Bolt stress detection refers to the process of measuring, analyzing, and evaluating the magnitude, distribution, and variation patterns of stress that bolts are subjected to in their working state using specific technical means and instrument equipment. Stress is the internal force generated by the interaction between different parts of an object when it deforms due to external factors such as stress, humidity, temperature field changes, etc. It is expressed in terms of the internal force per unit area. For bolts, stress testing aims to understand the actual load they bear in the connecting structure and determine whether they are within a safe and reasonable stress range.

The method of bolt stress detection:

Strain gauge method: A strain gauge is attached to the surface of a bolt. When the bolt deforms under stress, the resistance value of the strain gauge changes. The resistance change is converted into a strain value using a strain gauge, and then the strain value is converted into a stress value according to Hooke's law. This method has high accuracy and can accurately measure the strain and stress on the bolt surface. However, the quality of the strain gauge adhesion has a significant impact on the measurement results, and the adhesion process is relatively complicated.

Ultrasonic method: using the propagation characteristics of ultrasonic waves in bolts to detect stress. The propagation speed of ultrasonic waves is related to the stress state of the material. When there is stress in the bolt, the propagation speed of ultrasonic waves will change. By measuring the propagation time or frequency changes of ultrasonic waves in the bolt, the stress level of the bolt can be calculated. This method belongs to non-destructive testing and will not cause damage to bolts. It is suitable for the detection of in-service bolts, but the detection accuracy is slightly lower compared to the strain gauge method.

Optical measurement methods: including photoelastic method, moir é interferometry, etc. The photoelastic method utilizes the birefringence phenomenon generated by certain transparent materials under stress to measure stress by analyzing the optical path difference; The cloud pattern interference method utilizes the principle of grating interference to measure displacement and strain by recording the changes in grating fringes before and after deformation, and then calculates stress. Optical measurement method has the advantages of full field measurement and intuitiveness, but the equipment is complex and the operation is difficult. It is usually used in laboratory research or special occasions that require high measurement accuracy.

Bolts are prone to fatigue damage under long-term alternating loads, and the propagation of fatigue cracks can lead to bolt fracture. By regularly conducting bolt stress testing, the stress changes of bolts can be monitored, and signs of fatigue crack initiation and development can be detected in a timely manner. Taking corresponding measures in the early stage of cracking, such as replacing bolts or repairing them, can effectively prevent fatigue fracture, prolong the service life of bolts, and thus extend the service life of the entire equipment.