Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Tutunea-Fatan, O. Remus

Abstract

To accommodate the increasing need for vehicle emission reduction, automotive manufacturers are presently looking at the next generation of lightweight materials. Glass fibre-reinforced thermoplastic composites belong to this group and exhibit mechanical properties that resemble traditional metals but at a reduced weight and with improvements on other characteristics. Unfortunately, they are affected by processing-related warpage, especially when fabricated by means of the Long Fibre-reinforced Thermoplastics – Direct (LFT-D) manufacturing process, a technology that is valuable because of its high throughput and flow lengths. This occurs for many reasons but reinforcing LFT-D with Glass Mat Thermoplastics (GMT) – another material format with higher fibre content and isotropy – may overcome these issues altogether.

To validate this hypothesis, a complex demonstrator geometry was first selected. Then, the moulding of LFT-D was examined via thermography and moulding simulation to find thermal-related issues caused by the geometry and material. Following this investigation, LFT-D was co-moulded with GMT and the resulting warpage was compared to both LFT-D and GMT by means of a deformation energy-based warpage metric as well as an image correlation metric used for warpage pattern similarity assessment. Nearly 25% LFT-D volume replacement with GMT provided warpages similar to the base GMT material with minimal changes to the warpage pattern. Though, subsequent mechanical tests yielded inconclusive results – most likely due to the confounding effect of specimen warpage – the overall results suggest a good bonding, fusion and mixing of the two co-moulded materials. Further investigation of other warpage reduction methods could be considered in the future.

Summary for Lay Audience

Due to pressure from climate change and governments, automotive companies are looking for lightweight materials capable of improving vehicle driving range. Materials such as glass fibre-reinforced plastics can have strengths comparable to steel and aluminum but at a fraction of the weight. However, because of material design and the nature of manufacturing with these materials, they tend to deform from their designed shape – called warpage – leading to many downstream manufacturing issues. This work will explore the possibility of reinforcing a material that is prone to warp, namely the Long Fibre-reinforced Thermoplastics – Direct (LFT‑D) process with another material, Glass Mat Thermoplastics (GMT) to reduce the overall part warpage.

To do this, first the moulding of selected components using LFT-D was looked at, and several temperature-related inconsistencies were expectedly found, as these are possibly the largest contributor to warpage. Then LFT-D was moulded together with GMT and the resulting warpage was measured and found to be much lower than LFT-D on its own and quite close to GMT on its own. This overcame the temperature issues amongst other warpage causes and demonstrated the success of the method. To further validate the method, the strength of the materials was tested to ensure that they bonded properly during moulding, and the cross-sections were examined under a microscope. Both tests showed promising results, but the sample size was too small to make a fully justified conclusion. Thus, further work on this topic is legitimized and shows that co-moulding may be a favourable technique for manufacturers.

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