Answer:
Principal Plane: It is that plane in a stressed body over which no shearing stresses act. As we know that in a stressed body on different planes 2 different kind of stresses act normal stresses acting normal to the plane ans shearing stresses acting in the plane. The special planes over which no shearing stresses act and only normal stresses are present are termed as principal planes.
Principal Stress: The stresses in the principal planes are termed as normal stresses.
Anelasticity: It is the behavior of a material in which no definite relation can found to exist between stress and strain at any point in the stressed body.
Yield Point: It is the point in the stress-strain curve of a body at which the stress in the body reaches it's yield value or the object is just about to undergo plastic deformation if we just increase value of stress above this value. It is often not well defined in high strength materials or in some materials such as mild steel 2 yield points are observed.
Ultimate tensile strength: It is the maximum value of stress that a body can develop prior to fracture.
Hardness: it is defined as the ability of the body to resist scratches or indentation or abrasion.
Toughness: It is the ability of the body to absorb energy and deform without fracture when it is loaded. The area under the stress strain curve is taken as a measure of toughness of the body.
Elastic limit: The stress limit upto which the body regains it's original shape upon removal of the stresses is termed as elastic limit of the body.
