Military Specification Mil-S-901D covers shock event damage to equipment installed in Navy Ships. It is an 82 page document with the current revision dated March 17, 1989, titled “Shock Tests. H.I. (High Impact) Shipboard Machinery, Equipment and Systems, Requirements For”. Not to be confused with MIL-STD-901 which is a standard for men’s garrison caps. The intent of MIL-S-901D is to determine if equipment mounted in a Navy ship will survive an attack on the ship where large transient shocks are generated by collisions or explosions. As the specification states “…so as to represent an underwater explosion occurring …”.
There are two sub parts to 901D. Grade A devices are essential to the operation of the ship and must continue to operate after the shock event. Grade B devices are not essential to the operation of the ship but must not shed parts that might be a hazard to nearby personnel or adjacent equipment.
Testing to MIL-S-901D can be accomplished in two manners: Hammer Test or Barge Test.
The “Hammer Test” involves using a moving weight to impact upon an anvil plate such that a very large transient shock is imparted to the Unit Under Test. There are two categories of Hammer Tests: lightweight or medium weight. As the names imply, the tests are performed on appropriately named test machines on lightweight or medium weight equipment.
Lightweight testing is performed on equipment weighing less than 550 pounds including the supporting structure required for the test. Medium weight testing is limited to equipment weighing less than 7,400 pounds.
For Lightweight Testing, three blows at hammer heights of 1, 3 and 5 feet shall be applied parallel to each of the three mutually perpendicular axis of the item being tested.
Medium Weight Testing requires three blows for each perpendicular axis plus another group of three blows with the item in an inclined position.
A Barge Test or Heavy Weight Test is performed on a floating barge which has explosive charges detonated nearby in the water.
For Heavy Weight or Barge Testing, four explosions are performed with 60 pounds of HBX-1 explosive hanging 24 feet down in the water at distances of 40, 30, 25 and 20 feet from the barge. The first shot is located on a fore-and-aft axis and the last three shots are athwart ship. These are violent tests and are the gold standard for testing for shock.
Equipment Performance During/After Test
The equipment being tested shall be monitored for correct operation or damage resulting from the testing. For Grade A equipment, the equipment is allowed to shut down as a result of the shock event but must be able to automatically restart without any repairs. For Grade B equipment, the equipment can operationally fail but can’t create a hazard to personnel or to other Grade A equipment. It is obvious that both Grade A and Grade B equipment cannot show any signs of electrical shorts, release of flame, smoke or sparks.
After each test, the equipment may be inspected and any lose bolts, screws, etc., may be tightened with the presumption that fastener did not stretch as a result of the test.
Chassis Plans has designed several rugged computer systems to be in compliance with MIL-S-901D and can help you with your custom requirements.