MIL-STD-1660A APPENDIX H
c. Rejection criteria.
(1) Excessive settlement within the unit load, which is evidence of packaging failure or restraint method failure, shall constitute an unacceptable unit load. Packaging failure will be determined by inspection for permanent deformation, broken components, or inability to protect the contents. After removing the stacking load, the degree
of compaction should not be so excessive that the restraint method, e.g., strapping or stretch wrap, has lost all tension. If the loss of tension is not easily discernable, then the next phase of testing, the vibration test, should be invoked to aid in the determination.
(2) A tendency for the unit load to create an unstable and unsafe stacking condition shall also constitute an unacceptable unit load. Generally, a stack of units, which leans 10 degrees or more from the vertical angle, is unstable and unsafe.
H.5.2 Vibration test. a. Purpose.
(1) To evaluate the unitization restraint method for securing the load to the pallet/skid.
(2) To determine the reliability of the restraint method.
(3) To ensure that the restraint and unit load integrity will be maintained after the unit load has been subjected to vibration as could be experienced by the load in its journey from origination to destination.
b. Procedure.
(1) The unit load specimen shall be placed on, but not fastened to, the platform of a vibration tester of suitable size and weight-carrying capacity. If the unit load may be shipped in a stacked configuration, then a corresponding stack of specimens should be placed on the vibration tester. Unless failure occurs, the time period of vibration shall be 60 minutes, if the specimen is tested in one orientation. If tested in more than one position, the time period shall be 30 minutes for each orientation. Unless failure occurs, the specimen should be subjected to a second series of vibration periods as described above. Observations of unit load condition should be made and recorded after both series.
(2) Retainment devices shall be attached to the platform to prevent the specimen from moving off of or rotating on the platform during the test. The retainment devices should be adjusted to permit unrestrained movement of the specimen from its centered position of no more than 3 inches either forward or aft in the direction of vibration and no more than 1 inch side-to side across or aft in the direction of vibration. Forward and aft bulkheads/retainers used for this purpose should be rigid and have smooth-supportive surfaces such as plywood. Floor cleats adjacent and parallel to the unit load pallet/skid may be used to retain the side to side movement.
(3) The vibration imparted to the test specimen shall be at ½-inch amplitude (1-inch double amplitude) sinusoidal motion starting at a frequency of about three cycles per second (180 cycles per minute). The vibration speed should then be adjusted for each test position of the specimen to achieve the condition at which the pallet/skid of the unit load is just lifting from the vibration platform. This conditional shall be determined when a 1/16-inch feeler gage can be momentarily slid freely between each point common to the specimen and the platform at some instant during each cycle.
c. Rejection criteria.
(1) Failure of the unit load will be indicated by loss of package(s) from the unit or loss of securement to the pallet/skid.
(2) Loss of tension within the unit load restraint method shall also be cause for rejection. Loss of tension shall be determined by measuring any shifting of packages relative to other packages or relative to the pallet/skid. If the relative shifting/displacement exceeds 2 inches, the unit load is unacceptable. If the loss of tension is not easily discernable, then the next phase of testing, the drop test, should be invoked to aid in the determination.
(3) Damage to the packaging, which may compromise protection of the contents, shall constitute failure. H.5.3 Drop test (edgewise-drop).
a. Purpose.
(1) To examine the ability of the unit load to resist certain shock forces which could be imposed on it from typical rough handling and minor shipping hazards during transportation from origination to destination.
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