PSI - Issue 57

Lewis Milne et al. / Procedia Structural Integrity 57 (2024) 365–374 Lewis Milne et al. / Structural Integrity Procedia 00 (2019) 000 – 000

368

4

(a)

(b)

(c)

Figure 3 - Test specimens in the Instron 8801 Servohydraulic Test Machine(a) and the Shimadzu USF-2000A Testing Machine (b,c)

As a result, for the conventional frequency fatigue testing for Q355B, a different specimen design was used, which had the same gauge section geometry as the UFT specimen. This specimen geometry is given in Figure 2(c). This avoids the influence of size effects, and ensures that the only discrepancy between the two test cases is the frequency of the loading. Using different test geometries for the different materials means that the conventional frequency fatigue data for the two specimens cannot be directly compared, however as both materials are of equivalent grades and similar ferrite contents, similar frequency sensitivities would be expected, and thus the discrepancy between them can be used as a measure of how significantly size effects can skew results. 4. Experimental Procedure Conventional axial-loaded, stress controlled fatigue testing was carried out at 20Hz following the procedures specified in BS ISO 1099 (2017). All tests were carried out at R= -1, in environmental conditions and at room temperature using an Instron 8801 Servohydraulic Testing Machine.

500

S355JR 20Hz S355JR 20kHz Q355B 20Hz Q355B 20kHz Run Outs

450

400

350

54% increase in fatigue limit at 20kHz

300

250

Stress Amplitude (MPa)

200

150

1,00E+04 1,00E+05 1,00E+06 1,00E+07 1,00E+08 1,00E+09 1,00E+10

Number of cycles to failure

Figure 4 - 20Hz and 20kHz fatigue curves for S355JR (orange) and Q355B (green)