162 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 195 



data on the zero frequency shear modulus is obtained from the Young's 

 modulus for a static pull which is from 30,000 to 50,000 pounds/square 

 inch. Since the Young's modulus is three times the shearing modulus, 

 the zero frequency shearing modulus should not exceed 1.1 X 10 dynes/ 

 cm . Hence one may expect that other relaxations will occur at lower 

 frequencies. 



Fig. 34 shows the attenuation per wavelength for shear waves. The 

 solid line for 30°C represents the calculated attenuation per wavelength 

 for the model assumed. If all the dissipation were due to shear mech- 

 anisms, the calculated attenuations would occur as shown by the 30°C 



PULSED 

 OSCILLATOR 



A,B,C,D 

 AMPLIFIER 

 BUFFERS 



ATTENUATOR 



I 



V 



.SPECIMEN 



r 



Fig. 30 — Ultrasonic pulse method for measuring the velocities and attenua- 

 tions of highlj' attenuating plastics. 



10^x2.4 



12 16 20 24 28 32 36 

 FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 31 — Velocity of longitudinal waves in polyethylene plotted as a function 

 of temperature and frequency. 



