Glass Laminate Edge Strength via CTE Mismatch
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Solution Overview
Problem
Laminated glass products often experience tensile residual stresses at the edges, leading to issues like cracking, delamination, and optical distortion due to the lamination process, which can occur during manufacturing, shipping, or in-service use.
Innovation Solution
A glass laminate is formed with a combination of hot-formed and cold-formed plies, where the inner ply has a higher coefficient of thermal expansion than the outer ply, inducing compressive residual stresses at the edges through the cold forming process, thereby counteracting tensile stresses and enhancing the laminate's resistance to flaws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lamination process is performed using conventional glass plies, then the laminate can be manufactured, but tensile residual stresses are induced at the edges leading to cracking and delamination
Solution Approach 1:
The patent changes the material parameters of the glass plies by selecting materials with different coefficients of thermal expansion. The inner ply has a higher CTE than the outer ply, which fundamentally alters the stress distribution during cooling after cold forming, transforming the harmful tensile edge stresses into compressive ones.
Solution Approach 2:
The invention directly utilizes thermal expansion differences between materials. By cold-forming the laminate and then cooling it, the inner ply (with higher CTE) contracts more than the outer ply, inducing compressive residual stresses at the edges. This converts the harmful thermal expansion effect into a beneficial stress state.
2Shape
If cold forming is used to form the glass plies, then the laminate can be manufactured with complex shapes, but tensile residual stresses are induced at the peripheral edges
Solution Approach 1:
The patent changes the material parameters by selecting glass plies with different CTE values. This parameter change ensures that during cooling after cold forming, the stress distribution is reversed, creating compressive rather than tensile stresses at the edges, thus resolving the contradiction between achieving complex shapes and avoiding edge stresses.
Solution Approach 2:
The invention converts the harmful tensile residual stresses normally induced by cold forming into beneficial compressive stresses. By carefully selecting materials with different CTE values and controlling the cooling process, the cold forming operation that previously caused damage now generates protective compressive stresses at the edges.
3Device complexity
If the same coefficient of thermal expansion is used for both plies, then the lamination process is simpler, but tensile residual stresses occur at the edges during cooling
Solution Approach 1:
The patent deliberately changes the material parameter (CTE) to be different between plies, accepting increased material selection complexity as the cost of eliminating harmful tensile residual stresses. The inner ply is selected with a higher CTE than the outer ply, which fundamentally changes the stress behavior during thermal cycling.
Solution Approach 2:
The invention exploits thermal expansion differences between materials to control stress distribution. By selecting materials with different CTE values, the patent ensures that during cooling after cold forming, the inner ply contracts more than the outer ply, generating compressive residual stresses at the edges that prevent cracking and delamination.
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 approach results in a laminate with compressive residual stresses at the edges, making it more resistant to cracking, delamination, and optical distortion, improving its durability and performance in automotive glazing applications.
Implementation Method 1
a second coefficient of thermal expansion selected to be sufficiently higher than the first coefficient of thermal expansion to induce residual compressive stresses in the first ply due to cold forming therewith
Data Source
AI summary
A cold-formed glass laminate (100) may include a first ply (108) of 3D formed glass with a first thickness, a first strength, and a first coefficient of thermal expansion. The laminate (100) may also include a second ply (110) of 3D formed glass with a second thickness less than the first thickness, a second strength greater than the first strength, and a second coefficient of thermal expansion. The second coefficient of thermal expansion may be selected to be sufficiently higher than the first coefficient of thermal expansion to induce residual compressive stresses in the first ply (108) due to cold forming therewith. An adhesive layer (112) may be arranged between the first ply (108) and the second ply (110).