Monolithic Composite Part Densification via Pre-densified Stitching
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Solution Overview
Problem
Existing methods for producing thermostructural monolithic fibres/matrix composite parts struggle to effectively interconnect composite material skins with thread-like spacers that can withstand high internal and external pressures without damaging the stitching threads during densification.
Innovation Solution
The method involves forming a fibrous preform with a flexible core and outer frames joined by stitching threads, followed by pre-densification using CVI gas-phase infiltration to create a carbon layer, and then densifying with liquid-phase infiltration to form a C-C/SiC structure, allowing for controlled densification and protection of the stitching threads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If liquid-phase infiltration is used for densification, then densification is easy to control and cost is reduced, but the stitching threads may be damaged during the densification process
Solution Approach 1:
The patent applies preliminary action by performing CVI gas-phase infiltration before liquid-phase infiltration to pre-densify the preform and create a protective carbon layer on the stitching threads. This preliminary carbonization protects the organic stitching threads from damage during the subsequent liquid-phase silicon infiltration process, while still allowing controlled densification to proceed.
2Reliability
If CVI gas-phase infiltration is used for pre-densification, then the stitching threads are protected and densification is controlled, but the production time and process complexity increase
Solution Approach 1:
The patent applies parameter changes by using R-CVI (Rapid Chemical Vapour Infiltration) instead of conventional CVI, which significantly reduces the infiltration time while achieving the same pre-densification effect. This rapid infiltration process maintains the protective carbon layer formation on stitching threads but completes the process much faster, reducing overall production cycle time.
3Device complexity
If the core is removed after curing, then the sandwich structure is simplified, but the thread-like spacers may not be properly formed
Solution Approach 1:
The patent applies preliminary action by removing the flexible core from the sandwich structure before the densification process. This timing is critical because it allows the longitudinal channels that formed during stitching to be opened up, enabling proper resin impregnation and subsequent formation of thread-like spacers during densification. The core removal before densification ensures that the spacers form correctly without the core obstructing the process.
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 results in a rigid monolithic composite part with improved cost-effectiveness and performance, enabling the production of parts that can withstand extreme temperatures and pressures, while maintaining the structural integrity of the stitching threads.
Implementation Method 1
densifying the resulting structure by liquid-phase infiltration
Implementation Method 2
pre-densification is carried out in step B/ by CVI gas-phase infiltration (chemical vapour infiltration)
Data Source
AI summary
A fibrous preform (1) is produced, provided with a sandwich structure comprising an intermediate flexible core (4) and two outer fibrous frames (2, 3), respectively arranged on opposing outer faces of said flexible core (4) and assembled by sections of wire (8, 9) passing through said fibrous frames (2, 3), said preform (1) being impregnated with resin. Said preform is then hardened and the core (4) is removed, preferably by pre-densification with chemical vapour infiltration, and the structure produced is then densified with liquid-phase infiltration.