The automatic system for measuring residual stresses
by the hole-drilling strain gage method
The Ring-Core residual stress strain-gage method
The Ring-Core residual stress method is a semi-destructive method for residual stress measurements.
Unlike to the hole drilling method, the Ring-Core method needs to machine a core (external diameter of 18mm / internal diameter of 14mm) around a special strain gage rosette with 3 overlapped grids.
Compared with the hole drilling method, the ring-core method allows performing calculation of the residual stress up to higher depths (total depth of 4.0 – 5.0 mm) and it has a lower sensitivity to the eccentricity error.
For these reasons the Ring-Core method is generally suggested in the applications where the residual stress profile close to the surface is less interesting as for big forged parts.
MTS3000-RingCore: the Automatic system for RingCore measurements
Thanks to a long experience in residual stress measuring systems, SINT Technology has developed an automatic device for the determination of the residual stresses by the ring-core method.
The measurement chain is composed by:
a mechanical device including a special hollow milling cutter, a stepper motor for depth control and centering tools (laser beams and side camera);
an electronic control unit (the same used by the MTS3000-Restan system);
an additional electronic unit for the control & supply of the electric motor to machine the core;
a control software (RSM-RC) dedicated for the measurement setup & strain acquisition;
an evaluation software (EVAL-RC) for the calculation of the residual stress using different methods (differential, incremental and integral) starting from the acquired strains.
Key features of the MTS3000-RingCore system
The mechanical device of the RingCore system is developed to perform the following key-operations:
Milling the core (step-by-step mode) on several metals and in different locations of the specimen under test;
Determining the initial depth by electric contact (Zero Setting);
Centering the strain gage rosette;
Using the reference shaft for the strain installation;
Using the laser beams and the camera installed on the mechanical device of the system.