Variable Ratio Load/Strain Rate Biaxial Tensile Testing Machine Control Software Development And Experimental Study

In order to obtain the mechanical properties of metal materials under different loading path, biaxial tensile tests were carried out under different proportional loading conditions, while uniaxial tensile test has been unable to meet the demand. In this paper, based on the mechanical structure of the cruciform biaxial tensile test machine, research on the control system of variable ratio load/strain rate biaxial tensile testing machine was done to realize the variable proportional displacement, load, strain rate biaxial tension control of metal materials under different loading path.Variable scale load/strain rate biaxial tensile testing machine control system was made up of hardware and software. Servo control system and Siemens SIMITION D425motion controller were chosen according to the mechanical structure and movement mode of cruciform biaxial tensile test machine. Analog input signal of force sensor and strain gauge were connected to the controller through TM31A/D module, TTL signal of grating ruler was connected to the controller through the SMC30encoder module. Combined with the driver and servo motor, hardware platform of the control system was built.The control system software was made up of host computer control system and lower computer control system, while communication between the upper computer and the lower computer can be realized through TCP protocol. The PC software was composed of five layers, respectively UI interface layer, process planning layer, logic control layer, control layer and communication layer and TCP communication layer. Lower computer software was composed of four layers, respectively TCP communication layer, analysis layer, execution layer instruction and feedback layer. Based on the proposed speed chase method, variable displacement control strategy, variable load control strategy and variable strain rate control strategy were proposed so as to provide the control algorithm for the PC control system.In the upper computer control system, based on the VC++MFC framework and Microsoft Visual Studio.NET2003, multi threading technology and socket TCP network communication were used to finish the upper computer control software development. The variable displacement control strategy, variable load control strategy and variable strain rate control strategy were applied to the upper computer control software development to realize motion control of the variable scale load/strain rate biaxial tensile testing machine. In the lower computer control system, hardware configuration and the underlying system configuration were done based on the Siemens SIMOTION SCOUT software. The lower computer control system software was developed with ST language, which can realize the axis control, including the axis position control, speed control, shaft back to zero control, axis zero control, axis enable control and axis disable control etc.The accuracy of proposed biaxial tensile testing machine was verified by comparing the tests of TRIP590measured by the German Zwick/Roell Z100uniaxial tensile testing machine with the tests measure by proposed biaxial tensile testing machine. The variable proportional displacement, variable proportional load and variable proportional strain rate of the biaxial tensile testing machine of the Q235cruciform specimen was made as different proportion which included4:1,4:2,4:3,4:4, and it showed that the proposed biaxial tensile testing machine which was based on the variable proportional load/strain rate control system software, had a higher accuracy and reliability.In this paper, based on the mechanical structure of cruciform biaxial tensile test machine, the servo motion control system was chosen, the hardware platform of biaxial tensile test machine control system was built, the control strategy based on the speed chase method was proposed including variable displacement control strategy, variable load control strategy and variable strain rate control strategy. The control system software was developed to realize the biaxial tension control with variable displacement, load and strain rate. A lot of tests were done and the results showed that the control system can guarantee high control precision, providing experimental foundation for the study on the mechanical theory.