Carbon Fiber Bundle Microstructure for Strength-Toughness Balance
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Solution Overview
Problem
Current methods for enhancing the tensile strength of carbon fibers have not satisfactorily controlled the minute structure or achieved a balance in tensile strength and fracture toughness, leading to insufficient performance in carbon fiber-reinforced composites.
Innovation Solution
A bundle of carbon fibers is manufactured using a specific oxidation process and carbonization method that controls the stress-strain curve nonlinearity and orientation parameter of crystallites, resulting in a high tensile strength and shear modulus, thereby enhancing the fracture toughness and tensile strength of the carbon fiber-reinforced composite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If oxidation temperature is increased by using a plurality of ovens different in temperature, then tensile strength of carbon fiber is improved, but manufacturing complexity and process time increase
Solution Approach 1:
The oxidation process is divided into two distinct stages: a first oxidation process at a lower temperature (200-300°C) to form a controlled amount of oxygen-containing groups, and a second oxidation process at a higher temperature (300-400°C) to further develop the minute structure. This segmentation allows each oxidation stage to serve a specific function, achieving high tensile strength without requiring multiple ovens with different temperatures simultaneously.
Solution Approach 2:
The invention changes the oxidation parameters by controlling the temperature progression and duration of oxidation treatments. Specifically, the first oxidation process uses moderate temperature (200-300°C) for a controlled period, followed by a second oxidation at higher temperature (300-400°C). This parameter control optimizes the formation of oxygen-containing groups and minute structure, achieving high tensile strength (6.0 GPa or more) while simplifying the manufacturing setup.
2Strength
If oxidation time is extended to improve tensile strength, then fracture toughness increases, but productivity decreases
Solution Approach 1:
The oxidation process is segmented into two stages with different temperature and time characteristics. The first oxidation process (200-300°C) is performed for a relatively longer duration to establish the foundation of oxygen-containing groups, while the second oxidation process (300-400°C) is performed for a shorter duration to complete the minute structure development. This segmentation achieves high tensile strength (6.0 GPa or more) while reducing total processing time compared to single-stage long-duration oxidation.
Solution Approach 2:
The invention optimizes the balance between oxidation time and temperature by implementing a two-stage process. The first stage uses moderate temperature (200-300°C) for extended time to build oxygen-containing groups, and the second stage uses higher temperature (300-400°C) for shorter time to finalize the structure. This parameter optimization achieves the required tensile strength (6.0 GPa or more) while improving productivity by reducing overall oxidation time.
3Strength
If single-fiber fineness is reduced to improve tensile strength, then strength increases, but manufacturing precision requirements increase
Solution Approach 1:
Instead of relying solely on reducing single-fiber fineness to achieve high tensile strength, the invention changes the approach by optimizing oxidation parameters. The two-stage oxidation process (first at 200-300°C, then at 300-400°C) controls the formation of oxygen-containing groups and minute structure, achieving tensile strength of 6.0 GPa or more while maintaining standard single-fiber fineness (5.0-7.0 μm). This parameter change in oxidation treatment reduces the stringency of manufacturing precision requirements.
4Strength
If conventional oxidation methods are used to improve tensile strength, then strength increases, but fracture toughness remains insufficient
Solution Approach 1:
The oxidation process is segmented into two functional stages: the first oxidation process (200-300°C) primarily forms oxygen-containing groups on the fiber surface, while the second oxidation process (300-400°C) focuses on developing the minute structure and improving fracture toughness. This segmentation ensures that both tensile strength (6.0 GPa or more) and fracture toughness are optimized, as each stage targets specific structural aspects that contribute to overall fiber performance.
Solution Approach 2:
The invention changes the oxidation parameters by implementing a two-stage temperature protocol. The first stage (200-300°C) controls oxygen-containing group formation, and the second stage (300-400°C) optimizes the minute structure for enhanced fracture toughness. This parameter change ensures that both tensile strength (6.0 GPa or more) and fracture toughness are improved, addressing the limitation of conventional single-stage oxidation methods.
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 method produces carbon fibers with a tensile strength of 7.5 GPa or more and a high shear modulus, significantly increasing the tensile strength of the carbon fiber-reinforced composite while maintaining excellent balance between tensile modulus and strength.
Implementation Method 1
a first oxidation process that oxidizes a precursor fiber bundle for a polyacrylonitrile-based carbon fiber
Implementation Method 2
a carbonization process to obtain a bundle of carbon fibers
Data Source
Figure 1
AI summary
Provided is a bundle of carbon fibers in which a value A obtained from a nonlinear approximation formula of a stress σ-strain ε curve in a tensile strength test of resin-impregnated strands and an orientation parameter Π (%) of crystallites in a wide-angle x-ray diffraction measurement satisfy a predetermined relational expression, and whose tensile strength has a predetermined value or more, whose tensile modulus is within a predetermined range and in which a product E × d/W of a ratio d/W of a single-fiber diameter d to a loop width W just before loop fracture evaluated by a single-fiber loop test and a tensile modulus E of the strands has a predetermined value or more, or whose apparent single-fiber stress has a predetermined value or more when the number of fiber breaks by a single-fiber fragmentation method for a single-fiber composite is 0.30 breaks/mm and in which when the number of the fiber breaks by the single-fiber fragmentation method for the single-fiber composite is 0.30 breaks/mm, the number of fiber breaks by a double-fiber fragmentation method for the single-fiber composite is within a predetermined range. The present invention provides the bundle of carbon fibers that can provide a high-performance carbon fiber-reinforced composite having excellent tensile strength, and a method for manufacturing the same.