04/05/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation Proposal defense by Nikhil Patil on: "Additive Manufacturing of Soft Material Composites: Systematic Material Characterization & Structure Property Relationship."

Candidate Name: Nikhil Patil
Degree: Doctoral
Defense Date: Friday, April, 19, 2024
Time: 3  to 5 p.m.
Location: ETIC 345

Committee:

  • Advisor: Jay Park, Assistant Professor, Department of Plastics Engineering, University of Massachusetts Lowell
  • Amir Ameli, Assistant Professor, Department of Plastics Engineering, University of Massachusetts Lowell
  • Alireza Amirkhizi, Associate Professor, Department of Mechanical Engineering, University of Massachusetts Lowell
  • Eric Wetzel, Strategic Polymers Additive Manufacturing, US Army Research Lab

Brief Abstract:
Additive manufacturing (AM) enables rapid prototyping, and novel manufacturing supply chains, in industries such as automotive, aerospace, and medical. Among various additive manufacturing techniques studied to investigate additive manufacturing of elastomeric “soft” materials, FFF is particularly advantageous due to its solvent-free processing, cost to size ratio, ease of operation, and good shelf life of feedstock filaments. While material extrusion additive manufacturing techniques for soft materials have attracted significant attention, critical challenges need to be addressed. Soft materials are difficult to feed into filament print heads, due to insufficient grip and tear strength while passing through the drive wheels and buckling between drive and melt stages. These feed issues lead to inconsistent extrusion control and poor part accuracy. Soft materials are also more likely to string, smear, and sag during deposition, increasing the likelihood of geometric errors or print failures.

To address these issues, we investigate the structural stability and mechanical performance of coextruded ABS+TPE (core-shell) filaments by FFF. To enhance printability of a thermoplastic elastomer (TPE), a series of core-shell filaments comprising a TPE shell (Shore hardness 75 A) and a rigid ABS core are fabricated, with the ABS volume fraction varying from 11% to 78%. The presence of an ABS core imparts rigidity to the filament to inhibit buckling and allow for successful high-fidelity 3D printing. Printed specimens with less than 20% ABS preserve the shore hardness of 75 A, providing flexibility and a soft touch to the printed structures. Izod impact, 3-point bending, and tensile tests reveal tunable mechanical properties of parts printed in z-direction with ABS+TPE filaments. Lower ABS content exhibits higher flexibility and impact resistance, while higher ABS imparts higher stiffness and tensile strength.

Based on these investigations, Aim 2 of the research focus on achieving mechanical anisotropy based on the layer orientation direction. Printed layers oriented in 0° printing raster angle becomes stronger and stiffer, whereas the layers oriented at 90° printing raster angle becomes more flexible. Combining the uniqueness of ABS+TPE filaments with the phenomena of composite laminates, we developed structures to exhibit selective functionality to the printed specimen by tuning printing raster angle. Such assemblies can have vital importance in developing soft robotic arms, origami structures, stimuli responsive structures, etc. Aim 3 of research focus on investigating different grades of TPU’s and TPE’s having different shore A hardness (75A, 65A, 60A, 35A) and chemistry of synthesis (Silicone rubber based TPSiV, Polyester based TPU’s, Polyether based TPU’s) to enable additive manufacturing of soft materials. The investigation is based on rheological characterizations of feed materials (relaxation behavior) and its interpretations to properties of printed specimens. The rheological conclusions will be further extended to achieve enhanced mechanical performance of additively manufactured soft material composites.

Altogether, this PhD dissertation will be focused on enabling printability of soft materials by FFF and delve into the mechanical characterizations and structure property relationship between various soft materials (TPU’s and TPE’s) to develop additively manufactured soft material composites.