Scalmalloy® is a new aluminum-magnesium-scandium alloy specifically designed for Additive Manufacturing (AM). It exhibits excellent mechanical properties attributed to its fine-grain microstructure dispersed among coarser grains and without any preferential grain orientation. Because of its favorable strength to weight ratio, it has great potential for automotive and aerospace applications. The properties of Scalmalloy parts, however, depend on a variety of other factors besides microstructure, namely build orientation, layer orientation, manufacturing defects, etc. Thus, the influence of these factors on the mechanical failure behavior in general and fracture in particular should be thoroughly investigated. The material in question could also encounter high-strain rate loading during service in addition to quasi-static and fatigue loading. This warrants investigation of fracture behavior of additively printed coupons under rapid loading conditions.

In this work, Scalmalloy specimens were fabricated using a Laser Beam Powder Bed Fusion (LB-PBF) to investigate the effects of build orientation on failure properties including critical energy release rate and crack growth resistance. Four build orientations - horizontal, vertical, flat, and diagonal - were assessed experimentally under dynamic loading conditions. The experiments were carried out using a split Hopkinson pressure bar (SHPB) apparatus on edge notched three point bend geometries. The in-plane surface displacements near the crack were measured using two dimensional Digital Image Correlation (DIC) method and ultrahigh speed photography at 200,000 frames per second. The optical measurements from the start of the impact loading event to crack initiation and growth were then used to evaluate the fracture parameter histories directly without needing strain gage measurements on the incident and transmission bars of the SHPB apparatus. A hybrid experimental-numerical approach that combines DIC measurements and finite element analysis was adopted for evaluating instantaneous values of the J-integral.  To accomplish this, the in-plane displacement fields measured from DIC were mapped on to a corresponding finite element grid to compute the J-integral using domain integral approach available in the structural analysis software Abaqus. The differences in the critical energy release rates and post-initiation fracture behaviors of all four Scalmalloy builds were quantified. The measurements suggest that the J-integral values at crack initiation for the diagonally built specimens were the highest whereas the ones from the flat build were the lowest.  The specimens from the vertical and horizontal builds show intermediate values of critical J-integral.  The crack speeds for all specimens were low relative to the material wave speeds and each build showed a precipitously decreasing J-integral following crack initiation.


Role of Build Orientation on High-Strain Rate Fracture Behavior of Additively Manufactured Scalmalloy

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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