In
continuum mechanics, the
infinitesimal strain theory is a mathematical approach to the description of the
deformation of a solid body in which the
displacements of the material
particles are assumed to be much smaller (indeed,
infinitesimally smaller) than any relevant dimension of the body; so that its geometry and the constitutive properties of the material (such as
density and
stiffness) at each point of space can be assumed to be unchanged by the deformation.