Mechanical properties of solids

Elasticity

The property of a body by the virtue of which it tends to regain its original size and shape when the applied force is removed

Elastic deformation

Caused when a material is compressed, bent, or stretched

Plasticity

ability to be molded(no gross tendancy to regain its shape)

Elastic behaviour of solids

solid is deformed - atoms displaced from equilibrium position changes interatomic distances when force is removed interatomic forces drive them back( like spring ball system)

Hooke's Law

The law stating that the stress of a solid is directly proportional to the strain applied to it.(for small deformations)
constant is known as modulus of elasticity

deformation

when forces are applied on a body in such a manner that the body is still in static equilibrium it is deformed to a small or a large extent

restoring force

any force that always acts to pull a system back toward equilibrium

Stress

Restoring force per unit area

tensile stress

The force per unit cross-sectional area, measured in Pa

Types of stress

-tension, compression-longitudinal

-shearing
-hydraulic

types of strain

-longitudinal strain
-shearing strain
-volumetric strain

yield point (elastic limit)

point on the load deformation curve past which deformation is permanent(doesn't regain original shape)

yield strength (σy)

The stress required to produce a very slight yet specified amount of plastic strain( not reversible)(corresponding to yield point)

permanent set

a set that remains in place throughout the production

tensile strength

A measure of how much stress from pulling, or tension, a material can withstand before breaking.

fracture point

The point at which the material breaks

brittle / ductile

if Ultimate strength and fracture points are close then it's brittle if they're far apart it's ductile

Elastomers

substances like tissues of aorta rubber band etc which can be stretched to cause large strains(stress strain curve is a half parabola)

Young's Modulus

A measure of the stiffness of an elastic material and defined by stress/strain. ( tensile or compressive stress/longitudinal strain)

Shear Modulus

A term describing a solid's resistance to shear stress, denoted by the letter S and measured by the ratio of shear stress (F/A) to strain (x/h).

relationship between G AND Y

For most materials G= Y/3

Bulk Modulus

A term that describes a substance's resistance to compression under pressure, denoted by the variable B and measured by the ratio of stress (delta P) to strain (delta V/V)( same as stiffness)

Compressibility

(opposite of bulks modulus literally)it's reciprocal

delta=WL^3/4bd^3Y

a bar of length L depth d breadth b when loaded at the center sags by an amount delta

Buckling

as depth is increased unless load is exactly at the right place (difficult and improbable) the bar will bend a lot