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# Flexural strength

Flexural strength is also known as modulus of rupture, bend strength, or fracture strength. Flexural strength is measured in terms of stress, and thus is expressed in pascals (Pa) in the SI system.

For a rectangular sample under a load in a 3 pt bend setup: $\sigma = \frac{3FL}{2bd^2}$

• F is the load (force) at the fracture point
• L is the length of the support span
• b is width
• d is thickness

For a rectangular sample under a load in a 4 pt bend setup: $\sigma = \frac{FL}{bd^2}$

• F is the load (force) at the fracture point
• L is the length of the support (outer) span
• b is width
• d is thickness