Thin Glass Stress Gradient for Higher Fracture Resistance
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Solution Overview
Problem
Existing glass-based articles, particularly thin ones, lack the fracture resistance provided by thermally tempered glass, and chemically strengthened glass does not achieve the stress profiles of thermally tempered glass, limiting their application in thin, lightweight articles that require superior fracture resistance.
Innovation Solution
Chemically strengthened glass-based articles with a non-zero metal oxide concentration gradient along the thickness, featuring a stress profile with a compressive stress region extending to a depth of compression (DOC) of at least 0.16 times the thickness and a central tension region with a maximum tension value between 71.5/√(t) to 100/√(t), approximated by the equation Stress(x) = MaxT - (((CT_n * (n+1))/0.5^n) * |(x/t)-0.5|^n, where MaxT is the maximum tension value, CT_n is less than or equal to MaxT, and n is between 1.5 and 3.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal tempering is used to achieve high fracture resistance, then compressive stress layers are formed to prevent flaw propagation, but the glass article thickness must be at least 3 millimeters which is too thick for many applications
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the glass (specific metal oxide concentrations within defined ranges) and processing parameters (ion exchange temperature, time, and composition) to achieve a unique stress profile in thin glass articles that was previously only attainable in thick glass through thermal tempering
Solution Approach 2:
The patent creates a composite stress profile structure within the glass article, combining a compressive stress layer at the surface with a tensile stress layer in the interior, achieved through controlled ion exchange processes that generate multiple stress zones to prevent flaw propagation while maintaining thin dimensions
2Length of moving object
If chemical strengthening is used to reduce glass thickness, then thin glass articles can be produced, but the stress profile exhibits a flat central tension region with lower maximum CT value compared to thermally tempered glass
Solution Approach 1:
The patent changes the chemical parameters of the glass composition (specific metal oxide concentrations) and the ion exchange process parameters (temperature, time, salt composition) to generate a stress profile with a steep gradient in the central tension region, achieving a high maximum CT value that eliminates the flat region problem of conventional chemically strengthened glass
Solution Approach 2:
The patent applies local quality by creating a non-uniform metal oxide concentration distribution throughout the glass thickness, with specific concentration ranges at different depths, which generates the desired steep stress gradient in the central region while maintaining appropriate surface compressive stress
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 solution provides thin glass-based articles with improved fracture resistance, achieving greater surface compressive stress and maximum central tension values, enhancing their durability even when dropped on hard surfaces, and preventing failure.
Implementation Method 1
chemically strengthened glass-based articles do not exhibit the stress profile of thermally tempered glass-based articles
Implementation Method 2
to achieve the thermal strengthening and the desired residual stresses, a sufficient thermal gradient must be formed between the core of such articles and the surface
Data Source
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AI summary
Embodiments of a glass-based article including a first surface and a second surface opposing the first surface defining a thickness (t) of about 3 millimeters or less (e.g., about 1 millimeter or less), and a stress profile, wherein all points of the stress profile between a thickness range from about 0∙t up to 0.3∙t and from greater than about 0.7∙t up to t, comprise a tangent with a slope having an absolute value greater than about 0.1 MPa/micrometer, are disclosed. In some embodiments, the glass-based article includes a non-zero metal oxide concentration that varies along at least a portion of the thickness (e.g., 0∙t to about 0.3∙t) and a maximum central tension in the range from about 80 MPa to about 100 MPa. In some embodiments, the concentration of metal oxide or alkali metal oxide decreases from the first surface to a value at a point between the first surface and the second surface and increases from the value to the second surface. The concentration of the metal oxide may be about 0.05 mol% or greater or about 0.5 mol% or greater throughout the thickness. Methods for forming such glass-based articles are also disclosed.