Propeller Blade Internal Stiffener for Thermal Stress Reduction
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Solution Overview
Problem
Modern propeller blades face issues with foam core cracking due to thermal stresses and shear force transfer, which can be exacerbated by differences in thermal expansion coefficients between the foam core and structural layers, leading to potential structural failures.
Innovation Solution
Incorporating an internal stiffener with flange portions connected by a connecting portion, formed from materials like carbon or fiberglass, which is integrated into the spar foam core and structural layer to maintain the fixed relation between face and camber sides, reducing the likelihood of foam core cracking and enhancing structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If foam core is used in propeller blade to reduce weight, then weight is reduced, but thermal stress-induced cracking occurs due to difference in thermal expansion coefficients between foam core and structural layers
Solution Approach 1:
A stiffener is introduced as an intermediary element between the foam core and the structural layers (face and camber sides). The stiffener's flange portions are positioned between these layers and connected by a connecting portion, acting as a mediator that transfers shear forces and reduces thermal stresses, preventing cracking while maintaining the lightweight foam core structure.
Solution Approach 2:
The blade employs a composite structure combining foam core material with stiffener material (having different thermal expansion properties). This composite approach creates a multi-material system where the stiffener compensates for the thermal expansion mismatch between the foam core and structural layers, resolving the thermal stress issue while preserving weight benefits.
2Strength
If structural layers are added to foam core to enhance strength, then strength is improved, but shear force transfer causes thermal stresses leading to foam core cracking
Solution Approach 1:
The stiffener serves as a protective intermediary that intercepts and redistributes shear forces before they can transfer directly to the foam core. By positioning flange portions between the structural layers and connecting them, the stiffener mediates force transfer, preventing the harmful thermal stress concentration that would otherwise cause cracking in the foam core.
3Adaptability or versatility
If thermal expansion coefficients of foam core and structural layers are different, then material selection flexibility is improved, but thermal stress-induced cracking occurs
Solution Approach 1:
The stiffener converts the harmful effect of differential thermal expansion into a beneficial force distribution mechanism. By introducing the stiffener with its own thermal expansion characteristics, the system transforms the thermal stress problem into an opportunity for controlled force redistribution, where the stiffener's flexibility allows it to accommodate expansion differences while preventing crack propagation.
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 internal stiffener effectively transfers shear forces and reduces thermal stress-induced cracking, ensuring the structural integrity and stability of the propeller blade, thereby enhancing its performance and durability.
Implementation Method 1
The internal stiffener effectively transfers shear forces and reduces thermal stress-induced cracking
Implementation Method 2
thermal stresses and shear force transfer, which can be exacerbated by differences in thermal expansion coefficients between the foam core and structural layers
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A propeller blade (100) includes a foam core (104) having a slot formed through it from a camber side (125) to a face side (127). An internal stiffener (105) is disposed through the slot and includes flanges (107) in contact with both the camber and face sides (125, 127). A structural layer (106) surrounds at least a portion of the foam core (104) and is in contact with the flanges (107) on both the camber and face sides (125, 127).