Quantifying residual strains in specimens prepared by additive layer manufacturing

Residual stresses and strains are prevalent in many components, especially those that are made using additive layer manufacturing. The residual strains are superposed onto any applied load, which in experimental analysis may lead to inaccurate results. The manufacture of a component with known residual strains in all build orientations will enable it to be tested in its green state with results similar to an annealed counterpart. This study has been conducted to explore the relationship between the orientation build of the component, and its thickness in relation to the amount of residual strain it contains. The samples tested are made using Objet FullCure720 RGD720, and have an incremental thickness in order to determine the relationship between specimen thickness and residual strain. The test method used is photoelasticity, in which three analytical methods are implemented - Tardy compensation, Null-balance compensation and six-step phase-stepping. It was established that one of the build orientations possesses no residual strains, and the phase-stepping technique produces the most accurate results. This comparative analysis will aid the development of a simplistic method for manufacturing and testing components with minimal residual strains via additive layer manufacturing. Eliminating the need for post-processing will therefore enable time and cost savings. © The Society for Experimental Mechanics Inc. 2014.