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# What is the formula for stiffness of thickness?

The stiffness of a material in the context of its thickness is typically described by a property called “Flexural Rigidity” (D). Flexural rigidity quantifies how resistant a material or structure is to bending when subjected to a load. It takes into account both the material’s elastic modulus (E), which measures its stiffness, and the geometry of the structure, specifically the moment of inertia (I) and the span (L). The formula for flexural rigidity is as follows:

D=(EI)/L3​​

Where:

• D is the flexural rigidity.
• E is the modulus of elasticity of the material.
• I is the second moment of area of the cross-section (a geometric property related to the shape of the structure).
• L is the span or length of the structure.

This formula is used to calculate the flexural rigidity for beams or other structural elements subjected to bending loads. A higher value of flexural rigidity indicates greater resistance to bending, and it’s often used in structural analysis and design to ensure that beams and other elements meet specific stiffness and deflection requirements.