Cohesive forces stem from cohesive interactions between particles and can typically be classified into three levels of cohesion: adhesion, capillary and cementation [1]. Here, interactions between particles are limited to surface interactions such as in physico-chemical interactions with very short range or through solid or liquid bridges at the particle contact. Electrical forces such as van der Waals forces are considered negligible in macroscale mechanical behavior. This is due to the gravitational forces dominating the bulk forces in material flow. The cohesive forces between contacting particles form an association with the contacting normal force and the contact overlap or separation . Upon the application of a tensile force between the particles, the adhesive force resists the direction of separation and for a distance the bond is still held. The figure below shows two particles in contact through loading and unloading. The cohesive force resists the tensile force.  The distance at which the cohesive bond is broken differs from the distance for which the cohesive contact bond is formed. The distance at which the cohesive bond breaks leads to a hysteresis phenomenon.

(a) Formation of a cohesive contact. (b) Tensile strength due to the presence of cohesion. (c) Failure of the cohesive bond with a value of > 0. (d) The evolution of the normal force as a function of where represents the energy per unit area to break the cohesive contact [1].

[1] Farhang R., Dubois F., Discrete-Element Modeling of Granular Materials, John Wiley & Sons Inc. 2011