Flexibility

The science of elasticity is that part of mechanics that studies the relationships between reversible deformations of bodies and external forces that act on this body.

Flexibility (also known as elasticity or reciprocal stiffness) is a part of mechanics that studies the relationships between deformations of bodies and external forces that act on this body. In flexibility problems, it is then solved whether the deformation of the body or structure has not exceeded the permissible value.

One of the first to look for relationships between the forces acting on a body and the deformations of the body caused by these forces was the British physicist Robert Hooke, who in 1660 discovered (later named after him) the law of elasticity, describing a direct relationship between the extension of a spring and the loading force.

We usually express Hooke's law for tension (for small stresses and small strains) in the form ε = σ/E, where ε is the proportional elongation (ε = Δl / l), σ is the mechanical stress (σ = F / S) and E is Young's modulus of elasticity in tension ε. However, this linear dependence only applies if the stress in the material does not exceed the so-called limit of proportionality; after exceeding this limit, the material can still deform elastically, but Hooke's law then ceases to apply.

With an even greater load (exceeding the so-called limit of elasticity), irreversible changes already occur, such as plastic (permanent) deformation or (when exceeding the strength limit) disruption of the integrity of the material (rupture, cracking).

In tissue biomechanics, it is important to talk mainly about the biomechanical properties of connective tissue. From a histological point of view, we divide it into ligament, cartilage and bone. You will learn more about this issue in the section on elastic properties of tissues.

Related articles

 * Hooke's law
 * Young's modulus of elasticity