Page 16 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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PROPERTIES OF STRUCTURAL STEELS AND EFFECTS OF STEELMAKING AND FABRICATION

1.14 CHAPTER ONE

FIGURE 1.4 Curve shows the relationship between true stress and true
strain for 50-ksi-yield-point HSLA steel.

1.7 PROPERTIES IN SHEAR

The ratio of shear stress to shear strain during initial elastic behavior is the shear modulus G. According
to the theory of elasticity, this quantity is related to the modulus of elasticity E and Poisson’s ratio v by
G = E (1.1)
21 + v)
(
3
Thus a minimum value of G for structural steels is about 11 × 10 ksi. The yield stress in shear is
about 0.57 times the yield stress in tension. The shear strength, or shear stress at failure in pure shear,
varies from two-thirds to three-fourths of the tensile strength for the various steels. Because of the
generally consistent relationship of shear properties to tensile properties for the structural steels, and
because of the difficulty of making accurate shear tests, shear tests are seldom performed.

1.8 HARDNESS TESTS

In the Brinell hardness test, a small spherical ball of specified size is forced into a flat steel speci-
men by a known static load. The diameter of the indentation made in the specimen can be measured
by a micrometer microscope. The Brinell hardness number may then be calculated as the ratio of
the applied load, in kilograms, to the surface area of the indentation, in square millimeters. In prac-
tice, the hardness number can be read directly from tables for given indentation measurements.
The Rockwell hardness test is similar in principle to the Brinell test. A spheroconical diamond
penetrator is sometimes used to form the indentation and the depth of the indentation is measured
with a built-in, differential depth-measurement device. This measurement, which can be read directly
from a dial on the testing device, becomes the Rockwell hardness number.
In either test, the hardness number depends on the load and type of penetrator used; therefore,
these should be indicated when listing a hardness number. Other hardness tests, such as the Vickers
tests, are also sometimes used. Tables are available that give approximate relationships between the
different hardness numbers determined for a specific material.
Hardness numbers are considered to be related to the tensile strength of steel. Although there is no
absolute criterion to convert from hardness numbers to tensile strength, charts are available that give

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