THE LAWS OF ELASTICO-VISCOUS FLOW 407 



The apparatus employed for the investigation consisted of 

 a light pulley with radius of 8 cm., over which passed two cords, 

 the ends of which carried scale pans for holding weights. 



The specimen to be investigated had a diameter of 12 mm. at 

 the ends, while the intervening portion (75 mm. long) had a diame- 

 ter of 4 mm. One end was clamped to the supporting frame and 

 the other to the pulley, which rests on a knife-edge in the axis. 



The tests consisted in measuring the angular position of the 

 pulley by a micrometer at intervals of one minute while it is under 

 a constant torque. 



LAWS OF ELASTICO-VISCOUS PLOW 



The behavior of any solid under stress may be considered as 

 the resultant of four elements: (a) the elastic displacement, (b) 

 the elastico-viscous displacement, (c) the viscous displacement, 

 (d) the lost motion. These will be considered in turn. 



a) The elastic displacement. — -This is characterized by being 

 approximately proportional to the stress and independent of time. 1 

 A closer approximation is given by 



S 1 = C I Pe h > p * 



b) The elastico-viscous displacement. — -This is manifested in a 

 slow return when the stress is removed ; and it is assumed that the 

 same forces are brought into play during the direct motion. 



1 Doubtless there is some viscous resistance to this displacement, but it is very 

 small compared with that of cases b and c. 



* The symbols used in this discussion are : 



5 = displacement (twist) . 



P = applied torque. 



F = force, stress. 



C = functions of 0. 



T = melting-point. 



d — temperature. 



t = time. 



t = duration of previous strain. 



E, h, k, a, P 0) a, b, m, tt = constants. 



e = Napierian base. 



