Physics- Deformation of solids

Deformation

When an external force is applied on a body, it changes it’s shape and size or both.

Elastic deformation

If a body is able to gain it’s original size/shape back after removal of force then it is said to be “Elastic deformation”.

Plastic deformation

When a body is not able to gain it’s original size/shape after removal of force then it is said to be “Plastic deformation”

Elasticity

Property due to which, when a force is removed, the object can regain its original size/shape.
Elasticity is more for a stronger object.

Plasticity

Property due to which, when a force is applied and removed, it causes a permanent change in the object.

Elastic limit

Maximum Stress that can be applied before the object starts to deform permanently, even after the force is removed.

Stress

Internal restoring force developed per unit area when an external force is applied on a body.
Stress = Force/Area (Nm-2 or Pa)

Longitudinal stress

The force applied on an object in a single plane/axis that can cause a change in its length as the restoring force resists the body from changing it.
Perpendicular to the cross-sectional area.

Shearing stress

Force applied on an object that causes the object to tilt away but the base remains in the same spot.
Parallel to the surface.

Bulk/Hydraulic stress

Force is applied on an object from all directions, changing the volume.
Perpendicular to the object from all sides.

Strain

The deforming force applied to a body that causes a change in its length/shape/size.
Strain = change in dimension/original dimension —> dL/L

Longitudinal strain

The force that causes a change in a body’s length.

Shearing strain

A force that causes the body to tilt away but the base remains in the same spot.
Tan {theta} = perpendicular/base

Volumetric strain

When the force is applied on a body from all directions.
dV/V —→ Change in volume/original volume
Object immersed in a fluid experiences pressure from all sides.

Hooke’s Law

Within the Elastic limit, when a strain is applied on a body, an internal force of stress (restoring force) is produced in a body, acting in opposite direction.
stress = k * strain

Modulus of elasticity

The ratio of stress upon strain of a material within the elastic limit.
k = Stress/strain
k is more for stronger objects.

Young’s Modulus (Y or E)

Ratio of longitudinal stress to the longitudinal strain.
Depends on material, not its size/shape.
L.stress/L.strain —> F/A / dL/L = FL/AdL
(Nm-2 or Pa)

Stress-strain graph

A stress(y axis) - strain(x axis) graph shows a slope that represents elasticity.
The greater the angel from x axis of a slope, greater its elasticity.

[check out the proportionality graph!]

Ductile material

Materials that can undergo “Plastic deformation” of a Large scale before they break.
e.g: mild steel. copper, aluminium

Brittle Material

Materials that can undergo plastic deformation of a small scale before they break.
e.g: Glass, iron.

Elastomers

Materials that can return back to their original shape/size even after a large scale stress/strain is applied on them.
e.g: Rubber, heart vessel.

Elasticity depends upon

1. Nature of material. Stronger the material, greater its elasticity.

2. Type of deformation/stress applied.

Elastic fatigue

When an object is repeatedly provided with stress, it looses its ability or resistance to change back to its original shape/size.

Elastic potential energy

The energy stored in an object when it is stretched or compressed from its original shape.
F = -kx
E = ½ kx² or ½ Fx

Crystalline solids

Particles are arranged in a regular/repeating order.
The structure is made uniformly.
Like NaCl

Amorphous solids

Arranged in an irregular/random order.
Structure is not uniform.
Like Glass, plastics.

Polymeric solids

Long chain molecules formed by repeating strong units.
Chains can be linear/branched/linked.
Like PVC, nylon, polythene.