Date of Award

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Automotive Engineering

Committee Chair/Advisor

Dr. Srikanth Pilla

Committee Member

Dr. Gang Li

Committee Member

Dr. Philip Brown

Committee Member

Dr. Craig Clemons

Abstract

The global transportation industry is the second highest contributor to climate change. As a result, there has been a concerted effort to spearhead research in economical lightweighting technologies, as every 10 % reduction in weight will lead to to 6 – 8 % improvement in fuel efficiency. Additionally, the recent push for electrification and the emphasis on Corporate Average Fuel Economy (CAFE) standards have seen original equipment manufacturers (OEM’s) dive into lightweighting of materials to improve overall range and/or fuel-efficiency. Thermoplastic Olefins (TPOs) have in recent years carved out a niche in the automotive industry due to advantages such as increased impact resistance, lower production costs, short production times, and improving fuel efficiency on account of lower densities. TPO’s have been successfully used in interior and exterior automotive applications such as bumper fascia’s, trims, cladding, and wire insulation. Logically, the adoption of TPO foams either via conventional chemical agents or new physical blowing agents would be largely beneficial to the automotive sector given the need to drive down weight and increase efficiency.

However, conventional TPO foams have not seen widespread adoption in the automotive industry. Generally, TPO foams can be manufactured via two different approaches, viz., using either chemical or physical foaming agents in existing manufacturing processes like injection molding. TPO foams produced via chemical foaming agents are the current standard due to their low upfront costs and good molded-in color appearance but come with challenges in the form of unpredictable foaming in different cross-sections, decreased thermal stability and residual foaming agent migration induced by weather changes leading to pitting in class A painted surfaces. Alternatively, physically foamed TPO’s are yet to be adopted by a majority of the industry primarily due to higher upfront costs, splay marks on the surface that would fail the molded in color appearance requirements of almost all OEM, and the lower solubility of supercritical N2 in TPO’s making it challenging to foam. Lastly the lack of a holistic modeling pathway that couples manufacturing, microstructure, and mechanical responses pose a major impediment as they cannot be incorporated into current automotive product development cycles.

This study begins with developing a structure-property relationship for Super Critical Fluid (ScF) assisted IM TPO foams using a conventional IM tool to understand the current limitation of the process and tooling. Subsequently, a manufacturing-to-response pathway is developed to help simulate the process-structure-property relationship via the use of rheological, bubble growth, and FEA models via a mean filed homogenization approach. Furthermore, this work investigates the development of a proprietary tooling concept that can control pressure drop and cooling, both vital parameters in controlling cell nucleation and structure. Lastly, as a proof of concept, this work delves into the design and prototyping of an interior garnish part that serves as a demonstration of an industry-scaled TPO foamed product.

Author ORCID Identifier

0000-0002-0965-0355

Available for download on Wednesday, November 30, 2022

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