Acceleration | Accelerazione

MIL STD 810 G – Test Method 513.6 – Acceleration

 

SCOPE

 

Purpose
The acceleration test is performed to assure that materiel can structurally withstand the steady state inertia loads that are induced by platform acceleration, deceleration, and maneuver in the service environment, and function without degradation during and following exposure to these forces. Acceleration tests are also used to assure that materiel does not become hazardous after exposure to crash inertia loads.
Application
This test method is applicable to materiel that is installed in aircraft, helicopters, manned aerospace vehicles, air-carried stores, and ground/sea-launched missiles.
Limitations
Acceleration
As addressed in this method, acceleration is a load factor (inertia load, “g” load) applied slowly enough and held steady for a period of time long enough such that the materiel has sufficient time to fully distribute the resulting internal loads, and such that dynamic (resonant) response of the materiel is not excited. Where loads do not meet this definition, more sophisticated analysis, design, and test methods are required.
Aerodynamic loads
Materiel mounted such that any or all surfaces are exposed to aerodynamic flow during platform operations are subject to aerodynamic loads in addition to inertia loads. This method is not generally applicable to these cases. Materiel subject to aerodynamic loads must be designed and tested to the worst case combinations of these loads. This often requires more sophisticated test methods usually associated with airframe structural (static and fatigue) tests.
Acceleration versus shock
Acceleration loads are expressed in terms of load factors that, although dimensionless, are usually labeled as “g” loads. Shock environments (Methods 516.6 and 517.1) are also expressed in “g” terms. This sometimes leads to the mistaken assumption that acceleration requirements can be satisfied by shock tests or vice versa. Shock is a rapid motion that excites dynamic (resonant) response of the materiel, but with very little overall deflection (stress). Shock test criteria and test methods cannot be substituted for acceleration criteria and test methods or vice versa.

 

TEST PROCESS

 

Procedure I – Structural Test
  • Step 1. With the test item installed as in paragraph 4.5.1.2, bring the centrifuge to the speed required to induce the specified g level in the test item as determined from paragraph 2.3 and Table 513.6-I for the particular test item orientation. Maintain this g level for at least one minute after the centrifuge rpm has stabilized.
  • Step 2. Stop the centrifuge and inspect the test item as specified in paragraph 4.5.1.1.
  • Step 3. Operationally test and inspect the test item as specified in paragraph 4.5.1.1. If the test item fails to operate as intended, see paragraph 5 for analysis of results, and follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 4. Repeat this test procedure for the remaining five test directions noted in paragraph 4.5.1.2a, Step 2.
  • Step 5. Upon completing the tests in the six test directions, remove the test item from the centrifuge and, if required, perform one final operational check and physical inspection. See paragraph 5 for analysis of results.
Procedure II – Operational Test
Centrifuge
  • Step 1. With the test item installed as in paragraph 4.5.1.2, operationally test and inspect the test item as specified in paragraph 4.5.1.1.
  • Step 2. With the test item operating, bring the centrifuge to the speed required to induce specified g level in the test item as determined from paragraph 2.3 and Table 513.6-II for the particular test item orientation. Maintain this g level for at least one minute after the centrifuge rpm has stabilized. Conduct an operational check and document the results. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 3. Stop the centrifuge and operationally check and inspect the test item as specified in paragraph 4.5.1.1. If the test item fails to operate as intended, see paragraph 5 for analysis of results.
  • Step 4. Repeat Steps 1-3 for the five remaining orientations noted in paragraph 4.5.1.2a, Step 2.
  • Step 5. Upon completing the tests in the six test directions, remove the test item from the centrifuge and, if required, perform one final operational check and physical inspection. See paragraph 5 for analysis of results.
Track/rocket-powered-sled
  • Step 1. With the test item installed as in paragraph 4.5.1.2, operationally test and inspect the test item as specified in paragraph 4.5.1.1.
  • Step 2. With the test item operating, accelerate the sled to the level required to induce the specified g level in the test item as determined from paragraph 2.3 and Table 513.6-II for the particular test item orientation. Conduct a performance check while the test item is subjected to the specified g level. Document the results.
  • Step 3. Evaluate test run parameters and determine if the required test accelerations were achieved.
  • Step 4. Repeat the test run as necessary to demonstrate acceptable performance of the test item while under required test acceleration. Document the test run parameters.
  • Step 5. Repeat this test procedure for the five remaining test directions noted in paragraph 4.5.1.2a, Step 2. Upon completing the tests in the six test directions, operationally check and inspect the test item according to paragraph 4.5.1.1. See paragraph 5 for analysis of results.
Procedure III – Crash Hazard Acceleration Test
  • Step 1. With the test item installed as in paragraph 4.5.1.2, bring the centrifuge to the speed required to induce the specified g level in the test item as determined from paragraph 2.3 and Table 513.6-III for the particular test item orientation. Maintain this g level for at least one minute after the centrifuge rpm has stabilized.
  • Step 2. Stop the centrifuge and inspect the test item as specified in paragraph 4.5.1.1.
  • Step 3. Inspect the test item as specified in paragraph 4.5.1.1.
  • Step 4. Repeat this test procedure for the remaining five test directions noted in paragraph 4.5.1.2a, Step 2.
  • Step 5. Upon completing the tests in the six test directions, inspect the test item as specified in paragraph 4.5.1.1. See paragraph 5 for analysis of results.

 

NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.

 

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