# Upgrade of the Universal Testing Machine for the Possibilities of Fatigue Tests in a Limited Mode
## 8 TD1 and TD2 Transducer Calibration Processes
### Transducer TD2 Calibration Process  
During the implementation of the TD2 transducer calibration process, there were several issues that needed to be resolved. The first was that due to the nature of the experiment and the dimensions of the TD2 transducer, it was not possible to use the calibration methodology as for TD1, i.e., using a test jig with integrated LARM MSL30 measurement probes. This problem was solved by using elongation values calculated from the values of the loading forces taken from the FPZ 100/1 machine indicator. However, for this method of measurement, physical test specimens had to be clamped in the clamping jaws of the FPZ 100/1 machine, unlike the use of virtual specimens in the case of the TD2 calibration. The second problem was related to these test specimens or to the unsatisfactory deformation characteristics of the materials of these specimens. For calibration purposes, several test specimens with shapes and dimensions according to Figure 5b of material 14 109.3 were applied. The tensile diagram for a diameter of 7.75 mm according to Figure 4b or for a diameter of 9.61 mm according to Figure 9 of curve (a) resulted in a yield strength value \(\sigma_{y}\) of 317 MPa. Also considering the planned experimental measurements in the elastic-plastic or plastic deformation area, where the deformations could far exceed the deformations corresponding to a stress value of 317 MPa, the yield strength value for these purposes was very low. To increase the elastic deformation range, the specimen was primarily subjected to strain hardening by plastic deformation and secondarily to hardening and tempering. For completeness, the process parameters are also given: preheating at 600 \({}^{\circ}\)C for 10 min, heating at 830 \({}^{\circ}\)C for 15 min and finally tempering at 410 \({}^{\circ}\)C for 2 h.  
Figure 9 shows the tensile diagrams of 9.61 mm diameter specimens of 14 109.3 material in three structural states. Curve (a) represents the material in the original structural state with no change in mechanical properties. Curves (b) and (c) represent the specimen after the change in mechanical properties in the new structural states by expansion of the elastic deformation region. Curve (b) is the result of strain hardening by plastic deformation and curve (c) is the result of heat treatment of the specimen by hardening and tempering. These modifications gradually extended the elastic deformation area first to a force of \(F=50\) kN for method (b) and then to a force of \(F=80\) kN for method (c). For this value, a sufficiently large margin of the elastic deformation range was then already established. Figure 9: Tensile diagram of a 9.61 mm diameter specimen of 14 109.3 **(a)** in the original structural state without change in mechanical properties and after change in mechanical properties in the new structural state by expansion of the elastic deformation region as a result of (**b**) strain hardening and (**c**) heat treatment of the specimen by hardening and tempering. The measurement was performed at the maximum possible measured length \(l_{0}=50\) mm, identical to the maximum length of the measuring base of the TD2 transducer. Of the available Scale Factor SF values for the TD2, the most sensitive one of 2000:1 was used. To verify the correctness of the results, this measurement was performed three times. Since no significant differences between the measured data were found, it was possible to proceed to their evaluation. The length change values read from the \(\Delta l\) indicator of the FPZ 100/1 machine were, as in the case of the TD1 calibration, corrected by the appropriate Scale factor SF. Since it was not possible to use the LARM MSL30 probes for the accurate measurement of the compared direct elongation \(\Delta l\) on the clamping jaw side, the analytically calculated value of the measured length change \(\Delta l\) was used as the reference value for the construction of the calibration curves.