**Chinese Name:** Test Method for Flexural Strength of Glass Materials
**English Name:** Test Method for Flexure of Glass Material
**Approved by:** State Building Materials Industry Bureau
**Approval Date:** August 22, 1997
**Implementation Date:** January 1, 1998
**Standard Number:** JC/T 676–1997
This standard outlines a comprehensive procedure for determining the flexural strength of glass and glass-ceramic materials. It provides clear guidelines on the testing equipment, sample preparation, test procedures, and data analysis to ensure accurate and reliable results.
### 1. Scope
This method is designed to evaluate the flexural strength of various types of glass and glass-ceramic materials. It is particularly useful in quality control and material selection processes within the construction and manufacturing industries.
### 2. Test Principle
The test involves applying a static three-point bending load to a sample of specific dimensions until it fractures. The maximum bending stress at the cross-section is calculated to determine the flexural strength of the material. This approach ensures that the results are consistent and representative of real-world conditions.
### 3. Testing Equipment
#### 3.1 Testing Machine
- The loading rate must be controlled so that the load indication error does not exceed ±1%.
- The applied load should fall between 20% and 90% of the machine’s capacity to ensure accuracy.
- The indenter blade and support must be made of hardened steel with an elastic modulus of at least 200 GPa to avoid plastic deformation. The contact surfaces should have a surface roughness no greater than 1.6 μm.
#### 3.2 Measuring Tools
A vernier caliper or micrometer with an accuracy of 0.02 mm is required to measure the dimensions of the specimen accurately.
### 4. Specimen Preparation
- Each specimen should be 120 mm long, 20 mm wide, and have a thickness corresponding to the original plate.
- The cross-sectional corners should be precisely at 90° ± 0.5°.
- The samples must be free from visible defects such as cracks, chips, or scratches. The cutting edge should be on one face only.
- At least 15 specimens are required per test group to ensure statistical reliability.
### 5. Test Procedure
- Measure the width and thickness of the middle section of each specimen using a vernier caliper or micrometer.
- Adjust the span between the supports to 100 mm.
- Place the specimen on the supports with the cut edge facing up, ensuring equal overhangs on both sides.
- Apply a load at a displacement speed of 5 mm/min until the specimen breaks. Record the maximum load at failure.
- If the fracture occurs outside the central third of the specimen, discard the result and repeat the test.
- After each test, clean the indenter and supports to remove any residual glass fragments.
### 6. Data Analysis
- Flexural strength (σ) is calculated using the formula:
$$
\sigma = \frac{3PL}{2bd^2}
$$
Where:
- P = maximum load at break (N)
- L = span between supports (mm)
- b = width of the specimen (mm)
- d = thickness of the specimen (mm)
- Standard deviation (S) is calculated using:
$$
S = \sqrt{\frac{1}{n-1} \sum_{i=1}^{n} (\sigma_i - \bar{\sigma})^2}
$$
- Results should be reported as the mean value and standard deviation, rounded to three significant figures.
### 7. Test Report
The final report should include:
- The name of the requesting organization
- Sample details, including type, size, and identification number
- Dimensions of each specimen and the breaking load
- Flexural strength values, including individual, average, and standard deviation
- Information about the testing equipment used
- Details of the testing facility and personnel involved
This standardized method ensures consistency and precision in evaluating the mechanical properties of glass materials, supporting quality assurance and material performance assessment.
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