Wire arc additive manufacturing (WAAM) is a metal 3D printing method that enables large-scale structural elements with complex geometry to be built in a relatively efficient and cost-effective manner, offering revolutionary potential to the construction industry. Fundamental experimental data on the material and structural behaviour of WAAM elements are however lacking. Therefore, a comprehensive experimental study into the material properties, the cross-section and the member buckling behaviour of WAAM elements has been conducted and is reported herein.
Tensile tests on 137 WAAM steel coupons, covering different steel grades, finishes, thicknesses, extraction directions and locations, and deposition strategies, have been conducted. Microstructural characterisation has also been performed by means of optical microscopy (OM) and electron backscatter diffraction (EBSD). At the cross-section and member levels, four-point bending tests on 14 WAAM stainless steel tubular beams and flexural buckling tests on 18 WAAM stainless steel tubular columns have been undertaken, respectively. Owing to the geometric undulations inherent to the WAAM process, 3D laser scanning and digital image correlation (DIC) were employed in the material, beam and column testing programme to capture the geometric properties and deformation responses of the specimens, respectively. The present research focuses on WAAM elements subjected to predominantly static loading (rather than fatigue loading), with an emphasis on structural stability.
The examined WAAM steels exhibited consistent, almost isotropic mechanical properties, a Young’s modulus comparable to conventionally-produced steel plates, marginally lower strength, reflecting the slower cooling conditions than is customary, and good ductility. To describe the full stress-strain response of WAAM steels, material models were proposed and validated against the tensile test results and further experimental data collected from the literature. Following the beam and column tests, the applicability of the current cross-section and column design provisions in EN 1993-1-4 and AISC 370, as well as the continuous strength method (CSM), to WAAM stainless steel elements was assessed by comparing the test results with the strength predictions. The comparisons highlighted the need to allow for the weakening effect of the inherent geometric undulations of WAAM elements, in order to achieve safe-sided strength predictions.