Aircraft Engine Heat Shield Assembly with Slip Joints for Thermal Cycling
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Solution Overview
Problem
Aircraft engine heat shields experience high stress due to thermal cycling caused by exposure to exhaust gases, as existing skin panels are continuously fastened and unable to accommodate thermal expansion and contraction effectively, leading to stress from temperature gradients.
Innovation Solution
A heat shield assembly with a structural member, a heat shield panel, and slip joints that include wear buffers and slip fasteners with a clearance fit, allowing for thermal movement and reducing stress by providing a tolerance for expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If skin panels are continuously fastened to the support structure with rivets, then structural integrity is maintained, but thermal expansion and contraction cause high stress and temperature gradients
Solution Approach 1:
The fastening system transitions from a static continuous fastening to a dynamic system where panels can move relative to the support structure. Slip joints with clearance fits and gaps allow the heat shield panel to expand and contract thermally while remaining connected, converting the rigid static connection into a flexible dynamic one that accommodates dimensional changes.
Solution Approach 2:
The continuous fastening system is segmented into discrete slip joints at specific locations. Instead of continuous rivet fastening across the entire panel, the connection is divided into multiple separate slip joint locations, each providing localized movement capability. This segmentation allows different regions to handle thermal expansion independently.
2Stability of the object's composition
If skin panels are continuously fastened to accommodate structural requirements, then panel stability is maintained, but thermal cycling causes repeated high stress
Solution Approach 1:
The fastening system allows dynamic movement through slip joints with clearance fits and gaps, enabling the panel to accommodate thermal expansion and contraction without developing excessive stresses. This dynamic capability reduces repeated stress cycling that would otherwise lead to fatigue failures.
Solution Approach 2:
The fastening system changes its effective parameters under thermal loading. The clearance fit and gap dimensions are specifically designed to accommodate the expected range of thermal dimensional changes. As temperature varies, the panel moves within these clearance dimensions, changing the effective connection state from rigid to compliant.
3Stability of the object's composition
If heat shield panel is restricted from thermal movement, then positional stability is maintained, but mechanical loads and stress increase
Solution Approach 1:
The slip joint system provides controlled dynamic movement capability while maintaining overall positional stability. The panel can move within the clearance fit and gap dimensions during thermal cycling, but remains generally positioned relative to the support structure. This dynamic-stable hybrid approach reduces mechanical loads while preserving positional control.
Solution Approach 2:
The slip joint acts as an intermediary element between the heat shield panel and the support structure. It mediates the interaction by allowing controlled movement through clearance fits and gaps, reducing the direct transmission of thermal expansion forces to the rigid support structure while maintaining the panel's functional positioning.
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 reduces mechanical loads and stress on the heat shield panel by allowing it to thermally expand and contract freely, minimizing the risk of damage from engine exhaust while maintaining structural integrity and reducing aerodynamic drag.
Implementation Method 1
A gap defined by the clearance fit is sized to provide a tolerance for expansion and contraction of the heat shield panel relative to the fixed positional location
Implementation Method 2
the at least one wear buffer is engageable by the slip fastener during expansion and contraction of the heat shield panel
Data Source
AI summary
A heat shield assembly for use with an aircraft engine. The heat shield assembly includes a structural member, a heat shield panel adapted for exposure to aircraft engine exhaust, an index joint coupling the heat shield panel to the structural member in a fixed positional location, and a plurality of slip joints coupling the heat shield panel to the structural member. Each slip joint includes at least one wear buffer coupled to the heat shield panel, and a slip fastener insertable through a slip joint hole in the heat shield panel with a clearance fit. A gap defined by the clearance fit is sized to provide a tolerance for expansion and contraction of the heat shield panel relative to the fixed positional location, and the at least one wear buffer is engageable by the slip fastener during expansion and contraction of the heat shield panel.