# Stretched length

The stretched length is the original length of bent workpieces. When bending workpieces such as tubes, they inevitably shorten. Through the center of the workpiece runs the neutral fiber, an imaginary line that does not change in length. However, the outer areas of the bent workpiece have to cover longer distances than the neutral fiber, which is why the shortening occurs. The extent of this shortening depends, among other things, on the diameter of the workpiece. The larger the diameter of the tube, the greater the shortening. In order to determine what length output parts need before the bending process, a calculation of the stretched length helps. For this purpose, classical circular mathematics is used. In this way, the stretched length of the workpiece can be calculated from the tube diameter, the length of the tube section, the bending radius and the straight sections before and after the bend. The calculation becomes more complicated the more bends a part has; especially narrow sheets or small-diameter tubes require additional corrections to be included, since in these cases the neutral fiber shifts toward the inside of bends. There are a variety of programs to easily calculate the stretched length.