The specimen to be tested can have a round, square, rectangular or polygonal cross-section and the die deforms it plastically until a certain bending angle is reached:
- A defined bending angle (e.g. 90°)
- A bending angle of 180°, the specimen legs are parallel to each other at a fixed distance
- A bending angle of 180°, the specimen legs lie directly against each other
If the required bending angle is 180°, the specimen can be compressed using compression platens following the bending test.
With the force application from the die, the specimen is plastically deformed and bent. The contact surface of the specimen at the die is compressed and the opposite specimen surface is stretched. During the flexure test, tensile stress therefore occurs on one side of the specimen and compressive stress on the opposite side of the specimen.
Relative to the specimen cross-section, the stresses are greatest at the edges and are largely responsible for material failure. These maximum stresses on the edge are also referred to as bending stresses. When a yield strength or compressive yield strength of the material is reached, plastic yielding occurs.
When compared to the tensile test or compression test, in the flexure test there is no homogeneous distribution of stress across the specimen cross-section. The material is equally affected by tensile and compressive forces. Therefore, different limiting stresses often apply to a material in the flexure test versus a tensile or compression test.
Normally, the flexure test is performed at ambient temperature.