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National Advisory Committee for Aeronautics, Technical Notes - Correlation of Tensile Strength, Tensile Ductility, and Notch Tensile Strength with the Strength of Rotating Disks of Several Designs in the Range of Low and Intermediate Ductility

Burst tests were conducted on several designs of sound disks and
disks with defects. Results were compared with tensile strength, tensile
ductility, and notch tensile strength. The purposes of the investigation
were to determine the extent to which disk strength can be increased by
increasing tensile strength, to investigate the extent to which a corre-
lation exists between disk strength-and several mechanical properties of
materials at low ductilities, and to present some data on the influence
of several types of stress concentration on the strengths of disks made
from ductile and brittle materials.

For the brittle materials (that may have been subJect to chemical
segregations) the disk strength did not correlate with tensile strength.
For these low-ductility materials (elongation equal to or less than
4.0 percent) and for ductile materials for which notch strength data
were available, the disk strength was found to correlate better with the
combination of tensile strength and notch strength ratio than with the
combination of tensile strength and elongation. For disks possessing
much sharper stress raisers (defects), the notch tensile strength was
superior to the conventional tensile strength as a basis for correla—
ting disk strength with mechanical properties of the sound material.

In general, experimentally determined disk strengths for ductile
materials were slightly less than values predicted from tensile strength
values by the concept of average stress. In the case of brittle mater—
ials, the observed values were significantly less than the predicted
values. The rule that the strength reduction in_disks due to holes is
approximately equal to the percentage of diametral cross-sectional area
removed by the holes was sabstantiated for disks of ductile materials
having large central holes and mwderate size eccentric holes. The rule
was not substantiated for disks of ductile materials having small cen-
tral holes and the rule was not substantiated for disks made from.mater-
ials of low ductility.