Random Mat Fiber Structure for Resin Molding Flowability
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Solution Overview
Problem
Conventional fiber-reinforced resin molding materials face challenges in achieving a balance between good flowability during molding and high mechanical properties of molded articles, with existing solutions either compromising on flowability or mechanical strength, and often experiencing stress concentration at the end portions of fiber bundles.
Innovation Solution
A random mat comprising a chopped fiber bundle with specific structural features, including alternately formed separation-processed and not-separation-processed sections, obliquely cut to reduce stress concentration and enhance mechanical properties, is used in conjunction with a matrix resin to form a fiber-reinforced resin molding material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fiber bundle with a large number of single fibers is used, then flowability during molding is improved, but mechanical properties of the molded article deteriorate due to stress concentration at the end portions
Solution Approach 1:
The invention applies local quality by creating a non-uniform fiber distribution within the fiber bundle. Specifically, the fiber bundle has a higher concentration of fibers in the central portion and a lower concentration at the end portions. This local variation in fiber density allows the central region to provide structural strength while the reduced fiber concentration at the ends minimizes stress concentration, thereby resolving the contradiction between flowability and mechanical properties.
2Strength
If a fiber bundle with a small number of single fibers is used, then mechanical properties of the molded article are improved, but flowability during molding deteriorates
Solution Approach 1:
The invention resolves this contradiction by implementing local quality through spatially varying fiber concentration. The central portion maintains a high fiber concentration to ensure excellent mechanical properties and strength, while the end portions have a reduced fiber concentration that improves flowability during molding. This localized differentiation allows the fiber bundle to exhibit both high strength characteristics and good flowability simultaneously.
3Ease of manufacture
If conventional perpendicular cutting is used, then manufacturing simplicity is maintained, but stress concentration occurs at the end portions of the fiber bundle
Solution Approach 1:
The invention applies asymmetry by introducing a gradual transition in fiber concentration from the central portion to the end portions of the fiber bundle. Instead of a uniform or abrupt transition, the fiber concentration changes asymmetrically and gradually along the length of the bundle. This asymmetric gradient structure effectively reduces stress concentration at the end portions while maintaining manufacturing feasibility through controlled fiber placement techniques.
Data Source
AI summary
A random mat includes a chopped fiber bundle [A] obtained by obliquely cutting a partially separated fiber bundle [B] prepared by alternately forming separation-processed sections, each of which is separated into a plurality of bundles, and not-separation-processed sections, along the lengthwise direction of a fiber bundle, wherein the total cross-sectional area of reinforcing fibers exhibits a specific change amount between both tips of the chopped fiber bundle [A]; a production method produces the random mat; and a fiber-reinforced resin molding material uses the random mat.