Dual Viscosity UV-Curable Prepreg for Composite Repair

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Solution Overview

Problem

Conventional wet lamination processes for repairing fibre-reinforced resin matrix composite materials, such as wind turbine blades, face challenges with poor adhesion, handling difficulties, and inefficiencies due to temperature and humidity conditions, leading to unreliable and time-consuming repairs.

Innovation Solution

A dual viscosity prepreg system with a high viscosity matrix resin and a low viscosity wet resin, both curable by ultraviolet radiation, is used, along with a UV-blocking film and a holder for the prepreg, allowing for easy application and curing at ambient temperatures, ensuring strong adhesion and efficient repair.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional wet lamination process is used with liquid resin, then the resin can be applied to the substrate, but the resin drips and transfers onto non-repair areas requiring substantial post repair clean up

Engineering Contradiction:

Improveease of applicationVSAvoidresin dripping and transfer

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent uses a self-adhesive film with pressure-sensitive adhesive to hold the fibrous reinforcement material. This film acts as a carrier that prevents resin dripping and transfer during application, eliminating the need for post-repair cleanup while maintaining ease of application.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The self-adhesive film is a disposable component that is used once during the repair process and then discarded. It provides the necessary function of preventing resin transfer during application and is then removed, leaving no residue or cleanup required.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Ease of operation

If conventional prepreg is used without heating, then application is simpler, but adhesion between prepreg and substrate is poor

Engineering Contradiction:

Improvesimplicity of applicationVSAvoidadhesion strength

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The patent replaces the thermal activation system with a photoactivation system. Instead of using heat to activate the resin and achieve adhesion, the invention uses ultraviolet light to cure the resin at ambient temperature, maintaining simplicity of application while achieving strong adhesion.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the activation parameter from thermal energy to light energy. The resin formulation is modified to be photo-curable instead of thermally curable, allowing activation at ambient temperature through UV irradiation while maintaining strong bonding strength.

Inventive Principle:

Principle #35Parameter changes

3Temperature

If amine curing agents are used in epoxy resin, then the resin can cure at low temperatures, but the amine reacts with atmospheric carbon dioxide and moisture forming ammonium carbamate layer causing poor adhesion

Engineering Contradiction:

Improvecuring temperatureVSAvoidadhesion strength

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The patent replaces the chemical curing mechanism involving amine reactions with a photo-curing mechanism. Instead of using amine curing agents that react with atmospheric moisture and CO2, the invention uses photoinitiators that decompose under UV light to generate free radicals for polymerization, eliminating the harmful side reactions while maintaining low-temperature curing capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the chemical mechanism from amine-based thermal curing to photo-initiated polymerization. This parameter change in the curing chemistry eliminates the formation of ammonium carbamate layers while still enabling curing at ambient temperatures through UV light activation.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The dual viscosity prepreg system enables reliable, speedy, and durable repairs across varying environmental conditions, improving handling and adhesion, and reducing repair time and complexity, particularly suitable for large composite structures like wind turbine blades.

Implementation Method 1

both the matrix resin and the wet resin being curable by ultraviolet radiation

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Implementation Method 2

a first removable flexible film which acts as a barrier to ultraviolet radiation

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentUS9381707B2Repair of composite materials

Publication Date: 2016.07.05 GURIT (UK) LTD

AI summary

A prepreg comprising a fibrous reinforcement layer at least partially impregnated with a matrix resin having a first viscosity, a coating of a wet resin having a second viscosity on a first side of the fibrous reinforcement layer, the first viscosity being higher than the second viscosity, both the matrix resin and the wet resin being curable by ultraviolet radiation, a first removable flexible film which acts as a barrier to ultraviolet radiation on a second side of the fibrous reinforcement layer, and optionally a second removable protective flexible film covering the coating of wet resin.