Brittle Sheet Strength Testing via Adjustable Tensile Stress
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Solution Overview
Problem
Existing methods for testing the breaking strength of hard brittle materials like glass are limited in flexibility, as they rely on predetermined stress values defined by roller diameter and thickness, and may not detect delayed fractures due to stress corrosion cracking.
Innovation Solution
A method and apparatus that apply a predefined tensile stress to sheet-like elements made of hard brittle materials by passing them over rollers and exerting an additional tensile force, allowing for flexible stress value adjustment and detection of delayed fractures through monitoring for breakage under resultant tensile stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the glass is subjected to bending over a roller with fixed diameter, then the tensile stress is predetermined by the roller diameter and glass thickness, but it is not possible to test for arbitrarily selectable tensile stress values
Solution Approach 1:
The patent applies parameter changes by introducing an additional tensile stress component that can be independently adjusted. Instead of changing the roller diameter to alter the predetermined tensile stress, the invention modifies the stress parameters by adding a controllable tensile force in the advancement direction. This allows flexible selection of total tensile stress values without physical changes to the roller geometry.
Solution Approach 2:
The invention implements dynamics by making the tensile stress adjustable and variable during the testing process. The tensile force in the advancement direction can be dynamically controlled to achieve different stress levels, transforming the static stress determination (based on fixed roller diameter) into a dynamic system where stress can be adapted to different testing requirements.
2Reliability
If the glass is subjected to proof testing with short duration mechanical stress, then the test can be completed quickly, but stress corrosion cracking may not have sufficient effect and the glass may break at similar or lower stress at a later time
Solution Approach 1:
The invention applies preliminary action by subjecting the glass to a prolonged tensile stress period before the final strength assessment. The additional tensile force is applied in advance during the transport over rollers, allowing stress corrosion cracking to initiate and propagate during this extended period. This preliminary stress application ensures that latent defects are revealed before the glass enters service, improving the reliability of the strength prediction.
Solution Approach 2:
The invention implements continuity of useful action by maintaining tensile stress application throughout the entire transport process over the rollers. Rather than a brief impulse load, the tensile force is applied continuously during the passage over the rollers, maximizing the effect of stress corrosion cracking on any existing defects and ensuring a more reliable assessment of the glass's future performance.
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
Enables flexible testing of specific strength values and enhances the reliability of strength tests by detecting defects and reducing the likelihood of breakage during storage or processing, particularly suitable for thin glass applications.
Implementation Method 1
the element is bent thereby, so that each of the faces is subjected to a tensile stress in a portion in which the opposite face is in contact with a surface of the roller
Implementation Method 2
a tensile force is exerted on the element in the direction of advancement so that both faces are subjected to a tensile stress of at least 2 MPa
Data Source
AI summary
A method for testing the strength of a sheet-like element having two opposite faces and made of hard brittle material under tensile stress is provided. The method includes passing each of the faces of the element over a roller and thereby bending the element so that each of the faces is subjected to a first tensile stress in a portion in which the opposite face is in contact with a surface of the roller; exerting a second tensile force on the element in the direction of advancement so that both faces are subjected to the second tensile stress of at least 2 MPa so that the first and second tensile stresses add up to define a resultant tensile stress; and monitoring the element and determining whether the element has a defined breaking strength equal to the resultant tensile stress or whether the element breaks under the resultant tensile stress.