Testing method for axial force of high-strength bolts

Testing method for axial force of high-strength bolts

1. Calibration method

The commonly referred to tensile force calibrator is an axial force gauge. In order to ensure the installation quality of high-strength bolt connection pairs, a mobile axial force gauge used to detect axial force at the installation site is composed of a spoke type pressure sensor and a matching digital display instrument.

The mobile axial force meter is mainly suitable for installation sites, comparing the pre tightening force after tightening with the torque application tool used for on-site construction, in order to timely correct the on-site tightening torque. The calibration and verification of on-site tightening tools through mobile axial force meters provide some quality assurance for on-site construction quality.

2. Strain method

Stick the strain gauge on the measured object to make it stretch with the strain of the measured object, so that the metal foil inside will stretch or shorten with the strain. Many metals change their resistance as they mechanically elongate or shorten. The strain gauge is used to measure the strain by measuring the change of resistance.

The strain method is to use strain gauge to form the working principle of the bridge, and then package it to form a bolt axial force sensor device, and then install the sensor between the bolt and the connected piece, and place a gasket between the bolt and the sensor to make the sensor evenly stressed. As the sensor is squeezed by the bolt preload, the strain gauge inside the sensor changes, resulting in displacement strain. Measure the strain using the above principle method, and then calculate the preload based on the relationship between strain and stress.

3. Ultrasonic measurement method

People have been researching and exploring the relationship between sound waves and stress in theory for many years. In the 21st century, there are already ultrasonic measuring instruments for bolt stress on the market. Due to the direct measurement, high accuracy, and simplicity of ultrasonic stress measurement methods, especially the ability to regularly track and inspect bolts in service, their development is rapid.

The calculation principle of ultrasonic stress detection method is to first measure the sound time required for ultrasonic transmission back and forth in both stressed and unstressed states; Comparing the torque machine and stretching machine with the ultrasonic stress instrument, the results obtained by the instrument are very good with minimal error.