Stress (Mechanical Design)

In engineering and mechanics, stress is the internal resistance of a material to an applied load, expressed as force per unit area. It quantifies how intensely a material experiences force and helps predict failure under various loading conditions. Stress is calculated using the formula stress = force / area or σ = F / A, where σ (sigma) represents stress, F is the applied force, and A is the cross-sectional area over which the force is distributed.

Stress is force divided by cross-sectional area. Notice the stress developed is smaller in the wider ends of the bar.

Stress is typically measured in pascals (Pa) in the SI system, where 1 Pa = 1 N/m², though megapascals (MPa) and gigapascals (GPa) are more common in engineering applications. In the U.S. Customary system, stress is measured in pounds per square inch (psi) or kilopounds per square inch (ksi), where 1 ksi = 1000 psi.

Determining the cross-section is essential to find the stress developed.

Since different loading conditions affect materials in different ways, stress is further categorized into types such as tensile stress (pulling forces), compressive stress (pushing forces), and shear stress (sliding forces). Understanding stress is fundamental in material selection and structural design, ensuring components can withstand operational forces without failure.

Tensile Stress

Tensile Stress
Tensile stress refers to the stress experienced by a material when forces are applied that pull it apart, causing elongation. It occurs when a material is subjected to axial loads that act along its length, stretching the material. The formula for tensile stress is: tensile stress = force / cross-sectional area or σ = F...

Compressive Stress

Compressive Stress
Compressive stress occurs when a material is subjected to forces that push inward, attempting to shorten or crush it. It is the opposite of tensile stress and arises in components designed to bear loads that press against them, such as columns, struts, and machine frames. The formula for compressive stress is: compressive stress = force...

Shear Stress

Shear Stress
Shear stress occurs when forces act parallel to a material’s surface, causing adjacent layers to slide past each other. Unlike tensile and compressive stress, which act perpendicular to a surface, shear stress results from forces applied tangentially. The formula for shear stress is: shear stress = force / cross-sectional area or τ = F /...

Torsional Stress

Torsional Stress
Torsional stress occurs when a material is subjected to a twisting force, or torque, causing it to rotate about its axis. This type of stress is common in shafts, gears, and other rotating components where torque is transmitted. Torsional stress is a form of shear stress, as it results from forces acting tangentially along a...

Flexural Stress

Flexural Stress
Flexural stress, also known as bending stress, occurs when a material is subjected to a bending moment, causing it to experience both tension and compression. In a beam under bending, the material's outermost fibers experience the highest stress, with one side in tension and the opposite side in compression, while the neutral axis (centerline) remains...

Engineering Stress Vs. True Stress

Engineering Stress Vs. True Stress
Engineering stress and true stress are two ways of measuring stress in a material during deformation, particularly in tensile testing. The key difference lies in how the cross-sectional area of the specimen is considered in the calculation. Engineering Stress (Nominal Stress) is calculated by dividing the applied force by the original cross-sectional area of the...
Tensile Stress

Tensile Stress

Tensile stress refers to the stress experienced by a material when forces are applied that pull it...
Compressive Stress

Compressive Stress

Compressive stress occurs when a material is subjected to forces that push inward, attempting to shorten...
Shear Stress

Shear Stress

Shear stress occurs when forces act parallel to a material’s surface, causing adjacent layers to s...
Torsional Stress

Torsional Stress

Torsional stress occurs when a material is subjected to a twisting force, or torque , causing it to...
Flexural Stress

Flexural Stress

Flexural stress , also known as bending stress , occurs when a material is subjected to a bending moment,...
Engineering Stress Vs. True Stress

Engineering Stress Vs. True Stress

Engineering stress and true stress are two ways of measuring stress in a material during deformation,...