Date of Award

12-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aeronautics and Astronautics

Committee Chair

R. Byron Pipes

Committee Member 1

Jan-Anders Månson

Committee Member 2

Wenbin Yu

Committee Member 3

Vlastimil Kunc

Abstract

The Extrusion Deposition Additive Manufacturing (EDAM) process is an additive manufacturing technique that shows great potential for producing tooling and molds for traditional composite manufacturing methods. However, additive manufacturing processes are still optimized based on empirically calibrated process conditions and require costly trial and error approaches. During the EDAM process with composites, the temperature history of the printing material drives the evolution of internal stresses in a printed component, which could result in a failure of the print or excessive deformation. Therefore, a set of simulation tools was developed in this work to model the solidification behavior of a fiber reinforced semi-crystalline material. To be able to predict final part deformations and residual stress states in printed parts, physical phenomena like heat transfer, polymer crystallization, anisotropic thermoviscoelasticity and anisotropic material shrinkage were considered in EDAM printing process simulations. Appropriate models were chosen to describe these material phenomena and the material behavior was implemented via a user subroutine suite in Abaqus© 2017. Furthermore, experimental procedures were developed to characterize the material behavior required to accurately model the different phenomena. The simulation tools were successfully validated through measurements of residual deformations of printed geometries. Since the simulations are physics based, no calibration of the material input properties had to be carried out. As a result, these physics based process simulations can be readily adapted to predict deformations and residual stresses for large scale EDAM parts. Finally, the significance of the different physical phenomena was discussed and the importance of utilizing a thermoviscoelastic instead of a thermoelastic material description was highlighted based on the limitations of the latter approach to predict realistic final stress and deformations states.

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