Graded Carbon-Carbon Composites for Thermal Protection
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Solution Overview
Problem
Conventional laminated carbon-carbon composites used in heat shields for spacecraft during atmospheric reentry suffer from delamination due to thermally induced interlaminar tension and shear, leading to mechanical stress and potential failure, as the ablative layer is non-integral with the underlying layers.
Innovation Solution
The development of graded carbon-carbon composites with a densified base layer and a non-fully densified outer ablative layer, where the carbonaceous matrix is continuous and integral throughout, reducing porosity gradients and eliminating structural discontinuities between layers, thereby enhancing interlaminar mechanical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a sacrificial ablative layer is layered on a densified carbon-carbon composite to increase thermal protection, then thermal protection attributes are improved, but interlaminar tension and shear strength deteriorate due to thermal gradients inducing mechanical stress
Solution Approach 1:
The patent applies local quality by creating a graded porosity structure where the carbon-carbon composite transitions from a densified base layer (8-10% porosity) to a less densified ablative layer (20-40% porosity). This gradual transition in material properties at different locations reduces thermal gradients and associated mechanical stresses while maintaining thermal protection functionality.
Solution Approach 2:
The patent uses composite materials by combining carbon fibers with a carbonaceous matrix (such as phenolic resin) in a graded structure. The composite integrates a densified carbon-carbon base layer with an ablative layer containing carbonizable resin, creating a material system that provides both structural integrity and thermal protection through controlled porosity gradients.
2Strength
If multiple densification cycles are performed to reduce porosity and improve structural integrity, then mechanical strength is improved, but manufacturing complexity and time increase
Solution Approach 1:
The patent applies segmentation by dividing the manufacturing process into two distinct stages: first forming a densified base layer with 8-10% porosity through conventional multiple densification cycles, then applying and carbonizing an ablative layer containing carbonaceous matrix to achieve the final graded structure. This segmentation allows optimization of each stage independently.
Solution Approach 2:
The patent uses preliminary action by first creating a partially densified base layer with controlled porosity (8-10%) before applying the ablative layer. This preliminary densification establishes a stable substrate that reduces subsequent manufacturing complexity while maintaining structural integrity in the final graded composite.
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 significantly reduces delamination and enhances thermal protection and aerodynamic performance by creating a robust, monolithic structure that maintains mechanical integrity while absorbing thermal energy during reentry.
Implementation Method 1
heating the partially densified base layer and the carbonaceous matrix precursor above a carbonization temperature to form a graded carbon-carbon composite
Implementation Method 2
maintains mechanical integrity while absorbing thermal energy during reentry
Data Source
AI summary
Laminated carbon-carbon composites can be used as an ablative material, but they are often prone to delamination under thermally induced interlaminar shear and tension. Graded carbon-carbon composites with a sacrificial or ablative layer that is integral with one or more underlying layers and not fully dense can address these issues and provide other advantages. Such graded carbon-carbon composites can include a densified base layer containing a first portion of a carbonaceous matrix, and an outer ablative layer that is integral with the densified base layer and contains a second portion of the carbonaceous matrix. The carbonaceous matrix in the densified base layer has a first porosity, and the carbonaceous matrix in the outer ablative layer has a second porosity that is higher than that of the densified base layer. Methods for forming graded carbon-carbon composites can include heating a partially densified base layer and a carbonaceous matrix precursor above a carbonization temperature.