Unbalanced Spar Layup for Propeller Blade Thermal Stress
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Solution Overview
Problem
Modern propeller blades experience thermal stresses due to differences in coefficients of thermal expansion between the foam spar core and the structural layer, leading to potential deformation and reduced bond strength, especially during temperature changes in operation.
Innovation Solution
The spar layup is modified to an unbalanced configuration, with asymmetrical layering on either side of the mid-thickness location, incorporating more biased braids on one side and additional unidirectional plies to enhance thermal behavior and reduce tensile stresses, thereby improving the bond strength between the foam spar core and the structural layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a balanced spar layup configuration is used, then manufacturing simplicity is maintained, but thermal stresses increase due to coefficient of thermal expansion differences between foam core and structural layer
Solution Approach 1:
The patent applies asymmetry by transitioning from a balanced spar layup configuration to an unbalanced configuration. The unbalanced layup features asymmetrical layering where plies are positioned at different distances from the mid-thickness location of the structural layer, creating different stiffness characteristics on either side. This asymmetrical arrangement compensates for the coefficient of thermal expansion differences between the foam core and structural layer, thereby reducing thermal stresses during temperature changes while maintaining manufacturability through standardized braiding processes.
2Strength
If the structural layer is made thicker to improve bond strength, then bond strength increases, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies local quality by positioning plies at specific locations within the structural layer thickness rather than uniformly distributing them. The unbalanced layup configuration places plies at different distances from the mid-thickness location, creating zones of varying stiffness and stress distribution. This localized variation in ply positioning optimizes bond strength at the foam-core interface while avoiding the need for a uniformly thicker structural layer, thus preventing excessive device complexity.
3Reliability
If an unbalanced spar layup configuration is implemented to reduce thermal stresses, then thermal stress resistance improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by modifying the layup configuration parameters from a balanced to an unbalanced arrangement. The unbalanced configuration is defined by specific ply positioning parameters where plies are located at predetermined distances from the mid-thickness location. These parameter changes are designed to reduce thermal stresses while maintaining compatibility with existing braiding manufacturing processes, thereby avoiding excessive manufacturing precision requirements.
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
This configuration reduces thermal stresses and improves bond strength, preventing foam core cracks and enhancing the structural integrity of the propeller blades under operating loads.
Implementation Method 1
thermal stresses due to differences in coefficients of thermal expansion between the foam spar core and the structural layer
Data Source
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Figure 5
AI summary
A propeller blade (100) includes a foam core (205) and a structural layer formed of multiple layers (206a, 206b) that surrounds at least a portion of the foam core (205). The structural layer includes a mid-thickness location defined between the foam core and an outer edge of the structural layer and the multiple layers (206a, 206b) include at least one unidirectional layer (206b) and at least one biased layer (206b) disposed asymmetrically about the mid-thickness location.