Ceramic Truss Core Bonding via Bent Fiber Ends
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Solution Overview
Problem
The load-carrying ability of ceramic matrix composite (CMC) structures with a pin truss core is limited due to the limited bond strength between the CMC pins and the facesheets, especially when the facesheets are thin, as the CMC pins are brittle and prone to breaking if attempts are made to bend their ends for increased bonding.
Innovation Solution
Bending the outer ends of CMC pins by removing the matrix material to expose and flex the ceramic fibers, allowing them to extend parallel to the facesheets for improved bonding, which increases the bond area and load transmission capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the ends of CMC pins are bent to extend parallel to the facesheets for increased bonding area, then the bond strength between pins and facesheets is improved, but the pins may break due to their brittle nature
Solution Approach 1:
The pin structure is segmented into two distinct zones: a straight load-bearing portion that maintains structural integrity, and a bent bonding portion that provides enhanced adhesion. This segmentation allows the pin to simultaneously achieve high bond strength through the bent portion while maintaining reliability through the intact straight portion.
Solution Approach 2:
The pin exhibits local quality differentiation where only the distal end portion is bent to provide bonding surface area, while the majority of the pin remains straight to maintain load-bearing capacity. This localized bending approach maximizes bonding effectiveness without compromising the overall structural integrity of the pin.
2Reliability
If the CMC pins are kept straight to maintain structural integrity, then the pins are less prone to breaking, but the bond area between pins and facesheets is limited
Solution Approach 1:
The pin is divided into functional segments: a straight portion for load bearing and a bent portion for bonding. This segmentation resolves the contradiction by assigning different geometric configurations to different functional requirements, allowing both reliability and bond strength to be optimized simultaneously.
Solution Approach 2:
The bonding portion of the pin transitions from a one-dimensional straight configuration to a multi-dimensional bent configuration, creating additional bonding surface area. This dimensional change enables enhanced bond strength without requiring the entire pin to be bent, thus maintaining structural integrity.
3Weight of moving object
If the facesheets are made thin to reduce weight, then the overall structure weight is reduced, but the bond strength between pins and facesheets decreases
Solution Approach 1:
The bent portion of the pin creates a curved configuration that extends parallel to the facesheet surface, maximizing the bonding interface area within the limited thickness of thin facesheets. This curved geometry enables sufficient bond strength even when the facesheets are made thin for weight reduction.
Solution Approach 2:
By changing the geometric parameter of the pin from straight to bent in the distal portion, the bonding surface area is increased without increasing the overall pin diameter or facesheet thickness, thus maintaining the weight advantage while improving bond strength.
Data Source
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AI summary
A CMC sandwich used to fabricate CMC structures includes facesheets bonded to a core reinforced with a ceramic truss comprising an array of CMC pins. The binder matrix in the ends of the pins is removed, leaving exposed, flexible ceramic fibers. The exposed ceramic fibers are bent so as to extend parallel to the facesheets, and are bonded to one or more plies of the facesheets. The binder matrix in the ends of the ceramic pins may be removed by mechanical or chemical processes.