Dynamic fracture behavior of additively manufactured Scalmalloy®: Effects of build orientation, heat-treatment and loading-rate

Scalmalloy (R) specimens are fabricated using Laser Beam Powder Bed Fusion to investigate the role of build orientation, loading-rate, and heat-treatment on critical energy release rate and crack growth resistance behaviors. Four build orientations horizontal, vertical, flat, and diagonal are assessed under dynamic loading conditions. The experiments are carried out in a split-Hopkinson pressure bar apparatus on edge-notched threepoint bend geometries. The specimens with the horizontal build are studied also under quasi-static loading conditions to gain some insight into strain-rate sensitivity. The horizontal and flat build specimens are heat treated for dynamic tests to study the effect of heat-treatment on high strain-rate fracture performance. The in-plane surface displacements near the crack are directly measured using Digital Image Correlation and ultrahigh-speed photography to evaluate the fracture parameters in each of these cases. A hybrid experimental numerical approach that combines DIC measurements with finite elements is employed to evaluate the fracture behavior. The differences in the critical energy release rates and post-initiation fracture behaviors of Scalmalloy (R) under different conditions are quantified. The diagonal and horizontal builds outperform the vertical and flat builds in terms of dynamic crack initiation and growth characteristics. The quasi-static crack initiation and growth of the horizontal build specimens show significant strain-rate sensitivity relative to the dynamic counterparts. The heat-treatment of specimens result in marginal improvement of the dynamic fracture performance but does not affect the crack growth resistance behavior. Based on microstructural analyses, the melt-pool boundary orientation relative to crack front extension direction correlates well with the measured dynamic crack initiation and growth performance metrics.

Automated summary

The study on Scalmalloy (R) specimens reveals that horizontal and diagonal builds exhibit superior dynamic crack initiation and growth characteristics, while heat treatment has little impact on dynamic fracture performance. The analysis also shows significant strain-rate sensitivity in quasi-static crack initiation and growth of horizontal build specimens compared to their dynamic counterparts.