Design Of Ultrasonic Bolt Tightening Stress Detection System

With the rapid development of industrial manufacturing and production,bolt fastening connectors bear the main load in various equipment.In order to ensure the stable and reliable operation of the equipment,it is of great significance to adopt effective bolt stress detection technology.In the actual manufacturing process,ultrasonic testing technology can quickly and accurately detect changes in the axial stress of bolts without dismantling the equipment,and will not damage the structural features of the bolts.Ultrasonic bolt stress detection technology is a measurement method based on the acoustoelastic principle of ultrasonic waves.It measures the transit time difference of ultrasonic waves in the bolt axial direction by reflection method to calculate the stress of bolts under different deformation conditions.Regarding the problems of cumbersome testing,large human error and expensive equipment in the current bolt stress testing methods,the paper plans to develop a high-precision,automated stress testing equipment.Based on the thermal expansion principle of the metal medium and the ultrasonic acoustic elasticity principle,real-time high-precision detection of the bolt axial stress during the pre-tightening process and the corresponding relationship between the bolt stress and the ultrasonic acoustic time difference are realized.The paper analyzes the current development status of bolt tightening stress detection technology at home and abroad,and makes an overall plan for the ultrasonic bolt tightening stress detection system.According to the thermal expansion principle of the metal medium and the principle of ultrasonic acoustic elasticity,the corresponding relationship between the temperature and sound time in the ultrasonic bolt stress detection process is constructed,and the calculation process of different sound time difference algorithms is analyzed and compared.In this paper,the ultrasonic bolt tightening stress detection system adopts modular hardware circuit design,and the circuit analysis and design of the ultrasonic pulse excitation module,echo signal conditioning module,high-speed analog-to-digital conversion module and temperature acquisition module are carried out.The system development uses XILINX’s ZYNQ series chips to complete the cross-compilation of hardware programmable FPGA and software programmable ARM cores,to achieve multi-channel pulse excitation hardware programming design and 250 MSPS high-speed analog-to-digital converter data acquisition and storage.The paper obtains the corresponding relationship of the bolt linear expansion coefficient,the ultrasonic temperature compensation coefficient and the ultrasonic temperature sensitivity coefficient through the quantitative calibration experiment.Through continuous measurement,real-time monitoring of bolt axial stress changes during the bolt pre-tightening process.The stress resolution of this device is 0.36 MPa,which fully meets the current bolt tightening stress measurement requirements.