Graded Interlayer Composition to Reduce Thermal Expansion Stress
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Solution Overview
Problem
Existing interlayers for joining materials with different thermal expansion coefficients in high heat flux and erosion environments, such as divertors in nuclear fusion reactors, fail due to significant thermal expansion-induced stresses, despite previous grading attempts.
Innovation Solution
Implementing a composite interlayer with complex grading profiles, such as sigmoid or polynomial functions, to smoothly transition the thermal expansion coefficient between materials, using techniques like powder grading, laminated structures, or structural grading, to minimize stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear graded interlayer is used to join refractory metal and thermally conductive material, then the thermal expansion coefficient transitions more gradually, but thermal expansion induced stresses still cause failures
Solution Approach 1:
The patent changes the grading profile parameter from linear to non-linear (sigmoid or polynomial functions). This transforms the stress distribution by creating regions of lower stress concentration at the interfaces, thereby reducing thermal expansion induced failures while maintaining the gradual transition of thermal expansion coefficient.
Solution Approach 2:
The patent applies different grading characteristics at different locations within the interlayer. The sigmoid or polynomial profile creates localized regions with specific properties: gentler gradients near the refractory metal interface and steeper gradients in the middle section, optimizing stress distribution throughout the joint structure.
2Reliability
If a composite interlayer with graded composition is used, then the mismatch in thermal expansion coefficients is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent changes the compositional gradient parameter from linear to non-linear (sigmoid or polynomial), achieving better stress management while maintaining a single continuous interlayer structure. This avoids the need for multiple discrete layers or complex manufacturing processes.
Solution Approach 2:
The patent uses a composite interlayer made of two or more materials with different thermal expansion coefficients, arranged in a graded structure. This composite approach allows tuning of the thermal expansion profile to match the requirements of joining dissimilar materials while managing stress through the chosen grading function.
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
Significantly reduces thermal expansion-induced failures by evenly distributing stress across the interlayer, enhancing the durability and effectiveness of materials in extreme temperature conditions.
Implementation Method 1
the thermal expansion coefficient of the thermally conductive material will be very different to that of the refractory metal... an interlayer - a layer of material having a thermal expansion coefficient intermediate between that of the refractory metal and that of the thermally conductive material
Data Source
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AI summary
A method of joining first and second materials. The first material is a metal, a ceramic, or a composite material comprising carbon fibre, and the second material is a metal. The first material has a coefficient of thermal expansion, CTE, which is higher than a CTE of the second material. An interlayer is formed, having a high thermal expansion surface and a low thermal expansion surface. The CTE of the interlayer varies through its depth between the CTE of the first material and the CTE of the second material. The interlayer has four average coefficients of thermal expansion, aCTE, defined such that each aCTE is the average coefficient of thermal expansion over one quarter of the thickness of the interlayer. Each aCTE is less than the previous aCTE, where the first aCTE is next to the high thermal expansion surface. Either: the difference between the first and second aCTE is greater than the difference between the second and third aCTE, and the difference between the second and third aCTE is greater than the difference between the third and fourth aCTE; or the difference between the second and third aCTE is greater than both the difference between the first and second aCTE and the difference between the third and fourth aCTE.