PSI - Issue 37

Jin Kim et al. / Procedia Structural Integrity 37 (2022) 282–291 Kim et al./ Structural Integrity Procedia 00 (2021) 000 – 000 Fig. 4(b) shows the arithmetical mean height, , of the machined surfaces with ideal surface roughness for comparison with the theoretical value. CT of 217XG and 225XE shows higher than the ideal surface roughness, indicating a deterioration of surface quality caused by hard and abrasive SiC particles for both carbide and PCD tools. On the other hand, UAT has significantly improved the by 33.0% and 40.5% for 217XG, 52.5% and 58.2% for 225XE using carbide and PCD tools, respectively. This value is lower than the ideal surface roughness that resulted in the polishing of the feed grooves as well as the improvement in the surface of the machined grooves. 4.4. 3D macroscopic simulation results The Johnson-Cook plasticity parameters were first estimated from a non-linear regression of the Split Hopkinson Bar (SPHB) test. Details of the experimental results will be published in the near future. The obtained values are shown in Table 3. 289 8

Table 3 Johnson-Cook plasticity parameters for both composites

(MPa)

(MPa)

(K) 0̇ (s -1 )

J-C plasticity

n

m

(K) 821 821

217XG 225XE

410 325

360 450

0.092

0.9 0.5

2.8 3.5

298 298

1 1

0.07

The J-C damage parameters were calibrated with similar experimental output during CT using the PCD tool. The optimised parameters are given in Table 4.

Table 4 Johnson-Cook damage parameters for both composites

1

2

3

4

5

Fracture energy (J)

J-C damage

217XG 225XE

0.002

5.44

-3.1 -4.3

-0.008

1.6 2.1

6500 5500

0.0018

6.1

-0.01

Fig. 5(a) shows the 3D simulation of CT and UAT processes of 217XG/225XE workpiece assuming no tool wear. For 217XG, the average von Mises stress during CT in the shear zone was approximately 1.23 GPa. The average stress during full expansion and retraction motion of the tool in UAT was approximately 1.78 GPa and 0.71 GPa, respectively. Fig. 5(b) shows the net forces for CT and UAT of both composites. The average net cutting force, , is described as = √ 2 + 2 + 2 , (5) where , and represent the forces in tangential, radial, and feed direction, respectively. The net force simulation results compared with the experimental CT using the PCD tool, showed a decrease of 5.4% for 217XG and 9% for 225XE, respectively. Fig. 5(c) shows residual stresses in the radial direction in CT and UAT for 217XG, indicating radial and feed vibration induce compressive residual stresses.