High Frequency Shock

The military industry has been expressing interest in testing small packages at high SRS g’s and time-captured shock events with a large frequency bandwidth (upwards to 10 kHz). Until now, there were several limitations in providing a vibration testing equipment to meet those demands.

A majority of the test systems available did not have both high force capability to produce the high acceleration levels and high mechanical resonant frequencies to handle the large bandwidth requirements. Often times, alternative methods of testing (such as drop/pyro testers, loose bolts in fixtures, and specially tuned fixtures) lack the control necessary to maintain a consistent acceleration profile on the payload in question.

Meeting the Challenge - SAI180-S092-MXA

To meet those challenges, Unholtz-Dickie Corporation has developed a high frequency, high SRS vibration test system, the SAI180-S092-MXA, for testing small to medium-sized payloads at acceleration levels up to 5000 g SRS at frequencies to 10 kHz as well as extremely high half-sine shock pulses of up to 1200 g (see Figure 1).

In order to increase the armature resonance, a stiffer alloy was employed for the ribbed table to increase the resonance to 4600 Hz bare table. By using a lightweight aluminum coil, the resonant frequency does not drop as severely as with a copper coil; with a 10 lbs payload, the resonance only drops to 3900 Hz. It also keeps the armature weight down to 8 lbs.

The reliability of the newly designed armature was verified by producing over 10,000 continuous half-sine shock pulses at 1200 g without any signs of armature degradation.

Also, the amplifier was modified to generate an electrical resonance for increased performance of half-sine shock pulses at very small durations (less than 0.5 ms).

By mating the shaker to an amplifier that is capable of delivering 180 kVA of power, the following SRS results were attained:

Payload (lbs)	Frequency Range (Hz)³	Acceleration (g SRS)¹
2	1,000 - 5,000	5,000
2	1,000 - 10,000	3,000
10	1,000 - 5,000
10	1,000 - 10,000²
27	1,000 - 8,000	1,000

Notes

1. Q = 10
Notched at 8 kHz
SRS profiles below 1,000 Hz ramps down to 100 Hz

Figure 1: Actual result of a 1200 g, 2 ms half-sine pulse with a 2 lbs payload.

Result of a 1200 g, 2 ms Half-sine pulse with a 2 lbs Payload Waveform Graph

Figure 2: Actual time and frequency domain responses of 3000 g SRS up to 10 kHz with a 2 lbs payload.

Time and Frequency Domain Responses of 3000 g SRS up to 10 kHz with a 2 lbs Payload Waveform Graph

Figure 3: Actual time and frequency domain responses of 5000 g SRS up to 5 kHz with a 2 lbs payload.

Time and Frequency Domain Responses of 5000 g SRS up to 5 kHz with a 2 lbs Payload Waveform Graph