Structural integrity assessment of additively manufactured ABS, PLA and graphene reinforced PLA notched specimens combining Failure Assessment Diagrams and the Theory of Critical Distances

Abstract

ABSTRACT: Failure Assessment Diagrams (FADs) are a widely used engineering tool for the analysis of structural components containing cracks, and are included in recognised structural integrity assessment procedures such as BS7910 and API 579 1/ASME FFS 1. Their consistency and reliability has been demonstrated over the years through numerous laboratory validation tests and industrial applications. Nevertheless, both their theoretical definition and their subsequent validation have been performed in metallic materials and, therefore, their use in other types of materials still requires theoretical support and experimental validation. Moreover, FADs have been initially defined for the analysis of crack-like defects, whereas there are many situations where the defects that are, or might be, responsible for structural failure are not necessarily cracks. This is the case of (non-sharp) defects with a finite radius on their tip, which here will be referred to as notches. Simultaneously, additive manufacturing (AM) is an emergent technology that allows practically any type of geometry to be fabricated through a relatively simple process. One of the main AM techniques is fused deposition modelling (FDM), which consists in the extrusion of heated feedstock plastic filaments through a nozzle tip. The resultant printed materials have rather particular properties that are very dependent on the printing parameters and on the final state of internal defects. Concerning AM polymers and polymer-matrix composites, their use as structural materials, beyond their main current use in prototyping, requires the development of specific structural integrity assessment procedures. This paper provides FAD analyses for three additively manufactured (FDM) materials containing U-shaped notches: ABS, PLA and graphene reinforced PLA. The results show that the FAD methodology may be applied for the estimation of fracture loads in these particular materials, as long as linear-elastic fracture toughness values are used.