Ceramic Composite Fastener for Thermal Stress-Free High-Temperature Joints
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Solution Overview
Problem
Conventional metallic fasteners are inadequate for high-temperature applications as they loosen under elevated temperatures, and high-cost ceramic composite fasteners are not widely utilized due to their expense, posing challenges in reliably joining high-temperature composite structural assemblies.
Innovation Solution
A low-cost, lightweight, thermal stress-free mechanical fastener system featuring a 2-dimensional fiber-reinforced ceramic composite fastener with a semi-circular head and dove-tail shank, paired with refractory metal or ceramic thread forms and a backing washer, which ensures reliable joining of high-temperature composite structural elements by preventing thermal expansion and separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metallic fasteners are used for joining structural elements, then the joint is tight at room temperature, but the fastener loosens at elevated temperature due to thermal expansion
Solution Approach 1:
The patent changes the material parameters of the fastener by using ceramic composite materials with thermal expansion coefficients matched to the structural elements, rather than metallic materials. This parameter change enables the fastener to maintain dimensional stability and joint tightness across a wide temperature range from cryogenic to high-temperature service conditions.
Solution Approach 2:
The patent employs composite materials (ceramic matrix composites with fiber reinforcement) for the fastener to achieve both high-temperature capability and controlled thermal expansion properties. The composite structure allows tailoring of thermal and mechanical properties to match the structural elements being joined.
2Reliability
If excessive preloading is applied at room temperature to maintain tight joint at elevated temperature, then the joint remains tight, but the structural integrity of the joint is compromised
Solution Approach 1:
The patent changes the thermal expansion parameter of the fastener material to match the structural elements, eliminating the need for excessive preloading. The ceramic composite fastener maintains constant dimensions across temperature changes, preserving joint integrity without compromising structural strength.
3Reliability
If conventional ceramic composite fasteners are used, then thermal stress-free joining is achieved, but the manufacturing cost is prohibitively high
Solution Approach 1:
The patent segments the fastener system into modular components including the fastener body, head, and threaded portion, allowing separate manufacturing and assembly. This segmentation enables more cost-effective manufacturing processes while maintaining the thermal stress-free joining capability of ceramic composite materials.
Solution Approach 2:
The patent designs the fastener with universal features that can be used across different structural element configurations and temperature conditions. The standardized fastener design enables economies of scale in manufacturing while maintaining the specialized high-temperature performance characteristics.
Data Source
AI summary
A relatively low cost, lightweight and thermal stress-free mechanical fastener system having particular application for reliably joining together high temperature structural members (e.g., a pair of flat fiber-reinforced ceramic composite plates). The mechanical fastener system includes a ceramic composite fastener having a semi-circular head at one end to be countersunk in the structural members to be joined together and a dove tail retention feature formed in the shank or root at the opposite end. The composite fastener has a 2-dimensional (i.e., flat) profile that facilitates an economic manufacture thereof from densified ceramic composite material. A matched pair of thread forms having external threads and an internal dove tail relief to match the dove tail retention feature at the root of the composite fastener is held in face-to-face mating engagement with one another so as to establish a mechanical interlock around the root of the composite fastener. A 2-dimensional ceramic backing washer has a rectangular center hole dimensioned to receive the root of the composite fastener therethrough. A nut having internal threads that correspond to the external threads of the pair of thread forms is rotated into surrounding engagement with the thread forms to prevent a removal of the composite fastener and a separation of the structural members.