Embedded Grid Stiffening for Composite Damage Tolerance
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Solution Overview
Problem
Current isogrid and orthogrid stiffened composite structures exhibit poor damage tolerance due to the grid being susceptible to de-bonding from the skin's outer mold line after impact damage, limiting their use in aircraft and spacecraft designs despite offering low weight and excellent buckling performance.
Innovation Solution
The development of composite structures with a stiffening grid intimately embedded within the composite, produced by applying prepreg tows to a base course and overlapping them to form a grid structure, which is then cured to create a polymeric matrix that bonds the stiffeners within the substrate, enhancing damage tolerance and buckling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the grid is co-cured or bonded to the skin's inner mold line, then the manufacturing process is simplified and production efficiency is improved, but the grid becomes susceptible to de-bonding from impact damage to the skin's outer mold line, resulting in poor damage tolerance
Solution Approach 1:
The stiffening grid is nested within the composite structure by embedding it between the skin plies during the curing process. The grid becomes an integral part of the composite laminate, with resin flowing around and bonding to the grid elements from all sides, creating a nested configuration that protects the grid bond lines from impact damage while maintaining manufacturing efficiency.
Solution Approach 2:
The grid structure is transitioned from a surface-level attachment (2D bonding to inner mold line) to a three-dimensional embedded configuration within the thickness of the composite structure. This dimensional change allows the grid to be surrounded by composite material on multiple sides, providing superior damage tolerance while maintaining manufacturing simplicity.
2Strength
If the grid stiffening is built up on the skin's inner mold line, then the structural stiffness and buckling performance are improved, but the weight of the structure increases due to additional bonding material and larger bond lines
Solution Approach 1:
The grid is nested within the composite thickness, eliminating the need for large external bond lines and additional bonding material. This nesting approach maintains the stiffening function while reducing the overall weight by removing excess bonding material and minimizing the grid's external footprint.
Solution Approach 2:
The embedding process changes the physical parameters of the grid-skin interface by transitioning from surface bonding to volumetric integration. The resin flow around the embedded grid creates a distributed bonding pattern that provides equivalent or superior stiffness with reduced material usage and lower overall structure weight.
3Reliability
If the grid is embedded within the composite structure, then damage tolerance is significantly improved by protecting the grid from de-bonding, but the manufacturing precision requirements increase to ensure proper embedding depth and orientation
Solution Approach 1:
The grid is positioned and embedded within the composite structure during the preliminary stages of laminate assembly, before final curing. This preliminary embedding action ensures proper positioning and depth control while the resin is still in a workable state, reducing the need for post-manufacturing adjustments and minimizing precision challenges.
Solution Approach 2:
The resin system performs a self-leveling and self-bonding function during curing, automatically filling gaps and adhering to the embedded grid surfaces. This self-service mechanism reduces the need for high-precision manual positioning and compensates for minor placement variations, lowering the overall manufacturing precision requirements while maintaining excellent damage tolerance.
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
The embedded grid structure composite materials demonstrate improved damage tolerance and buckling performance, allowing for their use in aircraft and spacecraft designs while maintaining a lower weight, with weight savings of 15% to 35% compared to baseline quasi-isotropic composite layups.
Implementation Method 1
cured to create a polymeric matrix that bonds the stiffeners within the substrate
Data Source
AI summary
Described herein are composites that are composed of a plurality of plies with a stiffening grid intimately embedded within the composite. The composite structures have the improved buckling performance characteristics of known isogrid and orthogrid composite structures and yet have a significantly higher damage tolerance that permits such structures to be used in the formation of aircraft and spacecraft designs. Also described herein are methods for making the composites.