What is Flexural Strength and Why is it Important?

Buzzle introduces you to flexural strength and its importance in constructional mechanics and material science in this article. Read through to know more.
Testing methods
The two standard methods used to test the flexural strength of any material are: 'Third-point loading' and/or 'Center-point loading'. The former test requires application of a set of two equal loads at each 1/3rd point on the entire span of material, while the latter involves application of complete load at the center of the length of the material.

Flexural or compressive strength is the mechanical measure of maximum load bearing capability of a material without undergoing any permanent deformation. In simple terms, it is the extent to which an object or any material may resist breakage when bent.

The flexural strength of any material or object depicts the maximum stress experienced by it at the instant of its failure. It is symbolized by sigma or σ.

Flexural stress illustration

Mathematically,

Flexural strength σ = F/A
where, F = Axial force, and
A = Cross-sectional area of the object

Center point loading
Center point loading

Third point loading
Third-point loading

The above equation gives us the engineering stress value experienced just before the failure of an object and does not take into account the change in cross-sectional area during the time duration for which axial force is applied.

When an axial force is applied at any point on an object, like a beam or a rod, then the surface of the object that contains the point of contact of force is under compressive stress. On the other hand, the opposite surface of the object experiences tensile stress.

It is to be noted that, environmental conditions like temperature and moisture affect the flexural strength of a material to a great extent. Lower temperatures and dry air tends to extract moisture that binds the particles of the object, and hence, make it more brittle. However, higher temperatures and a humid climate helps the object retain moisture and thus, increases its flexural strength.

Difference Between Flexural and Tensile Strength

tensile vs flexural stress

There is always the possibility of some local defects being present in any object. When an object is put under tensile stress it tends to 'expand'. All the fibers or regions of an object experience an equal force. Any weak regions in such a case may give up and undergo deformation. Flexural stress, on the other hand, exerts both tensile and compressive force upon an object. This results in unequal distribution of forces among the fibers of the objects. The 'extreme fibers', i.e., the fibers at the surface of the object tend to experience maximum forces. Therefore, they are most vulnerable to breakage or rupture.

Usually, any homogeneous object will have the same tensile and flexural strength. In case if the extreme fibers are stronger, tensile strength tends to be lower than flexural strength. Whereas, when the extreme fibers are defective, then tensile strength is lower than the flexural strength.

Importance of Flexural Strength

Calculation of flexural strength is considered crucial in structural mechanics.
  • It helps in designing structural elements like beams, cantilevers, shafts, etc.
  • Aids in the study of materials and their properties.
  • Provides a parameter for development of stronger constructional materials.
  • Flexural strength helps in judging the quality of structures being used for construction.
  • It is a tool to predict both resistance and durability of objects.