Electro-optic Window Thermal Stress Mitigation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electro-optic window assemblies are susceptible to crack failures due to hoop stresses near the edges of substrates, particularly in applications where temperature gradients are significant, such as in aircraft windows exposed to solar heating and low ambient temperatures.
Innovation Solution
The electro-optic window assembly is designed with substrates that have a theoretical maximum thermal stress of less than 25 MPa, achieved by minimizing temperature gradients between the visible and shaded areas through a bezel structure and improved thermal conductivity, and enhanced mechanical properties such as boroaluminosilicate glass compositions and edge treatments like grinding or laser cutting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the electro-optic window assembly is designed with large visible area and peripheral portions, then the transmission of light is improved, but the thermal stress at the substrate edges increases due to temperature gradients
Solution Approach 1:
The patent applies different thermal management strategies to different regions of the substrate. The peripheral portions are designed with enhanced thermal conductivity or thermal coupling to the bezel to dissipate heat more effectively, while the visible area maintains high light transmission. This local differentiation allows the large visible area to transmit light while the peripheral regions manage thermal stress through improved heat dissipation pathways.
Solution Approach 2:
The patent changes thermal parameters (thermal conductivity, thermal mass, or thermal coupling) of the peripheral portions relative to the visible area. By modifying these thermal parameters locally at the edges, the assembly can maintain large visible areas for light transmission while controlling the thermal stress parameters at the substrate edges through optimized heat dissipation.
2Temperature
If the substrate edges are exposed to significant temperature gradients, then the electro-optic medium can respond effectively to solar heating, but crack failures occur due to hoop stresses near the edges
Solution Approach 1:
The patent implements protective measures in advance by designing the peripheral portions with enhanced thermal management capabilities before thermal stress occurs. The bezel structure and thermal coupling elements are pre-configured to dissipate heat and reduce temperature gradients at the edges, cushioning the substrate edges against thermal shock and preventing crack initiation before it occurs.
Solution Approach 2:
The bezel structure serves as an intermediary element between the substrate edges and the external environment. It mediates the thermal stress by providing a thermal management interface that controls heat flow to and from the substrate edges, reducing the direct impact of temperature gradients on the substrate and preventing crack failures while allowing the electro-optic medium to respond to solar heating.
3Area of stationary object
If the visible area is maximized relative to peripheral portions, then the aesthetic and functional performance is improved, but the thermal stress concentration at the edges increases
Solution Approach 1:
The patent applies local quality differentiation by designing the peripheral portions with specific thermal management properties distinct from the visible area. The peripheral portions may have different thermal conductivity, thickness, or material composition optimized for heat dissipation, while the visible area maintains properties optimized for light transmission. This allows maximization of visible area while the peripheral regions handle thermal stress concentration.
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 significantly reduces the likelihood of crack failures by minimizing thermal stresses at the substrate edges, ensuring the assembly can withstand radiation-induced thermal gradients without compromising its dimensions or performance.
Implementation Method 1
an electro-optic medium at least partially filling the cavity and configured to reduce the transmission of light viewed through the electro-optic window assembly
Implementation Method 2
achieved by minimizing temperature gradients between the visible and shaded areas through a bezel structure and improved thermal conductivity
Implementation Method 3
enhanced mechanical properties such as boroaluminosilicate glass compositions and edge treatments like grinding or laser cutting
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An electro-optic window assembly is provided that includes a first substantially transparent substrate comprising: a first surface, a second surface, and a first peripheral edge; and a second substantially transparent substrate comprising: a third surface, a fourth surface, and a second peripheral edge. The first and second substrates define a cavity. The assembly further includes an electro-optic medium at least partially filling the cavity and configured to reduce the transmission of light viewed through the electro-optic window assembly. Further, the electro-optic window assembly is configured such that the substrates each have a theoretical maximum thermal stress of less than approximately 25 MPa upon exposure of the window assembly to an application environment.