NASA-HDBK-7004C Force Limited Vibration Test

EUROLAB, with its state-of-the-art accredited laboratories and expert team, provides precise and fast testing services within the scope of NASA-HDBK-7004C testing. The purpose of force limited vibration testing is to reduce the overtesting associated with unrealistically high base reaction forces that occur at test item resonances in conventional base drive vibration testing.

The purpose of this standard is to provide an approach that can be followed consistently by those wishing to use force limitation without having to do extensive literature research or research and development before performing the test.

Inequality between the mechanical impedances of flight and vibration test mounting configurations is often the most important reason for overtesting in vibration tests. However, this may not be the only reason. A second contribution to vibration extreme testing is the uniformity of movement of the test item in its various attachments to the vibration testing equipment; this uniformity is often in contrast to the unrelated movement of attachments in the aircraft-mount configuration.

The degree of extreme testing associated with the uniformity of attachment movement in testing is usually higher at higher frequencies and when the flight mount configuration includes relatively widely spread attachments in the light flight structure stimulated by an unrelated source such as acoustic noise. Finally, overtesting may simply be the result of unrealistic test specifications, for example due to the cascade of margins associated with individual steps in the process used to develop specifications. Neither of these last two sources of extreme testing is discussed further in this handbook.

For the purposes of this standard, force limited vibration testing is any vibration test in which the reaction force at the base of the test item is measured and limited. In addition, a force-limited vibration test almost always involves measuring and checking the acceleration at the base of the test item, and may also include measuring and limiting acceleration or force responses at other locations of the test item.

For both analysis and testing, it is often convenient to think of the input acceleration as a control and the basic reaction force as a response, similar to the acceleration responses of the test item. The recommended method for measuring the fundamental reaction force is triaxial piezoelectric force meters, but other instruments, such as shaker armature current or strain gauges, may be useful in special situations.

EUROLAB assists manufacturers with NASA-HDBK-7004C test compliance. Our test experts, with their professional working mission and principles, provide you, our manufacturers and suppliers, the best service and controlled testing process in our laboratories. Thanks to these services, businesses receive more effective, high-performance and quality testing services and provide safe, fast and uninterrupted service to their customers.