Ceramic-to-Metal Rod Coupling With Threshold-Force Release
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Solution Overview
Problem
Mechanical coupling between ceramic and metal components in high-temperature applications is challenging due to differences in mechanical properties and thermal expansion coefficients, leading to stress concentrations, fracture risks, and unreliable torque transmission.
Innovation Solution
A kit comprising a ceramic element with a cylindrical bore and a metal rod with an outer tube and inner mandrel, where the rod is mechanically coupled to the ceramic element through projecting members and a resiliently deformable mandrel, allowing for secure translation and rotation while disengaging at a predetermined threshold force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal rod is rigidly coupled to a ceramic element, then torque transmission is reliable, but stress concentrations lead to ceramic fracture
Solution Approach 1:
The coupling mechanism transitions from a static rigid connection to a dynamic resilient connection. The inner mandrel can deform elastically under load, allowing the coupling to adapt to stress variations and prevent catastrophic failure while maintaining torque transmission capability
Solution Approach 2:
The system changes the mechanical parameters of the coupling by introducing elasticity through the inner mandrel's resilient portion. This allows the coupling stiffness to vary with applied load, providing high stiffness during normal operation and low stiffness during overload conditions to protect the ceramic element
2Strength
If a metal rod is rigidly coupled to a ceramic element, then mechanical coupling is strong, but thermal expansion differences cause stress concentrations
Solution Approach 1:
The resilient inner mandrel accommodates differential thermal expansion between the metal rod and ceramic element. When temperature changes occur, the mandrel's elasticity allows relative movement and stress redistribution, preventing stress concentration at the interface while maintaining the mechanical coupling
Solution Approach 2:
The coupling system effectively creates a composite structure combining metal (outer tube), resilient material (inner mandrel), and ceramic (bore element). This composite approach allows each material to contribute its favorable properties: metal for strength, resilient material for stress absorption, and ceramic for high-temperature stability
3Strength
If a resilient coupling is used to protect ceramic element, then fracture risk is reduced, but torque transmission reliability decreases
Solution Approach 1:
The resilient inner mandrel provides partial elasticity - enough to protect the ceramic element during overload conditions, but not so much that it compromises normal torque transmission. The mandrel remains elastic during service but can yield or deform under extreme loads, providing the right balance between protection and reliability
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 solution provides a reliable and durable mechanical coupling that prevents ceramic element fracture by disengaging the rod at a defined stress level, ensuring safe torque transmission and stability across a wide range of temperatures without requiring a through channel in the ceramic element.
Implementation Method 1
the stabilizing portion of said inner mandrel is radially resilient, such that the at least one projecting member can be dislodged from the at least one recess upon application onto the outer tube of a force greater than a predetermined threshold force
Implementation Method 2
ceramic materials have a relatively low coefficient of thermal expansion (CTE) compared with the CTE of metals. This is an important issue for applications at high temperatures, wherein the metal rod will expand more than the ceramic element upon raising the temperature from room temperature to service temperature
Data Source
Figure 1~2
Figure 3(a)~3(c)
Figure 4(a)~4(c)
AI summary
Kit of parts for mechanically coupling a ceramic element (1) to a rod comprising an outer surface made of metal, wherein: (a) the ceramic element (1) comprises a cylindrical ceramic bore (2) defined by a cylindrical bore wall and extending along a longitudinal axis, X1, wherein the cylindrical bore wall comprises at least one recess (4), and wherein the rod comprises: (b) an outer tube (8) comprising a jutting portion (8p) adjacent to an insert portion (8i), and further comprising: - an outer tube wall made of metal mating the cylindrical ceramic bore, - an outer tube bore comprising a cylindrical portion, (c) at least one projecting member (7b, 7p) having a geometry insertable into the at least one recess (4) of the ceramic element, (d) an inner mandrel (5) extending along an axis and having radial dimensions suitable for being inserted into the outer tube bore, (e) the insert portion (8i) of the outer tube can be inserted into the ceramic bore with the at least one projecting member (7b, 7p) engaged in the at least one recess (4), and with the jutting portion (8p) jutting out of the ceramic element (1), and wherein (f) the inner mandrel can be inserted into the outer tube bore, such that the at least one projecting member (7b, 7p) is resiliently stabilized in the at least one recess by a stabilizing portion (5s) of said inner mandrel, and the rod is thus mechanically coupled to the ceramic element in that the outer tube cannot translate along the longitudinal axis, X1, with respect to the ceramic bore wherein the stabilizing portion (5s) of said inner mandrel (5) is radially resilient, such that the at least one projecting member (7b, 7p) can be dislodged from the at least one recess (4) upon application onto the outer tube of a force greater than a predetermined threshold force required for decoupling the metal rod from the ceramic element.