What Is Strain Rate?

Strain rate is the change in the strain (deformation) of a material with respect to time. Its definition was first introduced by American metallurgist Jade LeCocq in 1867, and it is defined as "strain occurrence rate, which is the time rate of strain change." In physics ^[1] , strain rate is usually defined as the derivative of strain with respect to time. Its precise definition depends on how the strain is measured. Strain rate is a measure of the deformation speed of a material. The derivative of strain with time. Nanocrystals can obtain higher strength and toughness at high strain rates, but the elastic modulus of the material is not affected by this.

Strain rate is the change in strain (deformation) of a material with respect to time. Its definition was first introduced by American metallurgist Jade LeCocq in 1867, and it is defined as "strain occurrence rate, which is the time rate of strain change." In physics, strain rate is usually defined as the derivative of strain with respect to time. Its precise definition depends on how the strain is measured. Strain rate is a measure of the deformation rate of a material. The derivative of strain with time. Nanocrystals can obtain higher strength and better toughness at high strain rates.

In simple environments, a single number may be sufficient to describe the strain and therefore the strain rate. For example, when a long and uniform rubber band is gradually stretched by stretching at the ends, the strain can be defined as the ratio between the amount of stretch and the original length of the band,

among them

Is the original length, and L (t) is the length of each time t. Then the strain rate is,

Where v (t) is the speed at which the ends move away from each other.

When materials are subjected to parallel shear without changing the volume, the strain rate can also be expressed in singular; that is, when the deformation can be described as a set of infinitely small parallel layers that slide on each other in the same direction as if they were rigid sheets, without Change their spacing. ^[3]

In a more general case, when a material is deformed in various directions at different rates, the strain (and therefore the strain rate) around points within the material cannot be represented by a single quantity or even a single vector. In this case, the deformation rate must be represented by a tensor, and the linear mapping between vectors indicates how the relative velocity of the medium changes when a moving distance is a short distance from a point in a given direction. The strain rate tensor can be defined as the time derivative of the strain tensor, or as the symmetrical portion of the gradient of the material velocity (derivative with respect to position). ^[1]

Strain is basically a ratio of two lengths, so it is a dimensionless quantity (not dependent on the choice of measurement unit). Therefore, the strain rate is the inverse of time in size. In the International System of Units (SI), in seconds (

).