PROPERTIES OF
ENGINEERING MATERIALS
EM NOTES # 2
PROPERTIES OF ENGINEERING MATERIALS
• Chemical Properties – concerned with the chemical properties of materials
particularly in connection with corrosion, alloying, compound formation and
so forth
• Physical Properties – a description of physical behavior of a material includes
characteristics such as specific heat, thermal conductivity, coefficient of
expansion, color , refractive index, density and electrical resistivity.
• Mechanical Properties- Characteristics such as strength, hardness,
machinability, ductility, elasticity and plasticity are great interest to the
engineers in selecting materials for machines, structures and determine sizes
of various members to support loads adequately.
• Strain – is a deformation caused by the application of an external force,
When the materials is under strain the material has undergone some
deformation as the result of the application of an external force
• Stress-When internally distributed forces which tend to resist deformation
may be defined qualitatively as stress. Three types of stress: tension,
compression, shear.
all three kind of stress will be found in a material subjected to a load ,
Like for example in bending a combination of tension and compression and
some shear.
• Elasticity – the property of regaining the original shape upon the removal of
the external load . All materials are elastic although the range of elasticity
varies greatly in different material. For stone elasticity is small whereas rubber
deformation Is big. The elasticity in engineering does not refer to the amount
of elastic deformation but to the completeness of recovery after the
removal of the load.
• Hooke’s Law- states that within the elastic range of materials stress is
proportional to strain.
• Bulk Modulus of Elasticity sometimes called the volume modulus. This
condition indicates equals stresses I all directions
• Modulus of Rupture – of a material is a computed strength which does not
bear a specific relationship to the maximum stress the material will sustain
before fracture.
• Plasticity- if a force is applied to a material the relative position of the atoms
is changed and if when the force is removed the atoms return to their
original positions. The material is said to have been in a state of elastic strain.
• Resilience- The capacity of materials to absorb energy within the elastic
range
• Ductility- is that quality of a material by virtue of which it may be plastically
elongated.
• Toughness- The area under the the stress strain diagram up to the breaking
point is related to the amount of energy necessary to cause failure per unit.
Toughness means difficult to break .
• Malleability- If a material can be severely deformed plastically in
compression without fracture
• Hardness- for engineering materials means many things , hardness
sometimes means resistance to scratching, resistance to wear, resistance to
penetration , resistance to cutting.