Borescope Plug Shank Stress Reduction via Segmented Design
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Solution Overview
Problem
Borescope plugs in gas turbine engines are subject to high stresses at the shank, leading to decreased life and limited durability due to fixed positioning, which restricts movement and increases load transmission from turbine stator loads, vibration, and thermal gradients.
Innovation Solution
A borescope plug design with a separate mounting plate (base) and shank/plug section that allows for relative movement and rotation, incorporating a retainer and anti-rotation elements to distribute stresses and prevent plug member rotation, while maintaining sealing engagement with the borescope aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the borescope plug uses a fixed positioning design, then the plug member is securely held in place, but the shank is subjected to high stresses from turbine stator loads, vibration, and thermal gradients, leading to decreased life
Solution Approach 1:
The borescope plug is divided into separate components: a base assembly and a plug member assembly that can move relative to each other. The plug member is retained by a retainer that allows controlled movement, separating the function of secure positioning from stress transmission. This segmentation allows the plug member to move independently to accommodate thermal expansion and vibration while maintaining secure retention.
Solution Approach 2:
The design transitions from a fixed, rigid connection to a dynamic system where the plug member can move relative to the base. The retainer allows the plug member to move axially and rotate, accommodating dynamic operational conditions such as thermal gradients and vibration. This dynamic capability reduces stress on the shank while maintaining secure positioning during operation.
2Reliability
If the plug member is prevented from rotating, then sealing engagement is maintained, but the shank cannot accommodate thermal expansion and vibration, increasing stress
Solution Approach 1:
The retention function and sealing function are separated into different components. The retainer handles the retention and movement accommodation, while the plug member maintains sealing engagement independently. This allows the plug member to move within the retainer without compromising the seal, reducing stress transmission through the shank.
Solution Approach 2:
The retainer acts as an intermediary between the base and the plug member, allowing controlled movement while maintaining secure retention. This intermediary component absorbs the stress from thermal expansion and vibration, preventing direct transmission to the plug member shank while maintaining the sealing interface.
3Ease of manufacture
If the borescope plug is designed as a single integrated component, then manufacturing is simpler, but stress concentration at the shank leads to decreased durability
Solution Approach 1:
The borescope plug is divided into manufactureable modules: a base assembly with retainer and a separate plug member assembly. These modules can be manufactured independently using standard processes and then assembled together. This segmentation maintains manufacturing simplicity while eliminating stress concentration issues associated with monolithic designs.
Solution Approach 2:
The design changes the structural parameters from a monolithic integrated component to a modular assembly with controlled clearances and movement capabilities. This parameter change allows each component to be optimized for its specific function while maintaining ease of manufacture through standard assembly processes.
Data Source
Figure 1
Figure 1B
Figure 2
AI summary
A borescope plug (422; 522; 622; 722) for a gas turbine engine (20) includes a base (426; 526; 626; 726) attachable to a case and defining a base cavity, a shank (428; 528; 628; 728) having a base engagement element at a first end of the shank, and a plug member (430; 530; 630; 730) located at a second end of the shank, the plug member configured to plug a borescope aperture (424; 524; 624) in a borescope vane cluster. The base engagement element fits within the base cavity such that the base moveably retains the base engagement element and wherein the base engagement element can move within the base cavity.