Nickel and Carbon Steel from Overstrain. 691 



elastic limit — 60,000 — being somewhat higher than that 

 shown by the first test. The slope of the curves 3, 4, and 5 

 shows that in the recovery from overstrain the piece regained 

 the same modulus of elasticity as it had originally ; this is 

 indicated by the parallelism of the curves below the elastic 

 limit. The curves show that overstrain destroyed the elastic 

 properties of the piece and that these were'restored by subse- 

 quent rest. 



A summary of tension tests made on the carbon steel is 

 shown in fig, 3. The test, No. 1, shows the elastic limit of 

 the material to be 35,000 lbs. per sq. inch. This test was 

 continued until the piece was overstrained. Test No. 2, made 

 immediately after No. 1, shows that the elastic properties 

 were entirely destroyed by the original overstrain. After 

 a period of rest of 70 hours the piece was again tested, the 

 curve, No. 3, shows a recovery of the elastic limit and 

 modulus of elasticity. Tests 4 and 5, made after periods 

 of rest, indicated in fig. 3, show a continued rise in the elastic 

 limit, but no change in the modulus of elasticity. In test 

 No. 5 the piece was again overstrained. Test No. 3, made 

 immediately after this second overstrain, shows the elasticity 

 again destroyed. The piece was now immersed in boiling 

 water and subjected to its annealing effect for 15 min., when 

 it was again tested. This treatment restored the elasticity of 

 the material, shown by curve No. 7. The elastic limit, as 

 shown by this last test, is higher than before, but the modulus 

 of elasticity is the same. 



Figure 4 shows the results of torsion tests on nickel-steel. 

 The overstrain in the first test destroyed the elastic properties. 

 This is shown by the second test made immediately. Tests 

 3, 4, and 5, made at intervals shown on the drawing, show a 

 gradual recovery of the elastic limit and a return of the 

 modulus of elasticity. Test No. 5 was continued until the 

 piece was again overstrained. After 620 minutes the piece 

 was again tested, but showed no elasticity. It was immersed 

 in boiling- water 15 minutes and again tested (see curve No. 7), 

 showing the elastic limit higher than before, and the modulus 

 of elasticity restored. 



The results of the direct torsion tests made on carbon-steel 

 are shown in fig. 5. The original test shows an elastic limit of 

 28,000 inch-pounds moment. The test was continued until 

 the piece was overstrained, as in the preceding case, and 

 immediately retested showing an absence of elasticity. Tests 

 3, 4, 5, and 6 were made after different periods of rest. The 

 elastic limit gradually returned and even exceeded the original 

 amount bv 1200 inch-pounds, and the modulus of elasticity 



3 A2 



