Equivalent Natural Strain
| Natural strain | φ3 | = | |||
| Equivalent strain von Mises | φV,M | = | |||
| Equivalent strain Tresca | φV,T | = | |||
| Greatest degree of natural strain | φg | = |
| Natural strain | φ1 | = | ||||
| φ2 | = |
The natural strain refers to the logarithmic true strain.
The comparative strain is a measure of how the size of a sheet metal has changed during forming. There are different types of deformation that can occur in sheet metal forming, such as length change, transverse strain and volume change.
Equivalent strain measures the relative change in size of the sheet metal compared to its original size. It is calculated as the ratio of the change in size to the original size.
A higher value of the comparative strain means that the sheet has been deformed more, while a lower value indicates a less intensive deformation.
The comparative deformation is an important parameter in sheet metal forming to assess the forming quality and to optimize the process conditions.
The comparative strain φV,T according to Tresca 's hypothesis is the largest absolute logarithmic true strain, based on the tresca's yield criterion.
Another hypothesis frequently used in forming technology is the shape change energy hypothesis according to von Mises , from which the comparative shape change φV,M is calculated.9
Using the greatest degree of deformation φg, the forming force and forming work can be calculated relatively easily.