Deformation and stress characteristics of anchor bolt under axial impact

Coal burst has become one of the most prominent dynamic disasters affecting coal mine production because of its unique characteristics of easy occurrence,frequent occurrence and difficult in prevention and control. During the dynamic appearance of coal burst in roadway,the bolt support system is often accompanied by a certain impact of dynamic load. The research on the mechanical response of the bolt support system under the impact of dynamic load is of great significance to the prevention and control of coal burst. In order to study the response of different positions of the rod body to the impact load in the bolt support system,the No.500 lefthand nonlongitudinal bolt threaded steel bolt commonly used in coal mines is selected,the strain gauge is pasted at different positions along the axial direction of the bolt,and the axial impact load is applied to the support unit by using the comprehensive testbed of bolt mechanical properties. Laser displacement sensor and dynamic strain gauge are used to collect the deformation data of bolt and different positions respectively,and the deformation and time sequence characteristics of bolt are analyzed. The LSDYNA is used to reproduce the loading deformation process of bolt under axial impact load,and the stress and deformation characteristics of bolt at different positions are analyzed. The results show that ① under the initial tensile load of 171 kN,the 10 kJ axial impact energy instantaneously increases the load of the bolt to 438 kN,and then it is in the state of oscillation attenuation,and the attenuation speed gradually increases. ② The 10 kJ axial impact energy causes the bolt to oscillate,stretch and shrink within 30 ms,and finally produces 28.39 mm tensile plastic deformation. ③ The deformation of different positions of the bolt is greatly affected by the interface reflection effect of stress wave. Most of the plastic deformation occurs in the free section of the bolt. The closer it is to the interface,the greater the plastic deformation of the bolt. ④ The response of different positions of bolt to impact load is sequential,and the tensile and shrinkage deformations respond successively from the bolt tail to the end. ⑤ The anchoring effect can effectively restrain the bolt deformation and absorb the stress wave generated by impact. With the increase of anchoring depth,the amplitude of bolt stress and deformation response decrease significantly.