PSI - Issue 5

Tomasz Tomaszewski et al. / Procedia Structural Integrity 5 (2017) 840–847 Tomasz Tomaszewski et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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the size effect in the geometrical perspective. This required carrying out tests for tension load, compression load and four-point bending. A clamp for symmetrical bending ( R = -1) was designed and manufactured. The clamp featured adjustment of the supports position and thickness of the installed specimen. As a result, the tests were performed on a single clamp, which was adapted to the specimen size. For the purpose of eliminating the eventual impact of employing the clamp, the supports spacing and the force applied were sized identical to the specimens (Fig. 3, Table 5).

Table 5. Dimensions of four-point bending for two specimen sizes.

Dimensions

Type of geometry

Ø d [mm]

x 1 [mm]

x 2 [mm]

Standard specimen

8

25

44

Minispecimen

3

8.75

14.7

Fig 3. Scheme of four-point bending

3.3. Analysis of results

Fig. 4 includes graphical representation of the high-cycle fatigue test results for steel 1.4301. The experimental points for the presented fatigue characteristics σ a -N were approximated to linear regression line in bilogarithmic system and Basquin equation (Table 6).

Table 6. Fatigue characteristic σ a - N parameters.

Linear regression line log σ a = a log N + b

Basquin relation C = N ( σ a ) β

Correlation coefficient, R 2

Type of load

Type of geometry

a

b

C

β

Axial load, R = -1

Standard specimen

-0.0399 -0.0476 -0.0689 -0.1104

2.578 2.651 2.941 3.232

2.78·10 64 5.61·10 55 4.51·10 42 1.92·10 29

25.00 21.03 14.51

0.983 0.895 0.955 0.980

Minispecimen

Bending load, R = -1

Standard specimen

Minispecimen

9.06

Fig. 4. Fatigue characteristic σ a - N for various load and specimen shape