equipment. b. Test dura ti~. The test durations for shipboard applications should be based upon the anticipated deployment scenarios. A method for development of test durations is included in appendix 1. For tests which utilize the test levels from figure 514,3-33, the first duration should be two hOurs along each of three orthogonal axea. c. “fest set~.
Equipment should be mounted in its normal configuration with normal shock{vibration isolation mounts used throughout the teat. ,.. 0 METHOD 514.3 19 July 1983 514.3-54