**4. Discussion**

Steel bars manufactured by the WAAM process demonstrate the use of AM in construction. For this study, several samples were manufactured with each process to identify the influence of welding parameters. However, only one sample of each process was tested until fracture. The overall objective was the identification of an advanced test routine, which can be applied to further WAAM components as well. The steel bars, as manufactured and tested here, could represent reinforcement elements in concrete applications or standalone, respectively, parts of complex larger steel components structural members. Further, it is demonstrated that the use of manufacturing parameters, such as the welding process and the energy input, may result in a severe influence on the component and material properties. The energy reduced short arc welding processes led to a heterogeneous microstructure with hardness peaks at the layer interfaces, probably resulting from low annealing temperatures between A1 and A3. This is usually not favorable as mechanical properties become heterogeneous as well. Higher interpass temperatures could solve this issue also for welding processes with low heat input. However, the resulting lower weld pool viscosity may affect the resulting surface topography as well. The results from the microstructure and hardness testing of WAAM bars as well as the surface fracture images correspond well with theoretical findings from the literature (e.g., TTT-diagrams), weld parameters, and results from tensile tests. The conventional GMAW bar with lower, but homogeneous, hardness showed lower ultimate strength and higher areas of reduction at the fracture compared to the CMT-welded bars. However, the peak temperatures and annealing times should be controlled more intensively in future research as they control the grain size.

The surface topography and the geometric dimensions, here the bar diameter, depend on the process characteristics. A homogeneous diameter is preferable in terms of mechanical material utilization. However, in concrete applications, rougher surfaces may be beneficial due to better load transfer from concrete to reinforcement bars. Cyclically loaded components would benefit from smoother surfaces as observed in the case of CMT-welding. Next, the layer volume increases with increasing energy input, which is beneficial for economical manufacturing times.

CT scans did not show severe inner defects or irregularities in the manufactured steel bars, except a low number of single pores with a diameter of ~1000 μm. The di fferences in pore size and magnitude are explained by the welding time and weld pool size. However, this must be examined statistically in future research with higher numbers of specimens.

The applied test methodology captured both local elastic component behavior and integral material parameters. The full field strain measurements can identify the inhomogeneous material behavior. Most likely, the heterogeneous strain distribution results from geometric variations, i.e., the change of diameter and local notches at layer interfaces. However, future work will address the material properties of deposited weld metal depending on the applied weld process in more detail. The detected stress concentration is of large importance for plasticity-induced phenomena, such as crack initiation and fatigue.

Various parameter identification methods could be used to quantify the deviations of the material in further research, for example the virtual fields method [43]. The measurements on the material scale presented here are not su fficient to evaluate the behavior of more complex WAAM-components in its entirety and 360◦ digital image correlation systems could be utilized for the purpose of analyzing the deformation behavior of the entire component during a test, even in regions of large deformations where the ESPI system reaches its limits. When analyzing the component behavior, it is also necessary to evaluate the behavior under compressive loads in regards to buckling as the WAAM components are generally slender components.
