4.1 Test Facility
The required apparatus consists of either a centrifuge of adequate size or a track/rocket-powered sled test arrangement. Recommend a centrifuge for all Procedure I (Structural Test), Procedure III (Crash Hazard Acceleration Test), and most of Procedure II (Operational Test) evaluations. Use a track/rocket-powered sled test arrangement for Procedure II evaluations when strictly linear accelerations are required. In general, acceleration tests will not be instrumented. If there is need for test apparatus or test fixture/test item instrumentation, follow practices and procedures outlined in paragraph 6.1, reference j. Verification of the correct input acceleration to the test item will be according to procedures established at the test facility.
4.2 Controls
4.2.1 Calibrations
Ensure any acceleration measurement for test verification has been made by instrumentation properly calibrated to the amplitude and frequency ranges of measurement.
4.2.2 Tolerances
Maintain the acceleration level between 90 percent and 110 percent of the specified level over the full dimensions of the test item.
MIL-STD-810H METHOD 513.8
4.3 Test Interruption
Test interruptions can result from two or more situations, one being from failure or malfunction of test chambers or associated test laboratory equipment. The second type of test interruption results from failure or malfunction of the test item itself during required or optional performance checks.
4.3.1 Interruption Due To Laboratory Equipment Malfunction
- a. General. See Part One, paragraph 5.11, of this Standard.
- b. Specific to this Method.
- (1) If an unscheduled interruption occurs while the test item is at a specified test level, restart and run the complete test. If interruptions result in several new starts, evaluate the test item for fatigue damage. (Each application of acceleration is a single loading cycle. Duration of a loading cycle does not influence the severity of the test.)
- (2) If the test item is subjected to acceleration loads in excess of the level specified for the test, stop the test, inspect the test item and perform a functional test. Based on the inspection and functional test, make an engineering decision as to whether to resume testing with the same test item or with a new test item.
4.3.2 Interruption Due To Test Item Operation Failure
Failure of the test item(s) to function as required during mandatory or optional performance checks during testing presents a situation with several possible options.
- a. The preferable option is to replace the test item with a “new” one and restart from Step 1.
- b. A second option is to replace / repair the failed or non-functioning component or assembly with one that functions as intended, and restart the entire test from Step 1.
NOTE: When evaluating failure interruptions, consider prior testing on the same test item and consequences of such.
4.4 Test Setup
See Part One, paragraph 5.8.
4.5 Test Execution
The following steps provide the basis for collecting necessary information concerning the test item in a constant acceleration environment.
4.5.1 Preparation for Test
4.5.1.1 Pretest Standard Ambient Checkout
All items require a pretest standard ambient checkout to provide baseline data and additional inspections and performance checks during and after tests. Conduct inspections as follows:
- Step 1 Examine the test item for physical defects, etc., and record findings.
- Step 2 Prepare the test item for test, in its operating configuration if required, as specified in the test plan.
- Step 3 Obtain sufficient dimensional measurements of the test item to provide a reference guide for the evaluation of physical damage that may be induced during the tests.
- Step 4 Examine the test item/fixture/centrifuge/sled combination for compliance with the test item and test plan requirements.
MIL-STD-810H
METHOD 513.8
Step 5 If applicable, conduct an operational checkout in accordance with the test plan, and document the results. If the test item operates satisfactorily, proceed to paragraph 4.5.2 or 4.5.3 as appropriate. If not, resolve the problems and repeat this Step.
4.5.1.2 Mounting of the Test Item
Configure the test item for service application. Mount the test item on the test apparatus using the hardware that is normally used to mount the materiel in its service installation.
- a. Centrifuge mounting.
- Step 1 Determine the mounting location for the test item by measurement from the center of rotation of the centrifuge to the location on the centrifuge arm that will provide the g level established for the test. Mount the test item so that its center of gravity is at the location on the arm determined for the test load factor (g level). Calculate test levels as follows:
Where:
- test load factor (load factor within the centrifuge plane of rotation)
- K = 1.118 x 10⁻³, r in meters (K = 2.838 x 10⁻⁵, r in inches)
- r = radial distance in meters, (inches) from the center of rotation to the mounting location on centrifuge arm
- n = angular velocity of centrifuge arm in revolutions per minute (rpm)
Step 2 Orient the test item on the centrifuge for the six test direction conventions as follows:
- (a) Fore. Front or forward end of test item facing toward center of centrifuge.
