Sharp-Tipped Indenter for Chemically Strengthened Glass Strength Testing
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Solution Overview
Problem
Conventional methods for evaluating the strength of chemically strengthened glass, such as using Vickers or Knoop indenters, fail to accurately reflect the actual drop fracture scenario, particularly in reproducing slow cracking, which is a common failure mode in flat panel display devices, leading to inefficiencies and waste in testing.
Innovation Solution
A method involving an indenter with a sharp tip having a minimum cross-sectional angle of less than 120°, preferably 30° or more, is used to apply a static load vertically to the glass, allowing for more accurate measurement and reproduction of slow cracking by forming a flaw deeper than the compressive stress layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional indenters with large tip angles (Vickers or Knoop) are used to evaluate glass strength, then the evaluation can be performed easily and quickly, but the measurement results do not accurately reflect actual drop fracture conditions and fail to reproduce slow cracking
Solution Approach 1:
The patent changes the geometric parameter of the indenter tip angle from conventional large angles (Vickers 136°, Knoop 172.3°) to a sharp tip with minimum cross-sectional angle less than 120°. This parameter change enables the indenter to reproduce slow cracking that occurs in actual drop scenarios, thereby improving measurement accuracy without significantly impacting testing efficiency
Solution Approach 2:
The sharp-tipped indenter creates an indentation geometry that copies the stress distribution pattern of actual drop impact. By forming a flaw deeper than the compressive stress layer with a sharp tip, the test reproduces the slow cracking mechanism that occurs during real-world drop fracture, making the measurement results more representative of actual performance
2Measurement precision
If actual drop testing is performed to evaluate glass strength and reproduce slow cracking, then the measurement accurately reflects real-world conditions, but the process is time-consuming and results in waste of display devices
Solution Approach 1:
The sharp-tipped indenter performs preliminary action by creating a controlled indentation and flaw deeper than the compressive stress layer during the strength test. This preliminary flaw creation reproduces the conditions necessary for slow cracking without requiring actual drop testing, thereby achieving accurate measurement without time loss or device waste
Solution Approach 2:
The sharp-tipped indenter acts as an intermediary that transfers the essential characteristics of drop impact (sharp contact, localized stress) into a controlled laboratory test. This intermediary mechanism reproduces slow cracking behavior without requiring the complex and wasteful process of actual drop testing
3Weight of moving object
If the thickness of the cover glass is reduced to achieve weight reduction and thickness reduction, then the requirements for portable devices are met, but the strength decreases and the glass may crack during use or carrying
Solution Approach 1:
The patent changes the evaluation parameter from conventional indentation strength to slow cracking resistance using a sharp-tipped indenter. This parameter change enables accurate assessment of thin glass strength, allowing manufacturers to optimize glass thickness for weight reduction while ensuring sufficient strength through proper chemical strengthening
4Ease of manufacture
If conventional indentation methods are used to evaluate cover glass strength, then the evaluation process is simple, but the fracture pattern does not match the actual drop fracture pattern
Solution Approach 1:
The patent changes the indenter geometry parameter (tip angle less than 120°) to reproduce the stress distribution of actual drop impact. This simple geometric modification maintains ease of manufacture and testing while accurately reproducing the slow cracking fracture pattern observed in real-world drop scenarios
Data Source
AI summary
There are provided a method for measuring strength of a chemically strengthened glass, that reflects the state of actual drop fracture more appropriately, and can reproduce slow cracking in the chemically strengthened glass, a method for reproducing cracking of a chemically strengthened glass, and a method for producing a chemically strengthened glass. Load is applied to an indenter having a tip formed into a sharp shape having a minimum angle θmin of cross-section of less than 120°, the indenter is pushed into a chemically strengthened glass under a static load condition such that the tip is vertical to a surface of the chemically strengthened glass, and the load when the chemically strengthened glass cracks is measured.