PSI - Issue 14

Digendranath Swain et al. / Procedia Structural Integrity 14 (2019) 337–344 Swain et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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depth without any equi-biaxial nature of RS. The orientation of the major principal RS (Fig. 3b) on the xz2 side was almost constant for 0.9 mm depth whereas on the xy top layer it varied arbitrarily up to a depth of 0.4 mm and then it was constant. At this 0.4 mm depth, a small divergence of the principal stresses also can be seen in Fig 4a. It is also seen that the peak RS on the xy top layer does not occur along the x or y directions. This is in agreement with the scan strategy adopted during 3-D printing. No RS measurement was carried out on the yz sides assuming its behavior to be similar to that of xz sides. The RS measurement on the yz sides in sample V3 was planned only after heat treatment (stress relieving) operation.

Fig. 3. (a) Principal RS measured on the xz1 and xz2 surfaces and (b) the orientation of the principle residual stress directions w.r.t. to the strain rosette on the xz1 and xz2 surfaces, respectively.

Fig. 4. (a) Principal RS measured on the xz2 side and xy top layer and (b) the orientation of the principle residual stress directions w.r.t. to the strain rosette on the xz2 side and xy top layers, respectively.

3.2. Residual stress behavior after heat-treatment Heat-treatment was carried out in the sample-V3 after the RS measurements were accomplished again in the base plate removal condition. Meanwhile, another sample-H3 was also heat-treated without any prior RS measurement. RS was measured on yz sides of sample-V3 as planned whereas RS was measured on the xz sides and xy top surface on sample-H3 to compare with the non-heat treated state of sample-V3. The state of RS on the yz surfaces of sample-V3 is shown in Fig. 5a, which is one order lesser magnitude as compared to the non-heat treated condition (Fig. 3). Similarly, the measurement on the xz-sides of sample H3 (Fig. 5b) showed compressive surface RS with again one order lesser magnitude than the non-heat treated state. It was also observed that the strains on xz sides changed its sign after heat treatment and its magnitudes decreased significantly to small tensile values (Fig. 5c). This might be the reason why the surface stresses are compressive after heat treatment. However, the RS distributions on the yz side (sample-V3 after heat treatment) and xz (sample-H3) sides were different. This implies that the initial assumption of similar RS magnitudes on xz and yz surfaces were not correct. To confirm the RS behaviour on xz sides of sample-H3 (Fig. 5b), measurement was again taken on xz sides of the heat treated sample-V3 away from the previous drilling locations. Comparison of RS plotted in Figs. 5d and 5b confirms that the nature of RS were almost similar in both the samples on the xz sides. However, smaller magnitudes of RS were seen in sample-V3 which is in