A Novel Approach to Increase Dynamic Fracture Toughness of Additively Manufactured Polymer

An experimental study is performed to investigate the dynamic fracture of additive manufactured Acrylonitrile Butadiene Styrene (ABS). A single edge notched bending (SENB) specimen with three orientations, namely horizontal builds with 45°/−45° (H45), 0°/90° (H90) raster orientations, and vertical builds with layers perpendicular to the pre-crack (V0) are considered for this study. In addition, a novel toughening mechanism is explored by changing the surface topology to deflect the crack paths. A modified split Hopkinson pressure bar with a copper pulse shaper (to increase the raising time of incident loading pulse) is used to conduct a three-point bend impact experiment to characterize the dynamic fracture initiation toughness and crack dynamics of 3D printed specimens. Real-time crack initiation and propagation is captured by using a high-speed video camera. Using the load history diagram, accurate fracture initiation load is found to determine dynamic fracture initiation toughness. Fracture initiation toughness is increased by 138% for a V0 specimen configuration compared to H90. Three different sized circular patterns (with diameters of 1, 1.75 and 2.5 mm) and a square pattern (with a length of 1.53 mm) are considered to observe the effect of surface topology on the dynamic fracture initiation toughness. Introducing surface pattern to the specimen increases the fracture toughness by 58% as compared to specimens without surface pattern. Surface pattern also exhibits two steps of crack growth and decreases the initial crack propagation velocity significantly for all three orientations. Additionally, higher fracture initiation toughness is achieved with the increase in the size of the pattern and the change of the pattern shape.