Tag: properties of material substances

Whenever a deforming force is applied to a non-rigid substance, the substance undergoes deformation in dimension or shape. Elastic substances are those which come back to their original shape or dimensions after the deformation force is removed. Plastic substances are those which do not come back to their original shape or dimensions even after the deformation force is removed.

Whenever a deforming force is applied to a non-rigid substance, the substance undergoes deformation in dimension or shape. Plastic substances are those which do not come back to their original shape or dimensions even after the deformation force is removed.
Substances like clay, putty, mud etc., are highly plastic in nature

Plastic is a synthetic material made from a wide range of organic polymers such as polyethylene, PVC, nylon, etc., that can be moulded into shape while soft, and then set into a rigid or slightly elastic form. 

The property of a body to regain its original shape when the deforming force is removed from it or to oppose the change in its original shape is called elasticity.

Two prominent mechanisms of plastic deformation, namely slip and twinning occur . 
1. Slip involves sliding of blocks of crystal over one other along definite crystallographic planes, called slip planes. During slip each atom usually moves same integral number of atomic distances along the slip plane producing a step, but the orientation of the crystal remains the same.

2. Portion of crystal takes up an orientation that is related to the orientation of the rest of the untwined lattice in a definite, symmetrical way. The twinned portion of the crystal is a mirror image of the parent crystal.

The yield point is the point on a stressstrain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Yielding means the start of breaking of fibers.

The correct option is option(a)

Plasticity is defined as the property which enables a material to be deformed continuously and permanently without rupture during the application of force. This deformation determines the viscous behavior of the material and is irrecoverable.

Beyond the elastic limit, permanent deformation will occur. The elastic limit is therefore the lowest stress point at which permanent deformation can be measured. At yield point, permanent deformation occurs or the substance becomes plastic.

The correct option is option (b)

The yield point is the point on a stressstrain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Yielding means the start of breaking of fibers.

Thus, Hooke's law dosent hold good in this region, as stress is not proportional to strain in this region