Rapid Determination of Fatigue Properties of As-Built and Machined Wire+arc Additively Manufactured Steel Specimens

To confidently manufacture parts that satisfy mechanical strength requirements, additively manufacturing (AM) processes are desired to be repeatable and with minimal deviation in properties. Thereto an effective, rapid and practical testing procedure capable of determining the mechanical properties is needed. Fatigue is probably the most challenging mechanical property in this perspective, since its determination requires ample testing time and a vast quantity of specimens, which are not always feasible. This paper investigates the feasibility of a rapid determination method based on infrared thermography to derive the fatigue limit and fatigue curve of wire + arc additive manufactured steel components. The methodology involves step-wise loading of a specimen and monitoring the cumulative damage by measuring its surface temperature. It has been applied to both as-built and machined samples extracted from the same WAAM deposited wall in a region with consistent static strength and surface waviness. The as-built samples’ fatigue limit was less than 40% of the fatigue limit of the machined counterparts. The reduction in fatigue performance is attributed to surface waviness and the presence of an oxide layer at the as-built samples’ surface. The former acted as a stress raiser site, and the latter facilitated the crack initiation.