What is Flexural Strength?
Flexural strength, also known as modulus of rupture, bending strength, or transverse rupture strength, is a material property that quantifies its ability to resist deformation under a bending load. It represents the highest stress experienced within the material at its moment of rupture. Unlike tensile strength, which measures resistance to pulling forces, flexural strength focuses on resistance to forces that cause bending or curving.
How is Flexural Strength Measured?
Flexural strength is typically determined through a flexural test, most commonly a three-point or four-point bending test. In these tests, a sample of specific dimensions is supported at two points and a load is applied at the center (three-point) or at two points between the supports (four-point). The test continues until the sample fractures or yields, and the maximum stress before failure is calculated based on the applied load, geometry of the specimen, and support span.
Practical Applications and Importance
This property is crucial in the design and selection of materials for applications where components are subjected to bending, such as beams, floor tiles, consumer electronics casings, and dental ceramics. For brittle materials like ceramics, glass, and certain polymers, flexural strength is often a more relevant and easier-to-measure indicator of structural integrity than tensile strength, as these materials tend to fail under tensile stress much more readily than compression.
Factors Affecting Flexural Strength
Several factors influence a material's flexural strength, including its chemical composition, microstructure, temperature, and surface finish. For instance, the presence of internal defects, cracks, or surface scratches can significantly reduce flexural strength by acting as stress concentration points where failure initiates. Material thickness and geometry also play a critical role, as bending stresses are distributed differently depending on the cross-sectional shape.