Developing a Ti6Al4V specimen to induce residual stress deformations and cracks for use in metal additive manufacturing online monitoring

¹ Department of Mechanical and Mechatronic Engineering, Central University of Technology, South Africa, Free State, karabomoore@gmail.com
² National Laser Centre, Council for Scientific and Industrial Research, Meiring Naudè road, Brummeria, 0184, South Africa, DLouw@csir.co.za
¹ Department of Mechanical and Mechatronic Engineering, Central University of Technology, South Africa, Free State, dkouprianoff@cut.ac.za

^* Corresponding author: karabomoore@gmail.com

Abstract

In laser powder bed fusion factors such as residual stresses within the part, lead to deformations and cracks which impact the quality of the final product. Although residual stress and deformations have been thoroughly studied research and development of in-situ online monitoring requires a specimen that cracks in a predictable manner. This paper aims to show which sample geometry can be used to replicate cracks. The Ti6Al4V sample was designed based on known residual stress phenomena from literature of rapid heating and cooling cycles inducing compressive and tensile stresses during L-PBF. The sample was developed with the aid of computer aided design and simulation software using the inherent strain method. For the purpose of consistency, two identical samples were built simultaneously, and for the purpose of repeatability, two different builds were conducted. It was shown that the sample failed as predicted by the simulations due to the effective plastic strain and equivalent stress exceeding that of the mechanical properties. The sample developed can be used to test if cracks that form during the L-PBF build process can be predicted and detected.