Dynamic mode-I fracture toughness and damage sensing characterization in additively manufactured ABS nanocomposites

This study investigates damage monitoring and fracture toughness characterization of additively manufactured acrylonitrile butadiene styrene (ABS) embedded with carbon nanotubes (CNTs) under dynamic mode-I fracture loading conditions. A novel modified split-Hopkinson pressure bar (SHPB) setup along with high-speed imaging is used to understand the crack dynamics. Electrically conductive CNTs embedded ABS nanocomposite is referred to as ABS-EC in this study. A modified four-probe resistivity measurement technique is utilized to understand the piezo-resistance response of ABS-EC. The effect of four infill line orientations (0 degrees, 90 degrees, +/- 45 degrees, and 0 degrees/90 degrees) on quasi-static and dynamic mode-I fracture toughness and damage sensing characteristics are studied. Results reveal that the infill line orientations have a significant impact, where with +/- 45 degrees configurations demonstrating superior dynamic fracture toughness (2.54 MPa-m1/2) due to the kinking of the crack along the + 45 degrees/-45 degrees direction and the 90 degrees orientations exhibiting weaker interfaces. Real-time observations of crack dynamics validate these findings, emphasizing the role of filament alignment in determining crack pathways and fracture behavior. Among the four infill line orientations, 0 degrees/90 degrees shows the highest (500%) peak piezo-resistance response, whereas the 90 degrees orientation shows the lowest (95%). Moreover, convection oven annealing is explored, where substantial improvement in static fracture toughness (226% increase) for ABS is observed. However, annealing did not enhance the fracture toughness of ABS-EC because CNTs acted as a barrier to restrict the polymer's molecular chain movement for rearranging the porosity.