Transients in Mechanical Systems 



By J. T. MULLER 



Introduction 



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, conclu- 

 sions 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 sys- 

 tem. These tests are known as High Impact Shock Tests. 



A basic part of an electrical system is a damped resonant network consist- 

 ing of an inductance, a capacitance and a resistance. A mass, a spring and 

 a friction device is the equivalent mechanical network called a simple me- 

 chanical 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 essen- 

 tially 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. 



The system is excited by administering large spurts of mechanical energy 

 to the supporting table. The manner in which this energy is suppHed to the 

 base and the way it is dissipated through the system are the subjects of this 

 paper. 



The energy transfer to the supporting table is accomplished by the use 

 of huge hammers which strike the anvil with controllable speeds. The 

 action is assumed to be similar to that of an explosion, particularly to an 

 underwater explosion at close range or a near-miss. As to the real compar- 

 ison between the two, the reader is referred to the various manuscripts 

 published by the Bureau of -Ships. This particular phase of the subject is 



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