VOLUME XXV NUMBER 5 



THE 



JOURNAL OF GEOLOGY 



JULY-AUGUST 1917 



THE LAWS OF ELASTICO-VISCOUS FLOW 



A. A. MICHELSON 



University of Chicago 



When a solid is subjected to a strain beyond the "elastic limit," 1 

 its behavior may be summarized as follows: 



First: The application of the stress results in a rapid elastic 

 yield which, if inertia be negligible, is practically instantaneous. 

 If the stress be now removed, the specimen returns to its former 

 position. 2 



Secondly: This is followed by a slower yielding whose rate, if 

 the stress is not too great, diminishes with time and which ulti- 

 mately attains a constant value which may be zero. 



If the stress be now removed, the specimen returns almost 

 instantaneously to a point short of its original position and then 



1 The term "elastic limit" is very vague and should be replaced by limits which 

 may be characterized as follows: 



a) The first limit is that within which the specimen returns instantly to its original 

 zero. 



Beyond this first limit, if stress be instantly removed, the specimen promptly 

 returns to a position short of its original one, which we may designate as the "new 

 zero." 



b) The second limit is that beyond which the specimen does not return to its 

 original position or to the "new zero" even after a long time. 



c) The third limit is that value of the stress which produces rapid yielding or 

 rupture. 



2 In many cases the time interval between application and release of stress cannot 

 be made sufficiently short for complete, instantaneous recovery. 



40S 



