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EAS Doctoral Dissertation Defense by Md Fazlay Rabbi

When: Monday, May 10, 2021
10:00 AM - 12:00 PM
Where: Online
Description: EAS Doctoral Dissertation Defense by Md Fazlay Rabbi

Date: Tuesday May 10, 2021
Time: 10:00am
Topic: Mechanics of Additively Manufactured Polymer Composites

Zoom Teleconference: https://umassd.zoom.us/j/96640466766?pwd=S1A4TXM4VEVySmtkRlJNWGdDQWFwdz09

Meeting ID: 966 4046 6766

Abstract:

The aim of this dissertation is to investigate the mechanics of additively manufactured polymers under various loading conditions. First, an experimental study is performed to investigate the dynamic fracture properties of additive manufactured Acrylonitrile Butadiene Styrene(ABS). The effect of novel toughening mechanism through surface topology and printing orientation on dynamic fracture toughness and crack dynamics is explored. Fracture initiation toughness is increased by 138% for a vertical printing orientation compared to horizontal orientation.Introducing a surface pattern to the specimen increases the fracture toughness by 58% as compared to specimens without a surface pattern.

Additionally, higher fracture initiation toughness is achieved with the increase in the size of the pattern and the change of the pattern shape.

Later, an experimental investigation is performed to observe the electro-mechanical response of CB/ABS additive manufactured composite under quasi-static and dynamic loading conditions for the potential damage sensing applications. In the case of tensile loading, +45o/-45o printed specimens show a nonlinear change of electrical response due to a nonlinear failure mode. Filaments debonding is the major failure mode for 0o printed specimens under both tensile and shear loading. For mode-I fracture under both static and dynamic fracture loading, a minimal change of electrical response is observed before crack initiation due to the cancellation effect of the tension and compression on both sides of the neutral surface. Finally, a comprehensive experimental investigation is performed to observe the interfacial fracture toughness of bi-material additively manufactured composites. It is observed that process parameters have a significant impact on the bi-material interfacial fracture toughness. Improved molecular diffusion enhances the fracture toughness by 95% with the increase of the printing temperature.

Although printing speed has not any significant impact on fracture toughness, thinner layers provide a better bond strength and polymer wetting, resulting in a higher fracture initiation toughness compared to thicker layers. To improve the interfacial fracture toughness a post-processing such as isothermal annealing is performed at a wide range of temperatures for different durations. It is observed that fracture toughness improves significantly when specimens are annealed at the melting temperature of the polymers.

ADVISOR(S): Dr. Vijay Chalivendra. Department of Mechanical Engineering
(vchalivendra@umassd.edu, 508.910.6572)

COMMITTEE MEMBERS:
Dr. Jianyi Wang, Department of Physics
Dr. Jun Li, Department of Mechanical Engineering
Dr. Helio Matos, Department of Mechanical, Industrial and Systems Engineering,
University of Rhode Island

NOTE: All EAS Students are ENCOURAGED to attend.
Contact: > See Description for contact information
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