Tailoring the theory of critical distances to better assess the combined effect of complex geometries and process-inherent defects during the fatigue assessment of SLM Ti-6Al-4V

This work aims to apply the Theory of Critical Distances (TCD) to the fatigue assessment of additively manu-factured (AM) Ti-6Al-4V material produced via the selective laser melting (SLM) process. Modified alternatives to traditional TCD methods are considered. In this sense, it is sought to develop a fatigue prediction model that is better suited to assessing the impact of multiple stress-rising features which are located in close proximity to each other. Hereby, consideration has been given to modelling process-inherent surface roughness in combination with an internally positioned artificial defect, shaped as a feature that is reminiscent of a pore. Simultaneously, the research also seeks to circumnavigate a potential issue with respect to the current TCD methodology. This concerns the matter of applying TCD practices to components whereby the area of interest for conducting stress -distance analytics is on a size scale that is smaller than that of the critical distance length parameter itself. Several different strategies were attempted as a way to try and achieve meaningful modifications to the TCD process. Results show that it is possible to overcome such challenges that can often present themselves during the fatigue appraisal of AM metal parts. In this sense, the optimal novel strategy that was experimented with returned average error margins of 13.7% or better. It is anticipated that such models may assist in further optimising the accuracy of service life evaluation for metallic AM components that are intended for industry.

Automated summary

This study aims to apply the Theory of Critical Distances (TCD) to assess the fatigue of additively manufactured Ti-6Al-4V material. Modified alternatives to traditional TCD methods are considered to develop a better fatigue prediction model that takes into account multiple stress-rising features in close proximity. The research also addresses the issue of applying the TCD methodology to components with a smaller area of interest than the critical distance length parameter. Different strategies were attempted and an optimal novel strategy achieved average error margins of 13.7% or better, showing potential for improving the accuracy of service life evaluation for metallic AM components.