PSI - Issue 19

S. Periane et al. / Procedia Structural Integrity 19 (2019) 415–422

420

S.Periane et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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4.4. Four-point bending fatigue test

The four-point bending fatigue test is a constant amplitude load controlled test that was done using Instron 8872 equipped with servo hydraulic actuator. The machine is equipped with a ± 25 kN patented Dyna load cell featuring compensation for inertial loads caused by heavy grips and fixtures. The machine setup is shown in figure 7 were the sample is placed in between the top and the bottom supports the distance between the top supports is 10mm and for the bottom supports is 30 mm. The samples are always placed in the same direction of machining. The test was conducted at a frequency of 20Hz.

Fig. 7. Four-point bending fatigue test set up of Instron 8872 machine

4.4.1. Fatigue results of sample machined in dry and emulsion condition

In this test around 8 rectangular samples were machined under dry condition to the dimension of 60mm length 9mm width and 5mm height. Since roughness (µm) and residual stress values (MPa) were measured for all the samples gives a good understanding to correlate it the endurance limit of each sample. Although there are many methods to find the endurance limit of the sample, the staircase method by A. Cellier et al. (2014) is used in this test. In this method the number of cycles to failure is fixed to 10 5 cycles in order to calculate the endurance limit of each sample in a fixed time frame.

(b)

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Fig. 8. Endurance limit values for samples machined under dry condition and emulsion conditions