Dilatans

Dilatans refers to materials that exhibit dilatancy, a property in which the bulk volume increases when the material is subjected to shear. The term is often used interchangeably with dilatant materials or shear-thickening fluids. In geology and soil mechanics, dilatant behavior is common in dense granular media such as sand or gravel, where particle rearrangement under shear creates additional pore space and causes expansion; by contrast, looser materials may exhibit contractive, or negative, dilatancy under certain conditions.

The mechanism behind dilatancy involves microstructural rearrangements and the networks of contacts between particles. As shear forces act, grains must move past each other, which can require extra space and lead to dilation. The presence and properties of interstitial fluids can modify the response by changing effective stress and lubrication within the pore spaces, influencing both stiffness and strength of the material.

Dilatant behavior has important implications for engineering and natural processes. In soils, it affects shear strength, deformation, and phenomena such as pore-pressure changes during rapid loading or earthquake shaking, including the potential for liquefaction in saturated sands. In materials science, dilatant or shear-thickening fluids are studied for applications in impact protection, damping, and sometimes in suspension formulations.

Examples of everyday dilatants include cornstarch suspensions, which rapidly thicken under sudden force. While dilatans is a less common plural form in technical usage, it highlights the broader category of materials that respond to shear with an increase in volume. See also dilatancy, shear-thickening, and soil mechanics.