What Is the Flexural Modulus?
Flexural modulus is a measure of how a material will deform and strain when weight or force is applied. It describes the ability of a material, with a specific cross-section, to resist bending when placed under stress. This property is important in civil, mechanical, and aerospace engineering and design, and is frequently used to select correct materials for parts that will support loads without flexing.
Flexural modulus defines the relationship between a bending stress and the resulting strain. Strain is a measure of the amount that a material will deform when a stress is applied. Elastic strain is reversible and will disappear after the stress is removed, meaning the material will return to its original state. At high levels of stress, a material will permanently deform and will not return to its original dimensions. This is referred to as plastic strain or yielding.
Flexural modulus can be plotted in a stress-strain curve, which shows how strain changes with applied bending stress. The slope of this curve in the region where elastic strain occurs defines the flexural modulus of the material. The units of measure are pounds per square inch (psi) or Newtons per square meter, also known as pascals (Pa).
Flexural modulus is determined experimentally in a laboratory, using a sample of material with a specific shape and dimensions. The flexural test measures the force necessary to bend a beam of known dimensions that has a force applied at three points. The beam is supported on the bottom side near both ends and a force is applied to the top at the center point, between the bottom supports. This is known as three-point loading conditions. A force is applied and the deflection or movement of the beam is measured.
Flexural modulus has been determined for a wide variety of structural materials, including metals, wood, glass, concrete, and plastics. It is usually measured at ambient temperature conditions. The properties of some materials, like many plastics, will change with temperature. The flexural test is sometimes conducted at lower or higher temperatures, to simulate the intended end-use environment.
Ductile materials like steel and brass, which can be deformed a great deal before failure, have a well-defined flexural modulus. Brittle materials, like glass and concrete, have little or no plastic deformation before failure. For this reason, many brittle materials do not have a clearly defined flexural modulus, and are often described by their flexural strength — which is the maximum amount of bending stress that can be applied before rupture or failure of the material occurs.
Written by Dorothy Distefano
