Pre-compressed Braze for Fuel Nozzle Thermal Stress
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Solution Overview
Problem
Gas turbine engine fuel nozzle components face high thermal stresses due to temperature gradients and differential thermal expansion of materials, leading to potential cracks, leaks, and failure.
Innovation Solution
A low thermal stress assembly is created by brazing two components with a compressive pre-stress at ambient temperature, which is relieved at higher temperatures due to relative thermal expansion, reducing mechanical resistance and thermal gradients within the assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If components are fixed together with rigid joints, then structural strength is improved, but thermal stress increases due to differential thermal expansion
Solution Approach 1:
The patent changes the mechanical state parameter of the braze joint from tensile to compressive pre-stress. This compressive pre-stress counteracts the thermal expansion stresses that develop during heating, allowing the rigid joint to maintain strength while reducing net thermal stress. The compressive stress is applied at ambient temperature and is progressively relieved as temperature increases due to differential thermal expansion.
Solution Approach 2:
The patent explicitly utilizes differential thermal expansion between components with different thermal expansion coefficients. By designing the assembly to allow controlled relative movement between these components, the patent converts the potentially harmful thermal expansion differential into a mechanism that relieves compressive pre-stress and reduces thermal stress accumulation in the joint.
2Adaptability or versatility
If components are subjected to large temperature gradients, then operational capability is improved, but thermal stress increases causing cracks and failures
Solution Approach 1:
The patent applies preliminary anti-action by introducing compressive pre-stress into the joint before thermal loading occurs. This pre-applied compressive stress creates a residual stress state that opposes and counteracts the tensile thermal stresses that develop during operation with large temperature gradients, preventing crack initiation and propagation.
Solution Approach 2:
The compressive pre-stress in the braze joint acts as a cushion against thermal stress. This pre-applied stress state provides a buffer that absorbs and mitigates the harmful effects of thermal cycling and temperature gradients, protecting the joint from fatigue and failure over time.
3Adaptability or versatility
If different materials with different thermal expansion coefficients are joined, then functional performance is improved, but thermal stress increases due to thermal growth differential
Solution Approach 1:
The patent changes the stress state parameter in the joint from zero or tensile to compressive pre-stress. This parameter change allows the dissimilar materials to be joined rigidly while the compressive stress compensates for the thermal growth differential, reducing net stress and preventing failure despite the mismatch in thermal expansion coefficients.
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 effectively minimizes thermal stresses and mechanical resistance issues in fuel nozzle components by limiting extreme temperature gradients and maintaining a secure bond under high operating temperatures, enhancing the durability and reliability of the assembly.
Implementation Method 1
the braze being compressively pre-stressed therebetween at an ambient temperature β and being progressively relieved of compression upon increase in temperature above β due to relative thermal expansion of the first and second components
Implementation Method 2
creating a compressive pre-stress within at least the braze at an ambient temperature β by relative thermal contraction of the first and second components
Implementation Method 3
fastening the first and second components together by brazing at a liquidus temperature γ of the braze
Implementation Method 4
the body and the spacer are each exposed to only one of the hot air and the relatively colder fuel, thereby limiting extreme temperature gradients therewithin
Data Source
AI summary
An assembly that includes two components joined by a pre-compressed braze where the compression in the braze is progressively relieved upon relative thermal expansion of the two components. Also disclosed is a process for producing a pre-compressed braze.