** Anisotropy**: characteristic of a material for which its physical properties depend on the direction along which they are measured.

* Poisson’s coefficient* (

*): it is the ratio between the transversal contraction and the elongation of a rod, constituted by a given material, stressed by traction.*

**n*** Deformation*: we generally mean any alteration of the shape or size of a body caused by stress. It is a dimensionless quantity since it appears to be the ratio between two quantities having the same unit of measurement. Two types of deformation are distinguished: the deformation and, also called linear deformation, is the ratio between the variation in length of a stressed body and its initial length; the angular deformation g characterizes the variation that the angle existing between two fibers of an unstressed body undergoes after the application of a stress.

* Elasticity*: of a material it is said that it has an elastic behavior when, once the load with which it has been solicited has been removed, it returns to its original configuration, ie there are no deformations, while a material is said in which the deformations that occur under stress remain after removal of the load. Furthermore it is said that a material has a linear elastic behavior when under stress the deformations are directly proportional to the tensions (contrary to the non-linear elastic behavior).

* Isotropy*: characteristic of a material for which a physical property does not depend on the direction along which it is measured.

* Modulus of normal elasticity* (

*): o Young’s modulus, is the ratio between the normal traction tension (s) that occurs in a material subjected to a simple tensile stress and the deformation is parallel to the resulting tension (in elastic field).*

**E*** Tangential elasticity modulus* (

*): or shear modulus, is the ratio between the shear shear stress (t), which occurs in a shear stressed material, and the angular or shear deformation g; it is obtained once known E and n with the formula: G = ½ E / (1 + n).*

**G*** Plasticity*: property of a material for which a structural component formed by it remains in the deformed configuration even after the removal of the load that caused it.

* Stiffness*: it is the ratio between a load acting on a continuous system, defined geometrically and consisting of a specific material, and the resulting displacement.

* Tension*: from the dimensional point of view (N / m2 = Pa) it is a force on a surface and represents the internal force acting on each area unit belonging to a section of a body, which is opposed to traction, compression and cutting induced by the action of external forces. The resulting voltage can be broken down into three components, one along the perpendicular to the plane of the section, indicated with s and defined normal two-sided tension along two mutually orthogonal axes lying on the section plane, indicated with t and defined tangential stresses. The state of total tension in any point of a body is completely defined by six voltage values, three of which are normal and three are tangential.

Although they have the same dimensions, pressures and tensions are two different magnitudes in that pressure is applied to a surface when a distributed force acts on it, quantitatively defined by an area, while there is talk of the tension of a body externally stressed when we want to indicate the load intensity to which a point is subjected.

* Viscoelasticity*: characteristic of a material whose deformation does not depend only on the system of loads to which it is subject but also on their speed of application.