Ductility / Malleability: Toughness

4.
Ductility / Malleability
Ductility is the ability of a material to deform plastically (that is, stretch) without
fracturing and retain the new shape when the load is removed. Think of it as the
ability to stretch a given metal into a wire. Ductility is often measured using a tensile
test as a percentage of elongation, or the reduction in the cross sectional area of the
sample before failure. A tensile test can also be used to determine the Young’s
Modulus or modulus of elasticity, an important stress/strain ratio used in many design
calculations. The tendency of a material to resist cracking or breaking under stress
makes ductile materials appropriate for other metalworking processes including
rolling or drawing. Certain other processes like cold-working tend to make a metal
less ductile.
Malleability, a physical property, describes a metal’s ability to be formed without
breaking. Pressure, or compressive stress, is used to press or roll the material into
thinner sheets. A material with high malleability will be able to withstand higher
pressure without breaking.
3. Toughness
Measured using the Charpy impact test similar to Impact Resistance, toughness
represents a material’s ability to absorb impact without fracturing at a given
temperature. Since impact resistance is often lower at low temperatures, materials
may become more brittle. Charpy values are commonly prescribed in ferrous alloys
where the possibilities of low temperatures exist in the application (e.g. offshore oil
platforms, oil pipelines, etc.) or where instantaneous loading is a consideration (e.g.
ballistic containment in military or aircraft applications).
Toughness
The ability of a metal to deform plastically and to absorb energy in the process
before fracture is termed toughness. The emphasis of this definition should be placed
on the ability to absorb energy before fracture. Recall that ductility is a measure of
how much something deforms plastically before fracture, but just because a material
is ductile does not make it tough. The key to toughness is a good combination of
strength and ductility. A material with high strength and high ductility will have
more toughness than a material with low strength and high ductility. Therefore, one
way to measure toughness is by calculating the area under the stress strain curve from
a tensile test. This value is simply called “material toughness” and it has units of
energy per volume. Material toughness equates to a slow absorption of energy by the
material.
There are several variables that have a profound influence on the toughness
of a material. These variables are:
 Strain rate (rate of loading)

 Temperature
 Notch effect
A metal may possess satisfactory toughness under static loads but may fail

under dynamic loads or impact. As a rule ductility and, therefore, toughness decrease
as the rate of loading increases. Temperature is the second variable to have a major
influence on its toughness. As temperature is lowered,the ductility and toughness also
decrease. The third variable is termed notch effect, has to due with the distribution
of stress. A material might display good toughness when the applied stress is uniaxial;
but when a multiaxial stress state is produced due to the presence of a notch, the
material might not withstand the simultaneous elastic and plastic deformation in the
various directions.
Strength: The amount of force necessary for a material to deform. The

higher the force required to change the shape of the material, the stronger
the material is. Steel is notoriously difficult to pull apart, hence it has a
high strength. Silly putty, on the other hand, is not strong at all, and merely
requires a child’s touch to quickly deform this material into all sorts of
shapes..
Toughness: How well the material can resist fracturing when force is
applied. Toughness requires strength as well as ductility, which allows a
material to deform before fracturing.
tough materials are characterized by great deformation, high

tensile strength, and high compressive strength, such as
construction steel, wood and rubber. Tough materials should
be used in the structures bearing impact and vibration, such
as roads, bridges, cranes and beams.

Ductility / Malleability: Toughness

Uploaded by

Copyright:

Available Formats

Ductility / Malleability: Toughness

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Ductility / Malleability: Toughness

Uploaded by

Copyright:

Available Formats

4.

of a material. These variables are:

 Strain rate (rate of loading)

A metal may possess satisfactory toughness under static loads but may fail

Strength: The amount of force necessary for a material to deform. The

tough materials are characterized by great deformation, high

You might also like