Date of Award

8-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Automotive Engineering

Committee Member

Srikanth Pilla, Committee Chair

Committee Member

Paul Venhovens

Committee Member

Johnell Brooks

Committee Member

Gang Li

Committee Member

David Schmueser

Abstract

Transportation accounts for 14% of global greenhouse gas emissions. With a projected rise in GDP for more than half of the global population, the demand for transportation is only going to increase sharply. It is essential to reduce the overall weight of the automobile and ensure that its constituent materials are being reused with the minimal energy consumption during treatment and conversion. This is especially critical for the heaviest components in an automobile – its structure and closures. In this regard, carbon fiber reinforced composites have high light-weighting potential for automotive structures. However, most OEMs use thermoset polymers as matrix material, which are not recyclable. This has led to a great push towards the use of thermoplastics as matrix material in the future. A key issue associated with this possibility is the need for an optimal joining mechanism – since while structural adhesives are the most common joining mechanism used at present, most of these adhesives are thermoset polymers themselves that are also expensive and have longer curing time. Additionally, when used with thermoplastic matrix materials, these adhesives bring forth the problem of compatibility.

The ability to be joined in fast, strong and repeatable methods is crucial for automotive structures, given that a typical body structure has between 150-400 individual parts, and their timely and strong joining is essential to ensure their applicability for mass production. In this context, the ability to be fusion bonded (or welded) is one of the key advantages of FRTPCs over thermoset composites. Welding thermoplastic reinforced composites can be segregated into three major categories: resistive implant welding (RIW), vibration welding, and electromagnetic welding.

Resistive implant welding is an attractive technology due to faster cycle times, lower cost, higher design freedom, and ease of automation. Most research till date primarily focuses on processing and optimizing RIW joints for FRTPCs with high-performance polymer matrix materials that are typically used in aerospace. This dissertation primarily focuses on understanding the processability and optimizing RIW joint for FRTPC materials with engineering-grade polymers.

Moreover, research to date also predominantly uses only lap shear strength to characterize these joints. However, this is not enough to adequately understand the mechanical behavior of welded joints. In this dissertation, both lap shear and peel strength were experimentally evaluated, and finite element models were created to simulate these joints under large non-linear loads such as crash tests. This exercise provided in-depth insights into effects on the component-level performance of resistive implant welded structures and their behaviors in large deformation load cases such as crash tests.

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