Forces that tend to induce compressive stresses over one part of a cross-section and tensile stresses over the remainder are described as bending or flexural forces.
Bending can be accompanied by direct stresses, transverse shear, or torsional shear, depending on loading. Bending action in beams is often termed flexure, referring to transverse loading of the beam. The deflection of the specimen is the displacement of a point on the neutral axis of the beam from its original position under the action of the applied loads. The deflection, is an indication of the overall stiffness of the material.
In flexure or bend testing, the specimen is typically loaded flat on two solid support rods. A third rod is used for loading. This setup helps ensure three-point loading which allows the tensile forces to act from the centre loading point outward toward the two support rods. Once the specimen has been accurately measured using proper instruments and the machine has been properly set up, the loading continues in a slow, steady manner.
The flexure strength and modulus of rupture may be calculated based on these data. A load-versus-deflection curve or stress-strain curve can be plotted based on the data.