Structural integrity evaluation of three-dimensional-printed graphene-reinforced polylactic acid notched plates using failure assessment diagrams

Abstract

Failure assessment diagrams (FADs) constitute a well-known structural integrity evaluation tool that allows structural components containing crack-like defects to be assessed through a simultaneous analysis of fracture and plastic-collapse processes. FADs are included in the most recognized structural integrity assessment procedures/standards, such as BS7910 and API 579/ASME FFS-1, and their use is generally limited to metallic components containing crack-like defects. On the other hand, structural responsibilities are being assumed by three-dimensional-printed composites, and particularly by those obtained through FFF (fused filament fabrication), beyond their most extended use as prototyping materials. The resulting structural components may contain notch-type defects (e.g., grooves, corners, holes) that determine their corresponding structural integrity. Thus, it is necessary to define structural integrity assessment criteria for this kind of materials when containing any kind of stress risers, beyond crack-like defects. This work justifies the use of BS7910 Level 1 FAD, coupled with a notch correction derived from the theory of critical distances (TCD), to analyze graphene-reinforced polylactic acid (PLA) plates subjected to pure tensile loading conditions and containing U- and V-notches. The results reveal that, for U- and V-notches, the assessment points representing the plates at failure are located within the FAD area corresponding to unsafe conditions, providing conservative evaluations with moderate safety margins. For plates containing circular holes, the proposed approach provides unsafe predictions.