Date of Award

2017-01-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

Jack F. Chessa

Abstract

Ongoing research efforts in industry and academia have a focus on optimal build parameters that lead to suitable mechanical properties with minimum defects in parts manufactured by powder bed fusion additive manufacturing technologies, such as Electron Beam Melting (EBM) and Selective Laser Melting (SLM). Additional and significant resources, including energy, time, and money are spent as a result of obligatory post-manufacturing heat and/or mechanical treatment to ensure optimum mechanical properties. One intrinsic fault in these technologies, which contributes to the need for treatment processes after part fabrication, is the creation of residual stresses during these processes. Residual stresses remain in these AM parts after the build process is completed due to plastic deformation resulting from extreme thermal gradients driving thermal expansion and the cool-down phase. Build parameters, such as power and scanning speed, to optimize mechanical properties and lessen these undesirable flaws, are for the most part investigated with a trial-and-error approach. Numerical models, however, offer the less expensive alternative of investigating in depth the nature of residual stresses and thus testing build configurations that may predict and reduce the magnitude of these residual stresses. In this work, the underlying theory for a coupled thermal-displacement finite element model is introduced independently with simple FEA validation problems to build up to a more complex model. Abaqus User Subroutines for the mechanical, thermal, and expansion behavior are developed and tested. These subroutines allows for further definition of a state variable that can be passed along in the solution steps to consider the different phases the material systems go through in these processes. With a prototype model, the coupled-thermal displacement behavior was modelled with success, as the remaining residual stress terms and plastic strain overall agree in principle with published experimental results.

Language

en

Provenance

Received from ProQuest

File Size

111 pages

File Format

application/pdf

Rights Holder

Jesus Gerardo Reyes Schuldes

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