Table 1-2.Mechanical Properties of Metals/Alloys
Rockwell C number. On nonferrous metals, that are
Strength is the property that enables a metal to resist
deformation under load. The ultimate strength is the
maximum strain a material can withstand. Tensile
strength is a measurement of the resistance to being
pulled apart when placed in a tension load.
Fatigue strength is the ability of material to resist
various kinds of rapidly changing stresses and is ex-
pressed by the magnitude of alternating stress for a
specified number of cycles.
Impact strength is the ability of a metal to resist
suddenly applied loads and is measured in foot-pounds
Hardness is the property of a material to resist
permanent indentation. Because there are several meth-
ods of measuring hardness, the hardness of a material is
always specified in terms of the particular test that was
used to measure this property. Rockwell, Vickers, or
Brinell are some of the methods of testing. Of these tests,
Rockwell is the one most frequently used. The basic
principle used in the Rockwell testis that a hard material
can penetrate a softer one. We then measure the amount
of penetration and compare it to a scale. For ferrous
metals, which are usually harder than nonferrous metals,
a diamond tip is used and the hardness is indicated by a
softer, a metal ball is used and the hardness is indicated
by a Rockwell B number. To get an idea of the
property of hardness, compare lead and steel. Lead can
be scratched with a pointed wooden stick but steel
cannot because it is harder than lead.
A full explanation of the various methods used to
determine the hardness of a material is available in
commercial books or books located in your base library.
Toughness is the property that enables a material to
withstand shock and to be deformed without rupturing.
Toughness may be considered as a combination of
strength and plasticity. Table 1-2 shows the order of
some of the more common materials for toughness as
well as other properties.
When a material has a load applied to it, the load
causes the material to deform. Elasticity is the ability of
a material to return to its original shape after the load is
removed. Theoretically, the elastic limit of a material is
the limit to which a material can be loaded and still
recover its original shape after the load is removed.