Ceramic Fastener Assembly With Sleeve Locking for High-Temperature Clamp-Up
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Solution Overview
Problem
Ceramic fasteners used in high-temperature aerospace applications are expensive to manufacture and have limited strength due to the difficulty in machining threads, which compromises their ability to apply and maintain clamp-up tension.
Innovation Solution
A ceramic fastener assembly that includes a non-threaded ceramic fastener with indentations, a metal or plastic sleeve with protrusions that mate with the indentations, and a thermal spacer to isolate the metal/plastic components from high temperatures, allowing for improved clamp-up strength and reduced manufacturing costs by eliminating the need for machined ceramic threads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If threads are machined into ceramic fasteners, then the fastener can be used to clamp structures, but the manufacturing cost increases and manufacturing difficulty increases
Solution Approach 1:
The fastener system is divided into separate components: a ceramic fastener body and a metal sleeve with threads. The ceramic component is manufactured without threads, avoiding the costly and difficult machining process, while the metal sleeve provides the threading function. This segmentation allows each component to be optimized for its specific function.
Solution Approach 2:
A metal sleeve acts as an intermediary component between the ceramic fastener body and the nut. The sleeve is inserted over the non-threaded ceramic shank and provides the threaded interface for the nut, eliminating the need to machine threads directly into the ceramic material while still enabling clamping functionality.
2Temperature
If ceramic material is used for the fastener, then the fastener can resist high temperatures, but the manufacturing cost increases
Solution Approach 1:
The fastener system separates the high-temperature resistant function (ceramic fastener body) from the threading function (metal sleeve). This allows the ceramic component to be manufactured without the expensive and difficult thread machining process, reducing overall manufacturing cost while maintaining temperature resistance.
Solution Approach 2:
The metal sleeve and nut are used as sacrificial or replaceable components that can be manufactured more cheaply than ceramic threads. If damaged or worn, these metal components can be replaced without replacing the entire ceramic fastener, reducing long-term costs.
3Strength
If threads are machined into ceramic fasteners, then the fastener can engage with nuts, but the clamp-up strength is limited due to stress concentrations
Solution Approach 1:
By separating the ceramic fastener body from the threaded metal sleeve, the design eliminates stress concentrations that would occur if threads were machined into the ceramic. The smooth, non-threaded ceramic shank avoids stress concentration points, while the metal sleeve absorbs the threading-related stresses.
Solution Approach 2:
The fastener system combines ceramic and metal materials, each used where their properties are most advantageous. The ceramic provides high-temperature resistance and structural integrity, while the metal sleeve provides threading and flexibility, creating a composite system that overcomes the limitations of either material alone.
4Strength
If metal components are used in the fastener assembly, then the clamp-up strength is improved, but the components cannot withstand high temperatures
Solution Approach 1:
The assembly is segmented into a ceramic component that withstands high temperatures and metal components that provide clamping strength. The thermal spacer further segments the thermal environment, protecting metal components from direct exposure to high temperatures while allowing them to provide their strength benefits.
Solution Approach 2:
A thermal spacer acts as an intermediary thermal barrier between the high-temperature environment and the metal sleeve and nut. This protective intermediary allows metal components to be used in the assembly without direct exposure to temperatures that would compromise their properties.
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
The assembly effectively resists high temperatures while enhancing clamp-up strength and reducing manufacturing costs by using metal/plastic components with deformed threads, which provide increased tension forces without stress concentrations.
Implementation Method 1
A thermal spacer is provided at the backside of the structure to insulate the metal/plastic sleeve and nut from high temperatures
Data Source
AI summary
A ceramic fastener assembly for high temperatures. One embodiment is a fastener assembly that includes a ceramic fastener configured to engage a hole of a structure. The ceramic fastener includes a head and a non-threaded shank including one or more indentations around its perimeter. The fastener assembly also includes a sleeve configured to slide over the non-threaded shank of the ceramic fastener. The sleeve includes a hollow cylindrical body, an exterior surface with threads, and an interior surface with one or more protrusions configured to mate with the one or more indentations of the non-threaded shank. The fastener assembly further includes a nut configured to engage the threads of the sleeve to tighten the one or more protrusions with the one or more indentations of the non-threaded shank. The fastener assembly also includes a thermal spacer configured to thermally isolate the nut and the sleeve from the structure.