Static shoulder friction stir-based joining of structural polymer plate to a polymeric proton-exchange membrane

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master_Ahmed_Saad_2025.pdf (2.01 MB)

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School of Engineering | Master's thesis
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Date

2025-09-29

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Mechanical Engineering

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Degree programme

Master's programme in Mechanical Engineering

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en

Pages

97

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Abstract

Joining polymeric proton-exchange membranes to electrode polar plates, or other structural engineering materials, remains a critical bottleneck in the industrialization of proton exchange membrane fuel cells (PEMFCs). This thesis investigates a fastener-free architecture in which polyether-ether-ketone (PEEK) plates are joined using a static-shoulder friction stir welding (SSFSW) process, with and without the incorporation of a Nafion membrane at the butt joint interface. The study includes an initial screening comprising nine SSFSW parameter sets, in which the influence of rotational and travel speed was systematically explored using bead-on-plate (BOP) processing of PEEK and a validation stage, in which optimized parameters were applied to butt joints, both with and without Nafion. Weld quality was assessed through tensile testing, distortion measurement, and macro and microstructural analysis via light optical microscopy. The failure modes were analysed with a focus on joint efficiency, repeatability, and the effect of the Nafion on joint strength. The joint performance was benchmarked against the as-supplied PEEK base material and notched baseline specimens. The results demonstrate that the process is stable and repeatable, with optimum performance achieved at lower travel speeds and tool rotation. While further refinement is required to minimise distortion and improve the joint with Nafion, the findings highlight the potential of SSFSW for enabling polymer membrane integration in PEMFC applications.

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Supervisor

Vilaca, Pedro

Thesis advisor

Khadka, Prabilson

Keywords

static shoulder friction stir based joining, structural polymer; PEEK, polymer joining, Nafion membrane, bead on plate(BOP); friction stir processing, retreating side (RS)

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https://urn.fi/URN:NBN:fi:aalto-202510208302

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