Shear

Shear refers to the relative movement of material layers or particles caused by tangential forces. In powder and process engineering, shear occurs in particular during mixing, conveying, dosing, agglomeration or comminution, when particles slide against one another or along equipment surfaces.

Shear is frequently described in terms of the shear rate γ′ and the shear stress τ. It has a significant influence on the structure and properties of powders and granules. Depending on the intensity and duration of the stress, shear can lead to deagglomeration, particle destruction, dust formation, segregation or surface activation.

For many bulk materials, the classic Mohr-Coulomb condition for mechanical shear failure applies approximately.

τ = σ_n tan(φ)

• τ is the shear stress
• σ_n is the normal stress
• φ is the internal friction angle
• c is the cohesion