Off-set Resin Co-cure Prepreg for Composite Bonding
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Solution Overview
Problem
The aerospace industry faces challenges in bonding large or complex composite structures due to unpredictable joint strengths and the need for redundant mechanical fasteners, which increases costs and weight, particularly in aircraft manufacturing, where secondary bonding techniques often result in weak adhesive-adherent interfaces and co-cure processes are limited by complexity and size constraints.
Innovation Solution
A method involving the use of co-cure prepreg layers with specific off-set amine to epoxide molar ratios, allowing for the formation of a monolithic covalently bonded composite structure without the need for redundant fasteners, by coupling and curing prepreg layers with protected functional groups to achieve a seamless joint, enabling the assembly of large-scale composite structures in an out-of-autoclave process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If secondary bonding is used to join composite parts, then the bonding process is simple and effective, but the joint strength becomes unpredictable and requires redundant mechanical fasteners
Solution Approach 1:
The patent replaces mechanical fasteners with a chemical bonding system. A co-cure prepreg layer with blocked isocyanate groups is used to create a chemical bond between composite substrates, eliminating the need for mechanical fasteners while providing predictable and reliable joint strength through controlled chemical reactions at the interface.
Solution Approach 2:
The patent changes the chemical state of the bonding agent by using blocked isocyanate groups that are activated at specific temperatures. The blocking mechanism allows the adhesive to remain inactive during assembly and only become reactive during the curing process, providing controlled and predictable bonding behavior that resolves the reliability issue.
2Reliability
If co-cure process is used to join uncured composite parts, then chemical bonding is achieved, but the complexity of part shapes and size limitations prevent application to large structures
Solution Approach 1:
The patent segments the curing process into two distinct stages: first, assembly of uncured composite parts with the co-cure prepreg layer in place; second, thermal activation of the blocked isocyanate groups to complete the chemical bond. This segmentation allows complex large-scale structures to be assembled in an uncured state and then cured afterward, removing the size and shape constraints of traditional co-cure processes.
Solution Approach 2:
The patent performs preliminary assembly of composite parts in their uncured state before activating the chemical bonding. The co-cure prepreg layer is applied to the substrate while uncured, allowing easy assembly of complex geometries, and then the blocked isocyanate groups are thermally activated to complete the chemical bond, achieving reliable bonding without the constraints of traditional co-curing.
3Ease of manufacture
If blocked isocyanate groups are used in co-cure prepreg, then out-of-autoclave processing is enabled, but the curing process requires precise temperature control
Solution Approach 1:
The patent uses blocked isocyanate groups that are designed to decompose and release the active isocyanate functionality at specific temperature ranges. By selecting blocking agents with appropriate decomposition temperatures, the curing process can be controlled using standard industrial ovens without requiring autoclaves, while the temperature control requirements are managed through the inherent thermal characteristics of the blocking chemistry.
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
This method produces reliable, certifiable joints that reduce the part count and weight of aircraft by eliminating redundant fasteners, while allowing for the fabrication of complex composite structures without the limitations of traditional co-cure processes, enhancing the structural integrity and reducing manufacturing costs.
Implementation Method 1
the blocked isocyanate groups are decomposed at a second temperature to release the isocyanate functionality
Implementation Method 2
the isocyanate groups are reacted with hydroxyl groups on the composite substrates
Data Source
AI summary
A method for bonding composite substrates includes coupling a first co-cure prepreg layer having a first off-set amine to epoxide molar ratio onto a surface of a first composite substrate and coupling a second co-cure prepreg layer having a second off-set amine to epoxide molar ratio onto a surface of a second composite substrate. The first and second composite substrates are cured to the first and second co-cure prepreg layers, respectively, using a first cure cycle (including B-stage and cure temperatures) to form a first and a second co-cure prepreg layer portion. The method further includes coupling the first co-cure prepreg layer portion to the second co-cure prepreg layer portion and applying a second cure cycle to cure the first co-cure prepreg layer portion of the first composite substrate to the second co-cure prepreg layer portion of the second composite substrate to form a monolithic covalently bonded composite structure.