Evaluation of a thermomechanical model for prediction of residual stress during laser powder bed fusion of Ti-6Al-4V

• Published in: Additive manufacturing 2019-05, Vol.27 (C), p.489-502
• Main Authors: Ganeriwala, R.K., Strantza, M., King, W.E., Clausen, B., Phan, T.Q., Levine, L.E., Brown, D.W., Hodge, N.E.
• Format: Article
• Language: English
• Subjects: Additive manufacturing; ENGINEERING; Laser powder bed fusion; MATERIALS SCIENCE; MATHEMATICS AND COMPUTING; Residual stress; Thermomechanical modeling; Ti–6Al–4V
• ISSN: 2214-8604; 2214-7810
• DOI: 10.1016/j.addma.2019.03.034

The build-up of residual stresses in a part during laser powder bed fusion provides a significant limitation to the adoption of this process. These residuals stresses may cause a part to fail during a build or fall outside the specified tolerances after fabrication. In the present work a thermomechanical model is used to simulate the build process and calculate the residual stress state for Ti–6Al–4V specimens built with continuous and island scan strategies. A layer agglomeration, or lumping, approach is used to speed up the computations. A material model is developed to naturally capture the strain-rate dependence and annealing behavior of Ti–6Al–4V at elevated temperatures. Results from the thermomechanical simulations showed good agreement with synchrotron X-ray diffraction measurements used to determine the residual elastic strains in these parts. However, the experimental measurements showed higher residual strains for the specimen built with an island scan strategy; a trend not fully captured by the simulations. Parameter studies were performed to fully understand the advantages and limitations of the current simulation methodology. Reasons for both the computational and experimental findings are discussed.