HARDNESS:
Hardness
is a measure of the material’s resistance to localized plastic deformation
(e.g. dent or scratch).
DUCTILITY:
Ductility
measures the amount of plastic deformation that a material goes through by the
time it breaks.
Ductility is said to be the
property of a material to stretch without getting damaged. Metals having
ductile property can be stretched into wires. An example is copper wire.
MALLEABILITY:
Malleability is said to be the
property of a material to deform under compression. The metals having malleable
property can be rolled or beaten into sheets. An example is aluminium foil.In
more simple words, ductility means stretching to wires and malleability means
beating to sheets.
Ductility means that a metal can be
changed to another form by pulling, compression or twisting.On the other hand,Malleability
means that a metal can be changed into another form by beating or hitting it
hard.
A
metal’s ductility is measured by looking at its tensile strength. The tensile
strength inspects how far a metal could stretch without breaking. A metal’s
malleability is measured by looking at how much pressure it can withstand
without breaking.The bend test is the commonly used test for determining the ductility
of a metal.Gold and silver are the top ranking ductile and malleable metals.
The two properties of Malleability and ductility do not
always correlate in metals. For example, gold is both malleable and ductile and lead
is only malleable.
BRITTLENESS:
A material is Brittle if, when subjected to stress, it
breaks without significant deformation (strain). Brittle materials
absorb relatively little energy prior to fracture, even those of high strength.
Breaking is often accompanied by a snapping sound.
TWO MEASURES
OF DUCTILITY:
1) Percent Elongation (%El )
2) Percent Reduction In Area
• Highly ductile metals can exhibit
significant strain before fracturing, whereas brittle materials frequently
display very little strain.
• An overly simplistic way of viewing
ductility is the degree to which a material is “forgiving” of local deformation
without the occurrence of fracture.
Brittle
materials: %EL £ 5% at fracture
Ductile
materials: %EL and %RA both ³ 25%.
