PSI - Issue 19

S. Periane et al. / Procedia Structural Integrity 19 (2019) 415–422 S.Periane et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. Cutting force (N) and Roughness value (µm) for dry and emulsion machined The resultant force value gives us the idea that irrespective of the machining conditions force values are high for dry machining compared to emulsion machining. The samples machined under dry conditions have very good roughness value (µm) despite of higher cutting forces (N) compared to samples machined under emulsion condition.

a) b) Fig. 6. Cross sectioned microstructure of dry and emulsion machined samples

Figure 6 (a) shows the microstructures of dry machined sample were on the surface more deformed coarsened grains were present. This corasened and deformed grains are formed due to the compressive thermomechanical load on the machining surface. These deformed region upto to 50 µm from the machined face have more resistance to fatigue crack intiation and propagation. Due to which the dry machined samples withstand more cycles to failure than the emulsion machined samples for the sample stress values. Figure 6 (b) in which the emulsion machining shows very less deformed layer where the thermal effect during machining is reduced by emulsion liquid. Due to which the fatigue resistance of the emulsion samples sustains for less number cycles at the same time the crack initiation and propagation starts from the edge. In addition to the thermomechanical load more number of grain just adjacent to the machining zone are sheared along the feed direction of machining in dry condition. This is quite evident from the resultant force values of the dry machined samples. Whereas this shear effect is very less in emulsion machined sample due to which the resultant force is 38% lesser compared to dry machining.