3D-printing for Aerospace: Fatigue Behaviour of Additively Manufactured Titanium

Abstract: Laser powder bed fusion (L-PBF) and electron beam powder bed fusion(E-PBF) are two of the most common additive manufacturing (AM)methods which both provide the engineer with a great freedom of design.This means that parts with light weight, multifunctional applications andimproved performance could be achieved through innovative design solutionswhich have attracted a lot of interest from the aerospace industry.This PhD project has focused on the following fatigue related areas forL-PBF and E-PBF Ti6Al4V material which all need to be addressed beforeAM can be fully introduced to critical aerospace applications: effectof geometry, roughness and loading on fatigue life, improved fatigue lifethrough post processing, fatigue crack growth behaviour and fatigue predictionmethods.The results show that the rough as-built surface is the single most severefactor for fatigue but that the fatigue strength of at least L-PBF materialcan be improved to levels similar to conventionally manufactured materialusing surface post processing. Furthermore, the results verify that acumulative damage approach gives good accuracy in predicting fatiguelife for variable amplitude loading and that fatigue crack growth rates usingmaterial data from standard specimens can be used for damage toleranceanalysis independent of part geometry and stress level.The conclusion is therefore that the fatigue properties can be improved toacceptable levels and predicted using conventional methods. There arestill some challenges to solve, however, especially within non-destructivetesting before AM can be introduced to critical aerospace applications.