Gas Turbine Case Boss Geometry for Lower Stress Transitions
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Solution Overview
Problem
Gas turbine engine cases experience stress concentrations due to abrupt transitions from thin case walls to thick case bosses, leading to reduced service life, especially in high-pressure vessel diffuser cases.
Innovation Solution
Incorporating a perimeter step with a uniform height and radius into the boss of the gas turbine engine case, which is machined using 3-axis or multi-axis milling to create a gradual transition from the thin case wall to the thick boss, reducing stress concentrations and facilitating a simpler machining process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an abrupt transition from thin case wall to thick case boss is used, then manufacturing is simpler, but stress concentrations increase and case service life decreases
Solution Approach 1:
The patent applies curvature by introducing a radiused perimeter step at the transition zone between the thin case wall and thick case boss. This curved geometry eliminates the abrupt angular transition, distributing stress more evenly across the transition area and preventing stress concentration points that would lead to fatigue failure.
Solution Approach 2:
The patent segments the boss transition by introducing a perimeter step that creates distinct zones: a first portion of the boss with reduced thickness adjacent to the case wall, and a second portion with full thickness. This segmentation allows for a gradual thickness transition rather than an abrupt change, reducing stress concentrations while maintaining structural integrity.
2Strength
If additional structural components (doubners and triplers) are added to reinforce the case, then case strength increases, but device complexity and weight increase
Solution Approach 1:
The patent extracts the need for additional reinforcing components by modifying the boss geometry itself. The perimeter step and reduced thickness portion of the boss provide the necessary stress distribution and reinforcement function that would otherwise require separate doubler and tripler components, thereby simplifying the overall structure.
Solution Approach 2:
The patent merges the reinforcement function into the boss structure by making the boss itself the load-distributing element. The perimeter step and varied thickness design integrate the strengthening function directly into the existing boss geometry, eliminating the need for separate reinforcing components and reducing overall structural complexity.
Data Source
AI summary
A case for a gas turbine engine includes a case wall and a boss that extends from the case wall. The boss includes a perimeter step.