Chopped fiber bundle, molding material, and fiber reinforced plastic, and process for producing them
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Solution Overview
Problem
Conventional chopped fiber bundles used in molding materials face challenges in forming complex shapes due to stress concentration at the ends of reinforcing fibers, leading to cracks and reduced mechanical properties, especially when the fibers are cut to a uniform length of 25 mm, which limits their ability to form three-dimensional shapes.
Innovation Solution
A chopped fiber bundle design with a gradual increase and decrease in the number of reinforcing fibers along its length, featuring transition sections and a constant section, where the fibers are arranged to minimize stress concentration by sharing force gradually between adjacent bundles, and using carbon fibers with a specific range of 1,000 to 700,000 fibers, optimizing the fiber length between 5 to 100 mm to enhance mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chopped fiber bundles with uniform fiber length (25 mm) are used, then the manufacturing process is simple, but stress concentration occurs at fiber ends leading to cracks and reduced mechanical properties
Solution Approach 1:
The fiber bundle cross-sectional area is varied along its length, creating different local structures: larger cross-section in the middle portion and smaller cross-section at end portions. This local quality variation reduces stress concentration at fiber ends while maintaining manufacturing simplicity, resolving the contradiction between ease of manufacture and mechanical strength.
2Adaptability or versatility
If chopped fiber bundles are used to enable complex shape molding, then three-dimensional shapes can be formed, but stress concentration at fiber ends causes cracks that limit mechanical performance
Solution Approach 1:
By creating a fiber bundle structure with varying cross-sectional area along its length (smaller at ends, larger in middle), the invention locally modifies the stress distribution characteristics. This reduces stress concentration at fiber ends where cracks typically initiate, thereby improving reliability and crack resistance while maintaining the ability to form complex three-dimensional shapes.
3Strength
If continuous fibers are arranged regularly in material bases, then excellent mechanical properties and small dispersion are achieved, but complicated three-dimensional shapes cannot be formed
Solution Approach 1:
The continuous fiber bundles are segmented into chopped fiber bundles with controlled cross-sectional variations. This segmentation allows the fibers to be more adaptable for complex shape molding while the internal structure of each bundle (with larger middle portion and smaller end portions) maintains stress distribution characteristics that preserve mechanical property consistency.
Data Source
Figure 1
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Figure 5(a)~6(b)
AI summary
This invention provides a chopped fiber bundle comprising a large number of unidirectionally arranged reinforced fibers. The length of each of the reinforced fibers is in the range of 5 to 100 mm. The chopped fiber bundle has a transition segment in which the number of the reinforced fibers increases toward the central part of the chopped fiber bundle in the aligned direction of the reinforced fibers with both ends in the aligned of the reinforced fibers in the chopped fiber bundle being a starting point. The level of a change in total sectional area of the large number of reinforced fibers is not more than 0.05 mm2 per mm in the aligned direction of the reinforced fibers over the whole area in the longitudinal direction of the chopped fiber bundle.