PSI - Issue 18

Nikolas Baak et al. / Procedia Structural Integrity 18 (2019) 274–279 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3. Results and discussion It was shown that the feed force F f and the drilling torque M d are significantly influenced by the sulpher content and the feed rate. Figure 4a shows a comparison of the feed force F f for the three investigated feed rates and both melts. Figure 4b displays the dependence of the torque M d on the feed rate and the sulphur content. This diagrams display, as expected, an increase of F f and M d for increasing feed rates and a decrease for higher sulphur content.

(a)

(b)

Fig. 4. Comparison of (a) feed force vs. feed rate and (b) torque vs. feed rate, for S110 and S280 melts.

With higher feed force and torque higher drilling normal forces are expected, which lead to a greater influence of the surface layer. Figure 5 displays cyclic deformation curves for S280 specimens. The drop after each 10 4 cycles is explained by the intermittent experimental procedure. It can be seen, that the change in temperature  T (Fig. 5a) shows a slight higher increase for the specimen drilled with the feed rate 0.15 mm, whereas only a small differentiation between the feed rates 0.05 mm and 0.10 mm is possible. Since the plastic strain amplitude ε a,p (Fig. 6b) does not allow a separation between the specimen conditions, change in temperature measurements should be preferably applied for the assessment of feed rate influence on performance capability.

(a)

(b)

Fig. 5. Cyclic deformation curves for S280 specimen drilled with varying feed rate; (a) change in temperature and (b) plastic strain amplitude.

Figure 6 shows the coercive field strength versus the normalised number of cycles for both investigated melts and the three investigated feed rates. It can be seen, that the initial height for the specimens made of S280 is significantly higher than for the specimens made of S110. Moreover the initial height for the highest feed rate f = 0.15 mm is for both cases significantly lower than for the lower feed rates, which are in both cases on a comparable level.