218 Prof. E. L. Hancock : Effect of Combined 
pieces of shafting were the same size as those of carbon- 
steel. Curve 1 shows the result of a simple flexure test. 
Curves 2, 3, 4, and 5 show the results of flexure tests while 
the material was under a torque sufficient to produce a fibre 
stress in the outer fibre of 15,200, 22,800, 30,400, and 
38,000 lbs. per sq. inch, respectively. 
The change in the elastic limit in tension, torsion, and 
flexure due to the presence of another stress — torsion, tension, 
compression, and torsion — is shown in fig. 6. The abscissae 
represent the amount of the particular stress initially applied, 
and the ordinates the portion of the elastic limit (normal 
elastic limit) obtained in tension, torsion, and flexure as a 
result of the initial stress. All the results that have been 
obtained by the writer are shown in the diagram, so that, not 
only are the tests made during the past year represented, but 
also all those that have been reported heretofore. These points 
are averaged by lines 1, 2, 3, and 4 in fig. 7. The figure 
needs no explanation. 
The change in the unit stress at the elastic limit, part of 
deformation at elastic limit, and the modulus of elasticity 
are shown by fig. 8. The amount of stress applied initially 
is represented on the horizontal axis, and the corresponding 
change produced by this initial stress is shown on the vertical 
axis. It is seen that the unit stress at the elastic limit, 
deformation, and modulus of elasticity are all lowered by the 
stress initially applied. 
The results obtained from the tests of steel tubing, in 
torsion while under tension, are shown in Table I. The table 
shows that an amount of tension applied, equal to 0, 33, 50, 
69, 81, and 100 per cent, of the elastic limit in tension, pro- 
duces an elastic limit in torsion of 100, 68, 60, 43, 31, and 25 
per cent, of the normal elastic limit in torsion respectively. 
The same table also gives the results of the compression- 
torsion tests, showing that an amount of compression applied, 
equal to 0, 33, 50, 83, and 100 per cent, of the normal elastic 
limit in compression, produces an elastic limit in torsion of 
100, 73, 42, 36, and 27 per cent, of the normal elastic limit in 
torsion respectively. It is seen from this table, as well as from 
fig. 8, that the unit stress and unit strain at the elastic 
limit are lowered considerably due to the combined stresses, 
and that the modulus of elasticity is also lowered, but to less 
degree. That is, the strength of the material suffers most 
when combined stresses are acting. 
The results of the flexure tests on steel shafting are shown 
in Table II. Here the nickel-steel seems to withstand the 
combined stresses better than the mild carbon-steel. This is 
seen by comparing the percentage of normal elastic limit, for 
