The maximum resistance offered by any material. To the externally force/load.
◼️Load:
The external force which act on a rigid body are known as load.
◼️ Types of load:
Tensile load/force (pull in nature)
Compressive load/force (push in nature)
3. Shear force (acts tangential or perallel to the surface under action)
◼️ Tensile load & compressive load this two force are known as the direct force as thay acts normal to the surface.
◼️Stress:
When external force are applied on any body offers resistance force by developing internal opposite force. The resistance force per unit area is called as stress.
Where, 𝞂 is the direct stress, F is internal resistance force equal to the externally applied force and A is the normal (cross-sectional) area. The unit of stress is N/m². Which is also known as Pascal and represented as pa.
◼️ Types of stress:
Normal stress (𝝈n)
Shear stress (𝜏)
◼️ Normal stress further classified into two categories:
Tensile stress (𝞂t)
The force has tendency to elongate the body. Therefore the tensile stress try to resist the elongation in object.
2. Compressive stress (𝝈c)
The force has tendency to compress the body. Therefore, the compressive stress try to resist the compression in object.
◼️Shear stress (𝜏)
When equal and opposite force act parallel to the surface on any cross-sectional plane of the body, and has tendency to slid it's one part over the other at the plane, then the stress induced are known as shear stresses.
The unit of shear stress is also known as Pascal and represented as Pa.
◾ SI unit of shear stress is N/m²
◼️Strain (𝜺)
When external force are applied on any body and the body can not offer sufficient resistance force to opposite the externally applied force, then some deformation produced in strain.
The strain is dimensions less quantity and measures the deformation produced in a member by the loads.
◼️ Types of strain:
Normal strain (𝜺n)
Shear strain (𝜺s)
1. Normal strain:
When force act normal to the surface.
◼️Normal strain depending upon types of force:
a) Tensile strain (𝜺t)
When elongation in object is observed in the direction parallel to the applied force, the tensile force is developed.
B) Compressive strain (𝜺c)
When compression in object is observed in the direction parallel to the applied force, then compressive strain is developed.
2. Shear strain (𝜺s)
When equal and opposite force act parallel to the surface on any cross-sectional plane of the body and has tendency to slide it's one part over the other at that plane, then the body gets deformation by an angel Φ.
𝜺 = CC'/BC
= tan𝛟
= 𝛟 radian
◼️ Volumetric strain (𝜺v)
The ratio between the change in volume and the original is known as volumetric strain.
◼️Hooke's Law:
According to this law, within elastic limit, strain is proportional to stress.
◼️ Following elastic constants are important to understand.
1. Modulus of elasticity (E)
Within elastic limit, the ratio of normal stress to the normal strain is known as modulus of elasticity or elastic modulus or young modulus.
2.Modulus of rigidity (G):
Within elastic limit, the ratio of shear stress to the shear strain is known as modulus of rigidity or shear modulus.
3. Bulk modulus ( K):
It is the ratio of average stress intensity to the volumetric strain.
4. Poission's ratio ( V or 1/m):
When an object is deformed in longitudinal direction then simultaneously the lateral dimensions also change. It sis the ratio of lateral strain to the longitudinal strain.
◼️ Stress-strain curve for mild steel:
◼️ Salient points:
O - H : proportionality limit in which the material follows Hooke's Law.
A: Elastic points.
B: Upper yield point.
C: Lower yield point.
D: Neck formation region.
◼️ Modulus of resilience:
It is the area under the curve which is marked by the yellow area. It is the energy absorbed at unit volume up to elastic limit.
Modulus of resilience = 1/2 σ𝜺
◼️ Modulus of toughness:
It is the ratio of the whole curve ( point O -E). Energy absorbed at unit volume up to breaking point.
◼️Hooke's Law:
◼️ Following elastic constants are important to understand.
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