1C, Mi;. .1 Mr lit ON THE RECOVERY OF IRON FROM OVERSTRAIN. 



perfect, the material approximately obeying HOOKE'S law up to the maximum stress 

 of 35 tons per square inch. The load in this test was therefore increased beyond its 

 previous maximum amount. The extensmncter, however, was shortly removed for 

 fear of a suddea break, so that the top part of Curve No. 5 (shown dotted in the 

 diagram) was not obtained from extensometer readings. At a stress of about 41 tons 

 per square inch the specimen suddenly broke, unfortunately in the machine grips ; 

 before this stress was reached no yield-point had been passed, or it would have been 

 detected by a rapid falling of the horizontal beam of the testing machine. 



Recovery under Stress, and Effects of Hysteresis. 



Experiments were carried out to test the effect of keeping an overstrained specimen 

 loaded, instead of allowing it to rest in an unstressed condition, and it was found that 

 the material, whether kept stressed or unstressed, recovered at practically the same 

 rate. 



In the following table extensometer readings are given, which show the gradual 

 recovery from overstrain of two specimens, A and B. A was kept loaded to the 

 maximum stress employed to produce overstrain, while B was allowed to rest free 

 from load. 



TABLE comparing Recovery under Stress and Recovery when no Load was Acting. 



m experiment was carried out during a vacation in the Engineering Laboratory 



Jnivermty (Professor BAKR having kindly granted the use of apparatus 



tory), so that the conditions of experiment are somewhat different from 



ined at the beginning of this paper. A 10-ton single-lever testing machine 



and the load applied by thousands of pounds, instead of by tons 



*>r EWINGS extensometer was still used. The material tested was a half-inch 



