# Strain Rate

Strain rate is the rate of change in strain (deformation) of a material with respect to time.

The strain rate at some point within the material measures the rate at which the distances of adjacent parcels of the material change with time in the neighborhood of that point. It comprises both the rate at which the material is expanding or shrinking (expansion rate), and also the rate at which it is being deformed by progressive shearing without changing its volume (shear rate). It is zero if these distances do not change, as happens when all particles in some region are moving with the same velocity (same speed and direction) and/or rotating with the same angular velocity, as if that part of the medium were a rigid body.

The strain rate is a concept of materials science and continuum mechanics, that plays an essential role in the physics of fluids and deformable solids. In an isotropic Newtonian fluid, in particular, the viscous stress is a linear function of the rate of strain, defined by two coefficients, one relating to the expansion rate (the bulk viscosity coefficient) and one relating to the shear rate (the "ordinary" viscosity coefficient).

### Other articles related to "strain rate, rate":

Coble Creep
... The strain rate in a material experiencing Coble creep is given by where is the applied stress is the average grain boundary diameter is the diffusion coefficient in the grain boundary is the activation energy for ... However, the two mechanisms differ in their relationship between the strain rate and grain size ... In Coble creep, the strain rate is proportional to, whereas the strain rate in Nabarro-Herring creep is proportional to ...
Portevin–Le Chatelier Effect - Conditions That Affect The PLC Effect - Strain Rate
... While temperature related to rate of diffusion, strain rate determines the time that the dislocations take to overcome these obstacles and have a dramatic effect on the conditions of the PLC effect ... So generally the critical stress will decrease with imposed strain rate ... Also the a higher stress rate the lower the band speed ...
Liquid Metal Embrittlement - Characteristics - Test Parameters
... External parameters like temperature, strain rate, stress and time of exposure to the liquid metal prior to testing affect LME ... The upper limit is strain rate sensitive ... An increase in strain rate increases the upper limit temperature as well as the crack propagation rate ...
Constitutive Equation - Mechanical Properties of Matter - Deformation of Fluids
... a Newtonian fluid of viscosity μ, the shear stress τ is linearly related to the strain rate (transverse flow velocity gradient) ∂u/∂y (units s−1) ... xi coordinate directions, eij are the components of the strain rate tensor, Δ is the volumetric strain rate (or dilatation rate) and δij is the ...