Laser Deposition Joining of Composites for Wind Turbine Blade Repair

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Cost-effective repair methods for composite blades are critically needed for the wind energy industry. Wind turbine blades are subject to considerable wear and degradation, and their repairs are often necessary. Currently, most blade repairs are performed using wet epoxy resins. Such repairs have low joining strength and require long processing time. The research supported under this award will establish the foundation for a novel laser-based process to repair composite blades. During the process, a repair patch of glass fibers is joined employing a laser-deposition joining method utilizing fine glass powders as filler material. Laser-deposition joining repair of fiber-reinforced composites will also have applications where repair of composite structures is needed; for example, those in defense, aerospace, automotive, and compressed gas storage industries. Consequently, the results of this research will benefit the U.S. economy and society. The research objectives are: (1) establishing the relationship between glass powder stream temperature and operational parameters (such as laser power density and powder flow rate), (2) quantifying the effect of the glass powder stream temperature on the glass viscous flow behavior through the repair patch of glass fibers, and (3) establishing the relationship between glass powder stream temperature and deposition joint quality (in terms of infiltration depth, porosity, flexural properties, and delamination resistance). To achieve these objectives, three research tasks will be completed. First, numerical modeling of coaxial powder flow and laser-particle interaction will be performed to predict glass powder stream temperature. The modeling results under various operational conditions will be verified using experimental measurements of powder stream temperature. Second, multi-physics modeling will be performed to evaluate the effect of powder stream temperature on the glass melt viscous flow through the random arrays of fibers media. The infiltration depth of the glass fill and porosity of the cooled deposition joint will be predicted and validated against optical and scanning electron microscopy measurements. Finally, the effect of glass powder stream temperature on the joint integrity will be experimentally determined based on microscopy measurements of infiltration depth and porosity and mechanical testing of flexural properties and delamination resistance.