PSI - Issue 10

D.G. Ntritsos et al. / Procedia Structural Integrity 10 (2018) 288–294 D.G. Ntritsos et al. / Structural Integrity Procedia 00 (2018) 000 – 000

290

3

The specimen used is typical of the testing apparatus TERCO MT 3012-E. Its geometry is shown in Fig.2a. In this paper the effect of two adjacent stress concentration areas is studied, thus a second set of specimens is used, the geo metry of which is shown in Fig.2b. The difference is the second stress concentration area which is presented as a keyway. The keyway of the specimens of the second set is manufactured according to ISO/R 773:1969, directly related to the shaft diameter of 10 mm. The keyway geometry is common across mechanical engineering designs.

(a)

(b)

Fig. 2. Drawings of the specimens used in fatigue tests. (a) Single Notched; (b) Double Notched.

2.3. Manufacturing and heat treatment

The steel used for manufacturing the specimens according to the DIN standard for steels is CK45 grade and its chemical composition is shown on Table 1. The specimens were manufactured following the guidelines in ISO 1143:2010. after the machining process, the specimens were gradually polished in order to reduce surface roughness and then stress relieved in salt bath in order to eliminate remaining stresses.

Table 1. CK45 Chemical Composition. Chemical Element

Percentage

Carbon Silicon

0.45 0.25 0.65

Manganese

Sulfur

> 0.030

For the polishing process, four different grades of emery were used. The specimens were polished using one pass of 80 grit, 120 grit, 150 grit and 240 grit and lastly with a double pass of 320 grit. After the polishing process was done the specimens were stress relieved in salt bath in a set temperature of 350 o C for a time period of two hours. After that, the specimens were measured, marked in both ends to secure identification after the tests and finally put in a plastic container until the experiment process begun.

2.4. Experimental process

The experiment described is a typical fully reversed bending fatigue test. The experimental procedure was as follows:  The specimen is removed from the individual case it is kept in.  The specimen is secured in place in the testing machine.  The testing apparatus revolutions counter is reset to zero.  The machine is then turned on.  The force is gradually applied in the specimen