Traditional rock bolt inspection methods are destructive and limited. Non-destructive testing (NDT) based on the stress wave method can realize a fast and convenient quality detection of rock bolts. To verify the effectiveness of the stress wave-based anchor NDT method, a multi-functional experimental bench was customized on the basis of a bench-pull tension testing machine. Stress waves can be generated by applying axial loads on rock bolts and then collected using a non-destructive tester. The VMD decomposition method and Hilbert–Huang signal processing method were used to filter and analyze the stress wave signal. The influence of the axial loads of different magnitudes on the stress wave was then investigated. The results showed that the stress wave characteristics of the rock bolt changed with the increase in the axial load. It was found, correspondingly, that the stress wave amplitude decreased gradually and there was a trend of rapid decrease at the beginning and then a slower decline. The change in the time domain amplitude of the stress wave after noise reduction can be used to determine the magnitude of the load on the rock bolt during the elastic deformation stage. Further studies showed that the axial load on rock bolts inversely calculated by the stress-wave time-domain amplitude method is accurate and reliable, which can be validated by comparing the data measured by the rock bolt dynamometer. The research results shed light on the development of the NDT technology on rock bolt inspection, and make this testing method more convenient, efficient, and accurate.

The nondestructive testing technique used to evaluate the quality of bolt support by detecting the axial force is suitable for the bolt with a short construction time. For the bolt in the support state for a long time period, it may lead to the detection of small axial force only and ignore the fact that the bolt has entered the necking fracture stage, and thus fail to detect safety hazards in time. Three sets of parallel tests were conducted to solve the misjudgment of detection results due to the reduction of axial force when the bolt was in the necking fracture stage. Bolt deformation characteristics and stress wave propagation characteristics in bolts under axial tensile stress were studied by using the bolt tensile and stress wave detection test system which was modified and built independently. The results showed that (1) The diameter of the necking position decreases continuously during the tensioning process of the bolt and the rate of decrease increases abruptly during the necking fracture stage. (2) Due to the bolt stretching, the stress wave propagates in the bolt with different degrees of reflection and transmission, resulting in the attenuation of the stress wave energy; the energy attenuation ratio of the stress wave signal in the necking fracture stage reaches 35%, and the energy attenuation ratio increases exponentially as the necking continues to occur. (3) The frequency distribution of the stress wave signal during the bolt stretching process is from scattered to concentrated, the dominant frequency is gradually prominent and changes from low frequency to high frequency, the high-frequency signal is more sensitive to the cracks and necking of the bolt, and the dominant frequency is between 9500 and 10,000 Hz. (4) The average error of the stress wave method is 1.945% and the maximum and minimum values are 4.12% and 0.51%, respectively. The method is promising and provides a reference for the study of nondestructive testing of bolt stress waves in field support.