Engineering Materials – Deformation of Solid Materials

Deformation can be referred to as change of shape. In reality, all objects are deformable. Deformation of solid materials has two basics such as change in shape and change in volume of an object by applying external forces. Thus deformation is used as equal to distribution. In this article, we shall discuss deformation of solids in terms of concepts of stress and strain.

What is deformation?

Deformation means that body has undergone change in it dimensional pattern. In simple terms body has changed in shape or size. In engineering point of view it is change in shape of any object due to application of any internal or external force. On other hand, deformation is often measured in terms of strain. It can be both permanent as well as elastic in nature.

Definition of Elastic and Plastic deformation

Elastic deformation

When load is applied on material then it is deformed. If material returns to its original size and shape when load is releases, it is said to have qualified elastic deformation. Elastic deformation can be define as change in shape, size, length, dimension when force is removed and its returns to original shape, size. For example bending rubber hose is the example of elastic deformation.

Plastic deformation

On releasing load, if deformation retains then material is said to have faced plastic deformation. Plastic deformation is point beyond elastic limit where an elastic material losses its elastic properties. For example when we bend copper wire, it will retain nearly all of its deformation.

Types of deformation

Material deformation can be permanent or temporary. Permanent deformation is irreversible which stays even after removal of applied forces while temporary deformation disappears after removal of applied forces. There are two types of deformation like Elastic deformation and Plastic deformation.

Elastic deformation of solid is recoverable once stress is removed. So no part of object under stress has undergone permanent deformation. Plastic deformation of solid is permanent. One or more parts of object under stress have undergone permanent deformation and this permanent deformation under constant load is called creep.

However, for materials of visco-elastic, both permanent and recoverable deformations occur together which are dependent on time. When material focus to applied forces, so elastic deformation followed by plastic deformation. This move from elastic to plastic state is by yield strength of material. Also read Engineering materials: Brittle Fracture Mechanics and Considerations 

In Plastic deformation, breaking of atomic bond is caused by dislocation of atoms. In other words, plastic deformation is based on irreversible atoms displacements through distances from equilibrium positions.

Plastic deformation is different for crystalline and amorphous materials. For crystalline materials, deformation is able to process called slip that involves motion of dislocations. In amorphous material, plastic deformation takes place by viscous flow mechanism. In which atoms or ions slide applied under stress without any directionality.

Different between Plastic and Elastic deformation

Main difference between plastic and an elastic deformation is based on individual to regain their shape and size after an external force is applied to bodies. Generally, terms plastic and elastic are physical properties, used to describe an object. They describe attributes of materials such as rubber, plastic, metal etc.

When an external force is applied to surface of any material or body, this material undergoes deformation. Now, when force is removed, then material depending on its properties may or may not return to its original shape. Check Engineering Materials – Atomic Structure Introduction 

Plastic deformation occurs when bonds between atoms are broken and new ones are formed to make original shape. Elastic deformation occurs because atomic bonds are stretched when pressure is applied, so that they can return to their original positions after this pressure is removed. Now, if body returns to its original shape, then body is said to be elastic in nature

In fact to reach plastic deformation you always have to begin with elastic deformation. And once you reach yield point in one or more parts of object under stress these will undergo plastic deformation. Once you release stress, material will release its elastic energy once shape will not be same due to plastic deformations.

Behavior of metals

Engineering materials are often found to posses good mechanical properties so then they are suitable for application. Mechanical properties referred here are tensile, strength, ductility, toughness, fatigue strength, hardness etc. Therefore, it is important to understand plastic deformation behavior of materials.

  • Anelastic Strain- This is time-dependent recoverable strain
  • Hysteresis Behavior- as results this behavior comes from loading and unloading of material.
  • Bauschinger Effect – This effect show dependence of yield stress on loading path and direction

Plastic deformation is uniform but up to some extent of strain only. Plastic deformation is determined to phenomenon called necking. Under tensile stress, plastic deformation is characterized by strain hardening region and necking region.