# Upgrade of the Universal Testing Machine for the Possibilities of Fatigue Tests in a Limited Mode
## 7 Test Specimens and Test Materials  
For the calibration of the transducer extensometers TD1 and TD2 and for the low-cycle fatigue measurement process itself, several test specimens made in two shape modifications from two different steel materials were used.  
All specimens used in the TD1 extensometer measurements were made of material 12 010 according to STN or CSN (Slovak or Czech technical standard) 41 2010. Its equivalents are steels with the designation ISO C10, DIN C10, Ck 10 1.0301, e.g., according to [3]. This is a carbon steel for cementing intended for the production of pins and shafts. Material characteristics such as yield strength \(\sigma_{y}\) and ultimate strength \(\sigma_{u}\) (or \(f_{y}\) and \(f_{u}\) according to the Eurocode 3 standards) are given in the available sources in a wide range of 165-345 MPa for \(\sigma_{y}\) and 290 to 845 MPa for \(\sigma_{u}\). The specific value depends on several factors such as the type and degree of heat treatment and material thickness. Based on the measurements of the applied steel modification, a tensile diagram \(F\)-\(\Delta I\) was found according to Figure 4a with approximate values of 318 MPa for \(\sigma_{y}\) and 454 MPa for \(\sigma_{u}\).  
Figure 3: Electrical diagram of the Signal Conditioning Module SCM and its interfacing with the FPZ 100/1 machine and the MF624 I/O card in the PC.  
All specimens used in the TD2 extensometer measurements were made of material 14 109.3 according to STN or CSN 41 4109. Its equivalents are steels with the designation ISO Type 1-0 683/17-73, EURO 100 Cr6 EN94-73 or DIN 100 Cr6 17230-80. This is a chromium steel for rolling bearings in the soft annealed condition. Material characteristics such as yield strength \(\sigma_{\rm y}\) and ultimate strength \(\sigma_{\rm u}\) are quoted in the available sources in the range 423 to 468 MPa for \(\sigma_{\rm y}\) and 628 to 765 MPa for \(\sigma_{\rm u}\). The specific value again depends on several factors such as the type and degree of heat treatment and material thickness. Based on the measurements of the applied steel modification, a tensile diagram \(F\)-\(\Delta l\) was found according to Figure 4b with approximate values of 317 MPa for \(\sigma_{\rm y}\) and 699 MPa for \(\sigma_{\rm u}\). For the calibration of the TD2 transducer, specimens of this material with an actual diameter of 9.61 mm were further hardened and tempered by hardening and tempering for the purpose of calibrating the TD2 transducer to expand the elastic deformation region.  
The shape and dimensions of the test specimens of material 12 010 and of material 14 109.3 used in the calibration and fatigue tests are shown in Figure 5a,b. These were specimens with a cylindrical working part with a circular cross section. The circular cross-section diameters of 8 mm and 10 mm shown are nominal only. The actual diameter values as a result of surface treatments dropped to 7.75 mm and 9.61 mm. The tensile diagrams in Figure 4 were obtained for the 7.75 mm diameter specimens. The force levels \(F_{\rm TD1a}\), \(F_{\rm TD1b}\), \(F_{\rm TD2a}\) and \(F_{\rm TD2b}\) indicated in the tensile diagrams, and their corresponding normal stresses \(\sigma\) were later used in the low-cycle fatigue analysis. The use of test specimens of several shape, size, material modifications and structural states was related precisely to their different physical availability or unavailability during these measurements.  
Figure 4: Tensile diagrams in \(F\)-\(\Delta l\) system for test specimens with actual diameter 7.75 mm for materials: (a) 12 010; (b) 14 109.3.  
Figure 5: Shapes and dimensions of test specimens of materials 12 010 and 14 109.3 with nominal diameter: (a) 8 mm; (b) 10 mm.