Analysis of the Load Bearing Capacity of Cracked Additively Manufactured Polymers Using Failure Assessment Diagrams

Abstract

Failure Assessment Diagrams (FADs) are, in practice, the main engineering tool for the analysis of structural components containing cracks. They are utilised in well-known structural integrity assessment procedures, such as BS7910 and API 579 1/ASME FFS 1, and their reliability has been proven by numerous laboratory tests and industrial applications. However, they have been defined and validated in metallic materials, so their application in other types of materials requires demonstrating that the different assumptions taken when analysing metals are also valid for the particular material (non-metallic) being analysed. At the same time, additive manufacturing (AM) is a growing technology that allows complex geometries to be fabricated through a quite simple process. Among the different AM techniques, fused deposition modelling (FDM) is one of the most widely used, and consists in the extrusion of heated feedstock plastic filaments through a nozzle tip. The resulting printed materials have quite specific characteristics and properties, which are highly dependent on the printing parameters (e.g., raster orientation, printing temperature, etc.) and on the resulting state of internal defects. This paper provides FAD analyses for two additively manufactured (FDM) polymers: ABS and PLA. The results show that the FAD methodology may be applied for these two particular polymers, as long as linear-elastic fracture toughness values are used.