Isotropic vs Anisotropic

At a macroscopic scale, materials can be simply classified into two different properties, Anisotropic and Isotropic [1]. There are three subsets of Anisotropic; Monoclinic, Orthotropic and Transversely Isotropic. In this article, the five types of material properties will be introduced with example materials.

 

Figure 1. The image shows that Isotropic materials have the same mechanical properties in every direction and Anisotropic materials have dependant mechanical properties in different axis [1].

 

 

In materials engineering, Isotropic is defined as identical mechanical properties and thermal properties at any point in the x, y and z-axis [2]. When an external load is applied at any point in 3-axis, isotropic materials will have the same young's modulus, Poisson ratio, yield strength and thermal conductivity in all directions. In summary, Isotropy is uniform in all orientations and its physical property is homogeneous that the chemical bonds within it are all identical in all directions [3]. Glass, metal and polymers are typical isotropic materials.  

 

In contrast, anisotropy is dependent on the direction and has different mechanical properties in different directions. Typically a different chemical bonding in all directions is a condition [3]. Composite materials, many crystals and woods are typical anisotropic materials.

 

Anisotropic materials can be grouped into three subsets. 

1. Monoclinic - Similar to anisotropic material with slightly less non-uniformity, it has one plane of symmetry for material properties. All three axes are unequal in length, and two axes are perpendicular to each other (figure 2). The monoclinic unit cell is unique by a single axis, called an axis of twofold symmetry. The unit cell can be rotated by 180° without changing its appearance [4]. e.g. gypsum, beta-sulfur, kaolin etc.
2. Orthotropic - Similar to anisotropic material but with three planes of symmetry for material properties (figure 3). e.g. woods, structural steel beams etc.
3. Transversely Isotropic - At every point of this material there is one plane in which the mechanical properties are the same in all directions (figure 4).  e.g. Matrix with Fibres, graphite fibres, biological membrane etc.

 

Figure 2. The 3D model shows an example structure of the monoclinic property.

 

Figure 3. The above 3D model shows an example structure of the orthotopic property.

 

Figure 4. The above 3D model shows an example of the transversely Isotropic property.

 

 

 

 

[References]

[1]M. Tutsle, ""Isotropic" vs "Anisotropic" Materials", Knowswhy.com, 2017. [Online]. Available: https://www.knowswhy.com/difference-between-isotropic-and-anisotropic/. [Accessed: 05- Feb- 2022].

[2]"Isotropic and Orthotropic Materials - 2019 - SOLIDWORKS Help", Help.solidworks.com, 2022. [Online]. Available: http://help.solidworks.com/2019/english/SolidWorks/cworks/c_isotropic_orthotropic_materials.htm#:~:text=A%20material%20is%20isotropic%20if,in%20three%20mutually%20perpendicular%20directions. [Accessed: 05- Feb- 2022].

[3]"Difference Between Isotropic and Anisotropic | Difference Between", Differencebetween.net, 2017. [Online]. Available: http://www.differencebetween.net/science/chemistry-science/difference-between-isotropic-and-anisotropic/. [Accessed: 05- Feb- 2022].

[4]Britannica, The Editors of Encyclopaedia. "monoclinic system". Encyclopedia Britannica, 02- Feb- 2018. [Online]. https://www.britannica.com/science/monoclinic-system. [Accessed: 05- Feb- 2022].