Mechanical properties of materials:
A tensile test is generally conducted on a standard specimen to obtain the relationship
between the stress and the strain which is an important characteristic of the material.
In the test, the uniaxial load is applied to the specimen and increased gradually. The
corresponding deformations are recorded throughout the loading.
Stress-strain diagrams of materials vary widely depending upon whether the material is
ductile or brittle in nature.
If the material undergoes a large deformation before failure, it is referred to as ductile
material or else brittle material.
Initial part of the loading indicates a linear relationship between stress and strain, and the
deformation is completely recoverable in this region for both ductile and brittle materials.
This linear relationship, i.e., stress is directly proportional to strain, is popularly known as
Hooke's law.
σ = Eε
The co-efficient E is called the modulus of elasticity or Young's modulus.
Most of the engineering structures are designed to function within their linear elastic region
only.
After the stress reaches a critical value, the deformation becomes irrecoverable. The
corresponding stress is called the yield stress or yield strength of the material beyond
which the material is said to start yielding.
In some of the ductile materials like low carbon steels, as the material reaches the yield
strength it starts yielding continuously even though there is no increment in external
load/stress. This flat curve in stress strain diagram is referred as perfectly plastic region.
The load required to yield the material beyond its yield strength increases appreciably and
this is referred to strain hardening of the material.
In other ductile materials like aluminum alloys, the strain hardening occurs immediately
after the linear elastic region without perfectly elastic region.
After the stress in the specimen reaches a maximum value, called ultimate strength, upon
further stretching, the diameter of the specimen starts decreasing fast due to local
instability and this phenomenon is called necking.
The load required for further elongation of the material in the necking region decreases
with decrease in diameter and the stress value at which the material fails is called the
breaking strength.
In case of brittle materials like cast iron and concrete, the material experiences smaller deformation before rupture and there is no necking.
A tensile test is generally conducted on a standard specimen to obtain the relationship
between the stress and the strain which is an important characteristic of the material.
In the test, the uniaxial load is applied to the specimen and increased gradually. The
corresponding deformations are recorded throughout the loading.
Stress-strain diagrams of materials vary widely depending upon whether the material is
ductile or brittle in nature.
If the material undergoes a large deformation before failure, it is referred to as ductile
material or else brittle material.
Initial part of the loading indicates a linear relationship between stress and strain, and the
deformation is completely recoverable in this region for both ductile and brittle materials.
This linear relationship, i.e., stress is directly proportional to strain, is popularly known as
Hooke's law.
σ = Eε
The co-efficient E is called the modulus of elasticity or Young's modulus.
Most of the engineering structures are designed to function within their linear elastic region
only.
After the stress reaches a critical value, the deformation becomes irrecoverable. The
corresponding stress is called the yield stress or yield strength of the material beyond
which the material is said to start yielding.
In some of the ductile materials like low carbon steels, as the material reaches the yield
strength it starts yielding continuously even though there is no increment in external
load/stress. This flat curve in stress strain diagram is referred as perfectly plastic region.
The load required to yield the material beyond its yield strength increases appreciably and
this is referred to strain hardening of the material.
In other ductile materials like aluminum alloys, the strain hardening occurs immediately
after the linear elastic region without perfectly elastic region.
After the stress in the specimen reaches a maximum value, called ultimate strength, upon
further stretching, the diameter of the specimen starts decreasing fast due to local
instability and this phenomenon is called necking.
The load required for further elongation of the material in the necking region decreases
with decrease in diameter and the stress value at which the material fails is called the
breaking strength.
In case of brittle materials like cast iron and concrete, the material experiences smaller deformation before rupture and there is no necking.
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