Carbon Fiber Bundle Knot Strength via Staged Stabilization
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Solution Overview
Problem
Existing methods for producing carbon fiber bundles with high tensile strength and fracture toughness are inadequate, as they fail to effectively control the microstructure and knot strength, especially when increasing the number of filaments, leading to reduced productivity and composite quality.
Innovation Solution
A method involving a stabilization process with multiple temperature control stages, pre-carbonization, and carbonization in an inert atmosphere to achieve uniform heat treatment, increasing the number of filaments to 30,000 or more, and optimizing infrared spectrum peak intensity ratios to enhance knot strength and tensile modulus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of filaments is increased to improve productivity, then production efficiency is improved, but tensile strength and fracture toughness deteriorate
Solution Approach 1:
The patent applies local quality by creating a skin-core structure where the skin portion has different microstructural characteristics than the core portion. The skin portion has a higher degree of crystallinity and different orientation parameters, which provides enhanced strength and fracture toughness. This local differentiation allows the fiber bundle to maintain high performance even with increased filament count, resolving the contradiction between productivity and strength.
Solution Approach 2:
The patent utilizes parameter changes by controlling specific physical parameters during stabilization and carbonization processes. Key parameters include orientation parameters (fo1, fo2, fo3), crystallinity degree, and microstructural development. By precisely controlling these parameters through staged heating and stretching processes, the patent achieves optimal balance between filament count and mechanical properties, enabling high productivity without sacrificing tensile strength.
2Strength
If the stabilization temperature is increased to improve tensile strength, then fracture toughness is improved, but production time is extended
Solution Approach 1:
The patent applies segmentation by dividing the stabilization process into multiple stages with different temperature profiles and stretching ratios. Instead of a single prolonged high-temperature treatment, the process is segmented into sequential steps that achieve the same microstructural development more efficiently. This segmentation reduces total production time while maintaining fracture toughness by progressively developing the desired microstructure through controlled stages.
Solution Approach 2:
The patent implements continuity of useful action by integrating stretching and stabilization processes continuously rather than as separate batch operations. The fiber bundle undergoes continuous stretching and heating in a coordinated manner, maintaining productive action throughout the process. This continuous approach eliminates idle time between operations and achieves high fracture toughness efficiently by maintaining optimal processing conditions throughout.
3Strength
If multiple ovens with different temperatures are used to control microstructure, then tensile strength is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing a single stabilization apparatus that performs multiple functions: heating, stretching, and microstructural development. Rather than requiring separate ovens for each function, the apparatus integrates these operations in a unified system. This multi-functional design reduces device complexity while achieving the same tensile strength improvement through coordinated control of temperature and mechanical deformation in a single pass.
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 results in a carbon fiber bundle with a tensile modulus of 265 to 300 GPa, tensile strength of 6.0 GPa or more, knot strength of 820 N/mm2 or more, and a coefficient of variation in knot strength of 6% or less, significantly improving the production efficiency and quality of carbon fiber-reinforced composites.
Implementation Method 1
stabilization process... in oxidation ovens... extending, in oxidation ovens composed of a plurality of ovens, precursor fibers for carbon fiber
Implementation Method 2
increase the stabilization temperature using a plurality of ovens having different temperatures in the stabilization process... heat-treat the carbon fiber bundle at 280 to 400° C.
Implementation Method 3
carbonization process of carbonizing the fiber bundle obtained in the pre-carbonization process in an inert atmosphere having a maximum temperature of 1000 to 2000° C.
Implementation Method 4
extending, in oxidation ovens composed of a plurality of ovens, precursor fibers for carbon fiber that have passed through the ovens according to the density thereof
Data Source
AI summary
A carbon fiber bundle from which a carbon fiber composite material having high tensile strength can be obtained has the following configuration. Specifically, the carbon fiber bundle has a strand elastic modulus of 265-300 GPa, strand strength of at least 6.0 GPa, and knot strength of at least 820 N/mm2, and includes at least 30,000 filaments.