# Compressive strength facts for kids

Kids Encyclopedia Facts
Measuring the compressive strength of a steel drum

Compressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g. many concrete structures have compressive strengths in excess of 50 MPa, whereas a material such as soft sandstone may have a compressive strength as low as 5 or 10 MPa.

## Introduction

When a specimen of material is loaded in such a way that it extends it is said to be in tension. On the other hand if the material compresses and shortens it is said to be in compression.

On an atomic level, the molecules or atoms are forced apart when in tension whereas in compression they are forced together. Since atoms in solids always try to find an equilibrium position and distance between other atoms forces arise throughout the entire material which oppose both tension or compression.

The phenomena prevailing on an atomic level are therefore similar. On a macroscopic scale, these aspects are also reflected in the fact that the properties of materials in tension and compression are quite similar, at least for most materials.

Of course, the major difference between the two types of loading is the strain which would have opposite signs for tension (positive) and compression (negative).

## Compressive Strength

By definition, the compressive strength of a material is that value of uniaxial stress reached when the material fails completely. The compressive strength is usually obtained experimentally by means of a compressive test. The apparatus used for this experiment is the same as that used in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive load is applied. As can be imagined, the specimen (Usually cylindrical) is shortened as well as spread laterally. A stress against strain curve is plotted by the instrument and would look similar to the following:

## See also

In Spanish: Esfuerzo de compresión para niños

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