Plastic deformation is the permanent distortion that occurs when a material is subjected to tensile, compressive, bending, or torsion stresses that exceed its yield strength and cause it to elongate, compress, buckle, bend, or twist .
Where does plastic deformation occur?
Plastic deformation in the form of slip occurs along the close-packed lattice planes , where the energy requirement for dislocation motion is minimized. Slip inside a crystal progresses until the dislocation line reaches the end of the crystal, where it results in a visible step – a so called slip band.
How does plastic deformation occur in metals?
Plastic deformation of metals takes place predominantly by shearing : lattice planes in the material slide over each other, allowing macroscopic shape change without appreciably affecting the ordering and arrangements of atoms within the structure.
How does plastic deformation occur in a thermoplastic polymer?
Most thermoplastic melts are shear thinning (i.e., their apparent viscosity decreases with an increase in the steady-state shear rate). ... Just below the melting temperature, the polymer behaves in a rubbery manner. When stress is applied , both elastic and plastic deformation of the polymer occurs.
What are the modes of plastic deformation?
Plastic deformation occurs by the following modes: 1 . Slip 2. Twinning 3. Kink .
Why is plastic deformation permanent?
Plastic deformation is permanent in that the material is unable to return to its original size and shape after the load is removed .
How is plastic deformation calculated?
The plastic strain is obtained by subtracting the elastic strain, defined as the value of true stress divided by the Young’s modulus , from the value of total strain (see Figure 1).
What is plastic deformation of bone?
Plastic deformation refers to the deformation of a bone, without fracture of its cortices, that persists once the deforming force has been removed . It is not a common condition but is seen more frequently in children than in adults.
What is creep in plastics?
Creep is the tendency of a polymeric material to deform permanently under the influence of constant stress , as applied through tensile, compressive, shear, or flexural loading. It occurs as a function of time through extended exposure to levels of stress that are below the yield strength of the material.
What are the 3 stages of creep?
Primary Creep: starts at a rapid rate and slows with time. Secondary Creep : has a relatively uniform rate. Tertiary Creep: has an accelerated creep rate and terminates when the material breaks or ruptures. It is associated with both necking and formation of grain boundary voids.
How can we prevent plastic deformation?
Due to the anisotropy of the plastic, deformation is easily generated. In order to reduce the deformation, reinforcing ribs can be designed . The reinforcing ribs should be staggered.
What are the types of deformation?
When a rock is subjected to increasing stress it passes through 3 successive stages of deformation. Elastic Deformation — wherein the strain is reversible. Ductile Deformation — wherein the strain is irreversible. Fracture – irreversible strain wherein the material breaks.
Why is it called plastic deformation?
This type of deformation involves stretching of the bonds, but the atoms do not slip past each other. When the stress is sufficient to permanently deform the metal , it is called plastic deformation.
What kind of material is plastic?
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient . Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes.
What is plastic behavior?
For stresses beyond the elastic limit , a material exhibits plastic behavior. This means the material deforms irreversibly and does not return to its original shape and size, even when the load is removed. When stress is gradually increased beyond the elastic limit, the material undergoes plastic deformation.
Is plastic deformation reversible?
In physics and materials science, plasticity, also known as plastic deformation, is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces.
