Prepreg Charge Angled Cuts for Contoured Composite Stringers
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Solution Overview
Problem
Existing methods for producing contoured composite laminate stringers, such as punch forming, often result in ply wrinkling due to the tendency of plies to buckle or wrinkle during the forming process, which can negatively impact stringer performance and are not well-suited for high-volume production.
Innovation Solution
A method and material for forming contoured composite laminate stringers involve selecting a schedule of plies with specific fiber angles and lengths, including angled cuts in certain plies to allow for stretching during the forming process, creating a highly formable composite charge that reduces or eliminates ply wrinkling, enabling efficient production of contoured stringers with minimal strength knockdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If punch forming is used to produce contoured composite laminate stringers, then production speed and volume are improved, but ply wrinkling and buckling occur during the forming process
Solution Approach 1:
The composite charge is segmented into multiple plies with different fiber orientations (0°, 45°, 90°) and varying fiber lengths. This segmentation allows each ply to deform independently during forming, accommodating contour changes without collective wrinkling. The fiber cuts create discrete segments that can stretch and conform to the desired shape while maintaining structural integrity.
Solution Approach 2:
Different regions of the composite charge have locally optimized fiber lengths and orientations. The 0° plies have longer fibers (10-30 inches) for longitudinal strength, 45° plies have medium-length fibers (2-4 inches) for transverse flexibility, and 90° plies have shorter fibers for contour adaptation. This local differentiation allows each region to contribute optimally to both formability and structural performance.
2Strength
If fiber lengths are increased to maintain strength, then structural integrity is improved, but formability and stretch capability during contouring deteriorate
Solution Approach 1:
The fiber length parameter is systematically varied across different ply orientations and positions within the composite charge. By changing fiber length from 2 inches (45° plies) to 30 inches (0° plies), the structure achieves both short-fiber formability and long-fiber strength where needed. This parameter optimization allows the material to be formed into contoured shapes while maintaining the strength required for structural applications.
Data Source
AI summary
A composite charge used to compression form a stringer comprises multiple plies of unidirectional, prepreg having various fiber orientations. Certain of the plies have a pattern of angled cuts allowing the plies to stretch both longitudinally and transversely during forming, thereby reducing ply wrinkling in contoured areas of the stringer.