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National Advisory Committee for Aeronautics, Technical Notes - Torsional Elastic Properties of 16;8 Chromium Nickel Steel as Affected by Plastic Deformation and by Heat Treatment

During the past seven years, the National Bureau
of Standards has been studying properties of high—strength
aircraft metals, a project sponsored by the National
Advisory Committee for Aeronautics. The previous reports
of this investigation (references 1, 2, and 3) discussed
the tensile elastic properties-of metals with particular
reference to their elastic strength and modulus o£_elas-

ticity. A paper_by the same authors (reference 4)'de—
scribes the results of—an investigation, not sponsored by;
the.NACA, of—the tensile elastic properties of some metals

not included in the NACA reports.

Because the boundary between elastic and inelastic
strain is indefinite, it was found necessary to evaluate“"
the elastic strength in terms of a number of indices,
termed."proof stresses." These are the stresses necessary
- to cause permanent extensions of 0.001, 0.003, 0.01,

0.1 percent. The tensile stress—strain line for many
metals is curved; hence the tensile modulus of elasticity
cannot be expressed by a single numerical value but only

in terms of several indices. The indices used in the pre—
vious reports are the_modulus of elasticity at zero stress
30 and the linear and the quadratic stress coefficients_
of the modulus C and C'. When these various indices
are known, the tensile elastic properties of metals are
fairly Well defined. In earlier investigations studies
were made of the effect of plastic deformation and heat
treatment“ upon the tensile elastic "properties at 'both room

temperature (references 1 and 2) a'nd sub _zero t-emperature_u

(reference 3)

In many structures_and machines, forces that set up
large shearing stresses in drive.shafts and other connect—
ing members are transmitted as torques. A knowledge of
the reaction of met'als to pure shearing forces there-fore
is desirable. The- pha'se of- the -investigatioh now in prog—
ress deals with the shear elastic properties of di’fferent
high—strength aircraft metals based on tests of thin tubue
lar specimens sub-jeclfied. to torsional loading producing
shear.