Assertion: Yield strength is the stress required to produce a small specific amount of deformation.
Reason: The offset yield strength can be determined by the stress corresponding to the intersection of the stress-strain curve and a line parallel to the elastic line offset by a strain of 0.2 or 0.1%.
A. Both A and R are individually true and R is the correct explanation of A.
B. Both A and R are individually true but R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.

Hint:Elasticity is the capacity of a body to resist a distorting effect and to revert to its original size and form when that influence or force is removed in physics and materials science. When sufficient weights are applied to solid objects, they will deform; if the material is elastic, the item will return to its original shape and size following removal. Plasticity, on the other hand, occurs when an item fails to do so and stays in its distorted condition.

Complete step by step answer:
The elastic limit of a material is defined as the greatest stress that it can tolerate before permanent deformation occurs. It is the material's maximum limit before it may be deformed by plastic deformation. The material returns to its natural form once the tension or force is removed from it. Rubber and other elastomers have the highest elastic limit.

Hooke's law can be used to explain the behaviour. The point on a stress/strain curve when the linear, elastic deformation zone transitions into the non-linear, plastic deformation region is known as a material's proportional limit. The yield point on a stress-strain curve marks the end of elastic activity and the start of plastic behaviour in materials science and engineering.

When a material deforms plastically below the yield point, it returns to its original shape when the applied force is removed. Plastic deformation occurs when a portion of the deformation is permanent and non-reversible once the yield point is passed.

Hence option B is correct.

Note: Permanent deformation occurs when the elastic limit is exceeded. As a result, the elastic limit is the stress level at which permanent deformation may be measured. This necessitates a manual loading and unloading operation, with the precision of which is highly reliant on the equipment utilised and the operator's competence. The elastic limit of elastomers, such as rubber, is significantly higher than the proportionality limit. Plastic strain begins at extremely low loads, according to accurate strain measurements.