What is the term for materials whose elastic properties differ in all directions?

The term for materials whose elastic properties differ in all directions is "Anisotropic." Anisotropic materials exhibit different mechanical properties when measured along different axes. This behavior is crucial in many engineering applications because it affects how materials respond under various loads and conditions.

In contrast, isotropic materials have uniform properties in all directions, meaning their elastic properties are consistent regardless of the direction in which they are measured. Homogeneous materials are characterized by having uniform composition and properties throughout their volume but do not necessarily indicate directionality in those properties. Orthotropic materials, a subset of anisotropic materials, possess three mutually perpendicular planes of symmetry, leading to unique properties in three different directions, but are still directional.

Understanding the differences among these categories is vital in materials science and engineering, as it informs choices in material selection and design processes based on how materials will be used in practice.