Overview
Physical compression describes the process by which a material's volume decreases or its pressure rises when subjected to a compressive load. In solids and structural components this response is framed by compressive stress acting to shorten or densify the material, and by the change in volume that may accompany it. Compression is a central concept in physics and engineering, linking forces, deformations and energy.
Characteristics and behaviour
Different materials respond to compression in different ways. Solids can exhibit elastic compression (reversible) or plastic/irreversible compaction depending on their microstructure and stress level. Key properties used to describe this behaviour include compressive modulus, yield strength and compressive strength. Fluids and gases behave differently: liquids are nearly incompressible at ordinary pressures, while gases change volume substantially under pressure changes.
Measurement and testing
Engineers and scientists measure compressive properties using standardized tests and pressing equipment. Common tests include uniaxial compression tests, hydrostatic compression and instrumented indentations that record stress–strain curves. Results inform design limits, material selection and safety margins.
Compression of gases and thermodynamic aspects
Gas compression follows relationships such as the Ideal gas law under idealized conditions and more complex equations of state in practical systems. Compression may be isothermal (heat exchanged) or adiabatic (no heat exchange), which affects the pressure rise for a given volume reduction. Gas compression is fundamental to many engines and machines, including gas engines, the Diesel engine, other internal combustion systems and historical devices like the steam engine.
Applications and notable distinctions
- Structural design: sizing columns, bridges and load-bearing parts to resist compressive failure.
- Manufacturing: forming, compacting powders and densifying materials under pressure.
- Energy systems: compressors, engines and hydraulic circuits rely on controlled compression.
- Distinctions: compressive behaviour differs from tensile behaviour; many materials are stronger in compression than in tension.
Understanding compression requires combining mechanics, materials science and thermodynamics so that engineers can predict performance, avoid buckling or crushing, and harness compressed fluids in practical devices.