690 Prof. E. L. Hancock on Recovery of 



after No. 6 (see curve 7). The specimen was now allowed 

 to rest 472 days, when it was again tested. This last test 

 No. 8 shows the elasticity again restored, the elastic limit 

 raised, and the modulus of elasticity the same as originally. 



Tests made at Purdue University, 



Some tension tests of nickel-steel similar to those 

 outlined above, were made by Professor W. K. Hatt, and 

 reported by him in the ' Proceedings' of the Indiana Academy 

 of Science. The results obtained agree closely with those of 

 Muir. 



During the last three years further tests have been made 

 in the Laboratory for Testing Materials of Purdue University, 

 under the direction of Prof. E. J. Fermier and the writer. The 

 work planned included an investigation of the recovery of 

 structural carbon-steel and low nickel-steel from overstrain 

 in both tension and torsion. Part of this work has been 

 completed and the results are given in this paper. The work 

 completed may be divided into three parts, viz. : — 



(1) Recovery from overstrain in tension. 



(2) „ „ „ in direct torsion. 



(3) „ „ „ in reverse torsion. 



With the exception of the three and one half per cent, of 

 nickel, the nickel-steel had the same chemical composition as 

 the carbon-steel. The tension- test pieces were turned to a 

 diameter of 0*75 inch for a length of 9 inches. The torsion 

 specimens were 0*875 inch in diameter and about 20 inches 

 long ; they were left unturned, and were tested on a gauge 

 length of 10 inches. Torsional deformations were measured 

 with an Olsen troptometer. 



Results of Tests. 



Only a few typical curves are shown in this report. In 

 fig. 2 is shown the results of tension tests on nickel-steel. 

 The piece showed an elastic limit of 54,000 lbs. per sq. inch. 

 The first test was continued until the piece was overstrained. 

 Test No. 2, made 15 minutes later, shows that the elasticity 

 was destroyed by the overstrain in No. 1. After a period of 

 rest of 96 hours the piece was again tested. This test, No. 3, 

 indicates a recovery of the elastic properties, the elastic limit 

 now being 36,000 lbs. per sq. inch, and the modulus of elas- 

 ticity being about the same as before the first test. Test 

 No. 4, made 120 hours after No. 3, shows the elastic limit 

 still higher, it now being 48,000. Test No. 5, made 792 hours 

 after No. 4, shows the elasticity entirely restored. The 



