Transients in Mechanical Systems

A study of the response of an electrical network or system to the input of transients in the form of short-duration pulses is an accepted method of analysis of the network. By comparing the input and the output, conclusions may be drawn as to the respective merit of the various components. Until recently similar procedures were only of academic interest with mechanical systems. However, the tests for mechanical ruggedness, which are required of electronic gear in order to pass specifications for the armed forces, are an example of the application of transients to a mechanical system. These tests are known as High Impact Shock Tesls. A basic part of an electrical system is a damped resonant network consisting of an inductance, a capacitance and a resistance. A mass, a spring and a friction device is the equivalent mechanical network called a simple mechanical system and a combination of such networks is a general mechanical system. It is, of course, advantageous to keep the mechanical system as simple as possible without detracting from the general usefulness of the results obtained. The problems here considered are pertinent to a system which is essentially made up of a supporting structure or table and a resilient mounting array bearing the equipment (e.g. electronic gear) which is vulnerable to shock. (See Fig. 1.) A shock is the physical manifestation of the transfer of mechanical energy from one body to another during an extremely short interval of time. The order of magnitude of the time interval is milliseconds and quite frequently fractions of a millisecond.