Shock testing determines the ability of equipment to withstand the infrequent non-repetitive shocks encountered in handling, transportation, and service and to continue to function, where required. Also, shock tests verify that equipment will not detach from its mounting during these tests.
Shock testing in the laboratory can take two approaches. Simulation of either the specified shock conditions or the response of the system as measured in the field, known as a shock response spectrum (SRS), can be performed. The most common type of specified input simulation is known as classical shock testing. It consists of inputting various relatively non-complex waveforms such as rectangular, saw-tooth and half-sine. When testing is required to produce a shock pulse having a spectrum tailored to that of the actual measured environment, shock response spectrum simulation is performed.
The following sections provide further information on operational shocks and crash safety, ballistic shock, and high impact shock.
OPERATIONAL SHOCKS AND CRASH SAFETY
The operational shock test verifies that the equipment will continue to function within performance standards after exposure to shocks experienced, for example, during normal aircraft operations. These shocks may occur during taxiing, landing or when the aircraft encounters sudden gusts in flight. This test applies to all equipment installed on fixed-wing aircraft and helicopters.
The crash safety test verifies that equipment will not detach from its mountings or separate in a manner that presents a hazard during an emergency landing. It applies, for example, to equipment installed in compartments and other areas of an aircraft where equipment if detached during emergency landing, could present a hazard to occupants, fuels systems or emergency evacuation equipment.
Ballistic shock is a high-level generally single pulse shock, that results from the reaction loads of the firing of projectiles and ordnance. The test provides confidence that material can structurally and functionally withstand the shock effects caused by the high reaction loads on a structural configuration to which the material is mounted.
This test is performed to determine the ability of items to withstand shock such as produced by underwater explosions, collision impacts, near-miss gunfire, blasts caused by air explosions, handling, train coupling loads, etc. Shock testing provides confidence that material can physically and functionally withstand the relatively infrequent, non-repetitive shocks encountered in the service environments.
SHOCK TESTING OF SHIP COMPONENTS - HIGH IMPACT SHOCK TESTING PER MIL-S-901D
Shock testing is essential for shipboard machinery, equipment, systems, and structures, in order to verify the ability of these installations to withstand shock loadings, which may be incurred during wartime service due to the effects of explosive weapons. Military shipboard items are classified in accordance with several standard grades, classes, and types, each of which defines the unit's importance to essential ship operations, method of installation within the ship structure, and required performance during shock testing, respectively. Military specification MIL-S-901D details shock testing requirements for shipboard components, including the following classifications:
Grade A: Items which are essential to the safety and continued combat capability of the ship. The unit must survive shock testing fully intact and functional.
Grade B: Items whose operation is not essential to the safety and combat capability of the ship, but could become a hazard to ship operations as a result of exposure to shock. The unit is allowed to malfunction as a result of shock, but must remain fully intact due to the possibility of debris causing harm to personnel or other equipment.
Class I: Equipment required to meet shock specifications without the use of resilient or isolation mountings.
Class II: Equipment which meets shock requirements with the use of resilient mountings.
Class III: Equipment which may be mounted on a ship with or without the use of resilient mountings installed between the item and the ship structure; therefore required to meet both class I and class II requirements.
Shock Test Types:
Type A: Test of a principal unit, which is directly supported by the ship structure.
Type B: Test of a subsidiary component or item, which is a major part of a principal unit.
Type C: Test of a subassembly, which is a part of a principal unit or subsidiary component.
At AERO NAV LABS we have both medium and lightweight high intensity shock testing equipment. These machines operate by using a winch or pulley system to raise a massive steel hammer, which is subsequently released, swings like a pendulum, and strikes the anvil plate to which the equipment being tested is mounted. (This mechanism can be visualized in the above schematic of the medium weight shock machine from the MIL-S-901D specification.) The height to which the hammer is raised is determined by the weight supported by the anvil plate, including the test unit and the support fixture. Lightweight shock machines have a maximum capacity of 550 lbs, while medium weight shock machines have a capacity of 7,400 lbs. Lightweight shock testing consists of three increasingly energetic blows applied parallel to each of the three geometrical axes of the item being tested. However, medium weight shock testing requires a minimum of two blows in three orientations, but includes a third blow depending on the operating conditions required to be simulated during testing.
