QC/T 1153-2021Axial force test of bolts in automotive threaded joints - Ultrasonic piezoelectric ceramic method (English PDF)

3.1 Bolted joint

An assembly, which is composed of threaded fasteners and connected parts.

[Source: GB/T 16823.2-1997, 3.1]

3.2 Yield clamping force

The axial force, at which the bolt reaches yield, when tightened.

[Source: GB/T 16823.2-1997, 3.1]

3.3 Yield tightening torque

The torque, at which the yield clamping force is reached, when tightening.

[Source: GB/T 16823.2-1997, 3.1]

3.4 Ultimate clamping force

Maximum axial force, during tightening to bolt breakage.

[Source: GB/T 16823.2-1997, 3.1]

4.1 Requirements of test devices

4.1.1 Torque angle sensor

The allowable error of torque measurement shall be ±2%; the allowable error of angle measurement shall be ±1°.

4.1.2 Axial force sensor

The allowable error of the axial force sensor measurement shall be ±1%.

4.1.3 Ultrasonic measuring device

The data collection frequency shall not be lower than 1000 Hz; the signal is sensitive; the display resolution can distinguish the echo time difference. The measuring device shall contain a temperature compensation interface.

4.1.4 Piezoelectric ceramic sheet

The natural frequency of the piezoelectric ceramic sheet shall be between 2 MHz ~ 10 MHz.

4.1.5 Calibration pad

The calibration pad is used to adjust the clamping length during calibration; its rigidity shall comply with the provisions of 6.2 in GB/T 16823.3-2010.

5.2 Residual axial force test of bolt

5.2.1 The number and state of the test samples shall be checked. If the temperature changes, after the connection point is verified, by dynamic load, THEN, it shall be allowed to stand for a long enough time, to ensure that it returns to the ambient temperature.

5.2.2 An ultrasonic test device shall be set up, to test the residual axial force of the bolt AND compensate for the temperature difference, between the bolt test and the environment when the echo is zero.

5.2.3 If the bolt is tightened, in the elastic region, by the torque method, it shall directly test the time difference of the current bolt echo; compare with the calibration curve when the bolt is tightened, to directly read the residual axial force.

5.2.4 If the bolt is tightened to the yield area, by the torque-angle method, the bolt shall be loosened, based on the current ultrasonic propagation time of the bolt, as the zero reference, to test the ultrasonic propagation time difference of the bolt, after loosening; take the absolute value. Then calibrate the bolt on the axial force sensor, to generate the calibration curve of the yielded bolt. Directly compare the residual axial force of the bolt, on the calibration curve, through the absolute value of the time difference.