Recovery of Nickel and Carbon Steel from Overstrain. 689 



The question naturally arose in this connexion as to whether 

 or not the elasticity returned, and if so, what were the most 

 favourable conditions for early recovery. The most important 

 investigation of the subject, carried on in Europe, is reported 

 by Mr. J. Muir, in the Philosophical Transactions of the 

 Royal Society of London, vol. A, 1900. The report deals 

 with the recovery from overstrain in tension only, and includes 

 the following : — 



(a) Recovery from overstrain — Specimens allowed to rest. 



(b) ,, ,, „ Specimens kept under 



stress. 



(c) ,, „ „ Specimens kept at moderate 



temperature. 



(d) „ „ „ Specimens subjected to 



mechanical vibration. 



(e) „ „ ,, Specimens subjected to 



magnetic agitation. 

 The conclusions reached as a result of these investigations 

 are : — 



(a) Elastic properties gradually restored (see PL XVI. fig.l) . 



(b) Only a few tests made, but evidence seems to show that 



that treatment produces little effect, 



(c) Recovery accelerated to a considerable extent. 



(d) Recovery hindered. 



(<?) No appreciable effect upon recovery. 



The diagrams resulting from the tests of one of the specimens 

 of the series (a), as reported by Muir, in the article referred 

 to above, are shown in fig. 1 (PL XVI.). The material used for 

 this test was steel, one inch solid round, having an ultimate 

 strength of 64,000, a yield-point of 54,000, and a per- 

 centage of elongation in 8 inches of 23. As indicated in the 

 drawing (see fig. 1), the specimen was first stressed to the 

 yield-point (see curve 1). Ten minutes later test No. 2 was 

 made ; the corresponding curve shows that the overstrain in 

 the first test entirely destroyed the elastic limit and the 

 modulus of elasticity of the specimen. Tests 3, 4, and 5 

 were made after intervals of 4 hours, 23 hours, and 2 days 

 22 hours respectively. The corresponding curves show 

 that the elasticity is gradually restored by rest. Test No. 6, 

 made 6 days 3 hours after No. 1, shows the elasticity 

 restored, the elastic limit being even a little higher than 

 originally. This test was continued until a new yield- 

 point of the material was reached, that is, it was again 

 overstrained. This second overstrain again destroyed the 

 elastic properties, as shown by test No. 7 made 20 minutes 



Phil. Mag. S. 6. Vol. 13. No. 78. June 1907. 3 A 



