Glass Cover Fracture Resistance via Stress Profile Optimization
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Solution Overview
Problem
Portable electronic devices face challenges with cover glass damage from accidental drops, particularly due to flexure and sharp contact failures, which current ion-exchange techniques partially address but result in undesirable fracture conditions with high fragment production and aesthetic/functional constraints.
Innovation Solution
Development of a glass-based article with a specific stress profile featuring compressive and tensile regions, optimized by depth of compression and tensile stress factor, to enhance fracture resistance and reduce fragment production upon impact, while maintaining thinness and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ion-exchange technique is used to strengthen glass, then flexure resistance is improved, but sharp contact vulnerability increases due to high stress concentration from local indentations
Solution Approach 1:
The patent modifies the stress profile parameters by controlling the depth of compression (DOC) and tensile stress factor (KT) through ion-exchange process parameters. By optimizing these parameters, the glass achieves both flexure resistance and reduced sharp contact vulnerability, resolving the contradiction between these two properties.
Solution Approach 2:
The patent creates different stress states at different locations within the glass thickness. The surface regions have compressive stress for sharp contact resistance, while the interior has tensile stress for flexure resistance. This spatial variation in stress quality resolves the contradiction between surface durability and overall strength.
2Reliability
If ion-exchanged glass is used, then fracture resistance is improved, but undesirable fracture conditions occur resulting in high number of fragments and energized fragments
Solution Approach 1:
The patent controls the stress profile parameters (DOC and KT) to achieve a balanced stress distribution that prevents excessive energy storage. By optimizing these parameters, the glass maintains high fracture resistance while avoiding the conditions that lead to high fragment production and energized fragments.
3Length of moving object
If glass is made thinner, then device thinness requirement is met, but mechanical strength decreases
Solution Approach 1:
The patent uses ion-exchange to change the stress state parameters of thin glass, creating compressive surface stress and optimized tensile stress distribution. This allows thin glass to achieve adequate mechanical strength without increasing thickness, resolving the contradiction between thinness and strength.
4Strength
If compressive stress is induced in glass surface, then flexure failure resistance is improved, but stored energy increases leading to high fragment production upon fracture
Solution Approach 1:
The patent optimizes the stress profile by controlling DOC and KT parameters to achieve the right balance between compressive surface stress for flexure resistance and tensile interior stress to limit stored energy. This prevents excessive energy accumulation that would lead to high fragment production.
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-based article exhibits improved drop performance with reduced fragmentation, making it suitable for electronic devices by balancing strength, thinness, and aesthetic requirements, and providing new criteria for determining frangibility based on fracture toughness and stress profile properties.
Implementation Method 1
Glass can be made more resistant to flexure failure by the ion-exchange technique, which involves inducing compressive stress in the glass surface.
Data Source
AI summary
Glass-based articles are provided that exhibit improved fracture resistance. The relationships between properties attributable to the glass composition and stress profile of the glass-based articles are provided that indicate improved fracture resistance.