Rolled homogeneous armour

Rolled Homogeneous Armour, or RHA, is a theoretical basic type of steel plate, used as a baseline to compare the effectiveness of military vehicle armour. This can be used to protect the vehicles from spalls or blasts.

Fractography

Fractography is the study of fracture surfaces of materials to determine the cause of failure. The method is used to study fracture surfaces in any material, such as metals, ceramics, glasses and polymers.

Fracture mechanics

Fracture mechanics is a method for predicting failure of a structure containing a crack. It uses methods of analytical Solid mechanics to calculate the driving force on a crack and those of experimental Solid mechanics to characterize the material's resistance to fracture. 

Fracture mechanics can be divided into linear elastic fracture mechanics (LEFM) and elasto-plastic fracture mechanics (EPFM). 

Air Craft

"All man made contrivances which fly, that is to say which are kept in the air by forces produced by the air are called aircraft".
Eg: balloons, kites, aeroplanes etc.

There are two kinds of air crafts, those which are lighter than air and those which heavier than air. The lighter than means their weight by volume is less than that of air. Heavier than means the weight by volume is heavier than that of air. The former includes balloons, airships etc. and the later comprises kites and aero planes.

Drag

As the airplane moves through the air, there is another aerodynamic force present. The air resists the motion of the aircraft; this resistance force is called the drag of the airplane. Like lift, there are many factors that affect the magnitude of the drag force including:
" shape of the airplane
" "stickiness" of the air
" speed of the aircraft

Lift

To make an airplane fly, we must generate a force to overcome the weight. This force is called the lift and is generated by the motion of the airplane through the air. Lift is an aerodynamic force ("aero" stands for the air, and "dynamic" denotes motion). Lift is directed perpendicular (at right angle) to the flight direction.

Centre of Pressure

The center of pressure is defined just like the center of gravity, but using the pressure distribution around the body instead of the weight distribution.