Stitched Carbon Fiber Base Material for CFRP Form Stability
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Solution Overview
Problem
Conventional CFRP-forming base materials face challenges with form stability, shapability, and handleability, particularly in processing wet prepregs for three-dimensional shapes, due to issues like fiber disorder and elongation, which affect their ability to fit intricately curved surfaces and require labor-intensive cut-and-paste operations.
Innovation Solution
A stitched carbon fiber base material is developed with carbon fiber lines arrayed at angles between ±30° to ±60° to the stitching yarns' weaving direction, using a combination of chain stitch and 1/1 tricot weaves, and auxiliary yarns, with controlled stretch ratios and fiber areal weights, to ensure form stability and shapability, allowing for efficient processing and impregnation with thermosetting resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If unidirectional or bidirectional prepreg base materials are used, then resin impregnation is ensured and fiber strength is fully utilized, but labor-intensive cut-and-paste operations are required and manufacturing costs increase
Solution Approach 1:
The base material is segmented into multiple sheet layers with different fiber orientations (±45°) that are stitched together. This segmentation allows each layer to be optimized for specific directional strength while the stitching integrates them into a unified structure that eliminates the need for cut-and-paste operations.
Solution Approach 2:
The invention uses a composite structure combining multiple sheet materials with different fiber orientations, held together by stitching yarns. This composite approach creates a multiaxial base material that achieves both good resin impregnation and manufacturing efficiency by eliminating the need for post-cutting operations.
2Adaptability or versatility
If helically cut tubular woven fabric is used to create biased base material, then fiber array flexibility is improved, but the base material elongates in the lengthwise direction causing fiber disorder
Solution Approach 1:
The stitching yarns are introduced in advance to secure the fiber arrays before any elongation or deformation occurs during processing. This preliminary action prevents the fiber disorder that would otherwise result from lengthwise elongation, maintaining both flexibility and stability.
Solution Approach 2:
The invention changes the structural parameters by introducing stitching yarns at specific intervals and orientations, which fundamentally alters the mechanical behavior of the base material. The stitching creates a network that restricts lengthwise elongation while preserving the flexibility needed for fiber array adaptation.
3Productivity
If multiaxial stitched base material with high fiber areal weight is used, then labor saving in layering work is achieved, but resin impregnation becomes difficult due to high viscosity
Solution Approach 1:
The stitching yarns are strategically placed at specific locations and orientations to provide structural support where needed, rather than uniformly throughout the entire base material. This localized stitching approach maintains open spaces that facilitate resin penetration while still achieving labor-saving layering efficiency.
Solution Approach 2:
The multiaxial stitched structure inherently creates a porous network with channels formed by the stitching pattern. This porosity allows viscous resin to penetrate and impregnate the high fiber areal weight material effectively, resolving the contradiction between layering efficiency and impregnation ease.
4Stability of the object's composition
If stitched base material with rigid stitching yarns is used, then form stability is improved, but shapability deteriorates preventing proper fitting into curved surfaces
Solution Approach 1:
The stitching yarns are designed with dynamic characteristics that allow them to maintain rigidity during normal handling and processing, but become flexible when subjected to the forces involved in shaping operations. This dynamic behavior enables the base material to maintain form stability during manufacturing while acquiring the shapability needed to fit curved surfaces.
Solution Approach 2:
The invention carefully controls the physical parameters of the stitching yarns, such as fiber composition, yarn diameter, and stitch density, to achieve an optimal balance between stability and shapability. By adjusting these parameters, the base material can exhibit rigid behavior during handling but become sufficiently compliant during forming operations.
Data Source
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Figure 3(a)~3(b)
AI summary
An obj ect of the present invention is to provide a stitched carbon fiber base material which exhibits excellent form stability and shapability, ensures excellent handleability in processing a wet prepreg in CFRP manufacturing steps, and facilitates production of a three-dimensional shape, and to provide a wet prepreg using the same. Each sheet material (1) is formed by arraying carbon fiber lines (11, 11, ...), each having a predetermined width, in parallel with one another. Meanwhile, an array direction of the carbon fiber lines (11) of each sheet material (1) is set to form an angle in a range from ±30° to ±60° to a weaving advancing direction of a stitching yarn (2) . Moreover, a stretch ratio of the stitched base material in its lengthwise direction in a case where a load per inch width of the stitched base material is applied in the weaving advancing direction of the stitching yarn (2) is equal to or below 4% when the load is 5 N, and is equal to or above 10% when the load is 25 N.