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Strength of Materials |
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Strength : It is the resistance by which materials oppose the deformation.
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Stress : A measure of the average amount of force exerted per unit area.
 where s is the average
stress. It is also known as engineering stress or nominal stress. F is the force acting on the area A.
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Strain : The deformation of materials caused by the action of stress.
 where e is strain
in measured direction, lo is the original length of the material and
l is the current length of the material
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Hooke's Law: It states that for the materials loaded within elastic limits the stress is proportional to
strain.
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Total Stress : The resultant internal force which changes the size or shape of a body which acted on
by external forces.
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Unit Stress : It is the stress per unit area.
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Normal Stress : It is on a section. It is the stress which acts in a direction perpendicular to section
considered.
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Ultimate Stress : The ratio of the maximum load which a specimen sustains to its original area of the
cross-section.
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Elastic Limit : The maximum unit stress to which a material can be subjected and still is able to return
to its original form after removal of stress.
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Yield Point : The unit stress at which the deformation first increases noticeably without any increase in
the applied load. It is always above the proportional limit.
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Ultimate Strength : The highest unit stress it can sustain before rupturing.
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Breaking Strength : The stress at which the material tested ruptures.
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Modulus of Elasticity (E) : The constant that expresses the ratio of unit stress to unit deformation for all
values unit stress not exceeding the proportional limit of material. It is also called as Modulus of Rigidity.
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Factor of Safety : The ratio of ultimate strength of the material to the allowable stress.
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Elasticity : The ability of a material to deform and return to its original shape after removal of the load.
The amount of deformation is called Strain.
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Ductility : The ability of a material to undergo large permanent deformations in tension i.e., property which
enables a material to be beaten or rolled into thin sheets.
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Malleability : The ability of a material to undergo large permanent deformation in compression or property
which enables a material to be beaten or rolled into thin sheets. This property is important in metalworking.
Gold is the most malleable metal followed by aluminium.
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Toughness : The ability of a material to withstand high unit stress along with great unit deformation without
fracture.
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Stiffness : The ability of a material to resist deformation or deflection under stress.
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Hardness : The ability of a material to resist very small indentation abrasion and plastic deformation.
In other words, high resistance of a material to various kinds of shape change when force is applied.
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Creep (Flow of Metals) : The tendency of a solid material to slowly move or deform permanently under the influence of stresses.
It always increases with temperature. Creep deformation does not occur suddenly upon the application of stress. It
is time-dependent deformation.
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