Stress And Strain, Definition, Hooke’s Law, Difference Between Stress And Strain

Stress and Strain: In physics, there are two important terms called Stress and Strain, which help us understand how objects change their shape when forces act on them. When we apply force to an object, it can change its shape, and we call this change "deformation." This deformation can happen when we squeeze, squash, twist, shear, rip, or pull the object apart using external forces.

Define Stress and Strain

Stress: Stress, in simple terms, is the force or pressure experienced by a material when external factors like applied forces, uneven heating, or permanent changes affect it. This stress helps us understand how the material will respond, whether it will bounce back elastically, deform permanently, or behave like a fluid. It's a fundamental concept in understanding how materials react to different conditions.

Strain: Strain refers to the measure of deformation or change in shape that occurs in a material when it is subjected to stress. In simple terms, it's the amount of stretching, compressing, or twisting that a material undergoes in response to applied forces or loads.

Types of Stress

• Tensile Stress: This type of stress occurs when a material is pulled or stretched along its length. It leads to the elongation of the material.
• Compressive Stress: Compressive stress happens when a material is squeezed or compressed, causing it to shorten in length.
• Shear Stress: Shear stress occurs when two forces act parallel to each other but in opposite directions, causing the material to deform by sliding along a plane.
• Torsional Stress: Torsional stress is a twisting force applied to a material, resulting in its deformation along a circular path.
• Hydrostatic Stress: This type of stress is uniform in all directions and is exerted on a material submerged in a fluid (liquid or gas) at rest.
• Thermal Stress: Thermal stress arises due to differences in temperature within a material, leading to expansion or contraction and causing internal stresses.

Types of Strain

• Tensile Strain: This happens when the body is stretched or pulled, leading to a change in its length or area.
• Compressive Strain: On the other hand, this occurs when the body is squeezed or compressed, causing a change in its length or area in the opposite direction.

Relation Between Stress and Strain

Hooke’s Law

Stress-Strain Curve

Stress-Strain Curve Explanation

• Proportional Limit: This region follows Hooke's Law, where stress and strain are directly proportional. The graph point OA represents the proportional limit, and the ratio between stress and strain gives us Young's modulus.
• Elastic Limit: Up to this point on the graph, the material returns to its original shape once the load is removed. However, beyond this limit, the material doesn't fully recover, and plastic deformation begins.
• Yield Point: At the yield point, the material starts deforming plastically, meaning it experiences permanent changes in shape. There are two types of yield points: the upper yield point and the lower yield point.
• Ultimate Stress Point: This point on the graph represents the maximum stress the material can handle before it fails. If the stress exceeds this point, the material will fail.
• Fracture or Breaking Point: This is the point where the material fails completely and fractures or breaks apart.