Research On Measurement And Control System Of Variable Ratio Biaxial Tensile Testing Machine Based On Electromagnetic Heating

In the field of metal forming,in order to study the forming mechanism of materials under high temperature conditions,the mechanical properties and deformation laws of metal materials at different temperatures,strain rates and loading paths are explored.This paper is based on the biaxial tensile testing machine at room temperature and the measurement and control system of the Proportional high-temperature heating biaxial tensile tester were studied.For the study of ultra-high-strength steel in the case of local heating fixed mold roller variable Cross-section Roll Forming needs,analyze the heating method of domestic and foreign tensile test,adopt the high-frequency electromagnetic heating method,place the heating coil at 5-10mm below the heating test piece,and heat the central area of the sample through electromagnetic induction.The infrared temperature sensor is used to collect the real-time temperature of the tensile test piece,and through A/D conversion,based on the PID control algorithm,the output power of the high-frequency electromagnetic heating device is adjusted in real time,and the constant temperature control of the central region of the test piece is realized.In order to measure the strain of cross-shaped biaxially-stretched specimens,the advantages and disadvantages of the contact-type mechanical extensometers,non-contact laser extensometers,and video extensometers were compared with the use scenarios.The premise that heating the specimens was placed below the specimens was not possible.Then,the measurement can only be made on the top of the test piece,and a video extensometer with a moderate cost and high precision can be selected.The video extensometer is a non-contact industrial camera to collect images of each moment of the test piece,and through image recognition and calculation,to obtain the material strain of the test process.Adjust the focal length and light amount of industrial cameras,calibrate the measurement system,convert the actual length of each pixel of the image,and then each frame of image is filtered,threshold segmented,edge detected,and edge determined,and finally calculate the experimental process deformation.The control system of the variable proportional biaxial tensile tester adopts the SIMOTION D425 motion controller and selects the motor according to the design requirements of the maximum load of the biaxial tensile tester.According to the requirements of the selected force sensor,temperature sensor and heating device for analog input and output,TM31 module is selected to realize A/D and D/A conversion.In order to realize bidirectionally-stretched variable-proportional-load control,based on the PID control algorithm,the force of the force sensor is fed back to control the speed of the bi-directional four-axis motor.Development of measurement and control system software,based on the VC++ MFC application framework,development of image recognition program and four-axis motion control program,communication with motion controller through Socket network socket,to achieve variable-scale biaxial tensile test process data acquisition and image Identification and motion control.The QP1180 ultra high strength steel was subjected to 7 sets of biaxial tensile tests at 350℃.The error analysis was performed on the test results.The average error of the temperature control was 0.30%,the calibration error of the video extensometer was 0.71%,and the average error of the variable proportional load control 0.56%,the experimental results show that the thermal biaxial tensile tester scheme is effective,the control precision meets the experimental requirements,and has a certain engineering application value.