Partially Impregnated Prepreg Tapes for Void-Free Composite Laminates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The manufacturing of thick composite parts often results in porosity (voids) due to entrapped volatiles, which compromises mechanical properties and is costly to address with autoclaving, and existing vacuum bag processes produce inferior quality laminates with voids.
Innovation Solution
The use of partially impregnated prepregs with a resin content of 25-50% by weight, which allows for resin infusion during heating in a Vacuum Bag Only process, and a method to slit these prepregs into narrow-width tapes for automated placement without jamming, using a nonwoven veil and binder to facilitate air evacuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional fully impregnated prepregs are used in vacuum bag processing, then production cost is reduced, but voids form in the composite laminate due to entrapped volatiles
Solution Approach 1:
The prepreg is designed with non-uniform resin distribution: the resin-rich surface layer (5-20 mils thick) provides volatile entrapment and evacuation pathways, while the underlying fiber-rich region ensures structural integrity. This local differentiation allows the same material to simultaneously enable void-free curing and maintain mechanical properties.
Solution Approach 2:
The resin-rich surface layer is pre-formed on the prepreg before lamination, creating built-in volatile collection zones and evacuation pathways that are already in place before the curing process begins. This preliminary preparation eliminates the need for post-curing void repair and enables direct vacuum bag processing.
2Reliability
If resin content in prepreg is reduced to enable void-free curing, then void content decreases, but handling and automated placement become difficult due to excessive tackiness
Solution Approach 1:
The prepreg structure separates the resin-rich surface layer (providing volatile management) from the fiber-rich interior (maintaining handling properties). The resin content in the bulk is kept low (25-50% by weight) to reduce tackiness, while the surface layer thickness (5-20 mils) is optimized to provide sufficient volatile entrapment without excessive surface stickiness.
Solution Approach 2:
The invention creates a composite structure within the prepreg itself: a resin-rich polymer phase on the surface and a fiber-rich reinforcement phase in the interior. This internal composite architecture allows each region to perform its specialized function: the resin-rich layer manages volatiles while the fiber-rich core maintains structural integrity and handling characteristics.
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
This approach enables the production of void-free composite laminates suitable for automated fiber placement, maintaining mechanical integrity while reducing production costs and avoiding the limitations of autoclaving.
Implementation Method 1
a) a first layer of fibers is impregnated with a resin composition to form a fibrous laminate; b) the fibrous laminate is heated to cure the resin composition
Implementation Method 2
enclosing the stack of prepreg plies in a vacuum envelope... withdrawing air from the vacuum envelope to create a vacuum pressure sufficient for consolidating the stack of prepreg plies
Data Source
Figure 1A~2B
Figure 3~5
Figure 6~7
AI summary
Prepreg tapes suitable for automated placement process are formed by slitting a sheet of partially impregnated prepreg. The partially impregnated prepreg (13) is composed of unidirectional fiber tows partially embedded in a resin layer and has a continuous resin surface only on one side. In some embodiments, one or two nonwoven veil(s) is/are incorporated into the partially impregnated prepreg.