Co-cure prepreg tape with deprotected functional groups for composite bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The adhesive bonding of composite structures, particularly large or complex structures, faces challenges with unpredictable joint strengths and the need for redundant mechanical fasteners due to the limitations of existing methods like secondary bonding, co-bonding, and co-curing, especially in aerospace applications where complex shapes and sizes are involved.
Innovation Solution
A modified co-cure method using multifunctional epoxy resins with chemically protected polymerizable functional groups that undergo deprotection to form seamless, covalently bonded composite structures without the need for mechanical fasteners, allowing for 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 pre-cured composite parts, then the bonding process is simple and does not require simultaneous curing, but the joint strength is unpredictable and requires redundant mechanical fasteners
Solution Approach 1:
The invention uses a dual-cure resin system combining epoxy and cyanate ester resins that work together to achieve both immediate bonding and long-term structural integrity. The epoxy provides rapid initial cure for handling while the cyanate ester continues to cure at elevated temperatures to achieve final mechanical properties, creating a composite curing mechanism that ensures predictable joint strength without fasteners
Solution Approach 2:
The invention utilizes temperature-dependent curing kinetics where the epoxy resin cures at room or elevated temperatures to provide initial bond strength, then the cyanate ester resin cures at higher temperatures (200-300°C) to achieve final mechanical properties. This staged parameter change approach ensures predictable joint strength development while maintaining ease of manufacture
2Reliability
If co-curing is used to join uncured composite parts, then chemical bonding is achieved with strong joints, but it is difficult to handle and assemble complex three-dimensional shapes
Solution Approach 1:
The invention applies a coating of uncured resin to the bonding surfaces of pre-cured composite parts before assembly. This preliminary action creates a tacky surface that allows for easy positioning and assembly of complex three-dimensional shapes, while the subsequent curing process establishes strong chemical bonds. The pre-cured parts maintain their structural integrity during handling while the uncured coating provides bonding capability
Solution Approach 2:
The uncured resin coating acts as an intermediary layer between pre-cured composite parts, providing a manageable interface that allows for easy assembly of complex geometries. This intermediary layer can be positioned and adjusted before curing, while still enabling chemical bonding to the substrate, thus resolving the contradiction between bond strength and ease of operation
3Reliability
If secondary bonding with mechanical fasteners is used to meet FAA regulations, then certification is achieved, but the part count increases by up to 120,000 parts and weight by up to 5000 lbs
Solution Approach 1:
The invention replaces the mechanical fastening system with a chemical bonding system using dual-cure resin. The epoxy-cyanate ester resin system provides sufficient bond strength to meet FAA certification requirements for primary structures, eliminating the need for thousands of mechanical fasteners and reducing aircraft weight by up to 5000 lbs while maintaining reliability and compliance
4Reliability
If traditional autoclave-based co-curing is used, then strong chemical bonds are formed, but the process is constrained by autoclave size and cannot accommodate large-scale structures
Solution Approach 1:
The invention segments the curing process into two distinct stages: an initial cure stage that can occur at room or elevated temperatures without autoclave equipment, and a final post-cure stage that achieves full mechanical properties. This segmentation allows large-scale structures to be assembled and initially cured in situ, then post-cured in smaller sections or using alternative heating methods, thereby removing the autoclave size constraint while maintaining bond strength
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 enables the creation of predictable, certifiable composite structures with reduced part count and weight, eliminating the need for redundant fasteners and allowing for the fabrication of complex shapes without the constraints of traditional autoclave-based co-curing processes.
Implementation Method 1
applying a second temperature to facilitate deprotection of the chemically protected polymerizable functional groups to give unprotected polymerizable functional groups
Implementation Method 2
curing the first and second composite substrates to the co-cure prepreg tape at a first temperature to form a co-cure prepreg tape portion wherein the first and second composite substrates are fully cured
Implementation Method 3
cure the co-cure prepreg tape portion of the first composite substrate to the co-cure prepreg tape portion of the second composite substrate to form a single covalently bonded composite structure
Data Source
AI summary
A method for bonding composite structures which includes providing a first and second composite substrate and coupling a co-cure prepreg tape having chemically protected polymerizable functional groups onto a surface of both the first and second composite substrates. The first and second composite substrates are then cured to the co-cure prepreg tape at a first temperature to form a co-cure prepreg tape portion where the first and second composite substrates are fully cured and the co-cure prepreg tape is partially cured. The co-cure prepreg tape portion of the first composite substrate is then coupled to the co-cure prepreg tape portion of the second composite substrate and a deprotection initiator is applied to facilitate deprotection of the chemically protected polymerizable functional groups and cure the co-cure prepreg tape portion of the first and second composite substrates to form a single covalently bonded composite structure.