Laminated Glass Article with Differential CTE Core and Cladding
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Solution Overview
Problem
Glass articles, such as automotive windshields, often suffer from significant surface flaws that compromise their scratch resistance and strength, with existing technologies failing to maintain strength after abrasion or large flaw introduction.
Innovation Solution
A laminated glass structure comprising a core layer with a higher coefficient of thermal expansion and compressive stress, and a cladding layer with a lower coefficient of thermal expansion and tensile stress, where the core layer is formed from a glass composition with 50-80 mol% SiO2, 5-20 mol% Al2O3, and 1-8 mol% MgO, and the cladding layer from 60-70 mol% SiO2, 6-18 mol% Al2O3, 4-21 mol% B2O3, and 0.2-5 mol% MgO, to achieve a Knoop scratch threshold of at least 5 N and an indentation threshold of at least 20 N.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass articles are used in applications like automotive windshields, then they provide protective function, but surface flaws are introduced that compromise scratch resistance and strength
Solution Approach 1:
The patent employs a composite glass structure consisting of a core glass layer and a cladding glass layer with different compositions and properties. The core layer provides bulk strength while the cladding layer with lower CTE and higher chemical durability protects the surface from flaws and abrasion, thereby maintaining strength retention after surface damage occurs.
Solution Approach 2:
The cladding layer is specifically designed with different local properties (lower CTE, higher chemical durability) than the core layer to address surface-specific requirements. This localized property differentiation allows the surface to resist flaw formation and propagation while the bulk material maintains its structural strength.
2Reliability
If conventional glass compositions are used, then manufacturing is simple, but scratch resistance and durability are insufficient after surface abrasion
Solution Approach 1:
The patent uses a composite glass structure with a core layer and a cladding layer, each with specific compositional ranges. The core layer contains higher SiO2 (50-80 mol%) and Al2O3 (5-20 mol%), while the cladding layer has lower SiO2 (60-70 mol%), higher B2O3 (4-21 mol%), and different alkaline earth oxide content. This composite approach enhances scratch resistance and durability while maintaining manufacturability through established glass forming techniques.
Solution Approach 2:
The patent systematically varies compositional parameters between the core and cladding layers, specifically controlling SiO2, Al2O3, B2O3, and alkaline earth oxide content within defined ranges. These parameter changes create the necessary CTE mismatch and chemical durability differences to achieve superior scratch resistance without overly complicating the manufacturing process.
3Strength
If glass layers with different CTE are used to create stress distribution, then strength is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific compositional ranges for the core and cladding layers that inherently produce the desired CTE mismatch. The core layer has higher SiO2 and Al2O3 content while the cladding layer has higher B2O3 and different alkaline earth oxide content, creating a controlled thermal expansion difference that generates beneficial compressive stress in the cladding layer during cooling, without requiring excessive manufacturing precision.
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 glass article retains a significant portion of its strength after abrasion, with a ratio of retained strength at 25 psi to 5 psi abrasion pressure of at least 0.3, and exhibits improved scratch resistance and durability without the need for additional processing like ion-exchange treatments.
Implementation Method 1
A coefficient of thermal expansion (CTE) of the core layer is greater than a CTE of the cladding layer. The core layer comprises a tensile stress, and the cladding layer comprises a compressive stress.
Data Source
AI summary
A glass article includes a glass core layer and a glass cladding layer adjacent to the core layer. A coefficient of thermal expansion (CTE) of the core layer is greater than a CTE of the cladding layer. The core layer has a tensile stress, and the cladding layer has a compressive stress. A retained strength of the glass article is a strength determined after abrasion of an outer surface of the glass article with 1 mL of 90 grit SiC particles for 5 seconds at an abrasion pressure, and a ratio of the retained strength at an abrasion pressure of 25 psi to the retained strength at an abrasion pressure of 5 psi is at least about 0.3.