13-6] 



VIBRATION AND SHOCK 



699 



1.0 



0.6 

 0.4 



0.2 



0.1 



0.6 



0.04 

 0.03 



0.02 



0.01 



1.0 ^ 



Q 



0.5^ 



10.2 



0.1 

 0.05 



0.1 

 RATIO 



0.2 0.4 0.6 1 2 4 6 



FORCING FREQUENCY ^ gj 



UNDAMPED NATURAL FREQUENCY Q, 



10 



Fig. 13-8 Force and Displacement Transmissibility for a Viscously Damped, 

 Single-Degree-of-Freedom with Sinusoidal Excitation System Excited by Random 

 Vibration. (After C. E. Crede, "Vibration and Shock Isolators," Machine Design, 



Aug. 1954) 



The maximum transmissibility for sinusoidal excitation is now often 

 called the ^ of the resonance, by analogy with the usage which has long 

 been standard in electrical networks. This quantity is conveniently used 

 in a discussion of random vibration. It is important to remember that the 

 peak amplitudes plotted in Fig. 13-8 apply for steady-state vibration. It 

 requires a number of cycles to reach this peak. 



Let n be the number of cycles required to permit the vibration of mass M 

 to reach 95 per cent of its steady-state amplitude. 



Then: «^3^/x (13-10) 



The following expression is useful when c jcc is less than 0.2: 



t 



1 



- yJKM. 



c 



(13-11) 



