Flexure tests are carried out to obtain information on the flexural properties of materials intended for industrial use or research and development. In this article, we explain what a flexure test is, how and when it is performed and its usefulness in industry.
What is a flexure test?
A bending test is a method that is used when we want to check the bending strength of materials as well as other important properties in material innovation. Depending on the number of pressure points and the support of the test specimen, the following tests are distinguished:
- 1-point bending test
- 3-point bending test
- 4-point bending test
Bending tests are performed with the objective of obtaining information on the bending behavior of the material from the bending stress in one axis. In the case of brittle materials, the bending strength is determined in this way. In the case of ductile materials, the yield stress, the largest possible bending angle and Young’s modulus in the case of elastic deformation are determined.
How a bending test is performed
At its most basic level, a flexure test is performed on a universal testing machine by placing a specimen on two support anvils and bending it by applying a force on 1 or 2 load anvils to measure its properties. Typically, cylindrical test specimens are used which are placed in the center of the checking fixture and whose diameter is proportional to the width of the supports.
The test punch is moved down slowly and at a constant speed to load the specimen with increasing force until it breaks or reaches the previously determined deformation. The maximum load exerted during the bending test is called the breaking force.
Flexure tests are generally performed using a 3- or 4-point bending fixture and the variables, such as test speed and specimen dimensions, are determined by the ISO standard being used.
The bending test produces a tensile stress on the convex side of the specimen and a compressive stress on the concave side. This creates a shear stress zone along the midline.
During the test, the values of bending force and strain are recorded. The entire test sequence is then displayed on a stress-strain curve and the material characteristics are determined.
Types of materials to which flexural strength testing is applied
Bending tests are performed on materials that have an acceptably high ductility, usually metals or metallic materials, although they are also applied to any material that can undergo plastic deformation, such as polymers and plastics. These materials can take any feasible form, however, when used in a bend test they most commonly appear in the form of sheets, strips, rods, bushings and tubes.
What are bending tests used for in the materials industry
If you want to understand various aspects of the behavior of materials and their properties, a simple uniaxial tension or compression test does not provide all the necessary information. However, when the specimen is bent or flexed, it is subjected to a complex combination of forces including tension, compression and shear that provides a more complete understanding of the material properties.
For this reason, flexure tests are used to evaluate the reaction of materials to realistic loading situations. They are also commonly carried out in forensic engineering analysis to evaluate the behavior of materials.
The data obtained from bending tests are especially useful when a material is to be used as a support structure. For example, a plastic chair has to provide support in many directions. While the legs are in compression when in use, the seat will have to withstand the bending forces applied by the seated person. Manufacturers not only want to provide a product that can withstand the intended loads, but the material must also return to its original shape if any bending occurs.
One of the most popular uses of flexural testing is in the area of welds. The purpose is to ensure that the weld has fused properly with the base metal and that the weld itself does not contain any defects that could cause it to fail when it experiences bending stresses. The weld specimen is deformed by a guided bending test so that it forms a “U” by subjecting the material on the outside surface to a tensile force and the material on the inside to a compressive force. If the weld holds and shows no signs of fracture, it has passed the test and is considered acceptable.
In conclusion, flexure tests are essential to guarantee the performance of materials and their intended use in an optimal and efficient way. Don’t you want to miss the advances in the sector? Check out our materials innovation service and visit Infinitia news to keep up to date with the latest developments.