Effect of Fiber Length in Friction Stir Welding of Discontinuous Composites

Abstract:

Friction stir welding (FSW) is widely used to bond metals and polymers to create large structures from standardized geometric components. However, FSW has found more limited use in traditional continuous fiber reinforced composites due to the risk of damage to the reinforcing fibers, including fiber misorientation and fragmentation. The process is more amenable to discontinuous fiber composites, which often take the form of injection molding compounds reinforced with short, milled fibers, for which the mechanical performance is significantly degraded. An emerging class of materials, recycled carbon fiber nonwovens, contain long discontinuous fibers that imbue their composites with mechanical performance that bridges the gap between injection molding compounds and continuous fiber laminates, while also decreasing the energy footprint of the materials. This work evaluates this class of materials, alongside injection molding compounds, to develop new insights into the bonding of composite structures using friction stir welding. The bridging effect of discontinuous fibers across the bondline is evaluated using optical microscopy to link processing conditions and fiber length to the resulting performance. Fiber migration was observed in the weld area, though mechanical interlocking was the primary mechanism of bonding in the weld zone. While samples failed at a fraction of the neat materials nominal strength, increased fiber length was found to have a beneficial effect on the apparent tensile and lap shear strength on welds in this study. The new insights gained represent an important step towards the adoption of the FSW process as a means of rapidly manufacturing large composite structures made of carbon fiber/PPS or other fiber-reinforced polymers to enable deployable structures from standardized geometric components.

• Periodical: Materials Science Forum (Volume 1185)
• Pages: 99-109
• DOI: https://doi.org/10.4028/p-61pDv7
• Online since: April 2026
• Authors: Austin Clark, Philip Barnett, Elizabeth Mamros, Brian Young, Ihab Ragai*
• Keywords: Carbon Fiber Reinforced Polymers, FSW, Microstructure, Polyphenylene Sulfide

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