Sacrificial Overwrap for Wound-Tape Carbon Preform Densification
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Solution Overview
Problem
Carbon/carbon composites used in high-temperature applications face thermal-shock induced mechanical failure due to nonuniform thermal insulative and expansion characteristics, leading to interlaminar failure during densification, which is costly to prevent with multi-directional reinforcement.
Innovation Solution
Applying a sacrificial tape overwrap under tension to form-holding hoop stress on preforms before densification, preventing inter-layer delamination and failure without requiring additional inter-layer reinforcement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-directional reinforcement is used to control thermal expansion and prevent mechanical failure, then reliability is improved, but manufacturing cost increases significantly
Solution Approach 1:
A sacrificial overwrap is applied to the preform before the densification process begins. This overwrap pre-establishes compressive hoop stress in the preform walls, which counteracts the thermal-shock induced tensile stresses that would otherwise cause interlaminar failure during densification. The overwrap is removed after densification, having served its protective function.
Solution Approach 2:
The sacrificial overwrap is a temporary, low-cost component that is applied before processing and removed afterward. It provides essential mechanical support during the critical densification phase but is not part of the final product, allowing cost-effective protection without permanent complexity in the carbon/carbon component.
2Temperature
If thick-walled fabric-based laminates are densified to produce carbon/carbon composites, then thermal protection performance is improved, but interlaminar failure occurs due to thermal-shock induced stress
Solution Approach 1:
The sacrificial overwrap applies compressive stress to the preform walls before thermal shock occurs. This preliminary anti-action counterbalances the tensile stresses that develop during rapid heating and densification, preventing the interlaminar cracking that would otherwise occur in thick-walled laminates.
Solution Approach 2:
The overwrap changes the stress state parameters of the preform from tensile-dominant (which causes failure) to compressive-dominant (which prevents failure). By modifying the mechanical boundary conditions through the overwrap, the material can withstand the thermal shock without interlaminar failure.
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
Enables the production of low-cost, thick-walled carbon/carbon composites for thermal protection systems by controlling thermal-shock induced mechanical loading, eliminating interlaminar failure and defects during densification.
Implementation Method 1
applying a sacrificial tape overwrap to the first preform in a tensioned manner to form a second preform having the layers of preform tape subject to form-holding hoop stress by the tape overwrap
Implementation Method 2
layers of preform tape subject to form-holding hoop stress by the tape overwrap
Implementation Method 3
The second preform is then densified in a densification process to produce the densified carbon component
Data Source
AI summary
A method of making a densified carbon component includes wrapping a preform tape of carbon material about a mandrel to form a first preform having a laminated, multi-layer structure, and applying a sacrificial tape overwrap to the first preform in a tensioned manner to form a second preform having the layers of preform tape subject to form-holding hoop stress by the tape overwrap. The second preform is then densified in a densification process to produce the densified carbon component. During densification, the presence of the overwrap helps to prevent undesired delamination or similar defects from occurring.