Compressive stress is the force per unit area applied to an object that causes it to become shorter or more compact. It occurs when a material is subjected to squeezing forces that push inward from opposite directions. This is different from tensile stress, which occurs when forces pull a material apart, stretching it instead of compressing it.
For example, when you press both ends of a sponge together, the sponge shrinks in size. This happens because the applied force is compressing the material. Similarly, when a heavy object rests on a pillar, the weight of the object exerts a downward force, causing the pillar to experience compressive stress. If the stress is too high, the pillar might crack or buckle.
Formula
Compressive stress, denoted by the Greek symbol sigma σ, is given by:
σ C = F/A
Where:
– F: Applied compressive force
– A: Area over which the force is applied
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This formula quantifies the force applied per unit area of a material. The larger the applied force, the greater the compressive stress. However, if the area over which the force is distributed increases, the stress decreases.
Units
The SI unit of compressive stress is the Pascal (Pa), which is defined as one Newton per square meter (N/m²). This means that if a force of 1 Newton is applied uniformly over an area of 1 square meter, the resulting compressive stress is 1 Pascal. However, since the Pascal is a very small unit, larger units like megaPascals (MPa, 10 6 Pa) and gigaPascals (GPa, 10 9 ) are commonly used in engineering and materials science.
When materials experience stress, they undergo deformation, which is termed strain.
Compressive Strain
When a material is subjected to compressive stress, it deforms by reducing its length. This deformation is measured using compressive strain, which tells us how much a material shortens compared to its original length.
Compressive strain is denoted by the Greek symbol epsilon, ε, and is given by:
ε C = ΔL/L
Where:
– ΔL: Change in length
– L: Original length of the material
Since strain is the ratio of two lengths, it is dimensionless and indicates how much material has compressed relative to its original size.
Compressive Strain and Material Behavior
Different materials respond differently to compressive stress. Some materials, like rubber and soft metals, can undergo large compressive strains without breaking, while brittle materials like ceramics and concrete may crack or fail under high compression. Hooke’s Law describes the relationship between compressive stress and compressive strain for elastic materials:
σ C = E⋅ε C
Where E is Young’s modulus, a measure of a material’s stiffness. A higher Young’s modulus indicates greater resistance to deformation.
Compressive Stress vs. Tensile Stress
- References Compressive Stress | Definition & Formula – Study.com Elasticity – Physics.info Stress and Strain in Tension and Compression – Phys.libretexts.org Stress – Spark.iop.org
Article was last reviewed on Tuesday, June 10, 2025
