The MTS3000-RingCore is an automatic measurement system able to perform strain-gage ring-coring residual stress measurements. The complete measurement chain is composed by:
- Mechanical device (drilling unit for hollow milling cutter, digital camera & laser beams for centering)
- Electronic devices (control of advancing and drilling, zero setting surface)
- Dedicated software (software for the automatic control and back-calculation of residual stress)
- Digital strain gage amplifier (automatic acquisition of the strain gage rosette data)
The mechanical device of the MTS3000-RingCore allows to perform the core in the material around the strain gage rosette thanks to the hollow drill housed in its lower part. Moreover, the mechanical device includes also the electrical drilling motor, the belt/gear transmission of the drilling movement and a stepper motor for the control of the vertical movement.
A special hollow shaft is used for the connection of the drilling tool: this special configuration guarantees the electrical connections of the strain gage rosette cables. Four magnetic orientable and adjustable feet with high adhesion force are used to fix the mechanical device on the specimens under test. These special magnetic feet can be activated / deactivated by the user so to guarantee a simpler positioning of the mechanical device in the testing location.
Finally, the mechanical device includes 2 laser beam sources oriented at 90° and a camera, both focusing the drilling area: the combination of these two devices allows positioning the mechanical unit accurately centered with the strain gage rosette. Alternatively, a special hollow shaft allows the strain gage installation through the drilling axis, ensuring an implicit mutual centering between the drilling axis and the strain gage rosette.
The drilling tool developed for this measurement is a carbide hollow milling cutter. The external diameter of the cutter is 18mm and the internal diameter is 14mm. Depending on the material under test (and particularly its hardness), it is possible to use a drilling tool with 7 or 3 cutting teeth.
The MTS3000-RingCore system is automatically controlled by a dedicated software called RSM-RC. In analogy with the MTS3000-Restan system, this software allows the control of the drilling process, the setting of the measurement parameters (including strain gage type, amplifier and delay time) and the automatic acquisition of the strain values from the rosette during the measurement. The software allows also the acquisition of the images of the digital camera installed on the mechanical body of the device: this camera is used for the centering of the strain gage with the drilling axis thanks to the presence of two laser beams that are able to project two perpendicular lines directly on the tested workpiece. These can be aligned with the strain gage reference positioning lines.
Finally, the acquired data can be processed using the evaluation software EVAL-RC dedicated to the ring-coring measurements.
The EVAL-RC software allows the calculation of residual stress using the Differential method, the Incremental method and the Integral method. Moreover, the EVAL-RC software gives the possibility to make stress graphs in the depth, calculating the stress in a custom direction or plotting a Mohr circle of residual stresses.
