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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treatment on the RS behaviour at the xy top surface, wherein strains in sample-H3 were again much smaller than sample-V3 without heat treatment (Fig. 6a). This led to the RS at xy top surface to be one order smaller than non heat treated state (Fig. 6b). The strains after heat treatment were also almost isotropic (Fig. 6a). The state of stress on this surface was again almost equi-biaxial after heat-treatment as it was in the non-heat treated state. 4. Concluding Remarks A full-fledged RS measurement strategy involving incremental hole drilling strain gage method was successfully adopted to characterize RS in DMLS 3-D printed prismatic blocks of Ti-6Al-4V. This Ti alloy has been studied extensively in the literature. However, since the development of RS is pre-process, in-process and post-process parameter dependent, it was necessary to understand the RS behavior in the samples fabricated under the indigenization plans of ISRO. The RS measured on the xz sides of a sample before heat treatment showed that large magnitude RS got induced during 3-D printing along the z-direction. The RS on the xz sides were more than the UTS of the material which does not meet the criteria of ASTM E837-13a. This can be taken for indicative purposes for preliminary assessment. However, since such magnitude of RS has been already reported in literature (Yadroitsava and Yadroitsev (2015), van Zyl et al. (2016)), may be alternative methods of measurement can be attempted in future to confirm this. The RS on xz faces decreased at least by one order after stress relieving as evident from the measurements in the two samples. Moreover, the directional nature of RS vanished on the xz sides after heat treatment. Similarly, the RS on the xy top layer after stress relieving decreased by one order. The RS were equi-biaxial on the xy surface before and after heat treatment. The nature of RS on the yz surface of a sample after heat treatment was matching with xy top layer; hence there the RS behavior might be similar to xy surface before heat treatment. This also needs to be confirmed with further experiments. Overall, the post-heat treatment plan worked fine to eliminate the large RS in the above samples. Extension of such stress-relieving plans to actual components, without any severe distortions and warpage, would be a future challenge. Acknowledgements The authors have great pleasure in acknowledging Mr S N Suresh, Sr Tech A, EXMD/VSSC for his untiring support for setting up the MTS 3000 machine and instrumenting the samples with the strain rosettes. References Ali, H., Ma, L., Ghadbeigi, H., Mumtaza,K., 2017. In-situ Residual Stress Reduction, Martensitic Decomposition and Mechanical Properties Enhancement through High Temperature Powder Bed Pre-Heating of Selective Laser Melted Ti6Al4V. Materials Science and Engineering A 695, 211 – 220. Anderson, L. S., 2017. Evaluating Measurement Techniques: Establishing a Testing Framework for Residual Stress in Selective Laser Melted Ti 6Al-4V , Master’s Thesis, Faculty of Engineering at Stellenbosch University, South Africa. ASTM st andard F2792 − 12a: Standard Terminology for Additive Manufacturing Technologies. ASTM standard ASTM E837-13a: Standard test method for determining residual stresses by the hole-drilling strain-gage method. Chauke, L., Mutombo, K., Kgomo, C., 2013. Characterization of the direct metal laser sintered Ti6Al4V Components, 14 th Annual International RAPDASA 2013 Conference, Pretoria, South Africa. Frazier, W. E., 2014. Metal Additive Manufacturing: A review, Journal of Materials Engineering and Performance 23, 1917-1928 Herzog, D., Seyda, V., Wycisk, E., Emmelmann, C., 2016. Additive manufacturing of metals. Acta Materialia 117, 371 – 392. Li, C., Liu, Z. Y., Fang, X. Y., Guo, Y. B., 2018. Residual Stresses in Metal Additive Manufacturing. Procedia CIRP 71, 348-353. Lim, G., Lau, K., Cheng, W.S., Chiang, Z., Krishnan, M., Ardi, D.T., 2017. Residual Stresses in Ti-6Al-4V Parts Manufactured by Direct Metal Laser Sintering and Electron Beam Melting. In British Society of Strain Measurement, http://www.bssm.org/uploadeddocuments/ Conf%202017/2017%20papers/95_Guowei_Lim_formatted.pdf. Rendler, N. J., Vigness, I., 1966. Hole-Drilling Strain Gage Method of Measuring Residual Stresses. Experimental Mechanics 6, 577-586. van Zyl, I., Yadroitsava, I., Yadroitsev, I., 2016. Residual Stress in Ti6Al4V Objects Produced by Direct Metal Laser Sintering. South African Journal of Industrial Engineering 27, 134 – 141. Vishay Measurements Group, Inc. 1993. Measurement of residual stresses by the hole-drilling strain-gage method. Tech Note TN-503-6. Vishay Measurements Group, Inc., Raleigh, NC. Vrancken, B., 2016. Study of residual stresses in selective laser melting, Ph D Thesis, KU Leuven, Belgium Yadroitsava, I., Yadroitsev, I., 2015. Residual stress in metal specimens produced by direct metal laser sintering, Proceedings of the SFF symposium, Austin, Texas, USA.