GB/T 37781-2019Test methods for bending strength of glass (English PDF)

0.1 MPa

6) The time taken from loading to failure is in seconds, accurate to 1 s;

7) Whether the sample failure starts at the sample edge or starts at the center portion.

3.1 Bending strength

The maximum bending stress experienced when the sample is broken under bending load.

3.2 Bending stress

The tensile stress generated on the lower surface of the sample during the […]

5.1.4 Result calculation

5.1.4.1 The sample whose fracture occurs in the middle of the three equal parts of the longitudinal direction of the sample is an effective sample. Calculate only the bending strength of the effective sample. Calculate according to formula (1):

Where:

sigma b - The bending strength of sample, in megapascals (MPa);

P - The maximum load at which the sample breaks, in Newtons (N);

L - The distance between the sample supports, in millimeters (mm); b - Sample width, in millimeters (mm); d - Sample thickness, in millimeters (mm).

5.1.4.2 According to Appendix A, conduct data processing. USE the arithmetic mean and standard deviation of valid data to express. The result is accurate to […]

5.2 Four-point bending method

5.2.1 Testing machine

5.2.1.1 It is capable of realizing continuous, uniform, stepless loading from zero to maximum load and minimizing vibration during loading.

5.2.1.2 The device shall be capable of loading at equal stress rate.

5.2.1.3 The load measuring device equipped with the instrument keeps the measurement error within ±2.0% of the range.

5.2.1.4 The schematic diagram of four-point bending test is shown in Figure 2.

The backup roller and the bending roller have a diameter of 50 mm±1 mm and a length of not less than 365 mm. All the rollers can rotate freely. The distance Lb between the center lines of the two bending rollers is 200 mm±1 mm. The distance Ls between the center lines of the two backup rollers is 1000 mm±2 The side of the sample edge shall be perpendicular to the surface. The sample shall be prepared 24 h before the start of the test; before the test, stored in the test environment for at least 4 h.

5.2.3 Test procedures

5.2.3.1 Measurement of sample width

The width measurement is accurate to 1 mm. The width is measured at least 3 times at different positions of the sample and averaged.

5.2.3.2 Measurement of sample thickness

USE a Vernier caliper in accordance with GB/T 1216 to measure the sample thickness, accurate to 0.02 mm. The thickness is measured at the 4 corners of the sample and averaged.

5.2.3.3 Bending test

According to the requirements of Figure 2, place the sample. In order to prevent the debris from scattering, a layer of self-adhesive film is attached to the upper surface of the sample, to facilitate the determination of the source of the fracture.

PLACE a rubber mat [with a thickness of 3 mm, a hardness of (40±10)IRHC] between the sample and the bending roller and the backup roller. The bending test shall be carried out at an ambient temperature of (23±5)°C and a relative humidity of 40%~70%. In order to avoid the influence of thermal stress, during the test, the ambient temperature change shall not exceed 1 °C. During the test, at a loading rate of (2±0.4)MPa/s, apply a uniform load to the sample until the sample breaks. RECORD the maximum load Fmax and the time taken from the beginning of loading to the failure of the sample.

5.2.4 Result calculation

5.2.4.1 Bending strength of sample

The bending strength sigma bB is calculated according to formula (2):

Where:

sigma bB - The bending strength of sample, in megapascals (MPa); k - Dimensionless factor (ks when starting from the failure of the surface; ke The choice of three-point bending method or four-point bending method to measure the bending strength of glass may be agreed between the supplier and the purchaser; may also be determined according to the influencing factors of the strength test. See Appendix B.