A-A-52486
b. Resonance vibration frequency. When tested on a set up similar to that shown in figure 2, and after being subjected to vibration at 0.06 inch double amplitude over a frequency range of 2 to 60 cycles per seconds (cps), the mount shall be such as to preclude a natural or resonant vibration frequency within the carrier (railway or motor freight) vibration frequency range of 2 to 7 cps.
c. Resonance vibration fatigue. When tested on a set up similar to that shown in figure 2, the mounts shall be capable of withstanding, without damage, a total duration period of 21 ± 2 minutes when exposed for 3 sweeps to the frequency range of 2 to 60 cps and return to 2 cps. Each sweep time shall be 7 ± 1 minute. Vibration shall be steady state for 15 minutes when the resonant frequency is above 20 cps. Intermittent dwell testing is permitted to avoid overheating of elastomeric mounts.
3. Shock attenuation. With the mounts and dummy loads forming a center of gravity system along the vertical axis and an accelerometer mounted on the dummy load directly over the center of gravity, the shock test shall be carried in a set up similar to the one in SC c2a. The entire assembly shall be dropped flat to a hard non-yielding surface three times from a height of 12 ± 1/2 inches. The mounts shall evidence no damage and no shock greater than 15 g’s shall be registered.
4. Durability. The mounts shall be capable of withstanding, without evidence of damage, 50 drops from a height of 18 ± 0.5 inches. The contractor shall perform appropriate drop tests to verify conformance to this requirement.
d. Environmental requirements.
1. Accelerated aging. After exposure to accelerated temperature of 158 to 160 degrees Fahrenheit (°F) for a period of 7 days, two months from the first batch of 1000 and two from each subsequent batch of 2000 shall be allowed to cool to room temperature and then shall meet the requirements of SC c1 within 20 percent of the original room temperature values. The contractor shall devise and perform accelerated aging at temperature tests to verify conformance to this requirement.
2. Low temperature. The mounts shall evidence no damage and no shock greater than 35 g’s shall be registered when the entire assembly, after being subjected to a temperature of -38° to -40°F for 16 hours, is still or immediately after being remove from the cold chamber and subjected to SC c3 test.
3. High temperature. The mounts shall evidence no damage and no shock greater than 15 g’s shall be registered when the entire assembly, after being subjected to a temperature of 158° to 160°F for not less than 4 hours, is removed from the ventilated oven and subjected to SC c3 test.
e. Identification and markings. The mounts shall be marked for identification in accordance with the drawing for the specific part number. The cure date (month and year) and the manufacturer’s identification code (CAGE) shall also be molded into the resilient element. The mounts shall be visually examined during inspection to verify conformance to the identification requirements herein.
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