Equipment which is beyond the weight limits of AERO NAV's shock machines, (i.e. heavy-weight) can be tested on a barge. A water-filled former rock quarry is used as the venue for barge testing. The units being tested are mounted to the barge in a fashion similar to their intended shipboard mounting, and high explosives are detonated at specified depths and distances from the barge to simulate the required shock levels.
Dynamic (Operating) Shock Testing
AERO NAV LABORATORIES is capable of performing medium and lightweight high impact shock testing of principal units per MIL-S-901D while they are operating in the way they would function aboard a ship. This is known as dynamic shock testing and it ensures that items, which are essential to the safety and continued combat capability of a military ship, will continue to operate without failure even through the high shock stresses encountered during wartime explosions.
Dynamic shock tests are often performed on shipboard pumps at AERO NAV LABS, and an example can be seen in the photograph above. The pump is mounted to the medium weight shock machine and is connected via supported flex lines to a reservoir of the appropriate fluid so that it could perform its designed function throughout testing. A flow meter is often installed within the system so that the proper circulation of water, fuel, or other fluid can be monitored. AERO NAV LABS has the capability to perform dynamic shock tests on various types of shipboard equipment, including pumps, motors, electrical components, display monitors, navigation equipment, and many more.
Shock testing is specified in the following:
MIL-PRF-27, MIL-T-27, MIL-STD-202, MIL-J-641, MIL-STD-750, MIL-STD-798, MIL-STD-810, MIL-STD-901, MIL-I-983, MIL-STD-1344, MIL-E-2036, MIL-S-3928, MIL-S-4456, MIL-E-5272, MIL-E-5400, MIL-T-5422, MIL-T-7743, MIL-M-7969, MIL-E-8189, MIL-C-8384, MIL-F-8615, MIL-S-8805, MIL-M-10304, MIL-C-11015, MIL-R-11050, MIL-R-11539, MIL-R-12934, MIL-F-13926, MIL-R-15109, MIL-C-15240, MIL-C-15305, MIL-C-15514, MIL-C-15730, MIL-F-15733, MIL-P-15736, MIL-S-15743, MIL-D-15877, MIL-S-16036, MIL-H-16313, MIL-F-16377, MIL-E-16400, MIL-V-16556, MIL-R-16999, MIL-S-17000, MIL-M-17059, MIL-M-17060, MIL-T-17113, MIL-M-17185, MIL-T-17185, MIL-T-17275, MIL-T-17293, MIL-T-17301, MIL-V-17360, MIL-V-17361, MIL-V-17456, MIL-V-17639, MIL-V-17840, MIL-P-17869, MIL-V-18110, MIL-F-18327, MIL-T-18404, MIL-P-18472, MIL-R-18546, MIL-V-18683, MIL-H-18766, MIL-F-18870, MIL-F-18953, MIL-I-18997, MIL-F-19004, MIL-M-19097, MIL-E-19100, MIL-P-19131, MIL-M-19160, MIL-M-19633, MIL-H-19760, MIL-N-19900, MIL-I-20037, MIL-S-20708, MIL-C-21097, MIL-R-21098, MIL-D-21625, MIL-V-22052, MIL-V-22133, MIL-C-22317, MIL-S-22432, MIL-C-22437, MIL-H-22594, MIL-V-22687, MIL-S-22885, MIL-A-22895, MIL-B-23071, MIL-C-23200, MIL-B-23306, MIL-A-23798, MIL-A-23836, MIL-L-23886, MIL-P-23928, MIL-S-24062, MIL-E-24091, MIL-C-24095, MIL-E-24142, MIL-C-24166, MIL-L-24223, MIL-C-24308, MIL-R-24414, MIL-P-24423, MIL-V-24509, MIL-T-28800, MIL-E-39029, MIL-H-83511, MIL-S-008834, MIL-T-0014358, US COAST GUARD NO. 493, RTCA/DO-160, PPD NO. 802-6335704, PPD NO. 802-7651312, NAVSEA NO. 802-6215945, VDID 2012, GR-487-CORE, ASTM E-644-91, ASTM F1387-99, ASTM D-4003-92, SCL-7695, SCL-7722