Pultruded Spar Cap Strip With Toughened Bonding Surface
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Solution Overview
Problem
The challenge in manufacturing large wind turbine blades is the precise laying of fibre layers and providing spar caps with desired dimensions and tolerances, particularly in terms of width and thickness, and ensuring reliable fracture toughness in connections between pultruded strips and interlayers.
Innovation Solution
A pultruded fibre-reinforced strip with a core of carbon or glass fibres and a surface layer of polymeric fibres with low elastic modulus, designed to enhance fracture toughness in bonding areas, is used to form a spar cap, which can be stacked with similar strips and connected via interlayers embedded in resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pultruded strips are stacked to form spar caps, then manufacturing precision and dimensional control are improved, but fracture toughness in bonding areas deteriorates
Solution Approach 1:
The invention uses a composite material structure where the pultruded strip combines a core of high-modulus fibres (carbon or glass) with a surface layer of low-modulus polymeric fibres. This composite structure allows the core to provide dimensional stability and stiffness for manufacturing precision, while the polymeric surface layer provides toughness and crack resistance at bonding interfaces, thus resolving the contradiction between precision and fracture toughness.
Solution Approach 2:
The invention applies different material properties to different parts of the pultruded strip: the core region uses high-modulus fibres for structural rigidity and dimensional control, while the surface layer uses low-modulus polymeric fibres specifically at the bonding areas to enhance fracture toughness. This local differentiation of material quality allows simultaneous achievement of manufacturing precision and bonding reliability.
2Strength
If interlayers are added between pultruded strips, then structural connection is improved, but manufacturing complexity increases
Solution Approach 1:
The invention merges the interlayer function with the pultruded strip itself by incorporating the polymeric fibre surface layer directly onto the strip during pultrusion. This integration eliminates the need for separate interlayer materials and reduces manufacturing steps, as the strip's own surface layer provides the bonding and structural connection functions that would otherwise require additional interlayer components.
Solution Approach 2:
The pultruded strip is designed to be self-sufficient by incorporating the polymeric fibre surface layer that performs both structural and bonding functions. The strip's own surface layer serves as the bonding interface with adjacent strips and interlayers, eliminating the need for separate bonding agents or complex assembly processes, thus reducing manufacturing complexity while maintaining structural connection strength.
Data Source
AI summary
A pultruded fibre-reinforced strip configured to be stacked with one or more similar strips to form a spar cap of a wind turbine blade, comprisinga core comprising a plurality of first fibres embedded in a resin matrix, the plurality of first fibres being carbon fibres and/or glass fibres, anda surface layer enclosing and covering the core and comprising a plurality of second fibres Imbedded in the resin matrix, the majority of the plurality of second fibres having an elastic modulus less than 10 GPa.