GB/T 9966.9-2021Test methods for natural stone—Part 9: Determination of the dynamic modulus of elasticity by measuring the fundamental resonance frequency (English PDF)

4.1 Instruments and Equipment for Continuous Excitation Mode

4.1.1 Frequency generator with variable frequency. The minimum frequency range should be 20kHz.

4.1.2 For the transmitter and receiver sensors in contact with the sample, it is recommended to use adhesive materials (rubber, plaster, etc.) for slight fixation. The natural frequency of the receiver should be more than twice the predicted fundamental frequency of the sample resonance.

4.1.3 A device that can record or display the resonance generated by a sample.

4.1.4 Instruments and equipment capable of accurately measuring or calculating the fundamental resonant frequency of a sample. such as a frequency meter, with an accuracy of not less than 0.5%.

4.1.5 A working surface that is far from external vibrations and easy to measure.

4.1.6 Rigid metal specimen supports. The length shall be at least equal to the side length (b) or diameter (d) of the specimen cross-section, and the width shall be less than the specimen length (). 5%; the support can be a column with a square or rectangular cross-section. If the specimen is cylindrical, the support should have a notch. The position of the support is as follows. Figure 1.

4.2 Instruments and Equipment for Instantaneous Excitation Mode

4.2.1 Mechanical pulse generator. can be a hammer or electronic pulse generator.

4.2.2 Needle-type vibration receiving sensor. Its natural frequency should be more than twice the predicted fundamental frequency of the sample resonance.

4.2.3 A device that can record or display the resonance generated by the sample.

4.2.4 Instruments and equipment capable of accurately measuring or calculating the fundamental resonant frequency of a sample. such as a frequency meter, with an accuracy of not less than 0.5%.

4.2.5 A working surface that is far from external vibrations and easy to measure.

4.2.6 Rigid metal specimen supports. shall meet the requirements of 4.1.6.

4.3 Additional equipment for two excitation modes

4.3.1 Balance. accuracy is 0.01% of the measured mass.

4.3.2 Forced-air drying oven. can maintain the temperature at (65±5)°C.

4.3.3 Vernier calipers. accuracy of 0.1 mm or higher.

4.3.4 Standard rectangular block made of aluminum alloy. the cross-section is square, the side length is (40±1)mm, and the length is (160±1)mm.

4.4 Repeatability of testing instruments and equipment

A validation process should be performed before and after each test, using a standard aluminum alloy cube under (20±3) ambient conditions for repeatability. Sexuality test. The measured value of the fundamental resonant frequency of the standard rectangular block should not differ from the calibrated value by more than 0.5%, and the difference between the measured values before and after the same test should not exceed 0.5%. It should not exceed 0.1%.

5.1 Number of Samples

Prepare at least 6 samples from the same batch of test samples.

5.2 Sample Specifications and Shape

The specimen shape is either a cuboid or a cylinder. The cross-section of the cuboid is a square, and its length (b) is 4 times the side length (a). The length of the cylindrical specimen... () is 4 times the diameter (d).

5.3 Dimensional Deviation

The deviation of the sample dimensions l, b, and d is ±1.0 mm.

5.4 Anisotropic Surfaces

If the stone has anisotropic surfaces, such as bedding or foliation, the long axis of the sample should be parallel or perpendicular to the texture surface. Two flat surfaces should be used on the sample. The lines clearly indicate the direction of the anisotropic surface.

5.5 Sample preparation

Water saturation treatment can be performed before the experiment, or it can be omitted as required. In either case, the wet/dry state and temperature should be recorded in detail.

6.1 Preparatory Operations

If the sample is wet, wipe it clean with a wrung-out damp cloth before testing. Measure the geometric dimensions (L, 6, or d) of each specimen along the centerline. Accurate to 0.1 mm. Place the transmitter and receiver as shown in Figure 1.

6.2 Excitation Mode

6.2.1 Continuous Excitation Mode

The excitation frequency is measured using a frequency meter until the sample resonates. The maximum energy, i.e., when the sample resonates, is recorded by a receiver. The fundamental resonant frequency (f) is read from the frequency meter.

Note: When testing samples with relatively flat frequency response curves as shown in Figure 2, if the resonance state cannot be accurately measured, the fundamental resonance principle should be referenced.

6.2.2 Instantaneous Activation Mode

Repeat the excitation of the sample until three consecutive values are found in the range of the fundamental resonant frequency ±60 Hz.

6.3 Density Measurement

Place the sample in distilled or deionized water for 1 hour, then measure and calculate the bulk density according to GB/T 9966.3, converting the units to kilograms per cubic meter (kg/m³).