GB/T 38978-2020Refractory products—Determination of stress-strain (three-point bending method) (English PDF)

4.3 Deformation Measuring Device

4.3.1 The precision needs to reach 1 µm and shall be regularly calibrated.

4.3.2 When the contact-type displacement sensor is used, the deformation of the specimen is transferred to the displacement sensor through the transmission mechanism. When the extensometer is used for measurement, the precision of the extensometer is not lower than Level B-1. The precision of the extensometer used at high temperature can be calibrated at room temperature, but an attempt shall be made to calibrate it together with the high-temperature extension rod. For the automatic recording chart extensometer, before each test, the precision shall be calibrated on the site of the test.

4.3.3 Non-contact measurement may adopt laser, but it shall satisfy the accuracy requirements.

4.4 Test Furnace

4.4.1 The test furnace shall be able to simultaneously heat the loading device and the specimen. During the test, the temperature on the specimen shall be evenly distributed, and the temperature difference shall not exceed ± 10 °C.

4.4.2 For easily oxidized specimens, for example, specimens containing carbon, the atmosphere around the specimens in the test furnace shall be neutral or reductive, so as to protect the specimens from being oxidized.

4.5 Temperature Measuring Device

4.5.1 The temperature shall be measured through a thermocouple near the midpoint of the tension surface of the specimen.

4.5.2 The relations between the measured temperature and the midpoint temperature of the tension surface of the specimen shall be determined in advance and regularly checked.

4.5.3 During the test, the midpoint of the tension surface of the specimen shall be maintained at the test temperature.

4.6 Electric Drying Oven

It shall be controlled at the temperature of (110 ± 5) °C.

6.1 Room-temperature Test

6.1.1 Symmetrically place the specimen on the lower cutting edge. Install a displacement measuring device at the center of the contact surface between the specimen and the lower cutting edge.

6.1.2 Vertically and uniformly load the upper cutting edge in the middle of the pressure surface of the specimen, until the specimen breaks. The stress increase rate shall comply with the following stipulations:

---dense refractory products: (0.15 ± 0.015) MPa/s;

---thermal insulating refractory products: (0.05 ± 0.005) MPa/s.

6.1.3 Record the load value that the specimen bears and the corresponding central deformation during the loading process.

6.2 High-temperature Test

6.2.1 The test temperature shall be determined by relevant parties through negotiation.

It is recommended to use multiples of 100 °C (such as: 1,000 °C, 1,100 °C and 1,200 °C, etc.); if necessary, multiples of 50 °C (such as: 1,050 °C, 1,100 °C and 1,150 °C, etc.) may also be used.

6.2.2 Symmetrically place the specimen on the lower cutting edge in the test furnace.

At a specified rate, raise the temperature, generally at 4.5 °C/min ~ 5.5 °C/min. For dense shaped refractory materials, when the temperature exceeds 500 °C, the heating rate of 10 °C/min may be used.

6.2.3 When the test temperature is used, maintain the specimen at this temperature for a period of time, so that the temperature distribution on the specimen is uniform.

The temperature difference shall not exceed ± 10 °C; the temperature-holding time shall be indicated in the test report.

6.2.4 When the specimen is heated to the test temperature, start the timing of the temperature-holding time. For the fired refractory materials, the temperature-holding time is 30 min. For the unshaped refractory materials which have received thermal treatment, the temperature-holding time is 30 min. For the unshaped refractory materials which have not received thermal treatment, the temperature-holding time may be 60 min, or be determined by relevant parties through negotiation. The temperature-holding time and thermal treatment conditions of unshaped materials […]