Stress is defined as the intensity of force that acts per unit area.
There are three kinds of stresses  Normal stress, Shear stress, and Volumetric stress.
Normal stress [σ]  Normal stress occurs when a force acts perpendicular to the surface area.
Normal stress [σ] = 

Shear stress [τ]  Shear stress occurs when a force acts parallel to the surface area.
Shear stress [τ] = 

Volumetric stress [σ_{v}]  Volumetric stress occurs when a force acts such that it create in increase volume.
Strain is defined as the ratio of change in dimension to the original dimension.
There are three kinds of strains. Linear strain, Shear strain, and Volumetric strain.
Linear strain [ε]  Linear strain is defined as the ratio of change in dimension to original dimension.
Linear strain [ε] = 

Shear strain [Φ]  Shear strain is defined as the ratio of change in shear dimension to the original dimension.
Shear strain [φ] = 

Volumetric strain [ε_{v}]  Volumetric strain is defined as the ratio of change in volume to the original volume.
Volumetric strain [ε_{v}] = 

StressStrain curve is a graph that shows the relation between stress and strain for a material. StressStrain curve is drawn on the stressStrain graph which has Stress on X axis and Strain on Y axis.
Hooke's law states that for relatively small deformations of objects, the force required to create the deformation is directly proportional to the size of deformation.
Poisson's ratio [ν] is defined as the ratio of lateral strain to longitudinal strain.
Formula
Poisson's ratio [ν] = 

Young's modulus [E] is a measure of stiffness of an object, and is defined as the ratio of longitudinal stress to strain.
Young's modulus [E] = 

Rigidity modulus [G] is defined as the ratio of shear stress to shear strain.
Rigidity modulus [G] = 

Bulk modulus [G] is a measure of resistance of a body to external pressure. It is defined as the ratio of applied pressure to the decrease in volume (volumetric strain).
Bulk modulus [G] = 

An object undergoes a change in length when it is heated. If this length is restrained, then stress is induced in the object. This is known as temperature induced stress.
Coefficient of Expansion [α]  is defined as the change in length in an object of unit length when heated by a temperature difference of 1 unit
There are six different kinds of beams.
Cantilever beams, Simply supported beams, Overhanging beams, Continous beams, Fixed ended beams, and Cantilever  simply supported beams.
The different kinds of loads that can act on beams are  Point load, Uniformly distributed load [UDL], and Uniformly varying load [UVL]
The different kinds of supports that can act on beams are  Hinged support, Roller supports, and Fixed supports.
Shear force is an internal force that is induced in a beam when loads are applied to that beam. Shear force is defined as the algebraic sum of loads to the left or right of a point such that addition of these forces restores vertical equilibrium.
A Shear Fore Diagram (SFD) is a diagram that shows the variation in shear force along the length of a beam.
Bending moment is an internal force that is induced in a beam when loads are applied to that beam. Bending moment is defined as the sum of all moments due to external forces at one side of a section of beam. Bending moment at a point, say A, is determined by multipling the external force with the distance between point A and the point at which the force is acting.
A Bending Moment Diagram (BMD) is a diagram that shows the variation in bending moment along the length of a beam.
Point of Contraflexure is the point in a bending beam where the bending moment is zero, i.e. it the point where the bending moment changes its sign from positive to negative or vice versa.
In a bending moment diagram, the point of Contraflexure is the point at which the bending moment curve intersects with the zero line.
Point of maximum bending moment is the point in a shear force diagram where the shear force curve crosses over the zero line. The value of the bending moment is maximum at this point.
Macaulay's method is a method to find the deflections in a beam that is subject to point loads and discontinuous loads.
For the purposes for analysing the strength of cylinders  cylinders are broadly classified and thin cylinders and thick cylinders.
There are two kinds of stresses that act on cylinders  circumferential stresses and longitudional stresses.
For the purposes for analysing the strength of spheres  spheres are broadly classified and thin cylinders and thick cylinders.
Spheres are subjected to circumferential stress.
Efficiency of joints is defined as the ratio of theoritical stress to actual stress.
Efficiency [η] = 

There are three different kinds of springs.
1. Closed coil helical springs  Helical springs, in which wire is wrapped in a coil, are the most common springs. Closed coil helical springs can be designed to push, pull, or carry loads.
Equivalent springs  Equvalent springs are springs that replace combinations of springs  which can be springs in parallel, or springs in series.
Laminated springs  Laminated springs are semi elliptical springs, also known as leaf springs.
A closed coil helical spring can be subjected to two kinds of loads  Axial loads and Axial twists.
Equivalent springs are springs that replace combination springs. There are two kinds of combination springs  springs in series, and springs in parallel.
Laminated springs, also know as semi elliptical springs and leaf springs, are commonly used for the suspension in wheeled vehicles.
Shafts are mechanical components used for transmitting power through their rotational motion. Shafts are usually circular is in crosssection, and are subjected to torsional shear stresses within this crosssection.
Strength of shafts are measured by the maximum torque or power transmitted by the shaft.
Power of shaft is defined as the rotational work done per second. Rotational power is the product of torque and angular velocity.
The minimum force required to deform a shaft by twisting through a nunit dimension is called torsional rigidity.