PROGRAM | Mechanical Engineering

By: Soodabeh Sharafi Chair: Suresh Advani

ABSTRACT

Additive manufacturing (AM), due to its ease of prototyping can build intricate features without the need of an expensive mold and allow for design changes and tailorable properties to improve part functionality which makes it very attractive for part replacements.  Fused filament fabrication (FFF) or Fused Deposition Modeling (FDM) is a popular AM technique in which a high temperature polymeric composite material filament is melted and extruded through a  submillimeter narrow nozzle to create a part by printing layer by layer.

This work focuses on FFF-based Additive Manufacturing’s potential for producing high temperature intricate PAEK and PAEK composite components. While FFF with temperature-controlled ovens offers uniform temperature extrudate, the absence of external consolidation forces leads to weak interfaces, microscopic voids, local inhomogeneity, and affects the macroscopic mechanical properties. Understanding the role of processing and printing parameters in creation of microscopic flaws such as bonding between adjacent layers is crucial to address fracture toughness. The material characteristics that influence the macroscopic properties include deposition-related conditions, solidification dynamics, and the composition and rheological properties of resin and fiber microstructure. The multifaceted nature of these parameters necessitates extensive experimental studies, making an exhaustive study with permutations of all possible variables cost-prohibitive. To address this challenge, this research advocates for a multiscale physics-based modeling framework capable of determining the impact of process parameters across micro and macro scales. Constitutive multiscale modeling framework is developed to identify the most influential layer design and process parameters over mechanical properties and fracture toughness in additively manufactured components. This approach, rooted in the Mori-Tanaka homogenization methodology, employs dual-scale material model to predict the maximum stress and deflection at failure. It bridges the gap between the microscale material behavior and macroscale deformation. This modeling framework helped establish the interplay between fracture toughness, bonding between layers, porosity content, and void shape and sizes which are functions of material, geometric, and processing parameters. With this methodology layer design parameters and their intensity were optimized for desired mechanical performance. The optimized parameters were used  in FFF machine to manufacture test coupons for PAEK polymer and its composites and have shown enhanced properties compared to the results when parameters are chosen using the machine set slicing settings. The multiscale correlation between the toughness and porosity  and the correlation between strength and roughness is characterized using Instron for macroscale and SEM, micro CT and confocal for microscale to identify the role of process parameters and bridge micro and macroscale results for the printed PAEK and PAEK/Carbon Fiber Composites.

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