Investigating Fracture Properties of The Additively Manufactured PLA Using Sub-Size Specimens

Abstract In the absence of an acceptable test standard for determining fracture properties of a single edge notched sub-size non-metallic (plastic) specimen, the test method’s viability of the ASTM-5045’s energy approach and the Roberts and Newton solution for Charpy V-Notch (CVN) impact testing was investigated. The strain energy release rate (SERR) and fracture toughness were determined by subjecting the sub-size specimens of additively manufactured Polylactic Acid (PLA) to a three-point flexural and a CVN impact testing. A Fused Deposition Modelling (FDM) technique was adapted to manufacture thin specimens by sequentially layering a 100mm thick raster in (-45/45)° and (0/90)° orientation. The toughness values of the flexural specimens increase with the number of layers (specimen thickness) and are clearly influenced by the layer orientation. Thicker CVN impact test specimens, however, resulted in relatively lower toughness values. This was due to a reduction of constraints for plane strain conditions that the existing impact test standard/procedure considered. When compared with the impact testing method, the flexural testing using the energy approach demonstrates a better capability to capture the effect of an increase in the energy absorbed for the air gaps to plastically deform and for the delamination to take place in the sub-size specimens. The X-Ray Tomographic images of the flexural test specimens confirmed the presence of air gaps where the onset of the cracking and delamination were observed, whilst the micrographic images revealed mode I intra-laminar fracture for all test specimens.