About Bend Relief
You can use the Bend tool to add relief to bends on board segments. Relief helps to control the behavior of the material and to prevent unwanted deformation. Relief takes into account any material stretching necessary for unbending the model into an accurate flat model for manufacture. You can define relief settings during feature creation, or you can predefine them in the Relief area of the Preferences dialog box or using the Board parameters.
The following types of relief can be added to a bend:
No Relief
Slit Relief
Rectangular Relief
Obround Relief