dilatanciának

Dilatancy is a phenomenon observed in granular materials where the volume of the material increases when it is sheared. This means that as the material is deformed, its constituent particles move apart, creating more empty space between them. This effect is particularly noticeable in dense granular packings. When subjected to shear stress, the particles are forced to ride over each other, leading to an expansion of the bulk material.

The term "dilatancy" comes from the Latin word "dilatare," meaning to expand or spread out. It was first described by Osborne Reynolds in the late 19th century. Reynolds observed that a bag filled with sand would become less dense when shaken, indicating an increase in volume. He proposed that this was due to the particles rearranging themselves to occupy more space.

Dilatancy is a key characteristic of non-Newtonian fluids, specifically those classified as shear-thickening. In such fluids, viscosity increases with shear rate. Examples include mixtures of cornstarch and water (oobleck) or certain suspensions. When these materials are subjected to a sudden force, they resist deformation due to dilatancy. Conversely, when the shear stress is removed, the material can flow more easily. This property has applications in protective gear, such as impact-resistant vests, and in industrial processes involving granular flow. The degree of dilatancy depends on factors like particle shape, size distribution, and the initial packing density of the material.