3.2. Calibration of the stress coefficient
It is necessary to calibrate the detector before testing residual stress. In a laboratory environment, calibration can
be carried out by a tension and compression testing machine. It is based on the principle that a tension and
compression testing machine can provide standard stress value.
Before tensile test, it needs to prepare zero stress specimens. In order to relax the residual stress in the specimen,
annealing treatment or vibration aging treatment should be done to the specimen. The metallurgical composition and
texture as well as the surface roughness of the specimen material should be the same as those of the material to be
tested. Shape and size of the specimen should be meet the requirements of tensile samples of ISO 6892-1:2009 [11].
The surface roughness of calibration region should less than Ra 10