Overmolded Composite Connection Element for Aircraft Structures
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Solution Overview
Problem
Unidirectional composite materials in load-bearing structures face challenges with machining-induced interlaminar cracks and require multi-directional reinforcement for bearing stresses, leading to increased weight and cost, while existing reinforcement methods like metal brackets are bulky and create stress points.
Innovation Solution
Over-molding connection sites with a structural molding material composed of discontinuous fibers and a resin matrix, which provides a strong, lightweight, and machinable interface between unidirectional fiber load-bearing structures and aircraft bodies, utilizing compression molding and bond-enhancement surfaces like holes and grooves for secure attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If unidirectional fiber composite materials are used for load-bearing structures, then strength to weight ratio is improved, but machining the connection surfaces causes interlaminar cracks that lead to fatigue failure
Solution Approach 1:
The connection element is segmented into a first portion that is overmolded onto the load-bearing element and a second portion that interfaces with the support structure. This segmentation allows the first portion to be protected from machining while the second portion can be machined independently, preventing interlaminar cracks in the unidirectional fiber composite.
Solution Approach 2:
The connection element acts as an intermediary component between the load-bearing element and the support structure. It transfers loads between these two components while protecting the fragile unidirectional fiber composite interface from direct machining, thereby preventing interlaminar cracks and improving fatigue resistance.
2Strength
If multi-directional plies are added to reinforce bearing stresses at connection locations, then connection strength is improved, but weight and size of the structure significantly increase
Solution Approach 1:
The connection element provides localized multi-directional fiber reinforcement only at the connection portion where bearing stresses occur, while the main load-bearing element maintains its lightweight unidirectional fiber construction. This local quality approach strengthens the connection without significantly increasing the overall weight of the structure.
3Strength
If metal brackets and sleeves are used to reinforce connection points, then connection strength is improved, but the reinforcements become bulky, heavy, and create localized stress points
Solution Approach 1:
The connection element is made from fiber-reinforced composite material that combines the strength benefits of metal reinforcements with the weight and complexity advantages of composite materials. The composite construction provides adequate structural strength without the bulk and localized stress points associated with metal brackets and sleeves.
4Manufacturing precision
If the load-bearing structure is machined to achieve precise fit for structural joints, then connection precision is improved, but unidirectional fiber composites are difficult to machine without initiating interlaminar cracks
Solution Approach 1:
The connection element is segmented into a first portion that is overmolded onto the load-bearing element and maintains its composite integrity, and a second portion that can be machined independently to achieve precise fit. This segmentation allows high manufacturing precision in the machined second portion without compromising the structural integrity of the composite first portion.
Data Source
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AI summary
A load-bearing composite structure for connection to a support body or structure. The load-bearing structure includes a load-bearing element that is made up of continuous reinforcing fibers and a resin matrix. The load-bearing element has an attachment portion for connection to the support body. The load-bearing composite structure further includes a connection element that is formed using a molding material which is composed of discontinuous fibers and a resin matrix. The molding material is molded over the surface of the attachment portion of the load-bearing element.