- (b) Aft. Reverse the test item 180 degrees from fore position.
- (c) Up. Top of test item facing toward center of centrifuge.
- (d) Down. Reverse item 180 degrees from up position.
- (e) Lateral left. Left side of test item facing toward center of centrifuge.
- (f) Lateral right. Right side of test item facing toward center of centrifuge.
- Step 3 After the test item is properly oriented and mounted on the centrifuge, make measurements and calculations to ensure the end of the test item nearest to the center of the centrifuge will be subjected to no less than 90 percent of the g level established for the test. If the g level is found to be less than 90 percent of the established g level, either mount the test item further out on the centrifuge arm and adjust the rotational speed accordingly, or use a larger centrifuge to ensure the end of the test item nearest to the center of the centrifuge is subjected to at least 90 percent of the established g level. However, do not subject the opposite end of the test item (the end farthest from the center of the centrifuge) to over 110 percent of the established g level. For large test items, consider exceptions for load gradients based on the existing availability of large centrifuges in commercial or government test facilities.
- b. Track/rocket-powered-sled mounting. For track/rocket-powered sled mounting, mount the test item and associated test fixture or apparatus on the sled platform in accordance with the controlled acceleration direction of the sled. (Ensure the test fixture or apparatus has been designed to isolate sled vibrations from the test item.) Since the sled and test item experience the same g levels, only the orientation of the test item on the sled is critical. Orient the test item on the sled according to the acceleration directions shown on Figure 513.8-2 and the controlled acceleration direction of the sled for the six test directions.
- c. Shaker mounting. Before starting a test, review pretest information in the test plan to determine test details (test item configuration(s), levels, durations, failure criteria, item operational requirements, instrumentation requirements, facility capability, fixture(s), etc.).
Step 1 Select appropriate vibration exciters and fixtures.
MIL-STD-810H
METHOD 513.8
Step 2 Select appropriate data acquisition system (e.g., instrumentation, cables, signal conditioning, recording, analysis equipment).
Step 3 Operate vibration equipment without the test item installed to confirm proper operation.
Step 4 Ensure the data acquisition system functions as required.
4.5.2 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 513.8-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 4.5.1.2.a, 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.
4.5.3 Procedure II - Operational Test
4.5.3.1 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 513.8-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 4.5.1.2.a, 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.
4.5.3.2 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 513.8-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 acceleration was 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.
MIL-STD-810H
METHOD 513.8
4.5.4 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 513.8-III or Table 513.8-IV 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 4.5.1.2.a, 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.
4.5.5 Procedure IV – Strength Test
Step 1 Select the test conditions which are within the shaker displacement limits and mount the test item (or dynamic simulant item) on the vibration exciter. Use of a simulant may be desired to assess system drive signal magnitudes. Install accelerometers, force gages, and other instrumentation as required.
Step 2 If required; perform an operational check on the test item at standard ambient conditions. If the test item operates satisfactorily, proceed to Step 3. If not, resolve the problems and repeat this step.
Step 3 Subject the test item (or dynamic simulant) to the sine burst profile. The vibration control system will be in open loop control. Examine the data and adjust the parameters to achieve the required test level. If a dynamic simulant is used, then replace the simulant with the test item.
Step 4 Subject the test item in its operational configuration to the compensated sine burst waveform. It is often desirable to make an initial run at less than full level to ensure proper dynamic response and validate instrumentation functionality.
Step 5 Record necessary data.
Step 6 Examine the control acceleration time trace for conformance to the test profile. Perform a visual inspection of the test item. Conduct an operational check on the test item and record the performance data as required.
Step 7 Repeat Steps 4, 5, and 6 for the number of replications called out in the requirements document, or a minimum of three times for statistical confidence provided the integrity of the test configuration is preserved during the test.
Step 8 Remove the test item from the fixture/shaker and inspect the test item, mounting hardware, components, etc., for any signs of visual mechanical degradation that may have occurred during testing.
Step 9 If required, repeat Steps 1-8 for each excitation axis.
Step 10 Document the test series including the saving of all control and monitor digital time traces, and see paragraph 5.2.4 for analysis of results.