Theoretical and numerical framework for extrusion-based additive manufacturing applications

The main challenge in extrusion-based additive manufacturing (EB-AM) is synchronizing the parameters controlling the manufacturing process with the timescale of material evolution to ensure structural integrity during manufacturing. In their initial stage, the stiffness of EB-AM materials is relatively low, and therefore, the structure can undergo significant deformation and even failure while being manufactured. This work presents a theoretical and numerical framework that integrates the process parameters with material evolution in a unified way to model EB-AM processes. The significant contributions in this work are: (i) thermodynamically consistent constitutive models for evolving materials under loading, (ii) modeling the process of sequential material placement in EB-AM, and (iii) modeling viscoelastic materials with arbitrary compressibility in the context of finite strain theory. An important contribution in this work is the use of second law of thermodynamics to show the existence of inelastic processes in evolution of stiffening materials. An internal variable formalism is employed to model the inelastic strain associated with material evolution, and the corresponding evolution equation is derived. Then, a novel method to model the material placement in EB-AM is proposed. The method can accommodate various type of constitutive models, and can be easily implemented in existing finite element codes. The numerical models are validated via comparison with experimental data. Another important contribution is the treatment of evolving material compressibility. Commonly used materials in EB-AM, such as polymer and concrete, can feature a wide range of compressibility. At the start of the curing process, these materials are nearly incompressible, but can become compressible as they cure. Therefore, it is desirable to have a unified formulation that applies to materials with arbitrary compressibility. Starting from a compressible model, a displacement-pressure formulation is derived via Legendre transform in the context of finite viscoelasticity. Then, a stabilized finite element method based on variational multiscale method is developed to solve the resulting mixed initial-boundary-value problem. In addition, a novel time integration scheme is introduced to convert any explicit or implicit scheme into a stable scheme that preserves the determinant of the integrand. The proposed framework is employed in various settings such as contact-friction and thermo-chemo-mechanical problems. Applications of the framework to model concrete printing and frontal polymerization are presented.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Civil Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Anugraha Wijaya, Ignasius Pradipta

Contributors dc:contributor

• Masud, Arif
• Lopez-Pamies, Oscar
• Duarte, C. Armando
• Geubelle, Philippe H

• Additive Manufacturing
• Constitutive Models
• Evolving Materials
• Inelastic Strain
• Finite Deformation
• Concrete Printing
• Frontal Polymerization

Statement dc:rights

• Copyright 2024 Ignasius Pradipta Anugraha Wijaya

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127239

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127239