Response of structure is determined under impulses large enough to create severe strains. Electrodynamic shaker can provide impulses to nearly any point on structure and can deliver repeated pulses of varying force and duration

Anderson, P.

Birs, C.

English

NASA Technical Reports Server

March 1973	 B73-10057 
	
/	 NASA TECH BRIEF 
	
•	 Lyndon B. Johnson Space Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Dynamic Testing of Complex Structures 
S
The problem: 
Because it cannot be made by theoretical techniques, 
the prediction of the dynamic behavior of complex 
structures, such as automobiles or aircraft, requires 
special testing methods. 
The solution: 
The response of the structure is determined under 
impulses large enough to create severe strains. An 
electrodynamic shaker delivers an impulse load as large 
as 158 x 10 newtons (35,000 pounds force) for a 
duration as short as 0.8 millisecond. The shaker can 
provide impulses to nearly any point on the structure 
and can deliver repeated pulses of varying force and 
duration with practically no change in the test arrange-
ment. 
How it's done: 
An electrodynamic shaker is used to deliver the 
impulse. The shaker has a striker which delivers the 
impulse by impacting a striker-plate that is placed on the 
structure to be tested. The striker and striker-plate are 
both made from cemented tungsten because this impact
resistant material has the high modulus of elasticity 
necessary to achieve a short pulse duration. 
Connected between the striker and the shaker is a 
force transducer consisting of a quartz load link of 
158 x 10 3 newtons capacity held between a base and 
impact cap. 
The motion of the shaker is controlled by an exact 
waveform synthesizer. The shape of the synthesizer 
output is shown in Figure 1. The shaker is programmed 
to deliver the impulse at the point of maximum shaker 
velocity as shown in Figure 2. Because the gap between 
the striker and the striker-plate is held constant, the 
pulse amplitudes are varied by changing the duration of 
the velocity pulse. This adjusts the velocity of the shaker 
upon impact. An impulse of long duration may be 
delivered by shaping the velocity of the shaker, as shown 
in Figure 3, with the striker and striker-plate in 
contact. 
Impact Pulse - Amplitude -. 
Divisions— 1.13 x iO N (2500 Ibs) 
Shaker Velocity 
Amplitude Divisions 
25.4 cm/s (10 mIs)
Time 1 Millisecond
Figure 2 
Strain gauges placed on the structure are used to 
measure the effects of the impact. During a typical test, 
approximately forty specimen-responses are recorded 
for post-test analysis on a multiplex analog computer. 
(continued overleaf) 
+ 
11 
rn
10 
Time (In Milliseconds) 
Figure 1
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https://ntrs.nasa.gov/search.jsp?R=19730000057 2020-03-17T06:40:18+00:00Z
Time 
1 Millisecond
Figure 3
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Lyndon B. Johnson Space Center 
Code JM7 
Houston, Texas 77058 
Reference: TSP73-10057 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Charles Birs and Peter Anderson of

Grumman Aerospace Corp.

under contract to
Johnson Space Center 
(MSC-12569)
0 
B73. 10057	 Category 06	 0


Dynamic testing of complex structures

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