Epoxy-Sized Carbon Fiber Bundle for Open-Hole Tensile Strength
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Solution Overview
Problem
Current methods fail to significantly improve the open hole tensile strength of carbon fiber-reinforced composite materials, despite advancements in tensile modulus and single-fiber strength, due to inadequate control over single-fiber strength distribution and interfacial shear strength.
Innovation Solution
A sizing agent-coated carbon fiber bundle with an aliphatic epoxy compound and an aromatic epoxy compound is used, where the carbon fibers exhibit specific fiber breaks per unit length under stress, and the carbonization process is optimized to achieve high tensile strength and modulus, along with controlled bundle strength and interfacial adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the tensile modulus of carbon fiber is improved to reduce aircraft weight, then the rigidity of composite material is enhanced, but the open hole tensile strength remains insufficient
Solution Approach 1:
The invention changes the parameter of single-fiber strength distribution by controlling the number of fiber breaks at specific stress levels (15.3 GPa and 12.2 GPa). This parameter change in the fiber strength distribution, combined with optimized sizing agent composition (aliphatic epoxy compound and aromatic epoxy compound in specific ratios), resolves the contradiction by achieving both high open hole tensile strength and balanced mechanical properties
Solution Approach 2:
The invention uses a composite sizing agent system combining aliphatic epoxy compound (providing flexibility and adhesion) and aromatic epoxy compound (providing strength and rigidity). This composite approach allows the sizing layer to simultaneously improve interfacial adhesion for high open hole tensile strength while maintaining overall mechanical property balance
2Strength
If high draw tension is applied during carbonization to improve tensile modulus, then the tensile modulus increases, but the single-fiber strength distribution deteriorates
Solution Approach 1:
The invention applies preliminary action by optimizing the sizing agent coating before carbonization. The sizing agent with specific composition (aliphatic epoxy compound and aromatic epoxy compound in controlled ratios) is applied to protect the fiber surface and control strength distribution before the high draw tension carbonization process, preventing deterioration of single-fiber strength distribution while allowing tensile modulus improvement
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 approach results in carbon fiber-reinforced composites with enhanced open hole tensile strength and balanced mechanical properties, contributing to weight reduction and improved fuel efficiency in aircraft applications.
Implementation Method 1
a sizing agent containing an aliphatic epoxy compound (C) and an aromatic epoxy compound (D) coated on the carbon fiber bundle
Implementation Method 2
the carbonization process is conducted in an inert atmosphere at a temperature of 1200 to 2000°C
Implementation Method 3
tension applied to the pre-carbonized fiber bundle produced by the pre-carbonization in the carbonization process
Data Source
Figure 1~2
AI summary
The present invention provides a sizing agent-coated carbon fiber bundle having a sizing agent containing an aliphatic epoxy compound (C) and an aromatic epoxy compound (D) coated on the carbon fiber bundle, wherein the carbon fiber in the carbon fiber bundle is the one which exhibits, when measured by single-fiber composite fragmentation method, a number of fiber breaks of at least 2.0/mm when apparent single-fiber stress is 15.3 GPa and the number of fiber breaks of up to 1.7/mm when the apparent single-fiber stress is 12.2 GPa. Another aspect of the present invention is a prepreg containing such sizing agent-coated carbon fiber bundle, an epoxy compound (A), and an aromatic amine curing agent (B). The present invention provides a prepreg and a sizing agent-coated carbon fiber bundle used as a starting material for such prepreg for producing a carbon fiber composite material capable of realizing excellent tensile modulus and open hole tensile strength.